Cullinan Oncology (CGEM) 10-K 17 Mar 22 2021 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2021	Mar. 01, 2022	Jun. 30, 2021
Cover [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2021
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	FY
Entity Registrant Name	CULLINAN ONCOLOGY, INC.
Current Fiscal Year End Date	--12-31
Document Annual Report	true
Document Transition Report	false
Entity Central Index Key	0001789972
Entity File Number	001-39856
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	81-3879991
Entity Address, Address Line One	One Main Street
Entity Address, Address Line Two	Suite 520
Entity Address, City or Town	Cambridge
Entity Address, Country	MA
Entity Address, Postal Zip Code	02142
City Area Code	617
Local Phone Number	410-4650
Title of 12(b) Security	Common Stock, par value $0.0001 per share
Trading Symbol	CGEM
Security Exchange Name	NASDAQ
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
ICFR Auditor Attestation Flag	false
Entity Shell Company	false
Entity Public Float			$ 717,444,028
Entity Common Stock, Shares Outstanding		44,608,613
Auditor Name	KPMG LLP
Auditor Location	Boston, Massachusetts
Auditor Firm ID	185
Documents Incorporated by Reference	DOCUMENTS INCORPORATED BY REFERENCE The Registrant intends to file a definitive proxy statement pursuant to Regulation 14A in connection with its 2022 Annual Meeting of Stockholders within 120 days of the end of the Registrant’s fiscal year ended December 31, 2021. Portions of such proxy statement are incorporated by reference into Part III of this Annual Report on Form 10-K.

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 59,774	$ 168,198	[1]
Short-term investments	230,692	42,008	[1]
Prepaid expenses and other current assets	6,098	2,072	[1]
Total current assets	296,564	212,278	[1]
Property and equipment, net	77	130	[1]
Other assets	147	2,300	[1]
Long-term investments	140,397	0	[1]
Total assets	437,185	214,708	[1]
Current liabilities:
Accounts payable	3,169	9,679	[1]
Accrued expenses and other current liabilities	8,577	4,641	[1]
Total current liabilities	11,746	14,320	[1]
Long-term liabilities:
Deferred rent	65	74	[1]
Total liabilities	11,811	14,394	[1]
Commitments and contingencies (Note 11)
Stockholders' equity:
Common stock, $0.0001 par value, 150,000,000 and 34,900,878 shares authorized as of December 31, 2021 and December 31, 2020, respectively; 44,292,102 and 29,831,125 shares issued and outstanding as of December 31, 2021 and December 31, 2020, respectively.	4	3	[1]
Additional paid-in capital	584,714	292,348	[1]
Accumulated other comprehensive loss	(838)	(2)	[1]
Accumulated deficit	(158,909)	(93,339)	[1]
Total Cullinan stockholders' equity	424,971	199,010	[1]
Noncontrolling interests	403	1,304	[1]
Total stockholders' equity	425,374	200,314	[1]
Total liabilities and stockholders' equity	$ 437,185	$ 214,708	[1]
[1]	The consolidated balance sheet as of December 31, 2020 is derived from the consolidated financial statements as of that date and was retroactively adjusted, including shares and per share amounts, as a result of the Reorganization and Reverse Stock Split. See Note 3 to the consolidated financial statements for additional details.

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Dec. 31, 2021	Dec. 31, 2020
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	150,000,000	34,900,878
Common stock, shares issued	44,292,102	29,831,125
Common stock, shares outstanding	44,292,102	29,831,125

CONSOLIDATED STATEMENTS OF OPER

CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Income Statement [Abstract]
Revenue	$ 18,943	$ 0	[1]
Type of revenue [Extensible List]	us-gaap:LicenseMember	us-gaap:LicenseMember
Operating expenses:
Research and development	$ 57,751	$ 43,211	[1]
General and administrative	29,146	17,124	[1]
Total operating expenses	86,897	60,335	[1]
Loss from operations	(67,954)	(60,335)	[1]
Other income (expense):
Interest income	477	888	[1]
Other income (expense), net	(8)	(11)	[1]
Net loss	(67,485)	(59,458)	[1]
Net loss attributable to noncontrolling interest	(1,915)	(7,659)	[1]
Net loss attributable to common stockholders of Cullinan	$ (65,570)	$ (51,799)	[1],[2]
Net loss per share, basic and diluted	$ (1.52)	$ (2.60)	[1],[2]
Total weighted-average shares used in computing net loss per share, basic and diluted	43,077,330	19,887,307	[1],[2]
Comprehensive loss:
Net loss	$ (67,485)	$ (59,458)	[1]
Unrealized gain/(loss) on investments	(836)	2	[1]
Comprehensive loss	(68,321)	(59,456)	[1]
Comprehensive loss attributable to noncontrolling interest	(1,915)	(7,659)	[1]
Comprehensive loss attributable to Cullinan	$ (66,406)	$ (51,797)	[1]
[1]	The shares and per share amounts for the year ended December 31, 2020 were derived from the consolidated financial statements as of that date and were retroactively adjusted as a result of the Reorganization and Reverse Stock Split. See Note 3 to the consolidated financial statements for additional details.
[2]	The shares and per share amounts for the year ended December 31, 2020 were derived from the consolidated financial statements as of that date and were retroactively adjusted as a result of the Reorganization and Reverse Stock Split. See Note 3 to the for additional details.

CONSOLIDATED STATEMENTS OF STOC

CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands		Total		Common Stock		Noncontrolling Interests in Subsidiaries		Additional Paid-In Capital		Accumulated Other Comprehensive Loss		Accumulated Deficit
Balances at Dec. 31, 2019	[1]	$ 97,865		$ 2		$ 864		$ 138,543		$ (4)		$ (41,540)
Balances, shares at Dec. 31, 2019	[1]			18,738,734
Issuance of common stock equivalents net of issuance costs of $213	[1]	14,037						14,037
Issuance of common stock equivalents, shares	[1]			1,297,700
Issuance of common stock equivalents net of issuance costs of $6,359	[1]	124,841		$ 1				124,840
Issuance of common stock equivalents, shares	[1]			9,461,414
Noncontrolling interest acquired in Mica		5,673				5,673
Issuance subsidiary preferred stock		1,206				1,206
Issuance subsidiary common stock		1,183				1,183
Equity-based compensation		14,910				38		14,872
Equity-based compensation, shares				320,228
Stock option exercises		56						56
Stock option exercises ,shares				13,049
Unrealized gain (loss) on investments		2								2
Net loss		(59,458)	[2]			(7,659)						(51,799)
Balances at Dec. 31, 2020		200,314	[3]	$ 3	[1]	1,305	[1]	292,348	[1]	(2)	[1]	(93,339)	[1]
Balance at Dec. 31, 2020	[1]	200,315
Balances, shares at Dec. 31, 2020	[1]			29,831,125
Initial public offering net of issuance costs of $22,870		264,516		$ 1				264,515
Initial public offering net of issuance costs of $22,870, shares				13,685,000
Issuance of common stock under employee stock purchase plan		218						218
Issuance of common stock under employee stock purchase plan, shares				12,977
Issuance subsidiary preferred stock		923				923
Issuance subsidiary common stock		67				67
Equity-based compensation		24,375				23		24,352
Stock option exercises		3,281						3,281
Stock option exercises ,shares				763,000
Unrealized gain (loss) on investments		(836)								(836)
Net loss		(67,485)				(1,915)						(65,570)
Balances at Dec. 31, 2021		$ 425,374		$ 4		$ 403		$ 584,714		$ (838)		$ (158,909)
Balances, shares at Dec. 31, 2021				44,292,102
[1]	The consolidated balance sheets as of December 31, 2020 and 2019 are derived from the consolidated financial statements as of such date and was retroactively adjusted, including shares and per share amounts, as a result of the Reorganization and Reverse Stock Split. See Note 3 to the consolidated financial statements for additional details.
[2]	The shares and per share amounts for the year ended December 31, 2020 were derived from the consolidated financial statements as of that date and were retroactively adjusted as a result of the Reorganization and Reverse Stock Split. See Note 3 to the consolidated financial statements for additional details.
[3]	The consolidated balance sheet as of December 31, 2020 is derived from the consolidated financial statements as of that date and was retroactively adjusted, including shares and per share amounts, as a result of the Reorganization and Reverse Stock Split. See Note 3 to the consolidated financial statements for additional details.

CONSOLIDATED STATEMENTS OF ST_2

CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (Parenthetical) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2021	Dec. 31, 2020
Statement Of Stockholders Equity [Abstract]
Common stock equivalents, issuance costs	[1]		$ 213
Common stock equivalents, issuance costs	[1]		$ 6,359
Initial public offering, net of issuance costs		$ 22,870
[1]	The consolidated balance sheets as of December 31, 2020 and 2019 are derived from the consolidated financial statements as of such date and was retroactively adjusted, including shares and per share amounts, as a result of the Reorganization and Reverse Stock Split. See Note 3 to the consolidated financial statements for additional details.

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2021	Dec. 31, 2020
Operating activities:
Net loss		$ (67,485)	$ (59,458)	[1]
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization		53	62
Equity-based compensation expense		24,375	14,910
Amortization/Accretion on Marketable Securities		3,098	233
License expense in exchange for subsidiary common stock		67	1,183
Acquired in-process research and development assets			6,447
Changes in operating assets and liabilities:
Prepaid expenses and other current assets		(3,269)	(462)
Other assets			(18)
Accounts payable		(4,835)	5,581
Accrued expenses and other current liabilities		4,563	1,750
Net cash used in operating activities		(43,433)	(29,772)
Investing activities:
Purchases of property and equipment			(10)
Net cash acquired in Mica asset acquisition			1,450
Purchase of Marketable securities		(525,813)	(69,763)
Proceeds from sales and maturities of marketable securities		192,038	62,903
Net cash used in investing activities		(333,775)	(5,420)
Financing activities:
Proceeds from issuance of common stock equivalents	[2]		145,450
Proceeds from initial public offering		267,268
Payment of issuance costs related to common stock equivalents	[2]		(6,572)
Payment of deferred offering costs		(2,688)
Proceeds from issuance of noncontrolling interests		923	1,206
Proceeds from stock options exercise		3,281	56
Net cash provided by financing activities		268,784	140,140
Net decrease in cash and cash equivalents		(108,424)	104,948
Cash and cash equivalents at beginning of year		168,198	63,250
Cash and cash equivalents at end of year		59,774	168,198
Noncash financing activities
Deferred offering costs paid in the prior year		$ 65
Deferred offering costs in accounts payable and accrued expenses			$ 2,093
[1]	The shares and per share amounts for the year ended December 31, 2020 were derived from the consolidated financial statements as of that date and were retroactively adjusted as a result of the Reorganization and Reverse Stock Split. See Note 3 to the consolidated financial statements for additional details.
[2]	Changes in equity activities for the year ended December 31, 2020 were retroactively adjusted, including shares and per share amounts, as a result of the Reorganization and Reverse Stock Split. See Note 3 to the consolidated financial statements for additional details.

Nature of Business and Basis of

Nature of Business and Basis of Presentation	12 Months Ended
	Dec. 31, 2021
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Nature of Business and Basis of Presentation	(1) Nature of Business and Basis of Presentation Organization Cullinan Oncology, Inc., together with its consolidated subsidiaries (Cullinan or the Company), is a biopharmaceutical company developing a diversified pipeline of targeted oncology therapies for cancer patients. Cullinan’s predecessor company, Cullinan Pharmaceuticals, LLC was formed in September 2016 and was subsequently renamed Cullinan Oncology, LLC (the LLC) in November 2017. The LLC’s wholly-owned subsidiary, Cullinan Management, Inc. (Management), was formed in September 2016 and became the surviving entity in a reverse merger with the LLC in January 2021. In February 2021, the Company changed its name from Cullinan Management, Inc. to Cullinan Oncology, Inc. As of December 31, 2021, the Company had four development subsidiaries, or Asset Subsidiaries: Cullinan Amber Corp. (Amber), Cullinan Florentine Corp. (Florentine), Cullinan MICA Corp. (MICA) and Cullinan Pearl Corp. (Pearl). As of December 31, 2020, the LLC had five development subsidiaries: Amber, Cullinan Apollo Corp. (Apollo), Florentine, MICA and Pearl. Apollo was dissolved in August 2021. Reorganization, Reverse Stock Split and Initial Public Offering In January 2021, the Company completed its initial public offering (IPO) in which it issued and sold 13,685,000 shares of its common stock, including 1,785,000 shares sold pursuant to the full exercise of the underwriters’ option to purchase additional shares, at a price to the public of $ 21.00 per share. The shares began trading on the Nasdaq Global Select Market on January 8, 2021 under the symbol “CGEM”. The net proceeds received by the Company from the offering were $ 264.5 million, after deducting underwriting discounts, commissions and other offering expenses. Immediately prior to the effectiveness of the Company’s registration statement, the Company completed its reorganization, whereby the LLC merged with and into Management and Management was the surviving entity. Management was the registrant in the IPO. Pursuant to the Reorganization, all outstanding Redeemable Preferred Units, Non-Voting Incentive Units and common units converted into shares of Management common stock while common unit options were exchanged for stock options. Immediately following the Reorganization, the Company effected a one -for-7.0390 reverse stock split of its issued and outstanding shares of common stock (the Reverse Stock Split). Accordingly, all share and per share amounts for all periods presented in the accompanying consolidated financial statements prior to the Reorganization and notes thereto have been adjusted retroactively, where applicable, to reflect the effect of the Reorganization and Reverse Stock Split. Refer to Note 3 for additional details relating to the Reorganization and Reverse Stock Split. Liquidity The Company has incurred operating losses and negative cash flows from operations since its inception and expects to continue to generate operating losses for the foreseeable future. The Company’s ultimate success depends on the outcome of its research and development activities as well as the ability to commercialize the Company’s product candidates. The Company is subject to a number of risks including, but not limited to, the need to obtain adequate additional funding for the ongoing and planned clinical development of its product candidates. Due to the numerous risks and uncertainties associated with pharmaceutical products and development, the Company is unable to accurately predict the timing or amount of funds required to complete development of its product candidates, and costs could exceed the Company’s expectations for a number of reasons, including reasons beyond the Company’s control. The Company has incurred losses since inception and has an accumulated deficit of $ 158.9 million as of December 31, 2021. Since inception, the Company has funded its operations primarily through the sale of equity securities. The Company expects that its cash, cash equivalents and short-term investments of $ 290.5 million and long-term investments of $ 140.4 million as of December 31, 2021, will be sufficient to fund its operating expenses and capital expenditure requirements through at least the next twelve months from the date of issuance of these consolidated financial statements.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2021
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	(2) Summary of Significant Accounting Policies Basis of Presentation The accompanying consolidated financial statements of the Company have been prepared in conformity with accounting principles generally accepted in the United States of America (GAAP) and in accordance with applicable rules and regulations of the United States Securities and Exchange Commission (SEC) for financial reporting. The consolidated financial statements include accounts of the Company and its consolidated subsidiaries. All intercompany balances have been eliminated in consolidation. Any reference in these notes to applicable guidance is meant to refer to the authoritative GAAP as found in the Accounting Standards Codification (ASC) and Accounting Standards Updates (ASUs) of the Financial Accounting Standards Board (FASB). In the opinion of the Company's management, the consolidated financial statements reflect all adjustments, consisting of normal and recurring adjustments, considered necessary for a fair statement of the Company’s financial position, its results of operations and comprehensive loss and its cash flows for the periods presented. Use of Estimates The preparation of the accompanying consolidated financial statements in accordance with GAAP requires the Company’s management to make estimates and judgments that may affect the reported amounts of assets, liabilities, revenues, expenses and related disclosure of contingent assets and liabilities. On an ongoing basis, the Company’s management evaluates the estimates, including those related to expenses and accruals. The Company’s management bases its estimates on historical experience and on various other assumptions that are believed to be reasonable, the results of which form the basis for making judgments about the carrying values of assets and liabilities. Estimates and assumptions reflected in these consolidated financial statements include, but are not limited to, the fair value of the royalty transfer agreements, accrued research and development costs, the valuation of acquired in-process research and development asset and the fair value of equity awards issued by the Company and its subsidiaries prior to the IPO. Actual results may differ from these estimates under different assumptions or conditions. Principles of Consolidation The Company consolidates entities in which it has a controlling financial interest. The Company evaluates each of its subsidiaries to determine whether the entity represents a variable interest entity (VIE) for which consolidation should be evaluated under the VIE model, or alternatively, if the entity is a voting interest entity, for which consolidation should be evaluated using the voting interest model (VOE). The Company concluded that none of its subsidiaries is a VIE and has consolidated each subsidiary under the VOE. Under the VOE, the Company consolidates the entity if it determines 1) that it directly, or indirectly, has greater than 50% of the voting shares or other equity holders do not have substantive voting, participation, or liquidation rights, or 2) when the company has a controlling financial interest through its control of the board of directors, and the significant decisions of the entity are made at the board level. The Company has either created or made investments in the following Asset Subsidiaries: Consolidated Entities Relationship as of December 31, 2021 Date Control First Cullinan Amber Corp. Partially-owned Subsidiary December 2019 Cullinan Florentine Corp. Partially-owned Subsidiary December 2019 Cullinan Mica Corp. Partially-owned Subsidiary May 2020 Cullinan Pearl Corp. Partially-owned Subsidiary November 2018 Noncontrolling Interests To the extent that ownership interests in the subsidiaries are held by entities other than the Company, management reports these as noncontrolling interests on the consolidated balance sheets. Earnings or losses are attributed to noncontrolling interests under the hypothetical liquidation at book value (HLBV) method. The HLBV method is a point in time calculation that utilizes inputs to determine the amount that the Company and the noncontrolling interest holders would receive upon a hypothetical liquidation at each balance sheet date based on the liquidation provisions of the respective articles of incorporation. At December 31, 2021, investors and licensors held noncontrolling interests in Amber, Florentine, MICA and Pearl. At December 31, 2020, investors and licensors held noncontrolling interests in Amber, Apollo, Florentine, MICA and Pearl. Refer to Note 4 for details relating to the license agreements and Note 6 for details relating to the noncontrolling interests. For the years ended December 31, 2021 and 2020, $ 1.9 million and $ 7.7 million of net loss, respectively, were attributable to noncontrolling interests and are recorded in the consolidated statements of operations and comprehensive loss and disclosed within the noncontrolling interests in subsidiaries column in the consolidated statements of stockholders' equity. Comprehensive Loss Comprehensive loss is defined as the change in equity of a business enterprise during a period from transactions and other events and circumstances from nonowner sources. For years ended December 31, 2021 and 2020, the Company recognized $ 0.8 million in unrealized loss and less than $ 0.1 million in unrealized gain on investments, respectively. Segments The Company has determined that its Chief Executive Officer is the Chief Operating Decision Maker (CODM). The Company operates and manages the business as one reporting and one operating segment, which is the business of developing early stage cancer therapeutics. The Company’s CODM reviews financial information on an aggregate basis for purposes of allocating resources and evaluating financial performance. All of the Company’s assets are located in the United States. Concentration of Credit Risk and Other Risks and Uncertainties The Company has no significant off-balance sheet risk. Cash and cash equivalents are primarily maintained with two major financial institutions in the United States. Deposits at banks may exceed the insurance provided on such deposits. These deposits may be redeemed upon demand, and therefore, bear minimal risk. The Company is subject to certain risks and uncertainties and believes that changes in any of the following areas could have a material adverse effect on future financial position or results of operations: ability to obtain future financing; regulatory approval and market acceptance of, and reimbursement for, product candidates; performance of third-party clinical research organizations and manufacturers upon which the Company relies; protection of the Company’s intellectual property; litigation or claims against the Company based on intellectual property, patent, product, regulatory or other factors; and the Company’s ability to attract and retain employees necessary to support its growth. The Company is dependent on third-party manufacturers to supply products for research and development activities in its programs. In particular, the Company relies and expects to continue to rely on a small number of manufacturers to supply it with its requirements for drug substance and drug products related to these programs. These programs could be adversely affected by a significant interruption in the supply. Cash and Cash Equivalents The Company considers all highly liquid investments with original maturities of three months or less at the time of purchase to be cash equivalents. As of December 31, 2021 and 2020, cash equivalents consist of government-backed money market funds. Investments Investments not classified as cash equivalents with maturities of less than twelve months are classified as short-term investments in the consolidated balance sheets. Investments with maturities greater than twelve months for which the Company has the intent and ability to hold the investment for greater than twelve months are classified as long-term investments in the consolidated balance sheets. The Company generally holds investments in marketable securities. Marketable securities are carried at estimated fair value, with unrealized gains or losses included in accumulated other comprehensive income (loss) in stockholders’ equity. The fair value of marketable securities is based on available market information. The amortized cost of marketable securities is adjusted for amortization of premiums and accretion of discounts to maturity. Such amortization is included in interest income. Interest and dividends are also included in interest income. The Company periodically reviews its marketable securities for impairment and adjusts these investments to their fair value when a decline in market value is deemed to be other than temporary. Declines in fair value judged to be other-than-temporary on marketable securities, if any, are included in other income (expense), net. The Company recognized its short-term and long-term investments by security type at December 31, 2021: Amortized Gross Gross Estimated (in thousands) Short-term investments Corporate notes $ 98,642 $ — $ ( 95 ) $ 98,547 Commercial paper 114,174 — ( 27 ) 114,147 U.S. government notes 18,033 — ( 35 ) 17,998 Total short-term investments 230,849 — ( 157 ) 230,692 Long-term investments Corporate notes 117,868 — ( 596 ) 117,272 Asset-backed securities 3,044 — ( 8 ) 3,036 U.S. government notes 20,166 — ( 77 ) 20,089 Total long-term investments 141,078 — ( 681 ) 140,397 Total investments $ 371,927 $ — $ ( 838 ) $ 371,089 The Company recognized its short-term investments by security type at December 31, 2020: Amortized Gross Gross Estimated (in thousands) Corporate notes $ 12,780 $ — $ ( 3 ) $ 12,777 Commercial paper 24,473 — — 24,473 Asset-backed securities 4,757 1 — 4,758 Total investments $ 42,010 $ 1 $ ( 3 ) $ 42,008 Fair Value of Financial Instruments Certain assets and liabilities are carried at fair value under GAAP. The fair value hierarchy gives the highest priority to unadjusted quoted prices in active markets for identical assets (Level 1) and the lowest priority to unobservable inputs (Level 3). As required by FASB ASC Topic 820, Fair Value Measurement (ASC Topic 820) the Company’s financial assets are classified within the fair value hierarchy based on the lowest level of input that is significant to the fair value measurement. The three levels of the fair value hierarchy under ASC Topic 820, and its applicability to the Company’s financial assets, are described below: Level 1—Unadjusted quoted prices in active markets that are accessible at the measurement date of identical, unrestricted assets. Level 2—Quoted prices for similar assets, or inputs that are observable, either directly or indirectly, for substantially the full term through corroboration with observable market data. Level 3—Pricing inputs are unobservable for the asset, that is, inputs that reflect the reporting entity’s own assumptions about the assumptions market participants would use in pricing the asset. Asset-backed securities, commercial paper and corporate and U.S. government notes are primarily valued using market quotations or prices obtained from independent pricing sources which may employ various pricing methods to value the investments including matrix pricing. The following table sets forth the fair value of the Company’s financial assets as of December 31, 2021, allocated into Level 1, Level 2 and Level 3, that was measured on a recurring basis: Level 1 Level 2 Level 3 Total (in thousands) Cash and cash equivalents Cash $ 35,925 $ — $ — $ 35,925 Money market funds 23,849 — — 23,849 Total cash and cash equivalents 59,774 — — 59,774 Short-term investments Corporate notes — 98,547 — 98,547 Commercial paper — 114,147 — 114,147 U.S. government notes — 17,998 — 17,998 Total short-term investments — 230,692 — 230,692 Long-term investments Corporate notes — 117,272 — 117,272 Asset-backed securities — 3,036 — 3,036 U.S. government notes — 20,089 — 20,089 Total long-term investments — 140,397 — 140,397 Total cash, cash equivalents and investments $ 59,774 $ 371,089 $ — $ 430,863 The following table sets forth the fair value of the Company’s financial assets as of December 31, 2020, allocated into Level 1, Level 2 and Level 3, that was measured on a recurring basis: Level 1 Level 2 Level 3 Total (in thousands) Cash and cash equivalents Cash $ 22,007 $ — $ — $ 22,007 Money market funds 146,191 — — 146,191 Total cash and cash equivalents 168,198 — — 168,198 Short-term investments Corporate notes — 12,777 — 12,777 Commercial paper — 24,473 — 24,473 Asset-backed securities — 4,758 — 4,758 Total short-term investments — 42,008 — 42,008 Total cash, cash equivalents and investments $ 168,198 $ 42,008 $ — $ 210,206 Prepaid expenses and other current assets, accounts payable and accrued expenses and other current liabilities are carried at cost, which management believes approximates fair value due to their short term nature. Deferred Offering Costs The Company capitalizes costs that are directly associated with in-process equity financings until such financings are consummated at which time such costs are recorded against the gross proceeds of the offering. Should the in-process equity financing be abandoned, the deferred offering costs will be expensed immediately as a charge to operating expenses in the consolidated statements of operations and comprehensive loss. The Company incurred $ 2.7 million of deferred offering costs in 2020 and recorded such amounts against the gross proceeds of the Company’s IPO within the statements of stockholders’ equity for the year ended December 31, 2021. Property and Equipment Property and equipment are stated at cost less accumulated depreciation and amortization. Depreciation expense is recognized using the straight-line method over the estimated useful life of each asset as follows: Computers 3 years Office furniture and equipment 5 years Leasehold improvements Shorter of the useful life of the asset or the lease term Maintenance and repairs that do not improve or extend the life of the assets are expensed when incurred. Upon sale or retirement of assets, the cost and accumulated depreciation and amortization are removed from the consolidated balance sheet and any resulting gain or loss is reflected in the consolidated statements of operations and comprehensive loss in the period realized. Property and equipment consisted of the following: December 31, 2021 2020 (in thousands) Computers $ 70 $ 70 Office furniture and equipment 134 134 Leasehold improvements 105 105 Total property and equipment, gross 309 309 Less: accumulated depreciation ( 232 ) ( 179 ) Total property and equipment, net $ 77 $ 130 Depreciation expense was less than $ 0.1 million for each of the years ended December 31, 2021 and 2020. Accrued liabilities and other current liabilities Accrued expenses and other current liabilities consist of the following: December 31, 2021 2020 (in thousands) Accrued bonus $ 2,576 $ 1,763 Professional fees and other 973 1,049 Research and development costs 5,028 1,829 $ 8,577 $ 4,641 Asset Acquisitions The Company measures and recognizes asset acquisitions that are not deemed to be business combinations based on the cost to acquire the assets, which includes transactions costs. Goodwill is not recognized in asset acquisitions. In an asset acquisition, the cost allocated to acquire in-process research and development (IPR&D) with no alternative future use is charged to research and development expense at the acquisition date. Impairment of Long-Lived Assets Long-lived assets are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. Recoverability of assets to be held and used is measured by a comparison of the carrying amount of an asset to future undiscounted net cash flows expected to be generated. Impairment charges are recognized at the amount by which the carrying amount of an asset exceeds the fair value of the asset. Assets to be disposed of are reported at the lower of the carrying amount or the fair value less costs to sell. There was no impairment of long-lived assets for any of the periods presented. Revenue Recognition The Company recognizes revenue in accordance with ASC Topic 606, Revenue from Contracts with Customers, or ASC 606. This standard applies to all contracts with customers, except for contracts that are within the scope of other standards, such as leases, insurance, collaboration arrangements and financial instruments. Under ASC 606, an entity recognizes revenue when its customer obtains control of promised goods or services, in an amount that reflects the consideration which the entity expects to receive in exchange for those goods or services. To determine revenue recognition for arrangements that an entity determines are within the scope of ASC 606, the entity performs the following five steps: (i) identify the contract(s) with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when (or as) the entity satisfies a performance obligation. The Company only applies the five-step model to contracts when it is probable that the entity will collect the consideration it is entitled to in exchange for the goods or services it transfers to the customer. At contract inception, once the contract is determined to be within the scope of ASC 606, the Company assesses the goods or services promised within each contract and determines those that are performance obligations and assesses whether each promised good or service is distinct. The Company then recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) the performance obligation is satisfied. The Company enters into licensing arrangements for research and development, manufacturing and commercialization activities, which have components within the scope of ASC 606. Payments pursuant to these arrangements typically include non-refundable, upfront payments, milestone payments upon achieving significant development events, research and development reimbursements, sales milestones and royalties on future product sales. The amount of variable consideration is constrained until it is probable that the revenue is not at a significant risk of reversal in a future period. The contracts into which the Company enters generally do not include significant financing components. As part of the accounting for these arrangements, the Company must use significant judgment to determine: a) the number of performance obligations based on the determination under step (ii) above; b) the transaction price under step (iii) above; c) the stand-alone selling price for each performance obligation identified in the contract for the allocation of transaction price in step (iv) above, and d) the measure of progress in step (v) above. The Company uses judgment to determine whether milestones or other variable consideration, except for royalties, should be included in the transaction price as described further below. Non-Exclusive Licenses If the license to the Company’s intellectual property is determined to be distinct from the other promises or performance obligations identified in the arrangement, the Company recognizes revenue from non-refundable, upfront fees allocated to the license when the license is transferred to the customer and the customer is able to use and benefit from the license. In assessing whether a promise or performance obligation is distinct from the other elements, the Company considers factors such as the research, development, manufacturing and commercialization capabilities of the collaboration partner and the availability of the associated expertise in the general marketplace. In addition, the Company considers whether the collaboration partner can benefit from a promise for its intended purpose without the receipt of the remaining elements, whether the value of the promise is dependent on the unsatisfied promise, whether there are other vendors that could provide the remaining promise and whether it is separately identifiable from the remaining promise. For licenses that are combined with other promises, the Company utilizes judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition. The measure of progress, and thereby periods over which revenue should be recognized, are subject to estimates by management and may change over the course of the agreement. Such a change could have a material impact on the amount of revenue the Company records in future periods. Milestone Payments At the inception of each arrangement that includes milestone payments, the Company evaluates whether the milestones are considered probable of being achieved and estimates the amount to be included in the transaction price using the most likely amount method. If it is probable that a significant revenue reversal would not occur, the associated milestone value is included in the transaction price. Milestone payments that are not within the control of the Company or the licensee, such as regulatory approvals, are not considered probable of being achieved until those approvals are received. The Company evaluates factors such as the scientific, clinical, regulatory, commercial and other risks that must be overcome to achieve the respective milestone in making this assessment. There is considerable judgment involved in determining whether it is probable that a significant revenue reversal would not occur. At the end of each subsequent reporting period, the Company reevaluates the probability of achievement of all milestones subject to constraint and, if necessary, adjusts its estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis, which would affect revenues and earnings in the period of adjustment. Royalties For arrangements that include sales-based royalties, including milestone payments based on a level of sales, and the license of intellectual property is deemed to be the predominant item to which the royalties relate, the Company recognizes revenue at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied (or partially satisfied). To date, the Company has not recognized any royalty revenue resulting from any of its licensing arrangements. Research and Development Expenses Research and development costs are expensed as incurred and consist primarily of funds for employee wages and funds paid to third parties for the provision of services for product candidate development, clinical and preclinical development and related supply and manufacturing costs, and regulatory compliance costs. At the end of the reporting period, the Company compares payments made to third-party service providers to the estimated progress toward completion of the research or development objectives. Such estimates are subject to change as additional information becomes available. Depending on the timing of payments to the service providers and the progress that the Company estimates has been made as a result of the service provided, the Company may record net prepaid or accrued expense relating to these costs. Costs incurred to obtain licenses are recognized as research and development expense as incurred if the technology licensed has no alternative future use. Advance payments for goods or services to be received in the future for use in research and development activities are recorded as prepaid expenses. The prepaid amounts are expensed as the related goods are received or services are performed. The Company has entered into various research and development related contracts with parties both inside and outside of the United States. The payments related to these agreements are recorded as research and development expenses as incurred. The Company records accrued liabilities for estimated ongoing research and development costs. When evaluating the adequacy of the accrued liabilities, the Company analyzes progress of the studies or clinical trials, including the phase or completion of events, invoices received and contracted costs. Significant judgments and estimates are made in determining the accrued balances at the end of any reporting period. Actual results could differ from the Company’s estimates. To date, there have been no material differences between the Company’s accrued costs and actual costs. Patent Costs All patent-related costs incurred in connection with filing and prosecuting patent applications are expensed as incurred due to the uncertainty about the recovery of the expenditure. Amounts incurred are classified as general and administrative expenses in the consolidated statements of operations and comprehensive loss. Equity-Based Compensation Equity-based compensation is measured at the grant date for all equity-based awards made to employees and non-employees based on the fair value of the awards and is recognized as expense on a straight-line basis over the requisite service period, which is generally the vesting period. The Company has elected to recognize the actual forfeitures by reducing the equity-based compensation expense in the same period as the forfeitures occur. The Company estimated the fair of the stock options using the Black-Scholes option pricing model, which requires the input of objective and subjective assumptions. Certain assumptions used, including the fair value of the Company’s common stock prior to IPO and stock price volatility, represent management’s estimates and involve inherent uncertainties and the application of management’s judgment. As a result, if factors change and management uses different assumptions, equity-based compensation expense could be materially different for future awards. The Company classifies equity-based compensation in its consolidated statements of operations and comprehensive loss in the same manner in which the award recipient’s payroll costs are classified or in which the award recipient’s service payments are classified. Income Taxes The Company accounts for income taxes using the asset and liability method in accordance with FASB ASC Topic 740, Income Taxes. Current income taxes are based on taxable income for federal and state reporting purposes. Deferred income tax assets and liabilities are recognized for the future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases using enacted tax rates in effect for the year in which the differences are expected to affect taxable income. A valuation allowance is provided when it is more likely than not that some portion, or all of a deferred tax asset will not be realized. Due to the Company's lack of earnings history, the net deferred tax assets have been fully offset by a valuation allowance at both December 31, 2021 and 2020. The Company recognizes the effect of income tax positions only if those positions are more likely than not of being sustained. Recognized income tax positions are measured at the largest amount of benefit that is greater than fifty percent likely to be realized upon settlement. Changes in measurement are reflect in the period in which the change in judgment occurs. Net Loss per Share Basic and diluted net loss per share is determined by dividing net loss attributable to common stockholders by the weighted-average shares of common stock outstanding during the period, without consideration for potential dilutive shares of common stock, such as stock options, unvested restricted stock awards and shares issuable under the employee stock purchase plan. Accordingly, in periods in which the Company reports a net loss attributable to common stockholders, diluted net loss per share attributable to common stockholders is the same as basic net loss per share attributable to common stockholders, since dilutive shares of common stock are not assumed to have been issued if their effect is anti-dilutive. Therefore, the weighted-average shares used to calculate both basic and diluted net loss per share are the same for the periods presented. The Company excluded unvested shares of restricted stock awards, stock options and shares issuable under the employee stock purchase plan from the computation of diluted weighted-average shares outstanding as they would be antidilutive. Emerging Growth Company Status The Company is an emerging growth company, as defined in the Jumpstart Our Business Startups Act of 2012 (the JOBS Act). Under the JOBS Act, emerging growth companies can delay adopting new or revised accounting standards issued subsequent to the enactment of the JOBS Act until such time as those standards apply to private companies. The Company has elected to use this extended transition period for complying with new or revised accounting standards that have different effective dates for public and private companies until the earlier of the date that it (i) is no longer an emerging growth company or (ii) affirmatively and irrevocably opts out of the extended transition period provided in the JOBS Act. As a result, these consolidated financial statements may not be comparable to companies that comply with the new or revised accounting pronouncements as of public company effective dates. The JOBS Act does not preclude an emerging growth company from adopting a new or revised accounting standard earlier than the time that such standard applies to private companies. The Company expects to use the extended transition period for any other new or revised accounting standards during the period in which it remains an emerging growth company. Recently Adopted Accounting Pronouncements In August 2020, FASB issued ASU No. 2020-06 , Debt—Debt with Conversion and Other Options (Subtopic 470-20) and Derivatives and Hedging—Contracts in Entity’s Own Equity (Subtopic 815-40): Accounting for Convertible Instruments and Contracts in an Entity’s Own Equity (ASU 2020-06), which, among other things, provides guidance on how to account for contracts on an entity’s own equity. ASU 2020-06 simplifies the accounting for certain financial instruments with characteristics of liabilities and equity. Specifically, ASU 2020-06 eliminated the need for the Company to assess whether a contract on the entity’s own equity (1) permits settlement in unregistered shares, (2) whether counterparty rights rank higher than shareholder’s rights, and (3) whether collateral is required. In addition, ASU 2020-06 requires incremental disclosure related to contracts on the entity’s own equity and clarifies the treatment of certain financial instruments accounted for under this ASU on earnings per share. ASU 2020-06 may be applied on a full retrospective or modified retrospective basis. ASU 2020-06 became effective January 1, 2022 including interim periods presented within that year. Early adoption of the ASU is permitted by the Company effective January 1, 2021. The Company adopted ASU 2020-06 beginning on January 1, 2021. The adoption of ASU 2020-06 did not materially impact the Company’s consolidated financial statements and associated disclosures. Recently Issued Accounting Pronouncements Not Yet Adopted In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842), to increase transparency and comparability among organizations by recognizing a right-of-use asset and a lease liability on the balance sheet for all leases with terms longer than 12 months. Leases will be classified as either operating or financing, with such classifications affecting the pattern of expense recognition in the income statement. ASU 2016-02 is effective for fiscal years beginning after December 15, 2019, and early adoption is permitted. ASU 2016-02 was recently delayed for emerging growth companies that elected to adopt new accounting standards on the adoption date required for private companies and will be effective for the Company’s annual reporting period beginning on January 1, 2022 and interim periods beginning i

Reorganization and Reverse Stoc

Reorganization and Reverse Stock Split	12 Months Ended
	Dec. 31, 2021
Reorganization And Reverse Stock Split [Abstract]
Reorganization and Reverse Stock Split	(3) Reorganization and Reverse Stock Split Immediately prior to the completion of the IPO in January 2021, the LLC completed the Reorganization. Prior to the Reorganization, Management was a wholly-owned subsidiary of the LLC. The LLC was also the direct parent company of the Company’s development subsidiaries. Pursuant to the Reorganization, Management acquired all the assets of the LLC, including all of the stock the LLC owned of Amber, Apollo, Florentine, MICA and Pearl (collectively the Asset Subsidiaries), and assumed all of the LLC’s liabilities and obligations. Following the Reorganization, all of Management’s outstanding Preferred Stock automatically converted on a one -for-one basis into common stock of Management. The Company then effected the Reverse Stock Split. Immediately prior to completion of the Company’s IPO, the existing units of the LLC were cancelled and the number of shares of common stock exchanged and issued to the LLC’s unitholders in the Reorganization is shown in the below table by unit class, on a split adjusted basis: Cullinan Oncology, LLC Unit Type Number of Management's Adjusted for the Reverse Series C Preferred Units 66,599,045 9,461,414 Series B Preferred Units 63,141,016 8,970,154 Series A1 Preferred Units 50,000,000 7,103,280 Series Seed Preferred Units 16,000,000 2,273,050 Non-Voting Incentive Units 11,896,500 1,689,949 Common Units 34,747,722 4,936,415 Total shares issued 242,384,283 34,434,262 The amount presented for Non-Voting Incentive Units included unvested outstanding Non-Voting Incentive Units that were exchanged for restricted stock of Management. The amount presented for Common Units included the unvested outstanding Restricted Common Units, exchanged for Management’s restricted stock, and issued and unvested Common Unit Options, that were exchanged for Management’s stock options. The unvested awards are subject to the same time-based vesting conditions as the original awards. The Reorganization was accounted for as a reverse acquisition, where the LLC was determined to be the accounting acquirer and Management to be the legal acquiree, and recapitalization for financial reporting purposes. Accordingly, the historical financial statements of the LLC became the Company’s historical financial statements, including the comparative prior periods. All share and per share amounts in these consolidated financial statements and related notes have been retroactively adjusted, where applicable, for all periods presented. The shares of the Company’s common stock for periods prior to the Reorganization represent the outstanding units of the LLC recalculated to give effect to the Reorganization and Reverse Stock Split. All LLC units that were previously reported as Redeemable Preferred Units, or temporary equity, were converted to common stock of the Company upon the execution of the Reorganization and have been reclassified to stockholders’ equity for all periods presented, as if the Reorganization occurred at the beginning of the earliest period presented in the Company’s financial statements for the years ended December 31, 2020 and 2019: As of December 31, 2020 As Reported Adjustment As Adjusted (in thousands) Redeemable Preferred Units Series Seed Redeemable Preferred Units $ 3,956 $ ( 3,956 ) $ — Series A1 Redeemable Preferred Units 49,946 ( 49,946 ) — Series B Redeemable Preferred Units 97,909 ( 97,909 ) — Series C Redeemable Preferred Units 124,841 ( 124,841 ) — Total Redeemable Preferred Units 276,652 ( 276,652 ) — Stockholders' Equity (Members' Deficit) Non-Voting Incentive Units 1 ( 1 ) — Common Stock — 3 3 Additional paid-in capital 15,698 276,650 292,348 Accumulated other comprehensive loss ( 2 ) — ( 2 ) Accumulated deficit ( 93,339 ) — ( 93,339 ) Total Cullinan Stockholders' Equity (Members' Deficit) ( 77,642 ) 276,652 199,010 Non-controlling interests in subsidiaries 1,304 — 1,304 Total Stockholders' Equity (Members' Deficit) $ ( 76,338 ) $ 276,652 $ 200,314 As of December 31, 2019 As Reported Adjustment As Adjusted (in thousands) Redeemable Preferred Units Series Seed Redeemable Preferred Units $ 3,956 $ ( 3,956 ) $ — Series A1 Redeemable Preferred Units 49,946 ( 49,946 ) — Series B Redeemable Preferred Units 83,872 ( 83,872 ) — Series C Redeemable Preferred Units — — — Total Redeemable Preferred Units 137,774 ( 137,774 ) — Stockholders' Equity (Members' Deficit) Non-Voting Incentive Units 1 ( 1 ) — Common Stock — 2 2 Additional paid-in capital 770 137,773 138,543 Accumulated other comprehensive loss ( 4 ) — ( 4 ) Accumulated deficit ( 41,540 ) — ( 41,540 ) Total Cullinan Stockholders' Equity (Members' Deficit) ( 40,773 ) 137,774 97,001 Non-controlling interests in subsidiaries 864 — 864 Total Stockholders' Equity (Members' Deficit) $ ( 39,909 ) $ 137,774 $ 97,865

License and Collaboration Agree

License and Collaboration Agreements	12 Months Ended
	Dec. 31, 2021
License And Collaboration Agreements [Abstract]
License and Collaboration Agreements	(4) License and Collaboration Agreements The following table summarizes the impact of research and development costs related to the collaboration and license agreements on the Company’s consolidated statements of operations and comprehensive loss for the years ended December 31, 2021 and 2020. December 31, 2021 2020 (in thousands) Adimab $ 46 $ 1,318 Amber - MIT 71 333 Apollo - Wistar — 355 Florentine - Tubigen — 912 Pearl - Taiho 3,000 531 $ 3,117 $ 3,449 Adimab In November 2018, the Company entered into a collaboration agreement with Adimab, LLC (Adimab) (the Adimab Collaboration Agreement). Pursuant to the Adimab Collaboration Agreement, the Company selected a number of biological targets against which Adimab used its proprietary platform technology to discover and/or optimize antibodies based upon mutually agreed upon research plans. Under the Adimab Collaboration Agreement, the Company has the ability to select a specified number of additional biological targets against which Adimab will provide additional antibody discovery and optimization services. During the research term and evaluation term for a given research program with Adimab, the Company has a non-exclusive worldwide license under Adimab’s technology to perform certain research activities and to evaluate the program antibodies to determine whether the Company wants to exercise its option to obtain a royalty-free, fully paid, non-exclusive license to exploit such antibodies and sublicense through multiple tiers. Under the Adimab Collaboration Agreement, the Company paid a one-time, non-creditable, non-refundable technology access fee. The Company is also required to pay an annual access fee and research funding fees in connection with Adimab’s full-time employees’ compensation for performance of Adimab’s obligations under the Adimab Collaboration Agreement. The Company is also obligated to make certain research delivery, clinical and sales milestone payments to Adimab on a program-by-program basis, subject to certain reductions and discounts. The Company is obligated to pay certain royalty payments on a product-by-product basis at a low single-digit percentage of annual aggregate worldwide net sales. Such royalty obligations will expire on a country-by-country and product-by-product basis upon the later of (a) a certain low double-digit number of years after the first commercial sale of such product in such country and (b) the expiration of the last issued and not expired, permanently revoked, or invalid claim within a program patent covering such product. The Company may terminate the Adimab Collaboration Agreement at any time, for any reason, upon a specified period advance written notice. The term of the Adimab Collaboration Agreement expires upon the last research program’s evaluation term in the event no Adimab Option is exercised or in the event an Adimab Option is exercised, after the royalty term expires at the later of a specified period or invalid patent coverage of the relevant product. Amber—Massachusetts Institute of Technology In December 2019, Amber entered into an Exclusive Patent License Agreement with Massachusetts Institute of Technology (MIT) to develop a cancer immunotherapy product worldwide (the MIT License Agreement). Under the terms of the MIT License Agreement, Amber paid an upfront nonrefundable license fee of less than $ 0.1 million upon execution. Additionally, Amber issued 200,066 shares of its common stock to MIT and the licensed technology founder upon execution of its Series A Preferred financing in April 2020 as consideration for the licenses granted and incurred $ 0.2 million of license expenses. In June 2021, Amber issued 153,229 shares of its common stock to MIT as anti-dilution shares upon execution of an additional Series A Preferred financing and incurred less than $ 0.1 million of license expenses related to the shares issued during 2021. Amber is also responsible for paying non-refundable, creditable annual license maintenance fees in an increasing amount over a certain number of years and a fixed amount subsequent to this period of time. In addition, MIT granted to Amber an exclusive option to amend the initially determined field to include expansion fields, and such amendment would trigger the payment to MIT of an amendment fee. Additionally, Amber shall pay certain non-refundable, non-creditable milestone payments up to $ 7.0 million and $ 5.5 million to MIT upon the occurrence of certain clinical and regulatory events associated with its first and second indications, respectively, by product, and up to an additional $ 12.5 million upon the occurrence of cumulative net sales targets. Each milestone payment is paid one time only up to a certain payment amount. No milestones have been achieved to date under the MIT License Agreement. Under certain conditions upon a change in control of Amber, Amber is required to pay a specified change in control fee and Amber’s clinical and regulatory milestone payments shall be increased by 100 %. Furthermore, Amber is required to pay running low single digit royalty percentage on net sales of all licensed products for each reporting period, subject to certain offsets or reductions. The royalties due to MIT for net sales of the licensed product shall not be reduced by more than a mid-double digit percentage. Amber is also required to share any income from sublicensing the licensed products, with the percentage to be determined by the clinical phase of the licensed product, no greater than low-to mid-double digit percentages. Such royalty obligations will expire on a country-by-country and product-by-product basis upon the expiration or abandonment of all issued patents and filed patent applications within the patent rights. Apollo—The Wistar Institute In December 2018, Apollo entered into a license agreement with The Wistar Institute (Wistar) to discover and develop a novel Epstein-Barr Nuclear Antigen 1 (EBNA1) inhibitor (the Wistar Agreement). Under the terms of the Wistar Agreement, Apollo paid a nonrefundable up-front option and license fee and issued shares of Apollo common stock to Wistar in exchange for the worldwide, exclusive rights to research and develop Wistar’s EBNA1 inhibitor. The Wistar Agreement also provides for Wistar to receive milestone payments upon achievement of patent rights and product development targets and royalties on future sales of licensed products. In December 2018, the Company also entered into a Collaborative Research Agreement with Wistar to continue preclinical research and development with potential product candidate. These studies were budgeted to cost $ 1.5 million over a three-year timeline. In May 2020, Apollo terminated the licensing and collaboration agreement with Wistar and decided to discontinue further development of the EBNA1 inhibitor associated with that agreement, VK-2019. Florentine—Tübingen License Agreement In August 2020, Florentine entered into an Exclusive License Agreement (the Tübingen License Agreement) with Deutsches Krebsforschungszentrum (DKFZ), Eberhard Karls University of Tübingen, Faculty of Medicine (University of Tübingen) and Universitätsmedizin Gesellschaft für Forschung und Entwicklung mbH, Tübingen (UFE). Pursuant to the Tübingen License Agreement, DKFZ and University of Tübingen, collectively referred to as the Licensor, granted to Florentine an exclusive worldwide, milestone- and royalty-bearing license under certain licensed patent rights, applications, technical information and know-how, with the right to grant sublicenses through multiple tiers to research, develop, commercialize or otherwise exploit licensed products within the field. Florentine is required to pay to the Licensor an upfront, non-refundable, non-creditable option exercise fee of $ 0.6 million. As partial consideration for the licenses, Florentine issued to DKFZ and UFE 758,246 and 348,682 shares of Florentine common stock, respectively, who together own five percent ( 5 %) of Florentine’s fully diluted shares outstanding as December 31, 2021. DKFZ and UFE were also granted the right to appoint one representative to the board of directors of Florentine. Additionally, Florentine shall pay certain non-refundable, non-creditable milestone payments to the Licensor upon the occurrence of certain clinical and regulatory events related to a licensed product. Each milestone payment is paid one time only up to a certain payment amount. No milestones have been achieved to date under the Tübingen License Agreement. Pearl—Taiho Pharmaceuticals, Co. Ltd In February 2019, Pearl entered into a license and collaboration agreement with Taiho Pharmaceuticals, Co. Ltd (Taiho Pharma) to develop a novel epidermal growth factor receptor (EGFR) inhibitor (the Taiho License Agreement). As consideration for the license for worldwide exclusive development rights, excluding Japan, Pearl paid an initial, non-refundable, non-creditable license fee of $ 2.5 million and issued, to Taiho Ventures, LLC (Taiho Ventures) an affiliate of Taiho Pharma, 1,860,000 shares of its common stock in 2019. In addition, Pearl is obligated to pay non-refundable, non-creditable research and development, regulatory and sales milestone payments upon the occurrence of certain milestone events in an aggregate amount of up to $ 154.5 million for development, regulatory and sales milestones. Each milestone is payable only once. No milestones have been achieved to date under the Taiho License Agreement. Furthermore, Pearl is required to pay running low single digit to low double digit royalty percentages of annual aggregate net sales worldwide outside Japan on a country-by-country and product-by-product basis during the royalty term, subject to certain offsets, deductions or reductions related to loss or impairment of exclusivity in the territory. The obligation to pay royalties is imposed only once with respect to net sales of the same unit of a licensed product. Such royalty obligations will expire on a country-by-country and product-by-product basis upon the later of (a) the expiration of the last patent which covers a product in such country, (b) the expiration of any exclusivity granted by a regulatory authority and (c) a low double-digit anniversary following the first commercial sale of a product in such country. In the event (i) Taiho Pharma does not exercise its right of negotiation with respect to a licensed product or (ii) Taiho Pharma does exercise its right of negotiation, but the parties do not consummate a transaction, then at the time Pearl enters into a subsequent transaction with a third party for (a) less than all or less than substantially all of Pearl’s rights in a licensed product, Pearl is also obligated to pay Taiho Pharma a mid-single digit percentage of revenue from such transactions or (b) all or substantially all of Pearl’s rights in a licensed product, Pearl is obligated to pay Taiho Pharma a low single digit percentage of revenue from such transactions, provided, however, that such payment under (b) shall not be required following the consummation of Pearl’s initial public offering. In parallel with the execution of the Taiho License Agreement, Pearl entered into a Series A Preferred Stock Purchase Agreement with the Company and Taiho Ventures to sell up to 23,000,000 shares of Pearl’s Series A Preferred Stock for $ 1.00 per share for an aggregate purchase price of $ 23.0 million. The Company and Taiho Ventures invested $ 14.0 million in the initial closing. The Series A Preferred Stock Purchase Agreement obligated Pearl to sell, and the Company and Taiho Ventures to purchase, at $ 1.00 per share, the remaining 9,000,000 shares of Pearl’s Series A Preferred Stock at a subsequent closing, either upon the approval of Pearl’s board of directors or if the cash balance of Pearl is below $ 1.0 million. Pearl completed the second closing in August 2020. The Company determined that Pearl’s second Series A Preferred Stock tranche is separable and therefore a freestanding instrument, but the fair value of the tranche right is not material as of and for the year ended December 31, 2020. See Note 6 for further details. Pearl—Zai Lab License Agreement In December 2020, Pearl entered into a license agreement (Zai License Agreement) with Zai Lab Shanghai Company, Limited (Zai Lab), to grant Zai Lab, an exclusive royalty-bearing license to research, develop, commercialize and manufacture CLN-081 and products which contain CLN-081 in China, Hong Kong, Macau and Taiwan. Zai Lab will be primarily responsible for substantially all the costs related to the operations and control over the significant activities related to the exploitation of the licensed IP of CLN-081. As partial consideration of the license and rights granted to Zai Lab, Zai Lab paid Pearl a one-time, irrevocable, nonrefundable license fee of $ 20.0 million. In addition to the upfront fee, Zai Lab is obligated to pay Pearl, research and development, regulatory and sales milestone payments upon the occurrence of certain milestone events in the aggregate amount of up to $ 211.0 million, and tiered royalty payments based on the annual net sales of the licensed product. The upfront license fee was recognized in revenue. The Company will also recognize the milestone and royalty payments in revenue once they are earned. No milestones have been achieved to date under the Zai License Agreement. The upfront payment received by Pearl was subject to foreign tax withholdings. When the licensed IP and technology know-how was transferred to Zai Lab in January 2021, Pearl recognized revenue of $ 18.9 million, which represented the upfront fee less the foreign tax withholdings as Pearl does not expect to recover the amounts relating to the foreign tax withholdings. In connection with the Taiho License Agreement, Pearl is obligated to pay Taiho Pharma a percentage of future revenue received from Zai Lab, including the upfront payment that was received in January 2021. Upon receipt of the upfront payment, Pearl recognized $ 3.0 million payable to Taiho Pharma within research and development expenses in the consolidated statements of operations and comprehensive loss.

Cullinan-MICA Asset Acquisition

Cullinan-MICA Asset Acquisition	12 Months Ended
	Dec. 31, 2021
Asset Acquisition [Abstract]
Cullinan-MICA Asset Acquisition	(5) Cullinan-MICA Asset Acquisition On May 28, 2020 (the Acquisition Date), in accordance with the Series A Senior Preferred Stock Purchase Agreement (the Purchase Agreement), the Company purchased 5,385,787 shares of Series A Senior Preferred Stock (the Series A Senior Preferred Stock) of PDI Therapeutics, Inc. (PDI Therapeutics), for $ 7.1 million, and certain existing PDI Therapeutics shareholders purchased approximately 702,495 shares of the Series A Senior Preferred Stock for $ 0.9 million. Concurrently with the Series A Senior Preferred Stock purchase, PDI Therapeutics was renamed Cullinan MICA Corp. The terms of the Purchase Agreement included two additional closings for total proceeds of up to $ 26.0 million. On the Acquisition Date, MICA (formerly PDI Therapeutics) authorized the issuance of 72,890,797 shares, of which 39,000,000 was designated as common stock and 33,890,797 was designated as preferred stock. Of the authorized preferred stock, MICA designated 1,999,998 shares as Series A Junior Preferred Stock, 652,371 shares as Series A-1 Junior Preferred Stock, 11,451,514 shares as Series A-2 Junior Preferred Stock, and 19,786,914 shares as Series A Senior Preferred Stock (collectively the Series Preferred Stock). Following the initial close in May 2020, MICA had 22,829,406 shares outstanding, including 6,088,282 shares of Series A Senior Preferred Stock (of which the LLC held 5,385,787 shares), 602,784 shares of common stock, and 14,103,883 shares of Series A, A-1 and A2 Junior Preferred Stock described above. In addition, there were 2,034,457 shares of common stock underlying options reserved under MICA's equity plan (of which 1,826,402 was reserved for future issuances to MICA’s directors and officers, as well as former employees of PDI Therapeutics). Other than the Series A-1 Junior Preferred Stock, which shares are non-voting, the Series Preferred Stock of MICA vote equally with the shares of common stock of MICA. In addition to any other vote or consent, the vote or written consent of a majority of the holders of Series A Senior Preferred Stock is required for certain actions, including redemptions, dividends, distributions, dissolutions, creation of new classes of stock, mergers, sale of MICA or its assets, and amendments to the certificate of incorporation, as well as other actions. The other classes of Series Preferred Stock have voting rights pertaining to the increase or decrease in the authorized number of shares of their respective classes. The Company’s initial purchase represented approximately 24 % of MICA’s fully diluted shares outstanding, including shares reserved for future issuance, and 88.5 % of the Series A Senior Preferred Stock outstanding. The Company can increase its ownership to approximately 54 % of MICA’s fully diluted shares outstanding with the subsequent closings. Additionally, as part of the transaction and as outlined in the Voting Agreement dated May 28, 2020, among the Company and other stockholders of MICA, MICA increased the size of its board of directors from four to five directors, of which three directors are designated by the Company. The Company also entered into a Services Agreement with MICA under which the Company will perform functions required for MICA’s operations, including accounts payable, cash management, record keeping, research and development, and accounting services. Given the Company’s ownership of the Series A Senior Preferred Stock and its majority representation on MICA’s board of directors, the Company's obtained a controlling interest in MICA on the Acquisition Date. Further, the Company evaluated the MICA transaction and determined that MICA is not a variable interest entity; however, due to the controlling interest in MICA, the Company will consolidate MICA under the voting interest model. The Company evaluated the change in control of MICA and concluded that the change in control was an asset acquisition rather than a business combination as substantially all of the value in MICA resided in CLN-619, the IPR&D asset developed by MICA. The cost of the assets was calculated as the sum of the fair value of the Company’s investment in MICA, the fair value of the noncontrolling interests in MICA and the Company’s transaction costs. This cost was allocated to the assets acquired and liabilities assumed in the transaction based on their relative fair values. The amount allocated to the IPR&D asset acquired was $ 6.4 million and was charged to research and development expense within the consolidated statements of operations and comprehensive loss during the year ended December 31, 2020 as it had no alternative future use at the time of the acquisition. In December 2020, the stockholders and the board of directors of MICA approved an amendment to its equity plan that decreased the authorized amount of shares under its equity plan such that no further grants could be made under its equity plan. Any authorized but unissued shares under the equity plan were returned to the status of authorized, unissued shares of common stock. In June 2021, the MICA board authorized the first additional closing and the Company purchased an additional 5,385,787 shares of Series A Senior Preferred Stock for $ 7.1 million and certain existing shareholders purchased an additional 702,495 shares of Series A Senior Preferred Stock for $ 0.9 million pursuant to the MICA Purchase Agreement. Following the first additional closing, the Company’s ownership increased to 45 % of MICA’s fully-diluted shares outstanding and remain as such at December 31, 2021.

Common Stock and Noncontrolling

Common Stock and Noncontrolling Interest in Subsidiaries	12 Months Ended
	Dec. 31, 2021
Common Stock And Noncontrolling Interest In Subsidiaries [Abstract]
Common Stock and Noncontrolling Interest in Subsidiaries	(6) Common Stock and Noncontrolling Interest in Subsidiaries Common Stock As of December 31, 2021 and 2020, 150,000,000 and 34,900,878 shares of common stock of the Company were authorized, respectively. Each share of common stock entitles the holder to one vote and to receive dividends when and if declared by the board of directors of the Company. No dividends have been declared through December 31, 2021. The LLC’s outstanding Non-Voting Incentive Units have been retroactively adjusted to reflect the effect of the Reorganization and Reverse Stock Split. Refer to Note 3 for additional details relating to the Reorganization and Reverse Stock Split. Noncontrolling Interest in Subsidiaries Certain subsidiaries issue common stock in connection with licensing agreements and to employees, directors and consultants pursuant to subsidiary equity incentive plans. The holders of subsidiary common stock are entitled to one vote per share. The holders of subsidiary common stock are entitled to receive dividends when and if declared by the subsidiaries’ board of directors and distributions in either case only after the payment of all preferential amounts required to be paid to the holders of shares of preferred stock of the respective subsidiary. In November 2020, the LLC entered into Restricted Stock Contribution Agreements (Contribution Agreements) with Amber, Florentine and Pearl where the LLC exchanged common units of the LLC for restricted common stock held by LLC employees at each of the subsidiaries. The LLC’s outstanding restricted common units have been retroactively adjusted to reflect the effect of the Reorganization and Reverse Stock Split. Refer to Note 3 for additional details relating to the Reorganization and the Reverse Stock Split. Cullinan Amber Corp. In April 2020, in connection with its Series A Preferred Stock financing, Amber issued 3,000,000 shares of its Series A Preferred Stock to the Company for gross proceeds of $ 3.0 million. At any time following the initial closing, upon election of Amber’s board of directors, Amber may sell up to an aggregate of 9,000,000 shares of Amber’s Series A Preferred Stock at one or more subsequent closings at $ 1.00 per share. In April 2020, pursuant to the MIT License Agreement between Amber and MIT, Amber issued 400,132 shares of its common stock, in exchange for no additional consideration as set forth in the MIT License Agreement. In June 2021, upon election by Amber’s board of directors, Amber issued an additional 3,000,000 shares of its Series A Preferred Stock to the Company for gross proceeds of $ 3.0 million. In connection with the financing, Amber issued 153,229 shares of its common stock to MIT in exchange for no additional consideration, as set forth in the MIT License Agreement. Under the HLBV method, less than $ 0.1 and $ 0.2 million of losses were attributed to the noncontrolling interests for the years ended December 31, 2021 and 2020, respectively. Cullinan Apollo Corp. In December 2018, Apollo entered into a Series A Preferred Stock purchase agreement with the Company. The initial closing took place in December and Apollo sold 7,000,000 subsidiary shares of Series A Preferred Stock for gross proceeds of $ 7.0 million. Pursuant to the Series A Preferred Stock purchase agreement, at any time following the initial closing, upon the election of Apollo’s board of directors, Apollo could sell up to an aggregate of 11,000,000 Series A Preferred Stock shares at one or more subsequent closings at $ 1.00 per share. The Company dissolved Apollo in August 2021. The Company did no t allocate any losses to the noncontrolling interests for the years ended December 30, 2021 and 2020. Cullinan Florentine Corp. In August 2020, Florentine entered into a Series A Preferred Stock purchase agreement with the Company. The initial closing took place in August 2020 and Florentine sold 6,000,000 shares of its Series A Preferred Stock to the Company for gross proceeds of $ 6.0 million. At any time following the initial closing, upon the election of the Florentine’s board of directors, Florentine may sell up to an additional 6,000,000 shares of Series A Preferred Stock at one or more subsequent closings at $ 1.00 per share. Pursuant to the Tübingen License Agreement, Florentine issued 725,118 shares of its common stock, in exchange for no additional consideration as set forth in the Tübingen License Agreement. In December 2020, Florentine issued 6,000,000 additional shares of its Series A Preferred Stock to the Company for proceeds of $ 6.0 million under the Florentine Series A Preferred Stock purchase agreement. Florentine issued an additional 381,810 shares of its common stock to DFKZ and UFE as anti-dilution shares, in exchange for no additional consideration as set forth in the Tübingen License Agreement. In July 2021, Florentine issued 7,500,000 shares of Series B Preferred Stock to the Company for gross proceeds of $ 8.1 million under the Florentine Series B Preferred Stock purchase agreement. No additional shares of its stock were issued to DFKZ or UFE. The Company did no t allocate any losses to the noncontrolling interests for the year ended December 31, 2021. Under the HLBV method, $ 0.5 million of losses were attributed to noncontrolling interests for the year ended December 31, 2020. Cullinan MICA Corp. In May 2020, MICA issued 6,088,282 million shares of Series A Senior Preferred Stock, including 5,385,787 shares to the Company, at $ 1.31 per share. See Note 5 for further details. Using a market-based approach and an option-pricing allocation method, MICA determined the fair market value of MICA’s equity at acquisition was $ 12.8 million, of which $ 7.1 million was allocated to the Company’s Series A Senior Preferred Stock position, and $ 5.7 million was initially allocated to noncontrolling interests, including the Junior Preferred and Common Stockholders. In December 2020, the MICA board authorized the issuance of 3,367,804 shares of MICA common stock to the Company, at a purchase price of $ 0.23 per share for aggregate proceeds to MICA of $ 0.8 million. As a result of these transactions, the Company’s ownership interests in MICA increased to 35 % as of December 31, 2020. In June 2021, pursuant the first additional closing as described in Note 5, the Company’s ownership interests in MICA increased to 45 %. Under the HLBV method, $ 1.1 and $ 5.4 million of losses were attributed to noncontrolling interests for the years ended December 31, 2021 and 2020, respectively. Cullinan Pearl Corp. In February 2019, Pearl entered into a Series A Preferred Stock Purchase Agreement with Taiho Ventures to sell up to 23,000,000 shares of Pearl’s Series A Preferred Stock for $ 1.00 per share. Pearl completed the initial closing of its Series A Preferred Stock where Pearl issued 14,000,000 shares of Series A Preferred Stock for $ 14.0 million to the Company and Taiho Ventures. In connection with the Taiho License Agreement, Pearl issued 1,860,000 shares of its common stock to Taiho Ventures as anti-dilution shares, in exchange for no cash consideration. In August 2020, Pearl issued 9,000,000 additional shares of its Series A Preferred Stock for $ 9.0 million to the Company and Taiho Ventures. In connection with the Taiho License Agreement, Pearl then issued 1,206,000 to Taiho Ventures additional shares of its common stock as anti-dilution shares, in exchange for no additional consideration. In November 2020, pursuant a subscription agreement between the Company and Pearl, the Company purchased 2,730,227 shares of Pearl’s common stock at $ 0.44 per share, for an aggregate purchase price of $ 1.2 million. Under the HLBV method, $ 0.7 and $ 1.6 million of losses were attributed to noncontrolling interests for the years ended December 31, 2021 and 2020, respectively.

Equity-Based Compensation

Equity-Based Compensation	12 Months Ended
	Dec. 31, 2021
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Equity-Based Compensation	(7) Equity-Based Compensation Non-Voting Incentive Units Prior to the Reorganization, the LLC’s 2016 Equity Incentive Plan (the 2016 Plan) provided for the grant of Non-Voting Incentive Units to employees, consultants, advisors and directors, as determined by the board of directors. Vesting was determined by the board of directors. Awards typically provided for vesting of 25 % of units at the end of the first year of service with the remaining 75 % vesting ratably on a monthly basis over the following three-year period. Unvested Non-Voting Incentive Units may not be sold or transferred by the holder and are subject to repurchase by the LLC if service terminates prior to vesting at a price equal to the amount the recipient paid for the Non-Voting Incentive Units. These restrictions lapse according to the time-based vesting conditions of each award. Non-Voting Incentive Units were granted at a price of not less than the fair value of the Common Unit on the date of grant. The Non-Voting Incentive Units are subject to ASC 718 and are classified within equity. On the grant date, the fair value of the LLC’s Common Units for accounting purposes was determined by the board of directors, with input from management. Compensation expense is recognized on the Non-Voting Incentive Units using the fair value on the date of grant of $ 0.0001 per unit. Given the early stage nature of the underlying technology and inherent risks associated with obtaining regulatory approval and achieving commercialization, the Company used the current value method to fair value the Non-Voting Incentive Units granted since inception. In October 2020, the Board of Directors adopted the 2020 Unit Option and Grant Plan and decreased the number of units available for future grants under the 2016 Equity Incentive Plan such that no more Non-Voting Incentive Units could be issued under the plan. The Company did no t issue any Non-Voting Incentive Units during the year ended December 31, 2020. As part of the Reorganization in January 2021, the total outstanding Non-Voting Incentive Units were cancelled and 1,689,949 shares of the Company’s common stock were issued in exchange. The amounts presented for Non-Voting Incentive Units included unvested outstanding awards that were exchanged for restricted stock of the Company. The following table summarizes the Non-Voting Incentive Unit activities for the years ended December 31, 2021 and 2020 as if the Non-Voting Incentive Units were converted to restricted common stock of the Company at the earliest period presented: Number of Weighted Outstanding unvested as of December 31, 2019 580,334 $ 0.0001 Vested ( 407,844 ) 0.0001 Outstanding unvested as of December 31, 2020 172,490 0.0001 Vested ( 172,490 ) 0.0001 Outstanding unvested as of December 31, 2021 — 0.0001 Outstanding vested as of December 31, 2021 1,689,949 $ 0.0001 For the years ended December 31, 2021 and 2020, compensation expense and unrecognized compensation costs were nominal based on the grant date fair value of $ 0.0001 per share. All Non-Voting Incentive Units exchanged for restricted common stock were vested as of December 31, 2021. Restricted Stock and Stock Option Grants of the Subsidiaries Prior to the Reorganization, the respective boards of directors of certain subsidiaries have authorized equity incentive plans for the grant of stock options and restricted stock awards in the subsidiaries to employees, consultants, advisors and directors. Vesting is determined by each subsidiaries’ board of directors. Awards typically provide for vesting of 25 % of units at the end of the first year of service with the remaining 75 % vesting ratably on a monthly basis over the following three-year period. Unvested restricted shares may not be sold or transferred by the holder and are subject to repurchase by the subsidiaries if service terminates prior to vesting at a price equal to the amount the recipient paid for the restricted stock. These restrictions lapse according to the time-based vesting conditions of each award. Restricted common stocks are granted at a price of not less than the fair value of the common stock on the date of grant. The restricted stock and stock options are subject to ASC 718 and are classified within equity. The fair values of Pearl common stock in 2018, and of Amber and Florentine common stock in 2019, for accounting purposes was determined by their respective boards of directors, with input from management, at $ 0.0001 per share. Contribution and Unit Purchase Agreements with the Subsidiaries In November 2020, the LLC entered into the Contribution Agreements with each holder of restricted stock of Amber, Florentine and Pearl. Pursuant to the Contribution Agreements, each holder contributed their respective shares of the restricted stock of the subsidiaries and in exchange, received in aggregate 2,231,363 restricted common units of the LLC entity under the 2020 Unit Option and Grant Plan with an aggregate value equal to the value of the restricted stock contributed to the LLC (the Restricted Stock Contribution). The LLC exchanged 368,974 units of the LLC restricted stock for 511,530 units of Amber restricted stock, 513,656 units of the LLC restricted stock for 728,678 units of Florentine restricted stock and 1,348,733 units of the LLC restricted stock for 1,869,834 units of Pearl restricted stock pursuant to the Contribution Agreements. Simultaneous with the Restricted Stock Contribution, the board of directors of each of Amber, Florentine and Pearl accelerated the vesting of the unvested restricted stock immediately prior to the Restricted Stock Contribution. The acceleration facilitated the exchange of the units between the subsidiaries and the LLC. Subsequent to the exchange, all restricted common units of the LLC reverted to the original vesting schedule of the respective awards at the subsidiaries. Lastly, the board of directors of each of Amber, Florentine and Pearl terminated their respective stock option and grant plans. The remaining shares reserved for issuance under each respective stock option and grant plan for Amber and Florentine were retired to the status of authorized and unissued shares and in the case of Pearl, issued to the LLC in exchange for their fair value. The Contribution Agreement is determined to be a cancellation of the restricted stock issued at the subsidiaries with a concurrent grant of a replacement award at the LLC and is accounted for as a modification. Unit Purchase Agreement with Cullinan Pearl In November 2020, the board of directors of Cullinan Pearl authorized the entry into a Common Unit Purchase Agreement (Unit Purchase Agreement) with the LLC pursuant to which Pearl purchased 22,868 common units of the LLC for a purchase price of $ 0.61 per common unit, for an aggregate purchase price of less than $ 0.1 million. Pearl then transferred those common units to two directors of Pearl in exchange for the cancellation of an aggregate 93,000 subsidiary stock options issued to those directors. The common unit purchase between Pearl and the LLC and the subsequent exchange of the purchased units for the stock options issued to the directors is determined to be a cancellation of the stock options issued at Pearl with a concurrent grant of a replacement award at the LLC. The cancellation and concurrent grant of a replacement is accounted for as a modification. Pursuant to the Contribution and Unit Purchase Agreements, the LLC exchanged 2,254,231 units of the LLC for restricted stocks and stock options held by employees, consultants, advisors and directors of the subsidiaries. The exchange provided for $ 1.2 million in excess fair value and on the effective date of the exchange, the Company recognized $ 0.2 million and $ 0.1 million of modification expense within research and development expense and general and administrative expense, respectively, in the consolidated statements of operations and comprehensive loss. The remaining excess fair value will be recognized over the vesting terms. As part of the Reorganization in January 2021, all of the LLC units exchanged for restricted stock or stock options of the Subsidiaries were cancelled and 320,228 shares of the Company’s common stock were issued in exchange. The amounts presented for the exchange number of shares included unvested outstanding awards that were exchanged for restricted stock of the Company. For the years ended December 31, 2021 and 2020, the Company recognized $ 0.4 million and $ 0.2 million of equity-based compensation expense relating to the excess fair value within research and development expense and general and administrative expense categories, respectively, in the consolidated statements of operations and comprehensive loss. As of December 31, 2021 and 2020, there were $ 0.3 million and $ 0.7 million in unrecognized compensation cost expected to be recognized over estimated weighted-average amortization periods of 1.48 and 2.41 years, respectively. The following table summarizes the restricted common unit activities for the years ended December 31, 2021 and 2020 as if the restricted common units were converted to restricted common stock of the Company at the earliest period presented: Number of Incremental Fair Value Per Share Total units exchanged as of November 4, 2020 320,228 $ 3.87 Vested ( 128,358 ) 3.87 Outstanding unvested as of December 31, 2020 191,870 $ 3.87 Vested ( 102,987 ) 3.87 Outstanding unvested as of December 31, 2021 88,883 $ 3.87 Outstanding vested as of December 31, 2021 231,345 $ 3.87 2021 Stock Option and Incentive Plan The Company’s 2021 Stock Option and Incentive Plan (the 2021 Stock Plan) was adopted by the board of directors in December 2020 and the stockholders approved the plan in January 2021, prior to the completion of the Company’s IPO. The 2021 Stock Plan became effective on the day immediately prior to the effectiveness of the Company’s registration statement. The purpose of the 2021 Stock Plan is to encourage and enable the officers, employees, directors, consultants and other key persons of the Company whose judgment, initiative and efforts the Company largely depends on for the successful conduct of its business, to acquire a proprietary interest in the Company. The term of the options may be up to 10 years , and options are exercisable in cash or is net exercised. The exercise price of the options are determined based on the fair market value of the Company’s common stock on the date of grant with 25 % of the awards issued vesting on the first anniversary of the vesting commencement date, with the remaining portion of the awards vesting over the following 36 months in equal monthly installments. The 2020 Unit Option and Grant Plan (2020 Plan) was terminated once the 2021 Stock Plan was effective. As part of the Reorganization, all common unit options granted under the 2020 Unit Option and Grant Plan were cancelled and exchanged for stock options under the 2021 Stock Plan with the same vesting terms and conditions. This was considered a modification of the common unit options previously issued with no incremental fair value as there were no changes to the terms and conditions of the awards. The Company initially reserved 12,546,386 shares of common stock for issuance of awards under the 2021 Stock Plan, which included (i) split-adjusted 320,228 shares of restricted stock issued in exchange for restricted stock and stock options granted at the Subsidiaries, as referenced above, and (ii) split-adjusted equity awards comprised of 4,616,187 shares of common stock issuable upon the exercise of stock options at a weighted average exercise price of $ 4.30 that were issued in exchange for common unit options cancelled under the 2020 Unit Option and Grant Plan. The 2021 Stock Plan provides that the number of shares reserved and available for issuance under the 2021 Stock Plan will automatically increase each January 1, beginning on January 1, 2022, by 5 % of the outstanding number of shares of the Company’s common stock on the immediately preceding December 31 or such lesser number of shares as determined by the Company’s board or compensation committee. This number is subject to adjustment in the event of a stock split, stock dividend or other change in capitalization. The following table summarizes the activity related to stock option grants to employees and non-employees for the years ended December 31, 2021 and 2020 under the 2021 Stock Plan. This also includes the common unit options issued under the 2020 Plan that were cancelled and exchanged into stock options under the 2021 Stock Plan with the number of options issued and weighted average exercise price presented as if the Reorganization occurred at the earliest period presented: Number of Weighted Average Exercise Price Weighted Average Remaining Contractual Term (Years) Outstanding as of December 31, 2019 — $ — — Granted 4,616,187 4.30 — Exercised ( 13,050 ) 4.30 — Outstanding as of December 31, 2020 4,603,137 $ 4.30 9.84 Granted 5,481,816 23.82 — Exercised ( 763,000 ) 4.30 — Forfeited ( 63,214 ) 17.23 — Outstanding as of December 31, 2021 9,258,739 $ 15.77 9.22 Options exercisable as of December 31, 2021 3,271,196 $ 7.65 8.90 Options unvested as of December 31, 2021 5,987,543 $ 20.20 9.39 As of December 31, 2021 and 2020, there were $ 75.8 million and $ 14.2 million, respectively, in unrecognized compensation cost that are expected to be recognized over an estimated weighted-average amortization period of 3.15 and 2.68 years, respectively. As of December 31, 2021, the aggregate intrinsic value of options outstanding and options exercisable based on a fair value per share of $ 15.43 was $ 42.5 million and $ 29.1 million, respectively. As of December 31, 2020, the aggregate intrinsic value of options outstanding and options exercisable based on a fair value per share of $ 18.02 was $ 63.1 million and $ 28.6 million, respectively. The fair value of options is estimated using the Black-Scholes option pricing model, which takes into account inputs such as the exercise price, the value of the underlying common stock at the grant date, expected term, expected volatility, risk-free interest rate and dividend yield. The fair value of each grant of options during the years ended December 31, 2021 and 2020 were determined using the methods and assumptions discussed below: • The expected term of employee options is determined using the “simplified” method, as prescribed in the SEC Staff Accounting Bulletin (SAB) No. 107, whereby the expected life equals the arithmetic average of the vesting term and the original contractual term of the option due to the Company’s lack of sufficient historical data. The Company also elected to use the simplified method to determine the expected term of non-employee options. • The risk free interest rate is based on the treasury constant maturity rate published on the Federal Reserve website. • The expected volatility is based on historical volatilities of similar entities within the Company’s industry which were commensurate with the expected term assumption as described in SAB No. 107. • The estimated annual dividend yield is 0 % because the Company has not historically paid, and does not expect for the foreseeable future to pay, a dividend on its common stock. • The Company considered numerous objective and subjective factors in estimating the fair value of its common stock prior to the IPO, including the concluded equity value based on IPO and liquidation scenarios and their related timing and probabilities of occurrence. For the years ended December 31, 2021 and 2020, the weighted average grant date fair value of the options granted were $ 15.73 and $ 6.19 per share, respectively. The grant date fair value was estimated at the time of grant using the Black-Scholes option-pricing model using the following weighted average assumptions: Year Ended December 31, 2021 Year Ended December 31, 2020 Weighted average risk-free interest rate 1.02 % 0.51 % Expected term (in years) 6.00 5.98 Expected volatility 76.22 % 77.40 % Expected dividend yield 0.00 % 0.00 % For the year ended December 31, 2021, the Company recorded $ 8.7 million and $ 15.2 million of equity-based compensation expense within the research and development and general and administrative expense categories, respectively. For the year ended December 31, 2020, the Company recorded $ 5.6 million and $ 8.8 million of equity-based compensation expense within the research and development and general and administrative expense categories, respectively. These amounts are included in the consolidated statements of operations and comprehensive loss. 2021 Employee Stock Purchase Plan The 2021 Employee Stock Purchase Plan (the ESPP) was adopted by our board of directors in December 2020 and the stockholders approved the plan in January 2021, prior to the completion of the Company’s IPO. The ESPP became effective on the day immediately prior to the effectiveness of the Company’s IPO. The Company has initially reserved 416,665 shares of common stock for issuance to participating employees. The ESPP provides that the number of shares reserved and available for issuance under the ESPP will automatically increase each January 1, beginning on January 1, 2022, by the lesser of 833,330 shares of our common stock, 1 % of the outstanding number of shares of the Company’s common stock on the immediately preceding December 31, or such lesser number of shares as determined by the Company’s compensation committee. This number is subject to adjustment in the event of a stock split, stock dividend or other change in capitalization. For the twelve months ended December 31, 2021, the Company issued 12,977 shares of its common stock and recorded less than $ 0.1 million of equity-based compensation expense pursuant the ESPP. Equity-based compensation expense The Company recorded equity-based compensation in the following expense categories in the consolidated statements of operations and comprehensive loss: Year ended December 31, 2021 2020 (in thousands) Research and development $ 8,914 $ 5,912 General and administrative 15,461 8,998 Total equity-based compensation $ 24,375 $ 14,910

Related Party Transactions

Related Party Transactions	12 Months Ended
	Dec. 31, 2021
Related Party Transactions [Abstract]
Related Party Transactions	(8) Related Party Transactions MPM Capital is a significant investor in the Company through one of its managed funds. In October 2016, the Company also began receiving consulting and management services pursuant to agreements with a managing director at MPM Capital and a principal at F2 Ventures, also a significant investor in the Company. No expenses were incurred for the year ended December 31, 2021. For the year ended December 31, 2020, the Company incurred $ 0.2 million for management and advisory services, inclusive of their director compensation, in connection with those agreements. For each of the years ended December 31, 2021 and 2020, the Company paid MPM Capital less than $ 0.1 million for other operational support. These expenses were recorded as general and administrative expense. In April 2020, the Company entered into a consulting agreement (the Globeways Agreement) with Globeways Holdings Limited, or Globeways. Globeways and entities affiliated with F2 Ventures beneficially own in the aggregate greater than five percent of the Company’s outstanding shares and Globeways is beneficially owned by a member of the Company's board of directors. Pursuant to the Globeways Agreement, the board member provides leadership and advice regarding the Company’s scientific, clinical, product development and related activities and operations. Pursuant to the Globeways Agreement, the Company pays Globeways a consulting fee at a monthly rate of $ 25,000 . As the sole beneficial owner of Globeways, this board member receives all of the compensation paid to Globeways under the Globeways Agreements. For the years ended December 31, 2021 and 2020, the Company incurred less than $ 0.1 million and $ 0.2 million in costs related to this agreement, respectively. The agreement expired as of March 31, 2021. Royalty Transfer Agreements Between October 2019 and May 2020, each of the Asset Subsidiaries entered into royalty transfer agreements with MPM Oncology Charitable Foundation, Inc. and UBS Optimus Foundation (together, the Foundations). Under each of these respective agreements, each Foundation is entitled to receive a royalty equal to 0.5 % ( 1.0 % in aggregate) of all global net sales of any products developed by the applicable subsidiary, subject to limitations after patent expirations and on intellectual property developed after a change of control. The Company has deemed these royalty transfer agreements to be freestanding financial instruments that should be accounted for at fair value. Management of the Company has concluded that these instruments had no value at the inception of the agreements and at December 31, 2021 and 2020. Given the early-stage nature of the underlying technologies and inherent technical, regulatory and competitive risks associated with achieving approval and commercialization, the Company ascribed no value to the royalty transfer agreements as of December 31, 2021 and 2020. The Company currently does not have any applicable net sales from its products and as a result, has paid no royalties under these obligation as of December 31, 2021 and 2020 nor has the Company accrued any liability as of such dates. The Company will monitor these instruments for changes in fair value at each reporting date

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2021
Income Tax Disclosure [Abstract]
Income Taxes	(9) Income Taxes For the years ended December 31, 2021 and December 31, 2020, the Company did no t record a current or deferred income tax expense or benefit due to current and historical losses incurred by the Company. A reconciliation of the Company’s statutory income tax rate to the Company’s effective income tax rate is as follows: Year ended 2021 2020 Federal statutory rate 21.00 % 21.00 % State taxes, net of federal benefit 9.96 % ( 1.83 )% Permanent differences 0.01 % ( 0.01 )% Equity-based compensation 0.39 % — Tax credits ( 0.25 )% 0.77 % Valuation allowance ( 32.12 %) ( 12.65 %) Non-taxable income — ( 5.01 )% IPR&D — ( 2.28 %) Change in tax status 1.76 % — Return to provision 1.15 % — Other ( 1.90 )% — 0.00 % 0.00 % The net deferred income tax asset balance related to the following: December 31, 2021 2020 (in thousands) Deferred tax assets: Net operating loss $ 31,414 $ 18,563 Capitalized organizational and start-up expenses 140 148 Licenses 1,875 1,601 Accrued expenses 968 467 Research and development credit 1,563 1,859 Equity-based compensation 8,584 8 Gross deferred tax assets 44,544 22,646 Valuation allowance ( 44,552 ) ( 22,642 ) Net deferred tax asset ( 8 ) 4 Deferred tax liability Depreciation and amortization 8 ( 4 ) Net deferred tax asset $ — $ — As of December 31, 2021, the Company had federal and state net operating loss (NOL) carryforwards of $ 117.4 million and $ 119.0 million, respectively. The Company generated federal NOLs of $ 5.8 million prior to 2018, which begin to expire in 2036 . State losses also begin to expire in 2036 . The Company generated combined federal NOLs of $ 111.6 million, which can be carried forward indefinitely. As of December 31, 2021, the Company had federal and state research and development tax credit carryforwards of $ 1.3 million and $ 0.1 million, respectively, which begin to expire in 2037 and 2033 , respectively. The Company has state research and development tax credit carryforwards of $ 0.3 million which can be carried forward indefinitely. Utilization of the net operating loss carryforwards and research and development tax credits may be subject to a substantial annual limitation under Section 382 of the Internal Revenue Code of 1986 (Section 382) due to ownership change limitations that have occurred previously or that could occur in the future in accordance with Section 382, as well as similar state provisions. These ownership changes may limit the amount of NOL carryforwards that can be utilized annually to offset future taxable income. In general, an ownership change as defined by Section 382 results from transactions increasing the ownership of certain shareholders or public groups in the stock of a corporation by more than 50 percentage points over a three-year period. The Company has evaluated the positive and negative evidence bearing upon its ability to realize the deferred tax assets, which are comprised principally of net operating loss carryforwards, licenses, equity-based compensation and research and development credit carryforwards. Management has considered the Company’s history of net losses since inception and its lack of commercialization of any products and has concluded that it is more likely than not the Company will not realize the benefits of the deferred tax assets. The Company’s valuation allowance increased during the years ended December 31, 2021 and 2020 due primarily to the generation of net operating losses, as follows: Year ended 2021 2020 (in thousands) Valuation allowance at beginning of year $ 22,642 $ 10,653 Increases recorded to income tax provision 21,674 11,989 Increases recorded to OCI/Equity 236 — Valuation allowance at end of year $ 44,552 $ 22,642 The calculation of the Company’s tax liabilities involves dealing with uncertainties in the application of complex tax laws and regulations for both federal taxes and the states in which the Company operates or does business in. ASC 740 states that a tax benefit from an uncertain tax position may be recognized when it is more likely than not that the position will be sustained upon examination, including resolutions of any related appeals or litigation processes, on the basis of the technical merits. The Company records uncertain tax positions as liabilities in accordance with ASC 740 and adjusts these liabilities when its judgment changes as a result of the evaluation of new information not previously available. Due to the complexity of some of these uncertainties, the ultimate resolution may result in a payment that is materially different from the Company’s current estimate of the unrecognized tax benefit liabilities. These differences will be reflected as increases or decreases to income tax expense in the period in which new information is available. As of December 31, 2021 and 2020, the Company has no t recorded any uncertain tax positions in its consolidated financial statements. The Company recognizes interest and penalties related to unrecognized tax benefits on the income tax expense line in the accompanying consolidated statements of operations and comprehensive loss. As of December 31, 2021 and 2020, no accrued interest or penalties are included in the consolidated balance sheet. The Company files tax returns as prescribed by the tax laws of the jurisdictions in which it operates. In the normal course of business, the Company is subject to examination by federal and state jurisdictions in the United States. There are currently no pending tax examinations. The Company thus is still open under the U.S. statute from 2016 to the present. To the extent that the Company has tax attribute carryforwards, the tax years in which the attribute was generated may still be adjusted upon examination by the Internal Revenue Service and the state tax authorities to the extent utilized in a future period. The Company had not, as yet, conducted a study of research and development tax credit carryforwards. This study may result in an adjustment to the Company’s research and development credit carryforwards; however, until a study is completed, and any adjustment is known, no amounts are being presented as an uncertain tax position. A full valuation allowance has been provided against the Company’s research and development credits and, if an adjustment is required, this adjustment would be offset by an adjustment to the valuation allowance. Thus, there would be no impact to the balance sheets or statements of operations and comprehensive loss if an adjustment was required.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2021
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	(10) Commitments and Contingencies Operating Lease Rent expense for each of the years ended December 31, 2021 and 2020 was $ 0.6 million. In December 2017, the Company signed an operating lease for 7,531 rentable square feet of office space in Cambridge, Massachusetts which commenced on February 1, 2018 . The lease expires on June 30, 2024 . Rent expense will be recorded ratably over the lease period. The lease includes escalating rental payments, which are also being charged to rent expense ratably over the lease period. The following table summarizes future minimum payments due under the operating lease as of December 31, 2021: Years Ending December 31, (in thousands) 2022 $ 608 2023 618 2024 313 $ 1,539

Employee Benefit Plan

Employee Benefit Plan	12 Months Ended
	Dec. 31, 2021
Compensation And Retirement Disclosure [Abstract]
Employee Benefit Plan	(11) Employee Benefit Plan The Company maintains a defined contribution 401(k) plan (the 401(k) Plan) in which employees may contribute a portion of their compensation, subject to statutory maximum contribution amounts. The Company assumes all administrative costs of the 401(k) Plan. For each of the years ended December 31, 2021 and 2020, the expense relating to the matching contribution was $ 0.3 million and $ 0.1 million, respectively.

Net Loss per Share

Net Loss per Share	12 Months Ended
	Dec. 31, 2021
Earnings Per Share [Abstract]
Net Loss per Share	(12) Net Loss per Share The following table sets forth the calculation of basic and diluted net loss per share as if the Reorganization occurred at the earliest period presented: Year ended December 31, 2021 2020 (1) (in thousands, except share and per Numerator: Net loss attributable to common stockholders of Cullinan $ ( 65,570 ) $ ( 51,799 ) Denominator Total weighted-average shares used in computing net loss per share, basic and diluted 43,077,330 19,887,307 Net Loss per share: $ ( 1.52 ) $ ( 2.60 ) (1) The shares and per share amounts for the year ended December 31, 2020 were derived from the consolidated financial statements as of that date and were retroactively adjusted as a result of the Reorganization and Reverse Stock Split. See Note 3 to the for additional details. The following table sets forth equity instruments were excluded from the computation of the diluted net loss per share for the periods presented because their effect would have been anti-dilutive as if the Reorganization occurred at the earliest period presented: Year ended December 31, 2021 2020 Stock options 9,258,739 4,603,137 Restricted stock awards 88,883 364,360 Total 9,347,622 4,967,497

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2021
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying consolidated financial statements of the Company have been prepared in conformity with accounting principles generally accepted in the United States of America (GAAP) and in accordance with applicable rules and regulations of the United States Securities and Exchange Commission (SEC) for financial reporting. The consolidated financial statements include accounts of the Company and its consolidated subsidiaries. All intercompany balances have been eliminated in consolidation. Any reference in these notes to applicable guidance is meant to refer to the authoritative GAAP as found in the Accounting Standards Codification (ASC) and Accounting Standards Updates (ASUs) of the Financial Accounting Standards Board (FASB). In the opinion of the Company's management, the consolidated financial statements reflect all adjustments, consisting of normal and recurring adjustments, considered necessary for a fair statement of the Company’s financial position, its results of operations and comprehensive loss and its cash flows for the periods presented.
Use of Estimates	Use of Estimates The preparation of the accompanying consolidated financial statements in accordance with GAAP requires the Company’s management to make estimates and judgments that may affect the reported amounts of assets, liabilities, revenues, expenses and related disclosure of contingent assets and liabilities. On an ongoing basis, the Company’s management evaluates the estimates, including those related to expenses and accruals. The Company’s management bases its estimates on historical experience and on various other assumptions that are believed to be reasonable, the results of which form the basis for making judgments about the carrying values of assets and liabilities. Estimates and assumptions reflected in these consolidated financial statements include, but are not limited to, the fair value of the royalty transfer agreements, accrued research and development costs, the valuation of acquired in-process research and development asset and the fair value of equity awards issued by the Company and its subsidiaries prior to the IPO. Actual results may differ from these estimates under different assumptions or conditions.
Principles of Consolidation	Principles of Consolidation The Company consolidates entities in which it has a controlling financial interest. The Company evaluates each of its subsidiaries to determine whether the entity represents a variable interest entity (VIE) for which consolidation should be evaluated under the VIE model, or alternatively, if the entity is a voting interest entity, for which consolidation should be evaluated using the voting interest model (VOE). The Company concluded that none of its subsidiaries is a VIE and has consolidated each subsidiary under the VOE. Under the VOE, the Company consolidates the entity if it determines 1) that it directly, or indirectly, has greater than 50% of the voting shares or other equity holders do not have substantive voting, participation, or liquidation rights, or 2) when the company has a controlling financial interest through its control of the board of directors, and the significant decisions of the entity are made at the board level. The Company has either created or made investments in the following Asset Subsidiaries: Consolidated Entities Relationship as of December 31, 2021 Date Control First Cullinan Amber Corp. Partially-owned Subsidiary December 2019 Cullinan Florentine Corp. Partially-owned Subsidiary December 2019 Cullinan Mica Corp. Partially-owned Subsidiary May 2020 Cullinan Pearl Corp. Partially-owned Subsidiary November 2018
Noncontrolling Interests	Noncontrolling Interests To the extent that ownership interests in the subsidiaries are held by entities other than the Company, management reports these as noncontrolling interests on the consolidated balance sheets. Earnings or losses are attributed to noncontrolling interests under the hypothetical liquidation at book value (HLBV) method. The HLBV method is a point in time calculation that utilizes inputs to determine the amount that the Company and the noncontrolling interest holders would receive upon a hypothetical liquidation at each balance sheet date based on the liquidation provisions of the respective articles of incorporation. At December 31, 2021, investors and licensors held noncontrolling interests in Amber, Florentine, MICA and Pearl. At December 31, 2020, investors and licensors held noncontrolling interests in Amber, Apollo, Florentine, MICA and Pearl. Refer to Note 4 for details relating to the license agreements and Note 6 for details relating to the noncontrolling interests. For the years ended December 31, 2021 and 2020, $ 1.9 million and $ 7.7 million of net loss, respectively, were attributable to noncontrolling interests and are recorded in the consolidated statements of operations and comprehensive loss and disclosed within the noncontrolling interests in subsidiaries column in the consolidated statements of stockholders' equity.
Comprehensive Loss	Comprehensive Loss Comprehensive loss is defined as the change in equity of a business enterprise during a period from transactions and other events and circumstances from nonowner sources. For years ended December 31, 2021 and 2020, the Company recognized $ 0.8 million in unrealized loss and less than $ 0.1 million in unrealized gain on investments, respectively.
Segments	Segments The Company has determined that its Chief Executive Officer is the Chief Operating Decision Maker (CODM). The Company operates and manages the business as one reporting and one operating segment, which is the business of developing early stage cancer therapeutics. The Company’s CODM reviews financial information on an aggregate basis for purposes of allocating resources and evaluating financial performance. All of the Company’s assets are located in the United States.
Concentration of Credit Risk and Other Risks and Uncertainties	Concentration of Credit Risk and Other Risks and Uncertainties The Company has no significant off-balance sheet risk. Cash and cash equivalents are primarily maintained with two major financial institutions in the United States. Deposits at banks may exceed the insurance provided on such deposits. These deposits may be redeemed upon demand, and therefore, bear minimal risk. The Company is subject to certain risks and uncertainties and believes that changes in any of the following areas could have a material adverse effect on future financial position or results of operations: ability to obtain future financing; regulatory approval and market acceptance of, and reimbursement for, product candidates; performance of third-party clinical research organizations and manufacturers upon which the Company relies; protection of the Company’s intellectual property; litigation or claims against the Company based on intellectual property, patent, product, regulatory or other factors; and the Company’s ability to attract and retain employees necessary to support its growth. The Company is dependent on third-party manufacturers to supply products for research and development activities in its programs. In particular, the Company relies and expects to continue to rely on a small number of manufacturers to supply it with its requirements for drug substance and drug products related to these programs. These programs could be adversely affected by a significant interruption in the supply.
Cash and Cash Equivalents	Cash and Cash Equivalents The Company considers all highly liquid investments with original maturities of three months or less at the time of purchase to be cash equivalents. As of December 31, 2021 and 2020, cash equivalents consist of government-backed money market funds.
Investments	Investments Investments not classified as cash equivalents with maturities of less than twelve months are classified as short-term investments in the consolidated balance sheets. Investments with maturities greater than twelve months for which the Company has the intent and ability to hold the investment for greater than twelve months are classified as long-term investments in the consolidated balance sheets. The Company generally holds investments in marketable securities. Marketable securities are carried at estimated fair value, with unrealized gains or losses included in accumulated other comprehensive income (loss) in stockholders’ equity. The fair value of marketable securities is based on available market information. The amortized cost of marketable securities is adjusted for amortization of premiums and accretion of discounts to maturity. Such amortization is included in interest income. Interest and dividends are also included in interest income. The Company periodically reviews its marketable securities for impairment and adjusts these investments to their fair value when a decline in market value is deemed to be other than temporary. Declines in fair value judged to be other-than-temporary on marketable securities, if any, are included in other income (expense), net. The Company recognized its short-term and long-term investments by security type at December 31, 2021: Amortized Gross Gross Estimated (in thousands) Short-term investments Corporate notes $ 98,642 $ — $ ( 95 ) $ 98,547 Commercial paper 114,174 — ( 27 ) 114,147 U.S. government notes 18,033 — ( 35 ) 17,998 Total short-term investments 230,849 — ( 157 ) 230,692 Long-term investments Corporate notes 117,868 — ( 596 ) 117,272 Asset-backed securities 3,044 — ( 8 ) 3,036 U.S. government notes 20,166 — ( 77 ) 20,089 Total long-term investments 141,078 — ( 681 ) 140,397 Total investments $ 371,927 $ — $ ( 838 ) $ 371,089 The Company recognized its short-term investments by security type at December 31, 2020: Amortized Gross Gross Estimated (in thousands) Corporate notes $ 12,780 $ — $ ( 3 ) $ 12,777 Commercial paper 24,473 — — 24,473 Asset-backed securities 4,757 1 — 4,758 Total investments $ 42,010 $ 1 $ ( 3 ) $ 42,008
Fair Value of Financial Instruments	Fair Value of Financial Instruments Certain assets and liabilities are carried at fair value under GAAP. The fair value hierarchy gives the highest priority to unadjusted quoted prices in active markets for identical assets (Level 1) and the lowest priority to unobservable inputs (Level 3). As required by FASB ASC Topic 820, Fair Value Measurement (ASC Topic 820) the Company’s financial assets are classified within the fair value hierarchy based on the lowest level of input that is significant to the fair value measurement. The three levels of the fair value hierarchy under ASC Topic 820, and its applicability to the Company’s financial assets, are described below: Level 1—Unadjusted quoted prices in active markets that are accessible at the measurement date of identical, unrestricted assets. Level 2—Quoted prices for similar assets, or inputs that are observable, either directly or indirectly, for substantially the full term through corroboration with observable market data. Level 3—Pricing inputs are unobservable for the asset, that is, inputs that reflect the reporting entity’s own assumptions about the assumptions market participants would use in pricing the asset. Asset-backed securities, commercial paper and corporate and U.S. government notes are primarily valued using market quotations or prices obtained from independent pricing sources which may employ various pricing methods to value the investments including matrix pricing. The following table sets forth the fair value of the Company’s financial assets as of December 31, 2021, allocated into Level 1, Level 2 and Level 3, that was measured on a recurring basis: Level 1 Level 2 Level 3 Total (in thousands) Cash and cash equivalents Cash $ 35,925 $ — $ — $ 35,925 Money market funds 23,849 — — 23,849 Total cash and cash equivalents 59,774 — — 59,774 Short-term investments Corporate notes — 98,547 — 98,547 Commercial paper — 114,147 — 114,147 U.S. government notes — 17,998 — 17,998 Total short-term investments — 230,692 — 230,692 Long-term investments Corporate notes — 117,272 — 117,272 Asset-backed securities — 3,036 — 3,036 U.S. government notes — 20,089 — 20,089 Total long-term investments — 140,397 — 140,397 Total cash, cash equivalents and investments $ 59,774 $ 371,089 $ — $ 430,863 The following table sets forth the fair value of the Company’s financial assets as of December 31, 2020, allocated into Level 1, Level 2 and Level 3, that was measured on a recurring basis: Level 1 Level 2 Level 3 Total (in thousands) Cash and cash equivalents Cash $ 22,007 $ — $ — $ 22,007 Money market funds 146,191 — — 146,191 Total cash and cash equivalents 168,198 — — 168,198 Short-term investments Corporate notes — 12,777 — 12,777 Commercial paper — 24,473 — 24,473 Asset-backed securities — 4,758 — 4,758 Total short-term investments — 42,008 — 42,008 Total cash, cash equivalents and investments $ 168,198 $ 42,008 $ — $ 210,206 Prepaid expenses and other current assets, accounts payable and accrued expenses and other current liabilities are carried at cost, which management believes approximates fair value due to their short term nature.
Deferred Offering Costs	Deferred Offering Costs The Company capitalizes costs that are directly associated with in-process equity financings until such financings are consummated at which time such costs are recorded against the gross proceeds of the offering. Should the in-process equity financing be abandoned, the deferred offering costs will be expensed immediately as a charge to operating expenses in the consolidated statements of operations and comprehensive loss. The Company incurred $ 2.7 million of deferred offering costs in 2020 and recorded such amounts against the gross proceeds of the Company’s IPO within the statements of stockholders’ equity for the year ended December 31, 2021.
Property and Equipment	Property and Equipment Property and equipment are stated at cost less accumulated depreciation and amortization. Depreciation expense is recognized using the straight-line method over the estimated useful life of each asset as follows: Computers 3 years Office furniture and equipment 5 years Leasehold improvements Shorter of the useful life of the asset or the lease term Maintenance and repairs that do not improve or extend the life of the assets are expensed when incurred. Upon sale or retirement of assets, the cost and accumulated depreciation and amortization are removed from the consolidated balance sheet and any resulting gain or loss is reflected in the consolidated statements of operations and comprehensive loss in the period realized. Property and equipment consisted of the following: December 31, 2021 2020 (in thousands) Computers $ 70 $ 70 Office furniture and equipment 134 134 Leasehold improvements 105 105 Total property and equipment, gross 309 309 Less: accumulated depreciation ( 232 ) ( 179 ) Total property and equipment, net $ 77 $ 130 Depreciation expense was less than $ 0.1 million for each of the years ended December 31, 2021 and 2020.
Accrued Liabilities and Other Current Liabilities	Accrued liabilities and other current liabilities Accrued expenses and other current liabilities consist of the following: December 31, 2021 2020 (in thousands) Accrued bonus $ 2,576 $ 1,763 Professional fees and other 973 1,049 Research and development costs 5,028 1,829 $ 8,577 $ 4,641
Asset Acquisitions	Asset Acquisitions The Company measures and recognizes asset acquisitions that are not deemed to be business combinations based on the cost to acquire the assets, which includes transactions costs. Goodwill is not recognized in asset acquisitions. In an asset acquisition, the cost allocated to acquire in-process research and development (IPR&D) with no alternative future use is charged to research and development expense at the acquisition date.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets Long-lived assets are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. Recoverability of assets to be held and used is measured by a comparison of the carrying amount of an asset to future undiscounted net cash flows expected to be generated. Impairment charges are recognized at the amount by which the carrying amount of an asset exceeds the fair value of the asset. Assets to be disposed of are reported at the lower of the carrying amount or the fair value less costs to sell. There was no impairment of long-lived assets for any of the periods presented.
Revenue Recognition	Revenue Recognition The Company recognizes revenue in accordance with ASC Topic 606, Revenue from Contracts with Customers, or ASC 606. This standard applies to all contracts with customers, except for contracts that are within the scope of other standards, such as leases, insurance, collaboration arrangements and financial instruments. Under ASC 606, an entity recognizes revenue when its customer obtains control of promised goods or services, in an amount that reflects the consideration which the entity expects to receive in exchange for those goods or services. To determine revenue recognition for arrangements that an entity determines are within the scope of ASC 606, the entity performs the following five steps: (i) identify the contract(s) with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when (or as) the entity satisfies a performance obligation. The Company only applies the five-step model to contracts when it is probable that the entity will collect the consideration it is entitled to in exchange for the goods or services it transfers to the customer. At contract inception, once the contract is determined to be within the scope of ASC 606, the Company assesses the goods or services promised within each contract and determines those that are performance obligations and assesses whether each promised good or service is distinct. The Company then recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) the performance obligation is satisfied. The Company enters into licensing arrangements for research and development, manufacturing and commercialization activities, which have components within the scope of ASC 606. Payments pursuant to these arrangements typically include non-refundable, upfront payments, milestone payments upon achieving significant development events, research and development reimbursements, sales milestones and royalties on future product sales. The amount of variable consideration is constrained until it is probable that the revenue is not at a significant risk of reversal in a future period. The contracts into which the Company enters generally do not include significant financing components. As part of the accounting for these arrangements, the Company must use significant judgment to determine: a) the number of performance obligations based on the determination under step (ii) above; b) the transaction price under step (iii) above; c) the stand-alone selling price for each performance obligation identified in the contract for the allocation of transaction price in step (iv) above, and d) the measure of progress in step (v) above. The Company uses judgment to determine whether milestones or other variable consideration, except for royalties, should be included in the transaction price as described further below. Non-Exclusive Licenses If the license to the Company’s intellectual property is determined to be distinct from the other promises or performance obligations identified in the arrangement, the Company recognizes revenue from non-refundable, upfront fees allocated to the license when the license is transferred to the customer and the customer is able to use and benefit from the license. In assessing whether a promise or performance obligation is distinct from the other elements, the Company considers factors such as the research, development, manufacturing and commercialization capabilities of the collaboration partner and the availability of the associated expertise in the general marketplace. In addition, the Company considers whether the collaboration partner can benefit from a promise for its intended purpose without the receipt of the remaining elements, whether the value of the promise is dependent on the unsatisfied promise, whether there are other vendors that could provide the remaining promise and whether it is separately identifiable from the remaining promise. For licenses that are combined with other promises, the Company utilizes judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition. The measure of progress, and thereby periods over which revenue should be recognized, are subject to estimates by management and may change over the course of the agreement. Such a change could have a material impact on the amount of revenue the Company records in future periods. Milestone Payments At the inception of each arrangement that includes milestone payments, the Company evaluates whether the milestones are considered probable of being achieved and estimates the amount to be included in the transaction price using the most likely amount method. If it is probable that a significant revenue reversal would not occur, the associated milestone value is included in the transaction price. Milestone payments that are not within the control of the Company or the licensee, such as regulatory approvals, are not considered probable of being achieved until those approvals are received. The Company evaluates factors such as the scientific, clinical, regulatory, commercial and other risks that must be overcome to achieve the respective milestone in making this assessment. There is considerable judgment involved in determining whether it is probable that a significant revenue reversal would not occur. At the end of each subsequent reporting period, the Company reevaluates the probability of achievement of all milestones subject to constraint and, if necessary, adjusts its estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis, which would affect revenues and earnings in the period of adjustment. Royalties For arrangements that include sales-based royalties, including milestone payments based on a level of sales, and the license of intellectual property is deemed to be the predominant item to which the royalties relate, the Company recognizes revenue at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied (or partially satisfied). To date, the Company has not recognized any royalty revenue resulting from any of its licensing arrangements.
Research and Development Expenses	Research and Development Expenses Research and development costs are expensed as incurred and consist primarily of funds for employee wages and funds paid to third parties for the provision of services for product candidate development, clinical and preclinical development and related supply and manufacturing costs, and regulatory compliance costs. At the end of the reporting period, the Company compares payments made to third-party service providers to the estimated progress toward completion of the research or development objectives. Such estimates are subject to change as additional information becomes available. Depending on the timing of payments to the service providers and the progress that the Company estimates has been made as a result of the service provided, the Company may record net prepaid or accrued expense relating to these costs. Costs incurred to obtain licenses are recognized as research and development expense as incurred if the technology licensed has no alternative future use. Advance payments for goods or services to be received in the future for use in research and development activities are recorded as prepaid expenses. The prepaid amounts are expensed as the related goods are received or services are performed. The Company has entered into various research and development related contracts with parties both inside and outside of the United States. The payments related to these agreements are recorded as research and development expenses as incurred. The Company records accrued liabilities for estimated ongoing research and development costs. When evaluating the adequacy of the accrued liabilities, the Company analyzes progress of the studies or clinical trials, including the phase or completion of events, invoices received and contracted costs. Significant judgments and estimates are made in determining the accrued balances at the end of any reporting period. Actual results could differ from the Company’s estimates. To date, there have been no material differences between the Company’s accrued costs and actual costs.
Patent Costs	Patent Costs All patent-related costs incurred in connection with filing and prosecuting patent applications are expensed as incurred due to the uncertainty about the recovery of the expenditure. Amounts incurred are classified as general and administrative expenses in the consolidated statements of operations and comprehensive loss.
Equity-Based Compensation	Equity-Based Compensation Equity-based compensation is measured at the grant date for all equity-based awards made to employees and non-employees based on the fair value of the awards and is recognized as expense on a straight-line basis over the requisite service period, which is generally the vesting period. The Company has elected to recognize the actual forfeitures by reducing the equity-based compensation expense in the same period as the forfeitures occur. The Company estimated the fair of the stock options using the Black-Scholes option pricing model, which requires the input of objective and subjective assumptions. Certain assumptions used, including the fair value of the Company’s common stock prior to IPO and stock price volatility, represent management’s estimates and involve inherent uncertainties and the application of management’s judgment. As a result, if factors change and management uses different assumptions, equity-based compensation expense could be materially different for future awards. The Company classifies equity-based compensation in its consolidated statements of operations and comprehensive loss in the same manner in which the award recipient’s payroll costs are classified or in which the award recipient’s service payments are classified.
Income Taxes	Income Taxes The Company accounts for income taxes using the asset and liability method in accordance with FASB ASC Topic 740, Income Taxes. Current income taxes are based on taxable income for federal and state reporting purposes. Deferred income tax assets and liabilities are recognized for the future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases using enacted tax rates in effect for the year in which the differences are expected to affect taxable income. A valuation allowance is provided when it is more likely than not that some portion, or all of a deferred tax asset will not be realized. Due to the Company's lack of earnings history, the net deferred tax assets have been fully offset by a valuation allowance at both December 31, 2021 and 2020. The Company recognizes the effect of income tax positions only if those positions are more likely than not of being sustained. Recognized income tax positions are measured at the largest amount of benefit that is greater than fifty percent likely to be realized upon settlement. Changes in measurement are reflect in the period in which the change in judgment occurs.
Net Loss per Share	Net Loss per Share Basic and diluted net loss per share is determined by dividing net loss attributable to common stockholders by the weighted-average shares of common stock outstanding during the period, without consideration for potential dilutive shares of common stock, such as stock options, unvested restricted stock awards and shares issuable under the employee stock purchase plan. Accordingly, in periods in which the Company reports a net loss attributable to common stockholders, diluted net loss per share attributable to common stockholders is the same as basic net loss per share attributable to common stockholders, since dilutive shares of common stock are not assumed to have been issued if their effect is anti-dilutive. Therefore, the weighted-average shares used to calculate both basic and diluted net loss per share are the same for the periods presented. The Company excluded unvested shares of restricted stock awards, stock options and shares issuable under the employee stock purchase plan from the computation of diluted weighted-average shares outstanding as they would be antidilutive.
Emerging Growth Company Status	Emerging Growth Company Status The Company is an emerging growth company, as defined in the Jumpstart Our Business Startups Act of 2012 (the JOBS Act). Under the JOBS Act, emerging growth companies can delay adopting new or revised accounting standards issued subsequent to the enactment of the JOBS Act until such time as those standards apply to private companies. The Company has elected to use this extended transition period for complying with new or revised accounting standards that have different effective dates for public and private companies until the earlier of the date that it (i) is no longer an emerging growth company or (ii) affirmatively and irrevocably opts out of the extended transition period provided in the JOBS Act. As a result, these consolidated financial statements may not be comparable to companies that comply with the new or revised accounting pronouncements as of public company effective dates. The JOBS Act does not preclude an emerging growth company from adopting a new or revised accounting standard earlier than the time that such standard applies to private companies. The Company expects to use the extended transition period for any other new or revised accounting standards during the period in which it remains an emerging growth company.
Recently Adopted Accounting Pronouncements	Recently Adopted Accounting Pronouncements In August 2020, FASB issued ASU No. 2020-06 , Debt—Debt with Conversion and Other Options (Subtopic 470-20) and Derivatives and Hedging—Contracts in Entity’s Own Equity (Subtopic 815-40): Accounting for Convertible Instruments and Contracts in an Entity’s Own Equity (ASU 2020-06), which, among other things, provides guidance on how to account for contracts on an entity’s own equity. ASU 2020-06 simplifies the accounting for certain financial instruments with characteristics of liabilities and equity. Specifically, ASU 2020-06 eliminated the need for the Company to assess whether a contract on the entity’s own equity (1) permits settlement in unregistered shares, (2) whether counterparty rights rank higher than shareholder’s rights, and (3) whether collateral is required. In addition, ASU 2020-06 requires incremental disclosure related to contracts on the entity’s own equity and clarifies the treatment of certain financial instruments accounted for under this ASU on earnings per share. ASU 2020-06 may be applied on a full retrospective or modified retrospective basis. ASU 2020-06 became effective January 1, 2022 including interim periods presented within that year. Early adoption of the ASU is permitted by the Company effective January 1, 2021. The Company adopted ASU 2020-06 beginning on January 1, 2021. The adoption of ASU 2020-06 did not materially impact the Company’s consolidated financial statements and associated disclosures.
Recently Issued Accounting Pronouncements Not Yet Adopted	Recently Issued Accounting Pronouncements Not Yet Adopted In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842), to increase transparency and comparability among organizations by recognizing a right-of-use asset and a lease liability on the balance sheet for all leases with terms longer than 12 months. Leases will be classified as either operating or financing, with such classifications affecting the pattern of expense recognition in the income statement. ASU 2016-02 is effective for fiscal years beginning after December 15, 2019, and early adoption is permitted. ASU 2016-02 was recently delayed for emerging growth companies that elected to adopt new accounting standards on the adoption date required for private companies and will be effective for the Company’s annual reporting period beginning on January 1, 2022 and interim periods beginning in the first quarter of 2023. The Company will adopt ASU 2016-02 in the first quarter of 2022 using a modified retrospective approach under which the cumulative effect of initially applying the standard will be recognized as an adjustment to its opening 2022 retained earnings, with no restatement of prior year amounts. The Company will apply an optional package of practical expedients intended to ease transition to the standard for existing leases by, among its provisions, allowing the Company to carry forward its original lease classification conclusions without reassessment. The Company also intends to elect application of the practical expedient to not separate non-lease components from lease components for purposes of measuring its lease-related balances. Based on assessment efforts to date, the Company estimates that the adoption of ASU 2016-02 will result in initial increases in its long-term assets and liabilities of approximately $ 1.3 million to $ 1.4 million relating to its existing lease commitments that will become subject to balance sheet recognition. These balances will fluctuate over time as the Company's lease portfolio changes as a result of ongoing lease-related activity. The standard also requires enhanced quantitative and qualitative lease-related disclosures. Recognition of lease expense in the consolidated statement of operations and comprehensive loss will not significantly change. In December 2019, the FASB issued ASU No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes (ASU 2019-12), which is intended to simplify the accounting for income taxes. ASU 2019-12 removes certain exceptions to the general principles in Topic 740 and also clarifies and amends existing guidance to improve consistent application. The new standard became effective beginning January 1, 2022. The Company does not expect the adoption of ASU 2019-12 to have a material impact on its consolidated financial position and consolidated results of operations upon adoption.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2021
Accounting Policies [Abstract]
Schedule of Short-term and Long-term Investment Marketable Securities by Security Type	The Company recognized its short-term and long-term investments by security type at December 31, 2021: Amortized Gross Gross Estimated (in thousands) Short-term investments Corporate notes $ 98,642 $ — $ ( 95 ) $ 98,547 Commercial paper 114,174 — ( 27 ) 114,147 U.S. government notes 18,033 — ( 35 ) 17,998 Total short-term investments 230,849 — ( 157 ) 230,692 Long-term investments Corporate notes 117,868 — ( 596 ) 117,272 Asset-backed securities 3,044 — ( 8 ) 3,036 U.S. government notes 20,166 — ( 77 ) 20,089 Total long-term investments 141,078 — ( 681 ) 140,397 Total investments $ 371,927 $ — $ ( 838 ) $ 371,089 The Company recognized its short-term investments by security type at December 31, 2020: Amortized Gross Gross Estimated (in thousands) Corporate notes $ 12,780 $ — $ ( 3 ) $ 12,777 Commercial paper 24,473 — — 24,473 Asset-backed securities 4,757 1 — 4,758 Total investments $ 42,010 $ 1 $ ( 3 ) $ 42,008
Summary of Fair Value of Financial Assets Measured on Recurring Basis	The following table sets forth the fair value of the Company’s financial assets as of December 31, 2021, allocated into Level 1, Level 2 and Level 3, that was measured on a recurring basis: Level 1 Level 2 Level 3 Total (in thousands) Cash and cash equivalents Cash $ 35,925 $ — $ — $ 35,925 Money market funds 23,849 — — 23,849 Total cash and cash equivalents 59,774 — — 59,774 Short-term investments Corporate notes — 98,547 — 98,547 Commercial paper — 114,147 — 114,147 U.S. government notes — 17,998 — 17,998 Total short-term investments — 230,692 — 230,692 Long-term investments Corporate notes — 117,272 — 117,272 Asset-backed securities — 3,036 — 3,036 U.S. government notes — 20,089 — 20,089 Total long-term investments — 140,397 — 140,397 Total cash, cash equivalents and investments $ 59,774 $ 371,089 $ — $ 430,863 The following table sets forth the fair value of the Company’s financial assets as of December 31, 2020, allocated into Level 1, Level 2 and Level 3, that was measured on a recurring basis: Level 1 Level 2 Level 3 Total (in thousands) Cash and cash equivalents Cash $ 22,007 $ — $ — $ 22,007 Money market funds 146,191 — — 146,191 Total cash and cash equivalents 168,198 — — 168,198 Short-term investments Corporate notes — 12,777 — 12,777 Commercial paper — 24,473 — 24,473 Asset-backed securities — 4,758 — 4,758 Total short-term investments — 42,008 — 42,008 Total cash, cash equivalents and investments $ 168,198 $ 42,008 $ — $ 210,206
Summary of Estimated Useful Life of Property and Equipment	Property and equipment are stated at cost less accumulated depreciation and amortization. Depreciation expense is recognized using the straight-line method over the estimated useful life of each asset as follows: Computers 3 years Office furniture and equipment 5 years Leasehold improvements Shorter of the useful life of the asset or the lease term
Summary of Property and Equipment	Property and equipment consisted of the following: December 31, 2021 2020 (in thousands) Computers $ 70 $ 70 Office furniture and equipment 134 134 Leasehold improvements 105 105 Total property and equipment, gross 309 309 Less: accumulated depreciation ( 232 ) ( 179 ) Total property and equipment, net $ 77 $ 130
Summary of Accrued Expenses and Other Current Liabilities	Accrued expenses and other current liabilities consist of the following: December 31, 2021 2020 (in thousands) Accrued bonus $ 2,576 $ 1,763 Professional fees and other 973 1,049 Research and development costs 5,028 1,829 $ 8,577 $ 4,641

Reorganization and Reverse St_2

Reorganization and Reverse Stock Split (Tables)	12 Months Ended
	Dec. 31, 2021
Reorganization And Reverse Stock Split [Abstract]
Number of Shares of Common Stock Exchanged and Issued to Unitholders on Split Adjusted Basis	the existing units of the LLC were cancelled and the number of shares of common stock exchanged and issued to the LLC’s unitholders in the Reorganization is shown in the below table by unit class, on a split adjusted basis: Cullinan Oncology, LLC Unit Type Number of Management's Adjusted for the Reverse Series C Preferred Units 66,599,045 9,461,414 Series B Preferred Units 63,141,016 8,970,154 Series A1 Preferred Units 50,000,000 7,103,280 Series Seed Preferred Units 16,000,000 2,273,050 Non-Voting Incentive Units 11,896,500 1,689,949 Common Units 34,747,722 4,936,415 Total shares issued 242,384,283 34,434,262
Summary of LLC Units Previously Reported as Redeemable Preferred Units or Temporary Equity Converted Reclassified to Equity	All LLC units that were previously reported as Redeemable Preferred Units, or temporary equity, were converted to common stock of the Company upon the execution of the Reorganization and have been reclassified to stockholders’ equity for all periods presented, as if the Reorganization occurred at the beginning of the earliest period presented in the Company’s financial statements for the years ended December 31, 2020 and 2019: As of December 31, 2020 As Reported Adjustment As Adjusted (in thousands) Redeemable Preferred Units Series Seed Redeemable Preferred Units $ 3,956 $ ( 3,956 ) $ — Series A1 Redeemable Preferred Units 49,946 ( 49,946 ) — Series B Redeemable Preferred Units 97,909 ( 97,909 ) — Series C Redeemable Preferred Units 124,841 ( 124,841 ) — Total Redeemable Preferred Units 276,652 ( 276,652 ) — Stockholders' Equity (Members' Deficit) Non-Voting Incentive Units 1 ( 1 ) — Common Stock — 3 3 Additional paid-in capital 15,698 276,650 292,348 Accumulated other comprehensive loss ( 2 ) — ( 2 ) Accumulated deficit ( 93,339 ) — ( 93,339 ) Total Cullinan Stockholders' Equity (Members' Deficit) ( 77,642 ) 276,652 199,010 Non-controlling interests in subsidiaries 1,304 — 1,304 Total Stockholders' Equity (Members' Deficit) $ ( 76,338 ) $ 276,652 $ 200,314 As of December 31, 2019 As Reported Adjustment As Adjusted (in thousands) Redeemable Preferred Units Series Seed Redeemable Preferred Units $ 3,956 $ ( 3,956 ) $ — Series A1 Redeemable Preferred Units 49,946 ( 49,946 ) — Series B Redeemable Preferred Units 83,872 ( 83,872 ) — Series C Redeemable Preferred Units — — — Total Redeemable Preferred Units 137,774 ( 137,774 ) — Stockholders' Equity (Members' Deficit) Non-Voting Incentive Units 1 ( 1 ) — Common Stock — 2 2 Additional paid-in capital 770 137,773 138,543 Accumulated other comprehensive loss ( 4 ) — ( 4 ) Accumulated deficit ( 41,540 ) — ( 41,540 ) Total Cullinan Stockholders' Equity (Members' Deficit) ( 40,773 ) 137,774 97,001 Non-controlling interests in subsidiaries 864 — 864 Total Stockholders' Equity (Members' Deficit) $ ( 39,909 ) $ 137,774 $ 97,865

License and Collaboration Agr_2

License and Collaboration Agreements (Tables)	12 Months Ended
	Dec. 31, 2021
License And Collaboration Agreements [Abstract]
Summary of Research and Development Costs Related to Collaboration and License Agreements	The following table summarizes the impact of research and development costs related to the collaboration and license agreements on the Company’s consolidated statements of operations and comprehensive loss for the years ended December 31, 2021 and 2020. December 31, 2021 2020 (in thousands) Adimab $ 46 $ 1,318 Amber - MIT 71 333 Apollo - Wistar — 355 Florentine - Tubigen — 912 Pearl - Taiho 3,000 531 $ 3,117 $ 3,449

Equity-Based Compensation (Tabl

Equity-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2021
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Summary of Non-Voting Incentive Unit Activity	The following table summarizes the Non-Voting Incentive Unit activities for the years ended December 31, 2021 and 2020 as if the Non-Voting Incentive Units were converted to restricted common stock of the Company at the earliest period presented: Number of Weighted Outstanding unvested as of December 31, 2019 580,334 $ 0.0001 Vested ( 407,844 ) 0.0001 Outstanding unvested as of December 31, 2020 172,490 0.0001 Vested ( 172,490 ) 0.0001 Outstanding unvested as of December 31, 2021 — 0.0001 Outstanding vested as of December 31, 2021 1,689,949 $ 0.0001
Summary of Restricted Common Unit Activities	The following table summarizes the restricted common unit activities for the years ended December 31, 2021 and 2020 as if the restricted common units were converted to restricted common stock of the Company at the earliest period presented: Number of Incremental Fair Value Per Share Total units exchanged as of November 4, 2020 320,228 $ 3.87 Vested ( 128,358 ) 3.87 Outstanding unvested as of December 31, 2020 191,870 $ 3.87 Vested ( 102,987 ) 3.87 Outstanding unvested as of December 31, 2021 88,883 $ 3.87 Outstanding vested as of December 31, 2021 231,345 $ 3.87
Summary of Grant Date Fair Value	For the years ended December 31, 2021 and 2020, the weighted average grant date fair value of the options granted were $ 15.73 and $ 6.19 per share, respectively. The grant date fair value was estimated at the time of grant using the Black-Scholes option-pricing model using the following weighted average assumptions: Year Ended December 31, 2021 Year Ended December 31, 2020 Weighted average risk-free interest rate 1.02 % 0.51 % Expected term (in years) 6.00 5.98 Expected volatility 76.22 % 77.40 % Expected dividend yield 0.00 % 0.00 %
Schedule of Equity-based Compensation Expense Categories In Consolidated Statements of Operations and Comprehensive Loss	The Company recorded equity-based compensation in the following expense categories in the consolidated statements of operations and comprehensive loss: Year ended December 31, 2021 2020 (in thousands) Research and development $ 8,914 $ 5,912 General and administrative 15,461 8,998 Total equity-based compensation $ 24,375 $ 14,910
Employees and Non-Employees
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Summary of Activity Related to Stock Options Grants	The following table summarizes the activity related to stock option grants to employees and non-employees for the years ended December 31, 2021 and 2020 under the 2021 Stock Plan. This also includes the common unit options issued under the 2020 Plan that were cancelled and exchanged into stock options under the 2021 Stock Plan with the number of options issued and weighted average exercise price presented as if the Reorganization occurred at the earliest period presented: Number of Weighted Average Exercise Price Weighted Average Remaining Contractual Term (Years) Outstanding as of December 31, 2019 — $ — — Granted 4,616,187 4.30 — Exercised ( 13,050 ) 4.30 — Outstanding as of December 31, 2020 4,603,137 $ 4.30 9.84 Granted 5,481,816 23.82 — Exercised ( 763,000 ) 4.30 — Forfeited ( 63,214 ) 17.23 — Outstanding as of December 31, 2021 9,258,739 $ 15.77 9.22 Options exercisable as of December 31, 2021 3,271,196 $ 7.65 8.90 Options unvested as of December 31, 2021 5,987,543 $ 20.20 9.39

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2021
Income Tax Disclosure [Abstract]
Summary of Reconciliation of Statutory Income Tax Rate To Effective Income Tax Rate	A reconciliation of the Company’s statutory income tax rate to the Company’s effective income tax rate is as follows: Year ended 2021 2020 Federal statutory rate 21.00 % 21.00 % State taxes, net of federal benefit 9.96 % ( 1.83 )% Permanent differences 0.01 % ( 0.01 )% Equity-based compensation 0.39 % — Tax credits ( 0.25 )% 0.77 % Valuation allowance ( 32.12 %) ( 12.65 %) Non-taxable income — ( 5.01 )% IPR&D — ( 2.28 %) Change in tax status 1.76 % — Return to provision 1.15 % — Other ( 1.90 )% — 0.00 % 0.00 %
Summary of Net Deferred Income Tax Asset	The net deferred income tax asset balance related to the following: December 31, 2021 2020 (in thousands) Deferred tax assets: Net operating loss $ 31,414 $ 18,563 Capitalized organizational and start-up expenses 140 148 Licenses 1,875 1,601 Accrued expenses 968 467 Research and development credit 1,563 1,859 Equity-based compensation 8,584 8 Gross deferred tax assets 44,544 22,646 Valuation allowance ( 44,552 ) ( 22,642 ) Net deferred tax asset ( 8 ) 4 Deferred tax liability Depreciation and amortization 8 ( 4 ) Net deferred tax asset $ — $ —
Summary of Valuation Allowance	The Company’s valuation allowance increased during the years ended December 31, 2021 and 2020 due primarily to the generation of net operating losses, as follows: Year ended 2021 2020 (in thousands) Valuation allowance at beginning of year $ 22,642 $ 10,653 Increases recorded to income tax provision 21,674 11,989 Increases recorded to OCI/Equity 236 — Valuation allowance at end of year $ 44,552 $ 22,642

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2021
Commitments And Contingencies Disclosure [Abstract]
Summary of Future Minimum Payments Due Under Operating Lease	The following table summarizes future minimum payments due under the operating lease as of December 31, 2021: Years Ending December 31, (in thousands) 2022 $ 608 2023 618 2024 313 $ 1,539

Net Loss per Share (Tables)

Net Loss per Share (Tables)	12 Months Ended
	Dec. 31, 2021
Earnings Per Share [Abstract]
Summary of Calculation of Basic and Diluted Net Loss Per Share	The following table sets forth the calculation of basic and diluted net loss per share as if the Reorganization occurred at the earliest period presented: Year ended December 31, 2021 2020 (1) (in thousands, except share and per Numerator: Net loss attributable to common stockholders of Cullinan $ ( 65,570 ) $ ( 51,799 ) Denominator Total weighted-average shares used in computing net loss per share, basic and diluted 43,077,330 19,887,307 Net Loss per share: $ ( 1.52 ) $ ( 2.60 ) (1) The shares and per share amounts for the year ended December 31, 2020 were derived from the consolidated financial statements as of that date and were retroactively adjusted as a result of the Reorganization and Reverse Stock Split. See Note 3 to the for additional details.
Summary of Equity Instruments Excluded from Computation of Diluted Net Loss Per Share	The following table sets forth equity instruments were excluded from the computation of the diluted net loss per share for the periods presented because their effect would have been anti-dilutive as if the Reorganization occurred at the earliest period presented: Year ended December 31, 2021 2020 Stock options 9,258,739 4,603,137 Restricted stock awards 88,883 364,360 Total 9,347,622 4,967,497

Nature of Business and Basis _2

Nature of Business and Basis of Presentation - Additional Information (Details) $ / shares in Units, $ in Thousands	1 Months Ended	12 Months Ended
	Jan. 31, 2021USD ($)$ / sharesshares	Dec. 31, 2021USD ($)Subsidiary	Dec. 31, 2020USD ($)Subsidiary		Dec. 31, 2019USD ($)
Nature Of Business And Basis Of Presentation [Line Items]
Number of development subsidiaries | Subsidiary		4	5
Net proceeds received from offering	$ 264,500	$ 267,268
Reverse stock split conversion ratio		1
Reverse stock split		one-for-7.0390
Accumulated deficit		$ (158,909)	$ (93,339)	[1]	$ (41,540)
Long-term investments		140,397	$ 0	[1]
Cash, cash equivalents and short-term investments		$ 290,500
IPO
Nature Of Business And Basis Of Presentation [Line Items]
Common stock shares issued and sold | shares	13,685,000
Stock, price per Share | $ / shares	$ 21
Underwriters' Option
Nature Of Business And Basis Of Presentation [Line Items]
Common stock shares issued and sold | shares	1,785,000
[1]	The consolidated balance sheet as of December 31, 2020 is derived from the consolidated financial statements as of that date and was retroactively adjusted, including shares and per share amounts, as a result of the Reorganization and Reverse Stock Split. See Note 3 to the consolidated financial statements for additional details.

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Additional Information (Details)	12 Months Ended
	Dec. 31, 2021USD ($)Segment	Dec. 31, 2020USD ($)
Accounting Policies [Line Items]
Description of voting rights	Each share of common stock entitles the holder to one vote and to receive dividends when and if declared by the board of directors of the Company.
Net loss attributable to noncontrolling interests	$ 1,900,000	$ 7,700,000
Unrealized gain (loss) on investments	$ (836,000)	2,000	[1]
Number of reporting segments | Segment	1
Number of operating segments | Segment	1
Deferred offering costs		2,700,000
Impairment of long-lived assets	$ 0	0
Maximum
Accounting Policies [Line Items]
Unrealized gain (loss) on investments		100,000
Depreciation expense	100,000	$ 100,000
ASU 2016-02 | Maximum
Accounting Policies [Line Items]
Initial increases in long-term assets and liabilities effect of adoption of accounting standard	1,400,000
ASU 2016-02 | Minimum
Accounting Policies [Line Items]
Initial increases in long-term assets and liabilities effect of adoption of accounting standard	$ 1,300,000
[1]	The shares and per share amounts for the year ended December 31, 2020 were derived from the consolidated financial statements as of that date and were retroactively adjusted as a result of the Reorganization and Reverse Stock Split. See Note 3 to the consolidated financial statements for additional details.

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Schedule of Short-term and Long-term Investment Marketable Securities by Security Type (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Available For Sale Securities Fair Value To Amortized Cost Basis [Line Items]
Amortized Cost	$ 371,927
Gross Unrealized Gains	0
Gross Unrealized Losses	(838)
Estimated Fair Value	371,089
Short Term Investments
Available For Sale Securities Fair Value To Amortized Cost Basis [Line Items]
Amortized Cost	230,849	$ 42,010
Gross Unrealized Gains		1
Gross Unrealized Losses	(157)	(3)
Estimated Fair Value	230,692	42,008
Short Term Investments | Corporate Note Securities
Available For Sale Securities Fair Value To Amortized Cost Basis [Line Items]
Amortized Cost	98,642	12,780
Gross Unrealized Losses	(95)	(3)
Estimated Fair Value	98,547	12,777
Short Term Investments | Asset-backed Securities
Available For Sale Securities Fair Value To Amortized Cost Basis [Line Items]
Amortized Cost		4,757
Gross Unrealized Gains		1
Estimated Fair Value		4,758
Short Term Investments | Commercial Paper
Available For Sale Securities Fair Value To Amortized Cost Basis [Line Items]
Amortized Cost	114,174	24,473
Gross Unrealized Losses	(27)
Estimated Fair Value	114,147	$ 24,473
Short Term Investments | U.S. Government Notes
Available For Sale Securities Fair Value To Amortized Cost Basis [Line Items]
Amortized Cost	18,033
Gross Unrealized Losses	(35)
Estimated Fair Value	17,998
Long Term Investments
Available For Sale Securities Fair Value To Amortized Cost Basis [Line Items]
Amortized Cost	141,078
Gross Unrealized Losses	(681)
Estimated Fair Value	140,397
Long Term Investments | Corporate Note Securities
Available For Sale Securities Fair Value To Amortized Cost Basis [Line Items]
Amortized Cost	117,868
Gross Unrealized Losses	(596)
Estimated Fair Value	117,272
Long Term Investments | Asset-backed Securities
Available For Sale Securities Fair Value To Amortized Cost Basis [Line Items]
Amortized Cost	3,044
Gross Unrealized Losses	(8)
Estimated Fair Value	3,036
Long Term Investments | U.S. Government Notes
Available For Sale Securities Fair Value To Amortized Cost Basis [Line Items]
Amortized Cost	20,166
Gross Unrealized Losses	(77)
Estimated Fair Value	$ 20,089

Summary of Significant Accoun_6

Summary of Significant Accounting Policies - Summary of Fair Value of Financial Assets Measured on Recurring Basis (Details) - Recurring - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash and cash equivalents	$ 59,774	$ 168,198
Total short-term investments	230,692	42,008
Total long-term investments	140,397
Total cash, cash equivalents and investments	430,863	210,206
Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash and cash equivalents	59,774	168,198
Total cash, cash equivalents and investments	59,774	168,198
Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total short-term investments	230,692	42,008
Total long-term investments	140,397
Total cash, cash equivalents and investments	371,089	42,008
Cash
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash and cash equivalents	35,925	22,007
Cash | Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash and cash equivalents	35,925	22,007
Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash and cash equivalents	23,849	146,191
Money Market Funds | Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash and cash equivalents	23,849	146,191
Corporate Note Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total short-term investments	98,547	12,777
Total long-term investments	117,272
Corporate Note Securities | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total short-term investments	98,547	12,777
Total long-term investments	117,272
Commercial Paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total short-term investments	114,147	24,473
Commercial Paper | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total short-term investments	114,147	24,473
Asset-backed Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total short-term investments		4,758
Total long-term investments	3,036
Asset-backed Securities | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total short-term investments		$ 4,758
Total long-term investments	3,036
U.S. Government Notes
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total short-term investments	17,998
Total long-term investments	20,089
U.S. Government Notes | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total short-term investments	17,998
Total long-term investments	$ 20,089

Summary of Significant Accoun_7

Summary of Significant Accounting Policies - Summary of Estimated Useful Life of Property and Equipment (Details)	12 Months Ended
	Dec. 31, 2021
Computers
Property Plant And Equipment [Line Items]
Estimated useful life of property and equipment	3 years
Office Furniture and Equipment
Property Plant And Equipment [Line Items]
Estimated useful life of property and equipment	5 years
Leasehold Improvements
Property Plant And Equipment [Line Items]
Estimated useful life of property and equipment	Shorter of the useful life of the asset or the lease term

Summary of Significant Accoun_8

Summary of Significant Accounting Policies - Summary of Property and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Property Plant And Equipment [Line Items]
Total property and equipment, gross	$ 309	$ 309
Less: accumulated depreciation	(232)	(179)
Total property and equipment, net	77	130	[1]
Computers
Property Plant And Equipment [Line Items]
Total property and equipment, gross	70	70
Office Furniture and Equipment
Property Plant And Equipment [Line Items]
Total property and equipment, gross	134	134
Leasehold Improvements
Property Plant And Equipment [Line Items]
Total property and equipment, gross	$ 105	$ 105
[1]	The consolidated balance sheet as of December 31, 2020 is derived from the consolidated financial statements as of that date and was retroactively adjusted, including shares and per share amounts, as a result of the Reorganization and Reverse Stock Split. See Note 3 to the consolidated financial statements for additional details.

Summary of Significant Accoun_9

Summary of Significant Accounting Policies - Summary of Accrued Expenses and Other Current Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Accounts Payable And Accrued Liabilities Current [Abstract]
Accrued bonus	$ 2,576	$ 1,763
Professional fees and other	973	1,049
Research and development costs	5,028	1,829
Accrued expenses and other current liabilities	$ 8,577	$ 4,641

Reorganization and Reverse St_3

Reorganization and Reverse Stock Split - Additional Information (Details)	12 Months Ended
	Dec. 31, 2021
Reorganization And Reverse Stock Split [Abstract]
Reverse stock split conversion ratio	1

Reorganization and Reverse St_4

Reorganization and Reverse Stock Split - Number of Shares of Common Stock Exchanged and Issued to Unitholders on Split Adjusted Basis (Details) - shares	1 Months Ended	12 Months Ended
	Jan. 31, 2021	Dec. 31, 2021
Reorganization And Reverse Stock Split [Line Items]
Number of Management's Shares Issued	320,228
Cullinan Oncology, LLC
Reorganization And Reverse Stock Split [Line Items]
Number of Management's Shares Issued		242,384,283
Adjusted for the Reverse Stock Split		34,434,262
Series C Preferred Units | Cullinan Oncology, LLC
Reorganization And Reverse Stock Split [Line Items]
Number of Management's Shares Issued		66,599,045
Adjusted for the Reverse Stock Split		9,461,414
Series B Preferred Units | Cullinan Oncology, LLC
Reorganization And Reverse Stock Split [Line Items]
Number of Management's Shares Issued		63,141,016
Adjusted for the Reverse Stock Split		8,970,154
Series A1 Preferred Units | Cullinan Oncology, LLC
Reorganization And Reverse Stock Split [Line Items]
Number of Management's Shares Issued		50,000,000
Adjusted for the Reverse Stock Split		7,103,280
Series Seed Preferred Units | Cullinan Oncology, LLC
Reorganization And Reverse Stock Split [Line Items]
Number of Management's Shares Issued		16,000,000
Adjusted for the Reverse Stock Split		2,273,050
Non-Voting Incentive Units | Cullinan Oncology, LLC
Reorganization And Reverse Stock Split [Line Items]
Number of Management's Shares Issued		11,896,500
Adjusted for the Reverse Stock Split		1,689,949
Common Units | Cullinan Oncology, LLC
Reorganization And Reverse Stock Split [Line Items]
Number of Management's Shares Issued		34,747,722
Adjusted for the Reverse Stock Split		4,936,415

Reorganization and Reverse St_5

Reorganization and Reverse Stock Split - Summary of LLC Units Previously Reported as Redeemable Preferred Units or Temporary Equity Converted Reclassified to Equity (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020		Dec. 31, 2019
Redeemable Preferred Units
Total Redeemable Preferred Units
Stockholders' Equity (Members' Deficit)
Non-Voting Incentive Units
Common Stock	$ 4	3	[1]	2
Additional paid-in capital	584,714	292,348	[1]	138,543
Accumulated other comprehensive loss	(838)	(2)	[1]	(4)
Accumulated deficit	(158,909)	(93,339)	[1]	(41,540)
Total Cullinan Stockholders' Equity (Members' Deficit)	424,971	199,010	[1]	97,001
Non-controlling interests in subsidiaries	403	1,304	[1]	864
Total Stockholders' Equity (Members' Deficit)	$ 425,374	200,314	[1]	97,865	[2]
As Reported
Redeemable Preferred Units
Total Redeemable Preferred Units		276,652		137,774
Stockholders' Equity (Members' Deficit)
Non-Voting Incentive Units		1		1
Common Stock
Additional paid-in capital		15,698		770
Accumulated other comprehensive loss		(2)		(4)
Accumulated deficit		(93,339)		(41,540)
Total Cullinan Stockholders' Equity (Members' Deficit)		(77,642)		(40,773)
Non-controlling interests in subsidiaries		1,304		864
Total Stockholders' Equity (Members' Deficit)		(76,338)		(39,909)
Adjustment
Redeemable Preferred Units
Total Redeemable Preferred Units		(276,652)		(137,774)
Stockholders' Equity (Members' Deficit)
Non-Voting Incentive Units		(1)		(1)
Common Stock		3		2
Additional paid-in capital		276,650		137,773
Accumulated other comprehensive loss
Accumulated deficit
Total Cullinan Stockholders' Equity (Members' Deficit)		276,652		137,774
Non-controlling interests in subsidiaries
Total Stockholders' Equity (Members' Deficit)		276,652		137,774
Series Seed Redeemable Preferred Units
Redeemable Preferred Units
Total Redeemable Preferred Units
Series Seed Redeemable Preferred Units | As Reported
Redeemable Preferred Units
Total Redeemable Preferred Units		3,956		3,956
Series Seed Redeemable Preferred Units | Adjustment
Redeemable Preferred Units
Total Redeemable Preferred Units		(3,956)		(3,956)
Series A1 Redeemable Preferred Units
Redeemable Preferred Units
Total Redeemable Preferred Units
Series A1 Redeemable Preferred Units | As Reported
Redeemable Preferred Units
Total Redeemable Preferred Units		49,946		49,946
Series A1 Redeemable Preferred Units | Adjustment
Redeemable Preferred Units
Total Redeemable Preferred Units		(49,946)		(49,946)
Series B Redeemable Preferred Units
Redeemable Preferred Units
Total Redeemable Preferred Units
Series B Redeemable Preferred Units | As Reported
Redeemable Preferred Units
Total Redeemable Preferred Units		97,909		83,872
Series B Redeemable Preferred Units | Adjustment
Redeemable Preferred Units
Total Redeemable Preferred Units		(97,909)		(83,872)
Series C Redeemable Preferred Units
Redeemable Preferred Units
Total Redeemable Preferred Units
Series C Redeemable Preferred Units | As Reported
Redeemable Preferred Units
Total Redeemable Preferred Units		124,841
Series C Redeemable Preferred Units | Adjustment
Redeemable Preferred Units
Total Redeemable Preferred Units		$ (124,841)
[1]	The consolidated balance sheet as of December 31, 2020 is derived from the consolidated financial statements as of that date and was retroactively adjusted, including shares and per share amounts, as a result of the Reorganization and Reverse Stock Split. See Note 3 to the consolidated financial statements for additional details.
[2]	The consolidated balance sheets as of December 31, 2020 and 2019 are derived from the consolidated financial statements as of such date and was retroactively adjusted, including shares and per share amounts, as a result of the Reorganization and Reverse Stock Split. See Note 3 to the consolidated financial statements for additional details.

License and Collaboration Agr_3

License and Collaboration Agreements - Summary of Research and Development Costs Related to Collaboration and License Agreements (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Research and development costs	$ 57,751	$ 43,211	[1]
Collaboration and License Agreements
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Research and development costs	3,117	3,449
Collaboration and License Agreements | Adimab
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Research and development costs	46	1,318
Collaboration and License Agreements | Amber - MIT
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Research and development costs	71	333
Collaboration and License Agreements | Apollo - Wistar
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Research and development costs		355
Collaboration and License Agreements | Florentine - Tubigen
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Research and development costs		912
Collaboration and License Agreements | Pearl - Taiho
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Research and development costs	$ 3,000	$ 531
[1]	The shares and per share amounts for the year ended December 31, 2020 were derived from the consolidated financial statements as of that date and were retroactively adjusted as a result of the Reorganization and Reverse Stock Split. See Note 3 to the consolidated financial statements for additional details.

License and Collaboration Agr_4

License and Collaboration Agreements - Additional Information (Details) - USD ($)		1 Months Ended						12 Months Ended
		Jun. 30, 2021	Dec. 31, 2020	Aug. 31, 2020	Dec. 31, 2019	Feb. 28, 2019	Dec. 31, 2018	Dec. 31, 2021	Dec. 31, 2020
License And Collaboration Agreements [Line Items]
Common stock, shares issued			29,831,125					44,292,102	29,831,125
Aggregate purchase price	[1]								$ 145,450,000
Net upfront revenue								$ 18,943,000	$ 0	[2]
Series A Preferred Stock
License And Collaboration Agreements [Line Items]
Common stock, shares issued						9,000,000
Shares price per share						$ 1
Tubingen License Agreement
License And Collaboration Agreements [Line Items]
Non-refundable, non-creditable license fee				$ 600,000
Tubingen License Agreement | Fully Diluted Shares
License And Collaboration Agreements [Line Items]
Ownership percentage in outstanding shares								5.00%
Taiho License Agreement
License And Collaboration Agreements [Line Items]
Accounts Payable								$ 3,000,000
Pearl - Taiho | Series A Preferred Stock
License And Collaboration Agreements [Line Items]
Cash balance						$ 1,000,000
Pearl - Taiho | Collaboration and License Agreements
License And Collaboration Agreements [Line Items]
Non-refundable, non-creditable license fee						$ 2,500,000
Common stock, shares issued						1,860,000
Aggregate purchase price						$ 23,000,000
Pearl - Taiho | Collaboration and License Agreements | Maximum
License And Collaboration Agreements [Line Items]
Milestone payments						$ 154,500,000
Taiho Ventures | Series A Preferred Stock
License And Collaboration Agreements [Line Items]
Shares price per share						$ 1
Gross proceeds						$ 14,000,000
Taiho Ventures | Maximum | Series A Preferred Stock
License And Collaboration Agreements [Line Items]
Common stock, shares issued						23,000,000
Apollo - Wistar
License And Collaboration Agreements [Line Items]
Cost of studies budgeted							$ 1,500,000
Apollo - Wistar | Minimum
License And Collaboration Agreements [Line Items]
Timeline Period of studies							3 years
Amber—Massachusetts Institute of Technology
License And Collaboration Agreements [Line Items]
Common stock, shares issued		153,229			200,066
License expenses		$ 100,000			$ 200,000
Amber—Massachusetts Institute of Technology | Maximum
License And Collaboration Agreements [Line Items]
Nonrefundable license fee					100,000
Amber—Massachusetts Institute of Technology | Collaboration and License Agreements | Maximum
License And Collaboration Agreements [Line Items]
Milestone payments					12,500,000
Amber—Massachusetts Institute of Technology | Clinical and Regulatory Events First Indication | Maximum
License And Collaboration Agreements [Line Items]
Milestone payments					7,000,000
Amber—Massachusetts Institute of Technology | Clinical and Regulatory Events Second Indication
License And Collaboration Agreements [Line Items]
Milestone payments					$ 5,500,000
Amber—Massachusetts Institute of Technology | Clinical and Regulatory Events
License And Collaboration Agreements [Line Items]
Percentage of Milestone Payments					100.00%
DKFZ | Tubingen License Agreement
License And Collaboration Agreements [Line Items]
Common stock, shares issued				758,246
UFE | Tubingen License Agreement
License And Collaboration Agreements [Line Items]
Common stock, shares issued				348,682
Pearl—Zai Lab License Agreement
License And Collaboration Agreements [Line Items]
Nonrefundable license fee			$ 20,000,000
Net upfront revenue								$ 18,900,000
Pearl—Zai Lab License Agreement | Maximum
License And Collaboration Agreements [Line Items]
Milestone payments			$ 211,000,000
[1]	Changes in equity activities for the year ended December 31, 2020 were retroactively adjusted, including shares and per share amounts, as a result of the Reorganization and Reverse Stock Split. See Note 3 to the consolidated financial statements for additional details.
[2]	The shares and per share amounts for the year ended December 31, 2020 were derived from the consolidated financial statements as of that date and were retroactively adjusted as a result of the Reorganization and Reverse Stock Split. See Note 3 to the consolidated financial statements for additional details.

Cullinan-MICA Asset Acquisiti_2

Cullinan-MICA Asset Acquisition - Additional Information (Details)	Dec. 31, 2021shares	May 28, 2020USD ($)shares	Jun. 30, 2021USD ($)shares	Dec. 31, 2021USD ($)Milestoneshares	Dec. 31, 2020USD ($)shares	May 31, 2020shares
Schedule Of Asset Acquisition [Line Items]
Common stock, shares authorized	150,000,000			150,000,000	34,900,878
Common stock, shares outstanding	44,292,102			44,292,102	29,831,125
Voting agreement description				Voting Agreement dated May 28, 2020, among the Company and other stockholders of MICA, MICA increased the size of its board of directors from four to five directors, of which three directors are designated by the Company.
Acquired in-process research and development assets | $					$ 6,447,000
MICA
Schedule Of Asset Acquisition [Line Items]
Number of share authorized for issuance		72,890,797
Common stock, shares authorized		39,000,000
Preferred stock shares authorized		33,890,797
Number of shares outstanding						22,829,406
Common stock, shares outstanding						602,784
MICA Equity Plan
Schedule Of Asset Acquisition [Line Items]
Common stock, shares reserved						2,034,457
MICAs Directors and Officers, as well as Former Employees of PDI Therapeutics | MICA Equity Plan
Schedule Of Asset Acquisition [Line Items]
Common stock, shares reserved						1,826,402
Series A Senior Preferred Stock | MICA
Schedule Of Asset Acquisition [Line Items]
Preferred stock shares authorized		19,786,914
Ownership percentage in outstanding shares	88.50%			88.50%
Series A Senior Preferred Stock | MICA Board Authorized First Additional Closing
Schedule Of Asset Acquisition [Line Items]
Number of share purchased as part of asset acquisition			5,385,787
Share purchased price as part of asset acquisition | $			$ 7,100,000
Ownership percentage increased in outstanding shares	45.00%		45.00%
Series A Senior Preferred Stock | Certain Existing Shareholders | MICA Board Authorized First Additional Closing
Schedule Of Asset Acquisition [Line Items]
Number of share purchased as part of asset acquisition			702,495
Share purchased price as part of asset acquisition | $			$ 900,000
Series A Junior Preferred Stock | MICA
Schedule Of Asset Acquisition [Line Items]
Preferred stock shares authorized		1,999,998
Preferred stock shares outstanding						6,088,282
Series A Junior Preferred Stock | Cullinan Oncology, LLC
Schedule Of Asset Acquisition [Line Items]
Preferred stock shares outstanding						5,385,787
Series A-1 Junior Preferred Stock | MICA
Schedule Of Asset Acquisition [Line Items]
Preferred stock shares authorized		652,371
Series A-2 Junior Preferred Stock | MICA
Schedule Of Asset Acquisition [Line Items]
Preferred stock shares authorized		11,451,514
Series A, A-1 and A2 Junior Preferred Stock | MICA
Schedule Of Asset Acquisition [Line Items]
Preferred stock shares outstanding						14,103,883
Fully Diluted Shares | MICA
Schedule Of Asset Acquisition [Line Items]
Ownership percentage in outstanding shares	24.00%			24.00%
Ownership percentage can increase with subsequent closings	54.00%			54.00%
Research and Development Expense
Schedule Of Asset Acquisition [Line Items]
Acquired in-process research and development assets | $					$ 6,400,000
Series A Senior Preferred Stock Purchase Agreement
Schedule Of Asset Acquisition [Line Items]
Number of additional closings | Milestone				2
Series A Senior Preferred Stock Purchase Agreement | Series A Senior Preferred Stock | PDI Therapeutics, Inc.
Schedule Of Asset Acquisition [Line Items]
Number of share purchased as part of asset acquisition		5,385,787
Share purchased price as part of asset acquisition | $		$ 7,100,000
Series A Senior Preferred Stock Purchase Agreement | Series A Senior Preferred Stock | Certain Existing PDI Therapeutics Shareholders | PDI Therapeutics, Inc.
Schedule Of Asset Acquisition [Line Items]
Number of share purchased as part of asset acquisition		702,495
Share purchased price as part of asset acquisition | $		$ 900,000
Series A Senior Preferred Stock Purchase Agreement | Maximum
Schedule Of Asset Acquisition [Line Items]
Proceeds from preferred stock | $				$ 26,000,000

Common Stock and Noncontrolli_2

Common Stock and Noncontrolling Interest in Subsidiaries - Additional Information (Details) - USD ($)

May 28, 2020

Jul. 31, 2021

Jun. 30, 2021

Jan. 31, 2021

Dec. 31, 2020

Nov. 30, 2020

Aug. 31, 2020

May 31, 2020

Apr. 30, 2020

Feb. 28, 2019

Dec. 31, 2021

Dec. 31, 2020

Dec. 31, 2018

Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]

Common stock, shares authorized

34,900,878

150,000,000

34,900,878

Dividends declared

$ 0

Common stock, voting rights

Each share of common stock entitles the holder to one vote and to receive dividends when and if declared by the board of directors of the Company.

Shares sold/issued

29,831,125

44,292,102

29,831,125

Losses attributed to noncontrolling interests

$ (1,915,000)

$ (7,659,000)

[1]

Aggregate purchase price

[2]

145,450,000

Purchase of shares

2,254,231

Common Stock

Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]

Additional shares issued

13,685,000

Series A Preferred Stock

Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]

Shares sold/issued

9,000,000

Shares price per share

$ 1

Cullinan Amber Corp | HLBV

Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]

Losses attributed to noncontrolling interests

200,000

Cullinan Amber Corp | MIT License Agreement between Amber and MIT

Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]

Shares sold/issued

153,229

400,132

Cullinan Amber Corp | MIT License Agreement between Amber and MIT | Common Stock

Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]

Additional consideration received

$ 0

$ 0

Cullinan Amber Corp | Maximum | HLBV

Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]

Losses attributed to noncontrolling interests

$ 100,000

Cullinan Amber Corp | Series A Preferred Stock

Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]

Shares issued

3,000,000

3,000,000

Gross proceeds

$ 3,000,000

$ 3,000,000

Closing price per share

$ 1

Cullinan Amber Corp | Series A Preferred Stock | Maximum

Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]

Sale of stock

9,000,000

Cullinan Apollo Corp

Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]

Losses attributed to noncontrolling interests

0

0

Cullinan Apollo Corp | Series A Preferred Stock

Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]

Gross proceeds

$ 7,000,000

Shares sold/issued

7,000,000

Shares price per share

$ 1

Cullinan Apollo Corp | Series A Preferred Stock | Maximum

Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]

Shares sold/issued

11,000,000

Cullinan Florentine Corp | DFKZ and UFE Anti-dilution Shares

Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]

Additional shares issued

0

Cullinan Florentine Corp | HLBV

Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]

Losses attributed to noncontrolling interests

0

500,000

Cullinan Florentine Corp | Tubingen License Agreement

Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]

Shares sold/issued

725,118

Cullinan Florentine Corp | Tubingen License Agreement | Common Stock

Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]

Additional consideration received

$ 0

Additional shares issued

381,810

Cullinan Florentine Corp | Tubingen License Agreement | Common Stock | DFKZ and UFE Anti-dilution Shares

Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]

Additional consideration received

$ 0

Cullinan Florentine Corp | Series A Preferred Stock

Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]

Gross proceeds

$ 6,000,000

$ 6,000,000

Sale of stock

6,000,000

Closing price per share

$ 1

Additional shares issued

6,000,000

Cullinan Florentine Corp | Series A Preferred Stock | Maximum

Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]

Sale of stock

6,000,000

Cullinan Florentine Corp | Series B Preferred Units

Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]

Gross proceeds

$ 8,100,000

Additional shares issued

7,500,000

Cullinan Pearl Corp | HLBV

Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]

Losses attributed to noncontrolling interests

700,000

$ 1,600,000

Cullinan Pearl Corp | Subscription Agreement between Company and Pearl | Common Stock

Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]

Shares price per share

$ 0.44

Aggregate purchase price

$ 1,200,000

Purchase of shares

2,730,227

Cullinan Pearl Corp | Series A Preferred Stock

Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]

Gross proceeds

$ 9,000,000

Shares sold/issued

9,000,000

Cullinan Pearl Corp | Series A Preferred Stock | Taiho Ventures, LLC

Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]

Gross proceeds

$ 14,000,000

Shares sold/issued

14,000,000

Shares price per share

$ 1

Cullinan Pearl Corp | Series A Preferred Stock | Taiho License Agreement

Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]

Shares sold/issued

1,206,000

1,860,000

Additional consideration received

$ 0

Aggregate purchase price

$ 0

Cullinan Pearl Corp | Series A Preferred Stock | Maximum | Taiho Ventures, LLC

Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]

Shares sold/issued

23,000,000

MICA

Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]

Shares sold/issued

3,367,804

3,367,804

Shares price per share

$ 0.23

$ 0.23

Equity at acquisition

$ 12,800,000

Aggregate purchase price

$ 800,000

Ownership interest percentage

45.00%

35.00%

MICA | HLBV

Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]

Losses attributed to noncontrolling interests

$ 1,100,000

$ 5,400,000

MICA | Series A Senior Preferred Stock

Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]

Shares issued

6,088,282

Shares price per share

$ 1.31

Number of share purchased as part of asset acquisition

5,385,787

Equity at acquisition

7,100,000

MICA | Junior Preferred and Common Stockholders | Noncontrolling Interests in Subsidiaries

Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]

Equity at acquisition

$ 5,700,000

[1]

The shares and per share amounts for the year ended December 31, 2020 were derived from the consolidated financial statements as of that date and were retroactively adjusted as a result of the Reorganization and Reverse Stock Split. See Note 3 to the consolidated financial statements for additional details.

[2]

Changes in equity activities for the year ended December 31, 2020 were retroactively adjusted, including shares and per share amounts, as a result of the Reorganization and Reverse Stock Split. See Note 3 to the consolidated financial statements for additional details.

Equity-Based Compensation - Add

Equity-Based Compensation - Additional Information (Details) $ / shares in Units, $ in Thousands		Nov. 04, 2020shares	Jan. 31, 2021shares	Nov. 30, 2020USD ($)Director$ / sharesshares	Dec. 31, 2021USD ($)$ / sharesshares	Dec. 31, 2020USD ($)$ / sharesshares	Dec. 31, 2019$ / shares	Dec. 31, 2018$ / shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock, par value | $ / shares					$ 0.0001	$ 0.0001
Common stock, shares issued					44,292,102	29,831,125
Equity-based compensation expense | $					$ 24,375	$ 14,910
Purchase of shares				2,254,231
Aggregate purchase price | $	[1]					145,450
Common stock exchange in excess fair value | $				$ 1,200
Common stock issued in exchange of units			320,228
Research and Development Expense
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Equity-based compensation expense | $					8,914	5,912
Share-based payment, modification expense | $				200
Equity-based compensation expense | $					400
General and Administrative Expense
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Equity-based compensation expense | $					$ 15,461	8,998
Share-based payment, modification expense | $				$ 100
Equity-based compensation expense | $						200
Pearl
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock, par value | $ / shares								$ 0.0001
Amber and Florentine
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock, par value | $ / shares							$ 0.0001
Unit Purchase Agreement with Cullinan Pearl
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Purchase of shares				22,868
Shares price per share | $ / shares				$ 0.61
Common units transferred, Number of directors | Director				2
Aggregate subsidiary stock options, cancelled				93,000
Unit Purchase Agreement with Cullinan Pearl | Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Aggregate purchase price | $				$ 100
Restricted Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Award vesting period					3 years
Restricted common units, related to exchange agreement with subsidiaries		320,228
Unrecognized compensation cost | $					$ 300	$ 700
Estimated weighted-average amortization period					1 year 5 months 23 days	2 years 4 months 28 days
Restricted Stock | Cullinan Amber Corp
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Restricted common units, related to exchange agreement with subsidiaries				511,530
Restricted Stock | Cullinan Florentine Corp
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Restricted common units, related to exchange agreement with subsidiaries				728,678
Restricted Stock | Cullinan Pearl Corp
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Restricted common units, related to exchange agreement with subsidiaries				1,869,834
Restricted Stock | Tranche One
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting rights percent					25.00%
Restricted Stock | Tranche Two
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting rights percent					75.00%
Reorganization
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock, shares issued			1,689,949
2016 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Non- voting incentive units vesting percentage					25.00%
Non-voting incentive units remaining vesting percentage percentage					75.00%
Non-voting incentive units vesting period					3 years
Fair value of Non-voting incentive per units | $ / shares					$ 0.0001	$ 0.0001
Non-voting incentive units Issued						0
2020 Unit Option and Grant Plan | Restricted Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Restricted common units, related to exchange agreement with subsidiaries				2,231,363
Exchange with Amber | Restricted Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Restricted common units, related to exchange agreement with subsidiaries				368,974
Exchange with Florentine | Restricted Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Restricted common units, related to exchange agreement with subsidiaries				513,656
Exchange with Pearl | Restricted Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Restricted common units, related to exchange agreement with subsidiaries				1,348,733
2021 Stock Option and Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting rights percent					25.00%
Award vesting period					36 months
Unrecognized compensation cost | $					$ 75,800	$ 14,200
Common stock, shares reserved					12,546,386
Unrecognized compensation cost recognized weighted average period					3 years 1 month 24 days	2 years 8 months 4 days
Aggregate intrinsic value of options outstanding | $					$ 42,500	$ 63,100
Aggregate intrinsic value of options exercisable | $					$ 29,100	$ 28,600
Aggregate intrinsic value fair value per share | $ / shares					$ 15.43	$ 18.02
Annual dividend yield					0.00%
Weighted average fair value of options granted | $ / shares					$ 15.73	$ 6.19
Common stock issuable upon exercise of stock options, weighted average exercise price | $ / shares					$ 4.30
Split-adjusted restricted stock issued					320,228
Common stock issuable upon exercise of stock options					4,616,187
Increase in number of shares reserved and available for issuance percentage					5.00%
2021 Stock Option and Incentive Plan | Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Term of options					10 years
2021 Stock Option and Incentive Plan | Research and Development Expense
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Equity-based compensation expense | $					$ 8,700	$ 5,600
2021 Stock Option and Incentive Plan | General and Administrative Expense
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Equity-based compensation expense | $					$ 15,200	$ 8,800
ESPP
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock, shares issued					12,977
Common stock, shares reserved					416,665
Increase in number of shares reserved and available for issuance percentage					1.00%
Increase in number of shares reserved and available for issuance					833,330
ESPP | Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Equity-based compensation expense | $					$ 100
[1]	Changes in equity activities for the year ended December 31, 2020 were retroactively adjusted, including shares and per share amounts, as a result of the Reorganization and Reverse Stock Split. See Note 3 to the consolidated financial statements for additional details.

Equity Based Compensation - Sum

Equity Based Compensation - Summary of Non-Voting Incentive Unit Activity (Details) - $ / shares	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Limited Liability Company L L C Members Equity [Line Items]
Outstanding unvested ,Number of units beginning balance	172,490	580,334
Vested, number of units	(172,490)	(407,844)
Outstanding unvested ,Number of units ending balance	0	172,490
Outstanding vested, number of units	1,689,949
Outstanding unvested, Weighted average grant date fair value per unit beginning balance	$ 0.0001	$ 0.0001
Vested, Weighted average grant date fair value per unit	0.0001	0.0001
Outstanding unvested, Weighted average grant date fair value per unit ending balance	$ 0.0001	0.0001
Outstanding vested, Weighted average grant date fair value per unit		$ 0.0001

Equity-Based Compensation - Sum

Equity-Based Compensation - Summary of Restricted Common Unit Activities (Details) - Restricted Stock - $ / shares	Nov. 04, 2020	Dec. 31, 2020	Dec. 31, 2021
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total units exchanged as of November 4, 2020	320,228
Vested		(128,358)	(102,987)
Outstanding unvested, Ending balance		191,870	88,883
Outstanding vested as of December 31, 2021			231,345
Total units exchanged ,Incremental fair value per share	$ 3.87
Vested, Incremental fair value per share		$ 3.87	$ 3.87
Outstanding unvested , Incremental fair value per share ending balance		$ 3.87	3.87
Outstanding vested , Incremental fair value per share as of December 31, 2021			$ 3.87

Equity-Based Compensation - S_2

Equity-Based Compensation - Summary of Stock Options Grants (Details) - Employees and Non-Employees - $ / shares	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Beginning balance	4,603,137
Granted, Number of options	5,481,816	4,616,187
Exercised, Number of options	(763,000)	(13,050)
Forfeited, Number of options	(63,214)
Ending balance	9,258,739	4,603,137
Options exercisable, Number of options	3,271,196
Options unvested, Number of options	5,987,543
Granted, Weighted average exercise price	$ 23.82	$ 4.30
Exercised, Weighted average exercise price	4.30	4.30
Forfeited, Weighted average exercise price	17.23
Outstanding , Weighted average exercise price ending balance	15.77	$ 4.30
Options exercisable, Weighted average exercise price	7.65
Options unvested, Weighted average exercise price	$ 20.20
Outstanding , Weighted average remaining contractual term (Years)	9 years 2 months 19 days	9 years 10 months 2 days
Options exercisable, Weighted average remaining contractual term (Years)	8 years 10 months 24 days
Options unvested, Weighted average remaining contractual term (Years)	9 years 4 months 20 days

Equity-Based Compensation - S_3

Equity-Based Compensation - Summary of Grant Date Fair Value (Details) - 2021 Stock Option and Incentive Plan	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted average risk-free interest rate	1.02%	0.51%
Expected term (in years)	6 years	5 years 11 months 23 days
Expected volatility	76.22%	77.40%
Expected dividend yield	0.00%	0.00%

Equity-Based Compensation - Sch

Equity-Based Compensation - Schedule of Equity-based Compensation Expense Categories In Consolidated Statements of Operations and Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Equity-based compensation expense	$ 24,375	$ 14,910
Research and Development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Equity-based compensation expense	8,914	5,912
General and Administrative Expense
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Equity-based compensation expense	$ 15,461	$ 8,998

Related Party Transactions - Ad

Related Party Transactions - Additional Information (Details) - USD ($)	1 Months Ended	12 Months Ended
	Apr. 30, 2020	Dec. 31, 2021	Dec. 31, 2020
Related Party Transaction [Line Items]
Management and advisory services		$ 0	$ 200,000
Royalty percentage		1.00%
Royalties under obligation		$ 0	0
Globeways Holdings Limited | Globeways Agreement
Related Party Transaction [Line Items]
Related party transaction, description of transaction		In April 2020, the Company entered into a consulting agreement (the Globeways Agreement) with Globeways Holdings Limited, or Globeways. Globeways and entities affiliated with F2 Ventures beneficially own in the aggregate greater than five percent of the Company’s outstanding shares and Globeways is beneficially owned by a member of the Company's board of directors.
Consulting fee per month	$ 25,000
Consulting fee			200,000
UBS Optimus Foundation
Related Party Transaction [Line Items]
Royalty percentage		0.50%
Maximum | Globeways Agreement
Related Party Transaction [Line Items]
Consulting fee		$ 100,000
Maximum | MPM Capital
Related Party Transaction [Line Items]
General and administrative expense		$ 100,000	$ 100,000

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Income Tax Disclosure [Line Items]
Current income tax expense (benefit)	$ 0	$ 0
Deferred Income Tax Expense (Benefit)	$ 0	0
Operating loss carryforwards, limitations on use	an ownership change as defined by Section 382 results from transactions increasing the ownership of certain shareholders or public groups in the stock of a corporation by more than 50 percentage points over a three-year period.
Uncertain tax positions	$ 0	0
Accrued interest or penalties	0	$ 0
Federal
Income Tax Disclosure [Line Items]
Operating loss carryforwards	$ 117,400,000
Operating loss carryforwards expiration year	2036
Federal | Research and Development
Income Tax Disclosure [Line Items]
Tax credit carryforward	$ 1,300,000
Tax credit carryforward expiration year	2037
Federal | Prior to 2018 Tax Year
Income Tax Disclosure [Line Items]
Operating loss carryforwards	$ 5,800,000
Federal | NOL Current and Prior to 2018 Tax Year
Income Tax Disclosure [Line Items]
Operating loss carryforwards	111,600,000
State
Income Tax Disclosure [Line Items]
Operating loss carryforwards	$ 119,000,000
Operating loss carryforwards expiration year	2036
State | Research and Development
Income Tax Disclosure [Line Items]
Tax credit carryforward	$ 100,000
Tax credit carryforward expiration year	2033
State | Research and Development Tax Credit Carryforward Indefinitely
Income Tax Disclosure [Line Items]
Tax credit carryforward	$ 300,000

Income Taxes - Summary of Recon

Income Taxes - Summary of Reconciliation of Statutory Income Tax Rate To Effective Income Tax Rate (Details)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Effective Income Tax Rate Continuing Operations Tax Rate Reconciliation [Abstract]
Federal statutory rate	21.00%	21.00%
State taxes, net of federal benefit	9.96%	(1.83%)
Permanent differences	0.01%	(0.01%)
Equity-based compensation	0.39%
Tax credits	(0.25%)	0.77%
Valuation allowance	(32.12%)	(12.65%)
Non-taxable income		(5.01%)
IPR&D		(2.28%)
Change in tax status	1.76%
Return to provision	1.15%
Other	(1.90%)
Effective income tax rate reconciliation	0.00%	0.00%

Income Taxes - Summary of Net D

Income Taxes - Summary of Net Deferred Income Tax Asset (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Deferred tax assets:
Net operating loss	$ 31,414	$ 18,563
Capitalized organizational and start-up expenses	140	148
Licenses	1,875	1,601
Accrued expenses	968	467
Research and development credit	1,563	1,859
Equity-based compensation	8,584	8
Gross deferred tax assets	44,544	22,646
Valuation allowance	(44,552)	(22,642)	$ (10,653)
Net deferred tax asset	8	4
Deferred tax liability
Depreciation and amortization	$ (8)	$ (4)

Income Taxes - Summary of Valua

Income Taxes - Summary of Valuation Allowance (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Valuation Allowance [Abstract]
Valuation allowance at beginning of year	$ 22,642	$ 10,653
Increases recorded to income tax provision	21,674	11,989
Increases recorded to OCI/Equity	236
Valuation allowance at end of year	$ 44,552	$ 22,642

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Details) $ in Millions	1 Months Ended	12 Months Ended
	Dec. 31, 2017ft²	Dec. 31, 2021USD ($)	Dec. 31, 2020USD ($)
Lessee Lease Description [Line Items]
Rent expense | $		$ 0.6	$ 0.6
Operating lease commence date	Feb. 1, 2018
Operating lease expiration date		Jun. 30, 2024
Massachusetts
Lessee Lease Description [Line Items]
Operating lease rentable area | ft²	7,531

Commitments and Contingencies_2

Commitments and Contingencies - Summary of Future Minimum Payments Due Under Operating Lease (Details) $ in Thousands	Dec. 31, 2021USD ($)
Operating Lease Liabilities Payments Due [Abstract]
2022	$ 608
2023	618
2024	313
Future minimum payments due under operating lease	$ 1,539

Employee Benefit Plan - Additio

Employee Benefit Plan - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
401(K) Plan
Defined Benefit Plan Disclosure [Line Items]
Expense relating to matching contribution	$ 0.3	$ 0.1

Net Loss per Share - Summary of

Net Loss per Share - Summary of Calculation of Basic and Diluted Net Loss Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	[1],[2]
Numerator:
Net loss attributable to common stockholders of Cullinan	$ (65,570)	$ (51,799)
Denominator
Total weighted-average shares used in computing net loss per share, basic and diluted	43,077,330	19,887,307
Net Loss per share:	$ (1.52)	$ (2.60)
[1]	The shares and per share amounts for the year ended December 31, 2020 were derived from the consolidated financial statements as of that date and were retroactively adjusted as a result of the Reorganization and Reverse Stock Split. See Note 3 to the consolidated financial statements for additional details.
[2]	The shares and per share amounts for the year ended December 31, 2020 were derived from the consolidated financial statements as of that date and were retroactively adjusted as a result of the Reorganization and Reverse Stock Split. See Note 3 to the for additional details.

Net Loss per Share - Summary _2

Net Loss per Share - Summary of Equity Instruments Excluded from Computation of Diluted Net Loss Per Share (Details) - shares	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Equity instruments excluded from computation of diluted net loss per share (in shares)	9,347,622	4,967,497
Stock Options
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Equity instruments excluded from computation of diluted net loss per share (in shares)	9,258,739	4,603,137
Restricted Stock Awards
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Equity instruments excluded from computation of diluted net loss per share (in shares)	88,883	364,360