Cullinan Oncology (CGEM) 10-Q 14 Nov 22 2022 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2022	Nov. 04, 2022
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2022
Document Fiscal Year Focus	2022
Document Fiscal Period Focus	Q3
Entity Registrant Name	CULLINAN ONCOLOGY, INC.
Current Fiscal Year End Date	--12-31
Document Quarterly 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 1350
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 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
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		45,772,452

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Sep. 30, 2022	Dec. 31, 2021
Current assets:
Cash and cash equivalents	$ 242,657	$ 59,774
Short-term investments	333,294	230,692
Prepaid expenses and other current assets	6,124	6,098
Total current assets	582,075	296,564
Property and equipment, net	792	77
Operating lease right-of-use assets	4,496	0
Other assets	460	147
Long-term investments	29,414	140,397
Total assets	617,237	437,185
Current liabilities:
Accounts payable	1,516	3,169
Accrued expenses and other current liabilities	13,507	8,577
Income tax payable	11,398	0
Operating lease liabilities, current	696	0
Total current liabilities	27,117	11,746
Long-term liabilities:
Operating lease liabilities, net of current portion	3,992	0
Deferred rent	0	65
Total liabilities	31,109	11,811
Commitments and contingencies (Note 11)
Stockholders' equity:
Common stock, $0.0001 par value, 150,000,000 shares authorized as of September 30, 2022 and December 31, 2021; 45,743,027 and 44,292,102 shares issued and outstanding as of September 30, 2022 and December 31, 2021, respectively	5	4
Additional paid-in capital	610,965	584,714
Accumulated other comprehensive loss	(3,929)	(838)
Accumulated deficit	(20,913)	(158,909)
Total Cullinan stockholders' equity	586,128	424,971
Noncontrolling interests	0	403
Total stockholders' equity	586,128	425,374
Total liabilities and stockholders' equity	$ 617,237	$ 437,185

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Sep. 30, 2022	Dec. 31, 2021
Statement of Financial Position [Abstract]
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	150,000,000	150,000,000
Common stock, shares issued	45,743,027	44,292,102
Common stock, shares outstanding	45,743,027	44,292,102

CONSOLIDATED STATEMENTS OF OPER

CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Income Statement [Abstract]
Revenue	$ 0	$ 0	$ 0	$ 18,943
Type of revenue [Extensible List]	us-gaap:LicenseMember	us-gaap:LicenseMember	us-gaap:LicenseMember	us-gaap:LicenseMember
Operating expenses:
Research and development	$ 19,680	$ 12,680	$ 70,627	$ 36,873
General and administrative	10,086	5,695	28,902	15,677
Total operating expenses	29,766	18,375	99,529	52,550
Gain on sale of Cullinan Pearl	0	0	276,785	0
Income/(loss) from operations	(29,766)	(18,375)	177,256	(33,607)
Other income (expense):
Interest income	2,353	118	3,247	340
Other income (expense), net	0	(2)	(241)	(12)
Net income (loss) before income taxes	(27,413)	(18,259)	180,262	(33,279)
Income tax benefit	(2,523)	0	43,979	0
Net income (loss)	(24,890)	(18,259)	136,283	(33,279)
Net income (loss) attributable to noncontrolling interest	(86)	(909)	(1,713)	(223)
Net loss attributable to common stockholders of Cullinan	(24,804)	(17,350)	137,996	(33,056)
Comprehensive income (loss):
Net income (loss)	(24,890)	(18,259)	136,283	(33,279)
Unrealized gain (loss) on investments	(296)	57	(3,091)	(56)
Comprehensive income (loss)	(25,186)	(18,202)	133,192	(33,335)
Comprehensive income (loss) attributable to noncontrolling interest	(86)	(909)	(1,713)	(223)
Comprehensive income (loss) attributable to Cullinan	$ (25,100)	$ (17,293)	$ 134,905	$ (33,112)
Earnings (net loss) per share
Basic	$ (0.54)	$ (0.40)	$ 3.07	$ (0.76)
Diluted	$ (0.54)	$ (0.40)	$ 2.96	$ (0.76)
Weighted-average shares used in computing earnings (net loss) per share:
Basic	45,611	43,439	44,966	43,254
Diluted	45,611	43,439	46,580	43,254

CONSOLIDATED STATEMENTS OF STOC

CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive (Loss)	Retained Earnings (Accumulated Deficit)	Noncontrolling Interest in Subsidiaries
Balances at Dec. 31, 2020	$ 200,314	$ 3	$ 292,348	$ (2)	$ (93,339)	$ 1,304
Balances, shares at Dec. 31, 2020		29,831,125
Equity-based compensation	3,508		3,503			5
Unrealized loss on investments	(58)			(58)
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
Net income (loss)	1,419				(70)	1,489
Balances at Mar. 31, 2021	469,699	$ 4	560,366	(60)	(93,409)	2,798
Balances, shares at Mar. 31, 2021		43,516,125
Balances at Dec. 31, 2020	200,314	$ 3	292,348	(2)	(93,339)	1,304
Balances, shares at Dec. 31, 2020		29,831,125
Net income (loss)	(33,279)
Balances at Sep. 30, 2021	445,474	$ 4	569,835	(58)	(126,395)	2,088
Balances, shares at Sep. 30, 2021		43,660,909
Balances at Mar. 31, 2021	469,699	$ 4	560,366	(60)	(93,409)	2,798
Balances, shares at Mar. 31, 2021		43,516,125
Issuance of subsidiary preferred stock	923					923
Net issuance of common stock under equity-based compensation plans	180		180
Net issuance of common stock under equity-based compensation plans, shares		10,099
Equity-based compensation	4,165		4,159			6
Unrealized loss on investments	(55)			(55)
Issuance of subsidiary common stock	67					67
Net income (loss)	(16,439)				(15,636)	(803)
Balances at Jun. 30, 2021	458,540	$ 4	564,705	(115)	(109,045)	2,991
Balances, shares at Jun. 30, 2021		43,526,224
Net issuance of common stock under equity-based compensation plans	579		579
Net issuance of common stock under equity-based compensation plans, shares		134,685
Equity-based compensation	4,557		4,551			6
Unrealized loss on investments	57			57
Net income (loss)	(18,259)				(17,350)	(909)
Balances at Sep. 30, 2021	445,474	$ 4	569,835	(58)	(126,395)	2,088
Balances, shares at Sep. 30, 2021		43,660,909
Balances at Dec. 31, 2021	425,374	$ 4	584,714	(838)	(158,909)	403
Balances, shares at Dec. 31, 2021		44,292,102
Issuance of subsidiary preferred stock	1,153					1,153
Net issuance of common stock under equity-based compensation plans	1,566		1,566
Net issuance of common stock under equity-based compensation plans, shares		367,924
Equity-based compensation	6,565		6,559			6
Unrealized loss on investments	(2,296)			(2,296)
Net income (loss)	(12,892)				(12,098)	(794)
Balances at Mar. 31, 2022	419,470	$ 4	592,839	(3,134)	(171,007)	768
Balances, shares at Mar. 31, 2022		44,660,026
Balances at Dec. 31, 2021	425,374	$ 4	584,714	(838)	(158,909)	403
Balances, shares at Dec. 31, 2021		44,292,102
Net income (loss)	136,283
Balances at Sep. 30, 2022	586,128	$ 5	610,965	(3,929)	(20,913)	0
Balances, shares at Sep. 30, 2022		45,743,027
Balances at Mar. 31, 2022	419,470	$ 4	592,839	(3,134)	(171,007)	768
Balances, shares at Mar. 31, 2022		44,660,026
Net issuance of common stock under equity-based compensation plans	2,835	$ 1	2,834
Net issuance of common stock under equity-based compensation plans, shares		736,372
Equity-based compensation	8,608		8,602			6
Unrealized loss on investments	(499)			(499)
Issuance of subsidiary common stock	139					139
Net income (loss)	174,065				174,898	(833)
Balances at Jun. 30, 2022	604,618	$ 5	604,275	(3,633)	3,891	80
Balances, shares at Jun. 30, 2022		45,396,398
Net issuance of common stock under equity-based compensation plans	1,425		1,425
Net issuance of common stock under equity-based compensation plans, shares		346,629
Equity-based compensation	5,271		5,265			6
Unrealized loss on investments	(296)			(296)
Net income (loss)	(24,890)				(24,804)	(86)
Balances at Sep. 30, 2022	$ 586,128	$ 5	$ 610,965	$ (3,929)	$ (20,913)	$ 0
Balances, shares at Sep. 30, 2022		45,743,027

CONSOLIDATED STATEMENTS OF ST_2

CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (Parenthetical) $ in Thousands	3 Months Ended
	Mar. 31, 2021 USD ($)
Statement of Stockholders' Equity [Abstract]
Initial public offering, net of issuance costs	$ 22,870

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021
Operating activities:
Net income (loss)	$ 136,283	$ (33,279)
Adjustments to reconcile net income (loss) to net cash used in operating activities:
Gain on sale of Cullinan Pearl	(276,785)	0
Depreciation and amortization	34	41
Equity-based compensation expense	20,444	12,230
Amortization or accretion on marketable securities	1,894	1,973
Realized loss on marketable securities	109	0
License expense in exchange for subsidiary common stock	139	67
Loss on disposal of fixed assets	14	0
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(507)	(5,104)
Accounts payable	(1,654)	(5,980)
Accrued expenses and other current liabilities	6,950	1,790
Income tax payable	11,398	0
Net cash used in operating activities	(101,681)	(28,262)
Investing activities:
Purchase of marketable securities	(217,497)	(448,551)
Proceeds from sales and maturities of marketable securities	220,333	130,638
Proceeds from sale of Cullinan Pearl, net cash transferred with sale of $2,898	275,000	0
Purchase of property and equipment	(251)	0
Net cash provided by (used in) investing activities	277,585	(317,913)
Financing activities:
Proceeds from initial public offering	0	267,268
Payment of deferred offering costs	0	(2,688)
Proceeds from issuance of noncontrolling interests	1,153	923
Proceeds from issuance of convertible note	2,200	0
Repayment of convertible note	(2,200)	0
Proceeds from net issuance of common stock under equity-based compensation plans	5,826	579
Net cash provided by financing activities	6,979	266,082
Net increase (decrease) in cash and cash equivalents	182,883	(80,093)
Cash and cash equivalents at beginning of period	59,774	168,198
Cash and cash equivalents at end of period	242,657	88,105
Non-cash financing activities and supplemental cash flow information
Purchases of property and equipment included in accounts payable and accrued expenses and other liabilities	513	0
Cash paid for income taxes	32,582	0
Deferred offering costs paid in the prior year	$ 0	$ 65

CONSOLIDATED STATEMENTS OF CA_2

CONSOLIDATED STATEMENTS OF CASH FLOWS (Parenthetical) $ in Thousands	9 Months Ended
	Sep. 30, 2022 USD ($)
Statement of Cash Flows [Abstract]
net of cash transferred	$ 2,898

Nature of Business and Basis of

Nature of Business and Basis of Presentation	9 Months Ended
	Sep. 30, 2022
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 focused on modality-agnostic targeted oncology. 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. The Company completed the sale of its entire equity interest in its partially-owned subsidiary, Cullinan Pearl Corp. ("Cullinan Pearl"), to Taiho Pharmaceutical Co., Ltd (“Taiho”) in June 2022. Refer to Note 3 for additional details relating to the transaction. The sale of the Company's equity interest in Cullinan Pearl did not meet the criteria to be reported as a discontinued operation under the accounting principles generally accepted in the United States of America ("U.S. GAAP"). Therefore, prior period consolidated financial statements and disclosures have not been retroactively restated to reflect the impact of the sale of the Company’s equity interest in Cullinan Pearl. 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. Liquidity The Company has incurred operating losses, with the exception of the one-time gain on the sale of Cullinan Pearl in the nine months ended September 30, 2022, 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. In June 2022, the Company completed the sale of the Company’s equity interest in its partially-owned subsidiary, Cullinan Pearl, to Taiho for an upfront payment of $ 275.0 million. Refer to Note 3 for additional details relating to the transaction. Since inception, the Company has funded its operations primarily through the sale of equity securities and from licensing or selling the rights to its product candidates. The Company expects that its cash, cash equivalents and short-term investments of $ 576.0 million and long-term investments and interest receivable of $ 30.7 million as of September 30, 2022, will be sufficient to fund its operating expenses and capital expenditure requirements through at least twelve months from the date of issuance of these unaudited consolidated financial statements. Interest receivable is included in prepaid expenses and other current assets on the consolidated balance sheets and represents accrued and unpaid interest on the Company's marketable securities.

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2022
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	(2) Summary of Significant Accounting Policies Cullinan’s significant accounting policies have not changed materially from those disclosed in its annual audited consolidated financial statements and accompanying notes in the Annual Report on Form 10-K filed with the United States Securities and Exchange Commission (the “SEC”) on March 17, 2022 for the fiscal year ended December 31, 2021 (the “2021 10-K”), except for its accounting policy for leases. Basis of Presentation The unaudited consolidated financial statements of the Company have been prepared in conformity with U.S. GAAP and in accordance with applicable rules and regulations of the SEC for interim financial reporting and include the accounts of the Company, a wholly-owned subsidiary, and its majority-owned and controlled subsidiaries. The Company considers consolidation of entities over which control is achieved by means other than voting rights. Intercompany balances and transactions have been eliminated in consolidation. The Company operates as one segment, which is developing early-stage cancer therapeutics. In the opinion of the Company’s management, the unaudited consolidated financial statements reflect all adjustments, which are normal and recurring in nature, and necessary for fair financial statement presentation. The preparation of these unaudited consolidated financial statements and accompanying notes in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the amounts reported. Actual results could differ materially from those estimates. These unaudited consolidated financial statements and accompanying notes should be read in conjunction with the Company’s annual audited consolidated financial statements and accompanying notes included in the 2021 10-K. Leases On January 1, 2022, the Company adopted a new standard on leases (as amended, "ASC 842"), which requires lessees to recognize a lease liability and a right-of-use asset on the balance sheet for all leases, except certain short-term leases. In connection with its implementation of ASC 842, the Company adopted a package of three practical expedients, allowing it to carry forward its previous lease classification and embedded lease evaluations and not to reassess initial direct costs as of the date of adoption. The Company also adopted a practical expedient that allows it to combine lease and non-lease components for its real estate leases. The Company’s existing lease obligations relating to a single corporate location is subject to the new standard and resulted in operating lease liabilities and right-of-use assets ("ROU") being recorded on the Company’s consolidated balance sheets on the implementation date. The existing lease obligation is classified as an operating lease. The below table details the balance sheet adjustments recorded on January 1, 2022 in connection with the Company’s adoption of ASC 842 (in thousands): December 31, 2021 January 1, 2022 As Reported under ASC 840 ASC 842 Adjustments As Reported Under ASC 842 Assets Operating lease right-of-use asset $ — $ 1,311 $ 1,311 Liabilities Current portion of operating lease liabilities $ — $ 505 $ 505 Deferred rent $ 65 $ ( 65 ) $ — Noncurrent portion of operating lease liabilities $ — $ 871 $ 871 The Company determines if an arrangement is a lease at inception. A contract is or contains a lease if the contract conveys the right to control the use of an identified asset for a period of time in exchange for consideration. The Company classifies leases at the lease commencement date as operating or finance leases and records an ROU asset and a lease liability on the consolidated balance sheets for all leases with an initial lease term of greater than 12 months. Leases with an initial term of 12 months or less are not recorded in the balance sheet, and payments are recognized as expense on a straight-line basis over the lease term. The Company enters into contracts that contain both lease and non-lease components. Non-lease components may include maintenance, utilities, and other operating costs. The Company combines the lease and non-lease components of fixed costs in its lease arrangements as a single lease component. Variable costs, such as utilities or maintenance costs, are not included in the measurement of ROU assets and lease liabilities but rather are expensed when the event determining the amount of variable consideration to be paid occurs. Operating lease assets and liabilities are recognized at the lease commencement date based on the present value of the lease payments over the lease term using the discount rate implicit in the lease. If the discount rate is not readily determinable, the Company utilizes an estimate of its incremental borrowing rate based upon the available information at the lease commencement date. Operating lease assets are further adjusted for prepaid or accrued lease payments. Operating lease payments are expensed using the straight-line method as an operating expense over the lease term. The Company’s lease terms may include options to extend or terminate the lease when it is reasonably certain that the Company will exercise that option. Recently Adopted Accounting Pronouncements In December 2019, the Financial Accounting Standards Board issued ASU 2019-12, which is a new standard intended to simplify the accounting for income taxes. The Company adopted this standard on January 1, 2022. The adoption of this standard did not have a material impact on the Company's consolidated financial position and consolidated results of operations.

Sale of Cullinan Pearl and Co-D

Sale of Cullinan Pearl and Co-Development Agreement with Taiho	9 Months Ended
	Sep. 30, 2022
Debt Securities, Available-for-Sale [Abstract]
Sale of Cullinan Pearl and Co-Development Agreement with Taiho	(3) Sale of Cullinan Pearl and Co-Development Agreement with Taiho In June 2022, the Company sold its equity interest in its partially-owned subsidiary, Cullinan Pearl, which has worldwide rights to zipalertinib (CLN-081/TAS6417), excluding Japan and Greater China, to Taiho for an upfront payment of $ 275.0 million, with an increase to the purchase price in the amount of $ 2.9 million for cash held by Cullinan Pearl that was transferred with the sale. Pursuant to the share purchase agreement with Taiho, the Company is also eligible to receive an additional $ 130.0 million tied to epidermal growth factor receptor exon20 non-small-cell lung cancer regulatory milestones. The Company concluded the transaction was a sale of non-financial assets, which comprised mainly of intellectual property rights and related intangible assets, and that it transferred control of the non-financial assets at the closing of the sale. The Company recognized a gain on sale of Cullinan Pearl of $ 276.8 million within income from operations in its consolidated statements of operations and other comprehensive income (loss) for the nine months ended September 30, 2022. The table below sets forth the book value of the Cullinan Pearl assets and liabilities sold along with the calculation of the gain on sale based on the cash consideration received. (in thousands) Book value of assets sold Cash $ 2,898 Prepaid expenses and other current assets 619 Amounts attributable to assets sold 3,517 Book value of liabilities sold Accrued expenses and other current liabilities 2,404 Amounts attributable to liabilities sold 2,404 Total identifiable net assets sold 1,113 Upfront consideration, inclusive of cash transferred of $ 2,898 277,898 Gain on sale of Cullinan Pearl $ 276,785 During the nine months ended September 30, 2022, Cullinan Pearl issued $ 2.2 million of convertible notes to an affiliate of Taiho. The Company repaid these convertible notes at the closing of the Cullinan Pearl sale. Co-Development Agreement with Taiho In June 2022, concurrently with the closing of the sale of the Company’s equity interest in Cullinan Pearl, the Company entered into a co-development agreement with an affiliate of Taiho, pursuant to which the Company will collaborate to develop zipalertinib (CLN-081/TAS6417) and will retain the option to co-commercialize zipalertinib (CLN-081/TAS6417) in the U.S. Development costs for zipalertinib (CLN-081/TAS6417) incurred after the sale of the Company’s equity interest in Cullinan Pearl shall be shared equally between Taiho and the Company with each party receiving 50 % of any future pre-tax profits from potential U.S. sales of zipalertinib (CLN-081/TAS6417). The Company concluded that the co-development agreement with Taiho is a collaborative arrangement because the Company is an active participant in the development of zipalertinib (CLN-081/TAS6417). Payments made to or received from Taiho for zipalertinib (CLN-081/TAS6417) development activities after the sale are recorded within research and development expenses. For the nine months ended September 30, 2022, costs reimbursable by Taiho and reflected as a reduction to research and development expenses were $ 1.5 million, which had not been reimbursed by Taiho as of September 30, 2022. The Company also recorded research and development expense of $ 0.9 million related to its share of costs incurred by Taiho, which the Company had not yet reimbursed as of September 30, 2022. The net amount of $ 0.6 million due from Taiho was recorded within prepaid expenses and other current assets as of September 30, 2022.

Financial Instruments

Financial Instruments	9 Months Ended
	Sep. 30, 2022
Financial Instruments Pledged as Collateral [Abstract]
Financial Instruments	(4) Financial Instruments Investments The Company recognized its short-term and long-term investments by security type at September 30, 2022 as follows: Amortized Gross Gross Estimated (in thousands) Short-term investments Corporate notes $ 158,927 $ — $ ( 2,342 ) $ 156,585 Asset-backed securities 3,013 — ( 38 ) 2,975 Commercial paper 38,808 5 ( 37 ) 38,776 U.S. government notes 135,613 — ( 655 ) 134,958 Total short-term investments 336,361 5 ( 3,072 ) 333,294 Long-term investments Corporate notes 30,276 — ( 862 ) 29,414 Total long-term investments 30,276 — ( 862 ) 29,414 Total investments $ 366,637 $ 5 $ ( 3,934 ) $ 362,708 The Company recognized its short-term and long-term investments by security type at December 31, 2021 as follows: 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 Fair Value of Financial Instruments The following table sets forth the fair value of the Company’s financial assets that were measured at fair value on a recurring basis as of September 30, 2022: Level 1 Level 2 Level 3 Total (in thousands) Cash and cash equivalents Cash $ 122,913 $ — $ — $ 122,913 Money market funds 119,744 — — 119,744 Total cash and cash equivalents 242,657 — — 242,657 Short-term investments Corporate notes — 156,585 — 156,585 Asset-backed securities — 2,975 — 2,975 Commercial paper — 38,776 — 38,776 U.S. government notes — 134,958 — 134,958 Total short-term investments — 333,294 — 333,294 Long-term investments Corporate notes — 29,414 — 29,414 Total long-term investments — 29,414 — 29,414 Total cash, cash equivalents and investments $ 242,657 $ 362,708 $ — $ 605,365 The following table sets forth the fair value of the Company’s financial assets that were measured at fair value on a recurring basis as of December 31, 2021: 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 Prepaid expenses and other current assets, accounts payable and accrued expenses and other current liabilities were carried at cost, which management believes approximated fair value due to their short-term nature.

Accrued Expenses and Other Curr

Accrued Expenses and Other Current Liabilities	9 Months Ended
	Sep. 30, 2022
Accrued Expenses And Other Current Liabilities [Abstract]
Accrued Expenses and Other Current Liabilities	(5) Accrued Expenses and Other Current Liabilities Accrued expenses and other current liabilities consisted of the following: September 30, December 31, (in thousands) Accrued research and development expenses $ 8,365 $ 5,028 Accrued bonus 2,396 2,576 Other current liabilities 2,746 973 $ 13,507 $ 8,577

License and Collaboration Agree

License and Collaboration Agreements	9 Months Ended
	Sep. 30, 2022
License And Collaboration Agreements [Abstract]
License and Collaboration Agreements	(6) License and Collaboration Agreements For the nine months ended September 30, 2022, the Company recorded $ 0.5 million relating to the collaboration agreement with Adimab and $ 0.2 million relating to the license agreement (the "MIT License Agreement") with the Massachusetts Institute of Technology ("MIT") through Cullinan Amber Corp. ("Cullinan Amber") within research and development expenses. For the three months ended September 30, 2022, the company recorded less than $ 0.1 million relating to license and collaboration agreements. For the nine months ended September 30, 2021, the Company recorded $ 3.0 million under a revenue sharing agreement with Taiho upon receipt of an upfront payment for licensing the Greater China rights for zipalertinib (CLN-081/TAS6417) to Zai Lab (Shanghai) Co., Ltd. and $ 0.1 million relating to the MIT License Agreement. For the three months ended September 30, 2021, the company recorded less than $ 0.1 million relating to license and collaboration agreements.

Common Stock and Noncontrolling

Common Stock and Noncontrolling Interest in Subsidiaries	9 Months Ended
	Sep. 30, 2022
Common Stock And Noncontrolling Interest In Subsidiaries [Abstract]
Common Stock and Noncontrolling Interest in Subsidiaries	(7) Common Stock and Noncontrolling Interests in Subsidiaries Common Stock 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 September 30, 2022. Noncontrolling Interests 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. Cullinan Amber In June 2021, Cullinan Amber issued 3.0 million shares of its Series A Preferred Stock to the Company for gross proceeds of $ 3.0 million and 0.2 million shares of its common stock to MIT in exchange for no additional consideration, pursuant to the MIT License Agreement. In June 2022, Cullinan Amber issued 6.0 million shares of its Series A Preferred Stock to the Company for gross proceeds of $ 6.0 million and 0.3 million shares of its common stock to MIT in exchange for no additional consideration, pursuant to the MIT License Agreement. As of September 30, 2022, the Company held common shares and Series A Preferred Stock that represented 93.5 % of Cullinan Amber's outstanding equity. As of September 30, 2022, noncontrolling interests collectively held common shares that represented 6.5 % of Cullinan Amber's outstanding equity. The Company did not allocate any losses to the noncontrolling interests of Cullinan Amber for the three months ended September 30, 2022. Under the hypothetical liquidation book value ("HLBV") method, $ 0.1 million of losses were attributed to the noncontrolling interests of Cullinan Amber for the nine months ended September 30, 2022. The Company did not allocate any losses to the noncontrolling interests of Cullinan Amber for the three months ended September 30, 2021. For the nine months ended September 30, 2021, less than $ 0.1 million of losses were attributed to the noncontrolling interests of Cullinan Amber. Cullinan Florentine In July 2021, Cullinan Florentine Corp. ("Cullinan Florentine") issued 7.5 million shares of Series B Preferred Stock to the Company for gross proceeds of $ 8.1 million. In July 2022, Cullinan Florentine issued 3.75 million shares of Series B Preferred Stock to the Company for gross proceeds of $ 4.1 million. As of September 30, 2022, the Company held common shares, Series A Preferred Stock and Series B preferred stock that represented 95.6 % of Cullinan Florentine's outstanding equity. As of September 30, 2022, noncontrolling interests collectively held common shares that represented 4.4 % of Cullinan Florentine's outstanding equity. The Company did no t allocate any losses to the noncontrolling interests of Cullinan Florentine for each of the three and nine months ended September 30, 2022 and 2021. Cullinan MICA In June 2021, the Company purchased 5.4 million shares of Cullinan MICA Corp.’s ("Cullinan MICA") Series A Senior Preferred Stock for $ 7.1 million, and certain other existing investors purchased 0.7 million shares of Cullinan MICA’s Series A Senior Preferred Stock for $ 0.9 million. In March 2022, the Company purchased 6.7 million shares of Cullinan MICA’s Series A Senior Preferred Stock for $ 8.8 million, and certain other existing investors purchased 0.9 million shares of Cullinan MICA’s Series A Senior Preferred Stock for $ 1.2 million. As of September 30, 2022, the Company held common shares and Series A Senior Preferred Stock that represented 53.5 % of Cullinan MICA's outstanding equity. As of September 30, 2022, noncontrolling interests held common shares, Series A Junior Preferred Stock and Series A Senior Preferred Stock that represented 46.5 % of Cullinan MICA's outstanding equity. Under the HLBV method, $ 0.1 million and $ 1.2 million of losses were attributed to the noncontrolling interests of Cullinan MICA for the three and nine months ended September 30, 2022, respectively. Under the HLBV method, $ 0.3 million and $ 0.8 million of losses were attributed to the noncontrolling interests of Cullinan MICA for the three and nine months ended September 30, 2021, respectively. Cullinan Pearl Corp. In June 2022, the Company sold its equity interest in its partially-owned subsidiary, Cullinan Pearl, to Taiho. Refer to Note 3 for additional details relating to the transaction. Prior to the sale, the Company accounted for the noncontrolling interest using the HLBV method. The Company allocated $ 0.3 million of losses to noncontrolling interests for the nine months ended September 30, 2022. Under the HLBV method, $ 0.6 million of losses and $ 0.7 million of income were attributed to the noncontrolling interests of Cullinan Pearl for the three and nine months ended September 30, 2021, respectively.

Equity-Based Compensation

Equity-Based Compensation	9 Months Ended
	Sep. 30, 2022
Share-Based Payment Arrangement [Abstract]
Equity-Based Compensation	(8) Equity-Based Compensation Market-based restricted stock units ("RSUs") In June 2022, the Company granted market-based RSUs to its Chief Executive Officer. For equity awards with a market-based vesting condition, the Company recognizes compensation expense over the requisite service period using the fair value at the grant date. The number of shares issuable, if any, when a market-based RSU award vests, will depend on the degree of achievement of the corporate stock price metrics within the performance period of the award. The Company measures the fair value of market-based RSUs on the date of grant using a Monte Carlo simulation model. The Monte Carlo simulation requires the input of assumptions, including the Company's stock price, the volatility of its stock price, remaining term in years, expected dividend yield and risk-free rate. The Company used its own trading history to calculate the expected volatility of the market-based RSUs granted. The risk-free interest rate is determined by reference to implied yields available from U.S. Treasury securities with a remaining term equal to the expected term assumed at the grant date. The following table details the assumptions used in the Monte Carlo simulation model used to estimate the fair value of the market-based RSUs granted during the nine months ended September 30, 2022: Nine Months Ended Stock price $ 12.98 Volatility 82.5 % Remaining term (in years) 2.7 Risk-free rate 2.9 % Expected dividend yield 0.0 % The Company recorded equity-based compensation in the following expense categories in the consolidated statements of operations and comprehensive income (loss): Three Months Ended September 30, Nine Months Ended September 30, 2022 2021 2022 2021 (in thousands) Research and development $ 1,108 $ 2,458 $ 8,147 $ 6,320 General and administrative 4,163 2,099 12,297 5,910 Total equity-based compensation $ 5,271 $ 4,557 $ 20,444 $ 12,230

Related Party Transactions

Related Party Transactions	9 Months Ended
	Sep. 30, 2022
Related Party Transactions [Abstract]
Related Party Transactions	(9) Related Party Transactions Royalty Transfer Agreements Cullinan Amber, Cullinan Florentine and Cullinan MICA are each party to 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. The Company has concluded that these instruments had no value at the inception of the agreements. 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 September 30, 2022 and December 31, 2021. The Company currently does not have any applicable net sales from its products and as a result, has no t paid or incurred any royalties under these agreements as of September 30, 2022. The Company will monitor these instruments for changes in fair value at each reporting date.

Income Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2022
Income Tax Disclosure [Abstract]
Income Taxes	(10) Income Taxes During the three months and nine months ended September 30, 2022, the Company recorded an income tax benefit of $ 2.5 million and an income tax expense of $ 44.0 million, respectively. The income tax expense recorded for the nine months ended September 30, 2022 was driven by the expected tax from the gain on sale of Cullinan Pearl, partially offset by the release of valuation allowance for the expected utilization of current year and certain historical tax attributes against the gain from the sale. The income tax benefit recorded for the three months ended September 30, 2022 is due to the expected utilization of current year tax attributes against the gain from the sale of Cullinan Pearl. Refer to Note 3 for additional details on this transaction. The Company did no t record an income tax benefit or expense for the three and nine months ended September 30, 2021. The Company has evaluated the positive and negative evidence bearing upon its ability to realize its deferred tax assets, which primarily consist of net operating loss carryforwards. The Company has considered its history of cumulative net losses, estimated future taxable income and prudent and feasible tax planning strategies and has concluded that it is more likely than not that the Company will not realize the benefits of its deferred tax assets, outside of the tax losses that will be utilized against the gain on sale of Cullinan Pearl. As a result, as of September 30, 2022, the Company has maintained a full valuation allowance against its remaining net deferred tax assets.

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2022
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	(11) Commitments and Contingencies The Company enters into contracts in the normal course of business with contract research organizations, contract manufacturing organizations, and other third parties for preclinical research studies, clinical trials and testing and manufacturing services. These agreements generally include cancellation clauses. Indemnification agreements In the ordinary course of business, the Company may provide indemnification of varying scope and terms to vendors, lessors, business partners and other parties with respect to certain matters including, but not limited to, losses arising out of breach of such agreements or from intellectual property infringement claims made by third parties. In addition, the Company has entered into indemnification agreements with members of its board of directors and executive officers that will require the Company, among other things, to indemnify them against certain liabilities that may arise by reason of their status or service as directors or officers. The maximum potential amount of future payments the Company could be required to make under these indemnification agreements is, in certain cases, unlimited. To date, the Company has not incurred any material costs as a result of such indemnifications. The Company is not aware of any indemnification arrangements that could have a material effect on its financial position, results of operations or cash flows, and it has no t accrued any liabilities related to such obligations in its consolidated financial statements as of September 30, 2022 and December 31, 2021. Legal proceedings The Company is not currently party to or aware of any material legal proceedings. At each reporting date, the Company evaluates whether or not a potential loss amount or a potential range of loss is probable and reasonably estimable under the provisions of the authoritative guidance that addresses accounting for contingencies. The Company expenses as incurred the costs related to such legal proceedings.

Leases

Leases	9 Months Ended
	Sep. 30, 2022
Leases [Abstract]
Leases	(12) Leases The Company has an operating lease for approximately 8,000 square feet of office space in a multi-tenant building in Cambridge, Massachusetts, which commenced in February 2018 and goes through June 2024 . In August 2022, the Company entered into an additional operating lease (the "August 2022 lease") for approximately 14,000 square feet of office space in a multi-tenant building in Cambridge, Massachusetts through July 2026. Lease expense consisted of operating lease costs of $ 0.3 million and $ 0.6 million for the three and nine months ended September 30, 2022, respectively. Rent expense under the prior lease accounting standard was $ 0.2 million and $ 0.5 million for the three and nine months ended September 30, 2021, respectively. In September 2022, the Company entered into a sublease agreement through May 2024 for the approximately 8,000 square feet of office space that it leases in a multi-tenant building in Cambridge, Massachusetts. The Company expects to receive sublease payments of approximately $ 0.1 million in 2022, $ 0.6 million in 2023 and $ 0.3 million in 2024. These expected sublease payments are equal to the fixed payments that the Company is required to make under its lease. The following table summarizes supplemental cash flow information (in thousands): Nine Months Ended Cash paid for amounts included in measurement of lease liabilities: Operating cash flows from operating leases $ 456 ROU asset obtained in exchange for an operating lease liability $ 4,931 The following table summarizes the Company’s future minimum lease payments and reconciliation of lease liabilities (in thousands): September 30, 2022 Remainder of 2022 (1) $ ( 196 ) 2023 1,881 2024 1,738 2025 1,461 2026 872 Total future minimum lease payments 5,756 Less: imputed interest ( 1,068 ) Total lease liabilities at present value $ 4,688 Lease liabilities, current $ 696 Lease liabilities, non-current $ 3,992 (1) The Company's negative future lease payments for the remainder of 2022 represent a net cash inflow, which includes required lease payments in the fourth quarter and $ 0.3 million to be reimbursed by the lessor for improvements made to the newly leased office space pursuant the terms of the August 2022 lease. The following table summarizes lease term and discount rate: September 30, 2022 Weighted-average remaining lease term (in years) 3.4 Weighted-average discount rate 10.7 % As the Company’s operating leases did not provide an implicit rate, the Company used its incremental borrowing rate based on the information available in determining the present value of lease payments. The Company’s incremental borrowing rate was based on the term of the lease, the economic environment and reflects the rate the Company would have had to pay to borrow on a secured basis.

Earnings per Share

Earnings per Share	9 Months Ended
	Sep. 30, 2022
Earnings Per Share [Abstract]
Earnings per Share	(13) Earnings per Share The following table sets forth the calculation of basic and diluted earnings (net loss) per share: Three Months Ended Nine Months Ended 2022 2021 2022 2021 (in thousands, except per share data) Numerator: Net income (loss) attributable to common stockholders of Cullinan $ ( 24,804 ) $ ( 17,350 ) $ 137,996 $ ( 33,056 ) Denominator: Weighted-average common stock outstanding - basic 45,611 43,439 44,966 43,254 Dilutive effect of common stock issuable from assumed exercise of equity awards — — 1,614 — Weighted-average common stock outstanding - diluted 45,611 43,439 46,580 43,254 Earnings (net loss) per share: Basic $ ( 0.54 ) $ ( 0.40 ) $ 3.07 $ ( 0.76 ) Diluted $ ( 0.54 ) $ ( 0.40 ) $ 2.96 $ ( 0.76 ) The Company used the treasury stock method to determine the number of dilutive shares. The following table sets forth potential common shares that were excluded from the computation of the diluted net income (loss) per share for the periods presented because their effect would have been anti-dilutive: As of September 30, 2022 2021 (in thousands) Stock options 6,643 7,200 Restricted stock units 24 132 Employee Stock Purchase Plan 12 2 Total 6,679 7,334

Subsequent Events

Subsequent Events	9 Months Ended
	Sep. 30, 2022
Subsequent Events [Abstract]
Subsequent Events	(14) Subsequent Events In October 2022, the Company entered into stock purchase and transfer agreements (the "Purchase Agreements") with two of Cullinan MICA’s existing financial investors, Avalon Ventures and Bregua Corporation. Pursuant to the Purchase Agreements, the Company purchased a cumulative amount of 1,522,072 shares of Series A Senior Preferred Stock, 1,999,998 shares of Series A Junior Preferred Stock and 11,451,514 shares of Series A-2 Junior Preferred Stock (collectively, the “Shares”) of Cullinan MICA for a per share purchase price of $ 2.05 , representing an aggregate purchase price for the Shares of $ 30.7 million. As of October 31, 2022, the Company held shares that collectively represented 92 % of Cullinan MICA’s outstanding equity.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2022
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The unaudited consolidated financial statements of the Company have been prepared in conformity with U.S. GAAP and in accordance with applicable rules and regulations of the SEC for interim financial reporting and include the accounts of the Company, a wholly-owned subsidiary, and its majority-owned and controlled subsidiaries. The Company considers consolidation of entities over which control is achieved by means other than voting rights. Intercompany balances and transactions have been eliminated in consolidation. The Company operates as one segment, which is developing early-stage cancer therapeutics. In the opinion of the Company’s management, the unaudited consolidated financial statements reflect all adjustments, which are normal and recurring in nature, and necessary for fair financial statement presentation. The preparation of these unaudited consolidated financial statements and accompanying notes in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the amounts reported. Actual results could differ materially from those estimates. These unaudited consolidated financial statements and accompanying notes should be read in conjunction with the Company’s annual audited consolidated financial statements and accompanying notes included in the 2021 10-K.
Leases	Leases On January 1, 2022, the Company adopted a new standard on leases (as amended, "ASC 842"), which requires lessees to recognize a lease liability and a right-of-use asset on the balance sheet for all leases, except certain short-term leases. In connection with its implementation of ASC 842, the Company adopted a package of three practical expedients, allowing it to carry forward its previous lease classification and embedded lease evaluations and not to reassess initial direct costs as of the date of adoption. The Company also adopted a practical expedient that allows it to combine lease and non-lease components for its real estate leases. The Company’s existing lease obligations relating to a single corporate location is subject to the new standard and resulted in operating lease liabilities and right-of-use assets ("ROU") being recorded on the Company’s consolidated balance sheets on the implementation date. The existing lease obligation is classified as an operating lease. The below table details the balance sheet adjustments recorded on January 1, 2022 in connection with the Company’s adoption of ASC 842 (in thousands): December 31, 2021 January 1, 2022 As Reported under ASC 840 ASC 842 Adjustments As Reported Under ASC 842 Assets Operating lease right-of-use asset $ — $ 1,311 $ 1,311 Liabilities Current portion of operating lease liabilities $ — $ 505 $ 505 Deferred rent $ 65 $ ( 65 ) $ — Noncurrent portion of operating lease liabilities $ — $ 871 $ 871 The Company determines if an arrangement is a lease at inception. A contract is or contains a lease if the contract conveys the right to control the use of an identified asset for a period of time in exchange for consideration. The Company classifies leases at the lease commencement date as operating or finance leases and records an ROU asset and a lease liability on the consolidated balance sheets for all leases with an initial lease term of greater than 12 months. Leases with an initial term of 12 months or less are not recorded in the balance sheet, and payments are recognized as expense on a straight-line basis over the lease term. The Company enters into contracts that contain both lease and non-lease components. Non-lease components may include maintenance, utilities, and other operating costs. The Company combines the lease and non-lease components of fixed costs in its lease arrangements as a single lease component. Variable costs, such as utilities or maintenance costs, are not included in the measurement of ROU assets and lease liabilities but rather are expensed when the event determining the amount of variable consideration to be paid occurs. Operating lease assets and liabilities are recognized at the lease commencement date based on the present value of the lease payments over the lease term using the discount rate implicit in the lease. If the discount rate is not readily determinable, the Company utilizes an estimate of its incremental borrowing rate based upon the available information at the lease commencement date. Operating lease assets are further adjusted for prepaid or accrued lease payments. Operating lease payments are expensed using the straight-line method as an operating expense over the lease term. The Company’s lease terms may include options to extend or terminate the lease when it is reasonably certain that the Company will exercise that option.
Recently Adopted Accounting Pronouncements	Recently Adopted Accounting Pronouncements In December 2019, the Financial Accounting Standards Board issued ASU 2019-12, which is a new standard intended to simplify the accounting for income taxes. The Company adopted this standard on January 1, 2022. The adoption of this standard did not have a material impact on the Company's consolidated financial position and consolidated results of operations.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	9 Months Ended
	Sep. 30, 2022
Accounting Policies [Abstract]
Supplemental Balance Sheet Information Related to Operating Leases	The below table details the balance sheet adjustments recorded on January 1, 2022 in connection with the Company’s adoption of ASC 842 (in thousands): December 31, 2021 January 1, 2022 As Reported under ASC 840 ASC 842 Adjustments As Reported Under ASC 842 Assets Operating lease right-of-use asset $ — $ 1,311 $ 1,311 Liabilities Current portion of operating lease liabilities $ — $ 505 $ 505 Deferred rent $ 65 $ ( 65 ) $ — Noncurrent portion of operating lease liabilities $ — $ 871 $ 871

Sale of Cullinan Pearl and Co_2

Sale of Cullinan Pearl and Co-Development Agreement with Taiho (Tables)	9 Months Ended
	Sep. 30, 2022
Debt Securities, Available-for-Sale [Abstract]
Schedule of cash consideration received	The table below sets forth the book value of the Cullinan Pearl assets and liabilities sold along with the calculation of the gain on sale based on the cash consideration received. (in thousands) Book value of assets sold Cash $ 2,898 Prepaid expenses and other current assets 619 Amounts attributable to assets sold 3,517 Book value of liabilities sold Accrued expenses and other current liabilities 2,404 Amounts attributable to liabilities sold 2,404 Total identifiable net assets sold 1,113 Upfront consideration, inclusive of cash transferred of $ 2,898 277,898 Gain on sale of Cullinan Pearl $ 276,785

Financial Instruments (Tables)

Financial Instruments (Tables)	9 Months Ended
	Sep. 30, 2022
Financial Instruments Pledged as Collateral [Abstract]
Schedule of Short-term and Long-term Investment Marketable Securities by Security Type	Investments The Company recognized its short-term and long-term investments by security type at September 30, 2022 as follows: Amortized Gross Gross Estimated (in thousands) Short-term investments Corporate notes $ 158,927 $ — $ ( 2,342 ) $ 156,585 Asset-backed securities 3,013 — ( 38 ) 2,975 Commercial paper 38,808 5 ( 37 ) 38,776 U.S. government notes 135,613 — ( 655 ) 134,958 Total short-term investments 336,361 5 ( 3,072 ) 333,294 Long-term investments Corporate notes 30,276 — ( 862 ) 29,414 Total long-term investments 30,276 — ( 862 ) 29,414 Total investments $ 366,637 $ 5 $ ( 3,934 ) $ 362,708 The Company recognized its short-term and long-term investments by security type at December 31, 2021 as follows: 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
Summary of Fair Value of Financial Assets Measured at Fair Value on a Recurring Basis	The following table sets forth the fair value of the Company’s financial assets that were measured at fair value on a recurring basis as of September 30, 2022: Level 1 Level 2 Level 3 Total (in thousands) Cash and cash equivalents Cash $ 122,913 $ — $ — $ 122,913 Money market funds 119,744 — — 119,744 Total cash and cash equivalents 242,657 — — 242,657 Short-term investments Corporate notes — 156,585 — 156,585 Asset-backed securities — 2,975 — 2,975 Commercial paper — 38,776 — 38,776 U.S. government notes — 134,958 — 134,958 Total short-term investments — 333,294 — 333,294 Long-term investments Corporate notes — 29,414 — 29,414 Total long-term investments — 29,414 — 29,414 Total cash, cash equivalents and investments $ 242,657 $ 362,708 $ — $ 605,365 The following table sets forth the fair value of the Company’s financial assets that were measured at fair value on a recurring basis as of December 31, 2021: 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

Accrued Expenses and Other Cu_2

Accrued Expenses and Other Current Liabilities (Tables)	9 Months Ended
	Sep. 30, 2022
Accrued Expenses And Other Current Liabilities [Abstract]
Summary of Accrued Expenses and Other Current Liabilities	Accrued expenses and other current liabilities consisted of the following: September 30, December 31, (in thousands) Accrued research and development expenses $ 8,365 $ 5,028 Accrued bonus 2,396 2,576 Other current liabilities 2,746 973 $ 13,507 $ 8,577

Equity-Based Compensation (Tabl

Equity-Based Compensation (Tables)	9 Months Ended
	Sep. 30, 2022
Share-Based Payment Arrangement [Abstract]
Schedule of Assumptions Used to Estimate Fair value of Market-Based RSUs Granted	The following table details the assumptions used in the Monte Carlo simulation model used to estimate the fair value of the market-based RSUs granted during the nine months ended September 30, 2022: Nine Months Ended Stock price $ 12.98 Volatility 82.5 % Remaining term (in years) 2.7 Risk-free rate 2.9 % Expected dividend yield 0.0 %
Schedule of Equity-based Compensation Expense Categories In Consolidated Statements of Operations and Comprehensive Income (Loss)	The Company recorded equity-based compensation in the following expense categories in the consolidated statements of operations and comprehensive income (loss): Three Months Ended September 30, Nine Months Ended September 30, 2022 2021 2022 2021 (in thousands) Research and development $ 1,108 $ 2,458 $ 8,147 $ 6,320 General and administrative 4,163 2,099 12,297 5,910 Total equity-based compensation $ 5,271 $ 4,557 $ 20,444 $ 12,230

Leases (Tables)

Leases (Tables)	9 Months Ended
	Sep. 30, 2022
Leases [Abstract]
Supplemental Cash Flow Information Relating to Leases	The following table summarizes supplemental cash flow information (in thousands): Nine Months Ended Cash paid for amounts included in measurement of lease liabilities: Operating cash flows from operating leases $ 456 ROU asset obtained in exchange for an operating lease liability $ 4,931
Summarizes of future minimum lease payments	The following table summarizes the Company’s future minimum lease payments and reconciliation of lease liabilities (in thousands): September 30, 2022 Remainder of 2022 (1) $ ( 196 ) 2023 1,881 2024 1,738 2025 1,461 2026 872 Total future minimum lease payments 5,756 Less: imputed interest ( 1,068 ) Total lease liabilities at present value $ 4,688 Lease liabilities, current $ 696 Lease liabilities, non-current $ 3,992 (1) The Company's negative future lease payments for the remainder of 2022 represent a net cash inflow, which includes required lease payments in the fourth quarter and $ 0.3 million to be reimbursed by the lessor for improvements made to the newly leased office space pursuant the terms of the August 2022 lease.
Summarizes Lease Term and Discount Rate	The following table summarizes lease term and discount rate: September 30, 2022 Weighted-average remaining lease term (in years) 3.4 Weighted-average discount rate 10.7 %

Earnings per Share (Tables)

Earnings per Share (Tables)	9 Months Ended
	Sep. 30, 2022
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 earnings (net loss) per share: Three Months Ended Nine Months Ended 2022 2021 2022 2021 (in thousands, except per share data) Numerator: Net income (loss) attributable to common stockholders of Cullinan $ ( 24,804 ) $ ( 17,350 ) $ 137,996 $ ( 33,056 ) Denominator: Weighted-average common stock outstanding - basic 45,611 43,439 44,966 43,254 Dilutive effect of common stock issuable from assumed exercise of equity awards — — 1,614 — Weighted-average common stock outstanding - diluted 45,611 43,439 46,580 43,254 Earnings (net loss) per share: Basic $ ( 0.54 ) $ ( 0.40 ) $ 3.07 $ ( 0.76 ) Diluted $ ( 0.54 ) $ ( 0.40 ) $ 2.96 $ ( 0.76 )
Summary of Outstanding Equity Instruments Excluded from Computation of Diluted Net Income (Loss) Per Share	The following table sets forth potential common shares that were excluded from the computation of the diluted net income (loss) per share for the periods presented because their effect would have been anti-dilutive: As of September 30, 2022 2021 (in thousands) Stock options 6,643 7,200 Restricted stock units 24 132 Employee Stock Purchase Plan 12 2 Total 6,679 7,334

Nature of Business and Basis _2

Nature of Business and Basis of Presentation - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended		9 Months Ended
	Jun. 30, 2022	Jan. 31, 2021	Sep. 30, 2022	Sep. 30, 2021	Dec. 31, 2021
Nature Of Business And Basis Of Presentation [Line Items]
Proceeds from initial public offering		$ 264,500	$ 0	$ 267,268
Long-term investments and interest receivables			30,700
Accumulated deficit			(20,913)		$ (158,909)
Up-front payment	$ 275,000
Cash, cash equivalents, short-term investments and long-term investments			$ 576,000
IPO
Nature Of Business And Basis Of Presentation [Line Items]
Common stock shares issued and sold		13,685,000
Stock, price per Share		$ 21
Underwriters' Option
Nature Of Business And Basis Of Presentation [Line Items]
Common stock shares issued and sold		1,785,000

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Additional Information (Details)	9 Months Ended
	Sep. 30, 2022 Segment
Accounting Policies [Abstract]
Number of operating segments	1
Operating Lease Term	12 months

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Supplemental Balance Sheet Information Related to Operating Leases (Details) - USD ($) $ in Thousands	Sep. 30, 2022	Jan. 01, 2022	Dec. 31, 2021
Operating lease right-of-use assets	$ 4,496		$ 0
Operating lease liabilities, current	696		0
Deferred rent	0		65
Noncurrent portion of operating lease liabilities	3,992		0
As Reported
Operating lease right-of-use assets		$ 1,311	0
Operating lease liabilities, current		505	0
Deferred rent		0	65
Noncurrent portion of operating lease liabilities		$ 871	$ 0
Adjustment
Operating lease right-of-use assets	1,311
Operating lease liabilities, current	505
Deferred rent	(65)
Noncurrent portion of operating lease liabilities	$ 871

Reorganization and Reverse Stoc

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	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020
Stockholders' Equity (Members' Deficit)
Common Stock	$ 5			$ 4
Additional paid-in capital	610,965			584,714
Accumulated other comprehensive loss	(3,929)			(838)
Accumulated deficit	(20,913)			(158,909)
Total Cullinan Stockholders' Equity (Members' Deficit)	586,128			424,971
Non-controlling interests in subsidiaries	0			403
Total Stockholders' Equity (Members' Deficit)	$ 586,128	$ 604,618	$ 419,470	$ 425,374	$ 445,474	$ 458,540	$ 469,699	$ 200,314

Sale of Cullinan Pearl and Co_3

Sale of Cullinan Pearl and Co-Development Agreement with Taiho - Additional Information (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended
	Jun. 30, 2022	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Defined Benefit Plan Disclosure [Line Items]
Repayment of convertible notes				$ 2,200	$ 0
net of cash transferred				2,898
Gain on sale of Cullinan Pearl		$ 0	$ 0	(276,785)	0
Research and development		19,680	$ 12,680	70,627	$ 36,873
Prepaid expenses and other current assets		619		619
Pearl - Taiho
Defined Benefit Plan Disclosure [Line Items]
Repayment of convertible notes				2,200
net of cash transferred	$ 2,900
Additional receive payments from the party	130,000
Receive upfront payment from party	$ 275,000
Gain on sale of Cullinan Pearl				(276,800)
Percentage of profits from potential sales	50%
Research and development				1,500
Research and Development Expense Related to Share of Costs				900
Prepaid expenses and other current assets		$ 600		$ 600

Sale of Cullinan Pearl and Co_4

Sale of Cullinan Pearl and Co-Development Agreement with Taiho - Schedule of cash consideration received (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2022 USD ($)
Book Value of Asset Sold [Abstract]
Cash	$ 2,898
Prepaid expenses and other current assets	619
Amounts attributable to assets sold	3,517
Book Value Of Liability Sold [Abstract]
Accrued expenses and other current liabilities	2,404
Amounts attributable to liabilities sold	2,404
Total identifiable net assets sold	1,113
Upfront consideration, inclusive of cash transferred of $2,898	277,898
Gain on sale of Cullinan Pearl	$ 276,785

Sale of Cullinan Pearl and Co_5

Sale of Cullinan Pearl and Co-Development Agreement with Taiho - Parenthetical (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2022 USD ($)
Debt Securities, Available-for-Sale [Abstract]
Upfront consideration, cash transferred	$ 2,898

Financial Instruments - Schedul

Financial Instruments - Schedule of Short-term and Long-term Investment Marketable Securities by Security Type (Details) - USD ($) $ in Thousands	Sep. 30, 2022	Dec. 31, 2021
Available For Sale Securities Fair Value To Amortized Cost Basis [Line Items]
Amortized Cost	$ 366,637	$ 371,927
Gross Unrealized Gains	5	0
Gross Unrealized Losses	(3,934)	(838)
Estimated Fair Value	362,708	371,089
Long Term Investment
Available For Sale Securities Fair Value To Amortized Cost Basis [Line Items]
Amortized Cost	30,276	141,078
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(862)	(681)
Estimated Fair Value	29,414	140,397
Long Term Investment | U.S. Government Notes
Available For Sale Securities Fair Value To Amortized Cost Basis [Line Items]
Amortized Cost		20,166
Gross Unrealized Gains		0
Gross Unrealized Losses		(77)
Estimated Fair Value		20,089
Long Term Investment | Corporate Note Securities
Available For Sale Securities Fair Value To Amortized Cost Basis [Line Items]
Amortized Cost	30,276	117,868
Gross Unrealized Gains		0
Gross Unrealized Losses	(862)	(596)
Estimated Fair Value	29,414	117,272
Long Term Investment | Asset-backed Securities
Available For Sale Securities Fair Value To Amortized Cost Basis [Line Items]
Amortized Cost		3,044
Gross Unrealized Gains		0
Gross Unrealized Losses		(8)
Estimated Fair Value		3,036
Short Term Investments
Available For Sale Securities Fair Value To Amortized Cost Basis [Line Items]
Amortized Cost	336,361	230,849
Gross Unrealized Gains	5	0
Gross Unrealized Losses	(3,072)	(157)
Estimated Fair Value	333,294	230,692
Short Term Investments | U.S. Government Notes
Available For Sale Securities Fair Value To Amortized Cost Basis [Line Items]
Amortized Cost	135,613	18,033
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(655)	(35)
Estimated Fair Value	134,958	17,998
Short Term Investments | Corporate Note Securities
Available For Sale Securities Fair Value To Amortized Cost Basis [Line Items]
Amortized Cost	158,927	98,642
Gross Unrealized Gains		0
Gross Unrealized Losses	(2,342)	(95)
Estimated Fair Value	156,585	98,547
Short Term Investments | Asset-backed Securities
Available For Sale Securities Fair Value To Amortized Cost Basis [Line Items]
Amortized Cost	3,013
Gross Unrealized Gains	0
Gross Unrealized Losses	(38)
Estimated Fair Value	2,975
Short Term Investments | Commercial Paper
Available For Sale Securities Fair Value To Amortized Cost Basis [Line Items]
Amortized Cost	38,808	114,174
Gross Unrealized Gains	5	0
Gross Unrealized Losses	(37)	(27)
Estimated Fair Value	$ 38,776	$ 114,147

Financial Instruments - Summary

Financial Instruments - Summary of Fair Value of Financial Assets Measured on Recurring Basis (Details) - Recurring - USD ($) $ in Thousands	Sep. 30, 2022	Dec. 31, 2021
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash and cash equivalents	$ 242,657	$ 59,774
Total short-term investments	333,294	230,692
Total long-term investments	29,414	140,397
Assets Fair Value Disclosure, Total	605,365	430,863
Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash and cash equivalents	242,657	59,774
Total short-term investments	0	0
Total long-term investments	0	0
Assets Fair Value Disclosure, Total	242,657	59,774
Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash and cash equivalents	0	0
Total short-term investments	333,294	230,692
Total long-term investments	29,414	140,397
Assets Fair Value Disclosure, Total	362,708	371,089
Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash and cash equivalents	0	0
Total short-term investments	0	0
Total long-term investments	0	0
Assets Fair Value Disclosure, Total	0	0
U.S. Government Notes
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total short-term investments	134,958	17,998
Total long-term investments		20,089
U.S. Government Notes | Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total short-term investments	0	0
Total long-term investments		0
U.S. Government Notes | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total short-term investments	134,958	17,998
Total long-term investments		20,089
U.S. Government Notes | Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total short-term investments	0	0
Total long-term investments		0
Cash
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash and cash equivalents	122,913	35,925
Cash | Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash and cash equivalents	122,913	35,925
Cash | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash and cash equivalents	0	0
Cash | Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash and cash equivalents	0	0
Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash and cash equivalents	119,744	23,849
Money Market Funds | Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash and cash equivalents	119,744	23,849
Money Market Funds | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash and cash equivalents	0	0
Money Market Funds | Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash and cash equivalents	0	0
Corporate Notes
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total short-term investments		98,547
Total long-term investments		117,272
Corporate Notes | Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total short-term investments		0
Total long-term investments	0	0
Corporate Notes | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total short-term investments		98,547
Total long-term investments		117,272
Corporate Notes | Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total short-term investments		0
Total long-term investments		0
Corporate Note Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total short-term investments	156,585
Corporate Note Securities | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total short-term investments	156,585
Total long-term investments	29,414
Corporate Note Securities | Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total short-term investments
Total long-term investments	0
Commercial Paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total short-term investments	38,776	114,147
Commercial Paper | Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total short-term investments	0	0
Commercial Paper | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total short-term investments	38,776	114,147
Commercial Paper | Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total short-term investments	0	0
Asset-backed Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total short-term investments	2,975
Total long-term investments		3,036
Asset-backed Securities | Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total short-term investments	0
Total long-term investments		0
Asset-backed Securities | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total short-term investments	2,975
Total long-term investments		3,036
Asset-backed Securities | Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total short-term investments	$ 0
Total long-term investments		$ 0

Accrued Expenses and Other Cu_3

Accrued Expenses and Other Current Liabilities - Summary of Accrued Expenses and Other Current Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2022	Dec. 31, 2021
Accounts Payable and Accrued Liabilities, Current [Abstract]
Accrued research and development expenses	$ 8,365	$ 5,028
Accrued bonus	2,396	2,576
Other current liabilities	2,746	973
Accrued expenses and other current liabilities	$ 13,507	$ 8,577

License and Collaboration Agr_2

License and Collaboration Agreements - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
License And Collaboration Agreements [Line Items]
Research and development costs	$ 19,680	$ 12,680	$ 70,627	$ 36,873
Maximum | Collaboration and License Agreements
License And Collaboration Agreements [Line Items]
Research and development costs	$ 100	$ 100
Pearl - Taiho
License And Collaboration Agreements [Line Items]
Research and development costs			1,500
Pearl - Taiho | Collaboration and License Agreements
License And Collaboration Agreements [Line Items]
Research and development costs				3,000
Adimab | Collaboration and License Agreements
License And Collaboration Agreements [Line Items]
Research and development costs			500
MIT | Collaboration and License Agreements
License And Collaboration Agreements [Line Items]
Research and development costs			$ 200	$ 100

Common Stock and Noncontrolli_2

Common Stock and Noncontrolling Interest in Subsidiaries - Additional Information (Details) - USD ($)	1 Months Ended					3 Months Ended			6 Months Ended	9 Months Ended
	Jul. 31, 2022	Jun. 30, 2022	Mar. 31, 2022	Jul. 31, 2021	Jun. 30, 2021	Sep. 30, 2022	Sep. 30, 2021	Mar. 31, 2021	Jun. 30, 2022	Sep. 30, 2022	Sep. 30, 2021	Dec. 31, 2021
Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]
Dividends declared						$ 0				$ 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						45,743,027				45,743,027		44,292,102
Losses attributed to noncontrolling interests						$ (86,000)	$ (909,000)			$ (1,713,000)	$ (223,000)
HLBV
Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]
Losses attributed to noncontrolling interests						100,000
Common Stock
Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]
Additional shares issued								13,685,000
Noncontrolling Interest in Subsidiaries | HLBV
Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]
Losses attributed to noncontrolling interests										$ 100,000
License Agreement between Amber and Massachusetts Institute of Technology | Common Stock
Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]
Additional consideration received					$ 0				$ 0
Maximum | Noncontrolling Interest in Subsidiaries | HLBV
Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]
Losses attributed to noncontrolling interests							100,000				100,000
Cullinan Amber Corp | License Agreement between Amber and Massachusetts Institute of Technology | Common Stock
Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]
Shares issued		300,000							300,000
Shares sold/issued					200,000
Cullinan Amber Corp | Series A Preferred Stock
Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]
Shares issued		6,000,000			3,000,000				6,000,000
Gross proceeds		$ 6,000,000			$ 3,000,000
Percentage of share purchased as part of asset acquisition										93.50%
Ownership interest percentage										6.50%
Cullinan Florentine Corp | HLBV
Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]
Losses attributed to noncontrolling interests						0	0			$ 0	0
Cullinan Florentine Corp | Series A Preferred Stock
Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]
Percentage of share purchased as part of asset acquisition										95.60%
Ownership interest percentage										4.40%
Cullinan Florentine Corp | Series B Preferred Units
Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]
Gross proceeds	$ 4,100,000			$ 8,100,000
Additional shares issued	3,750,000			7,500,000
MICA | HLBV
Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]
Losses attributed to noncontrolling interests						$ 100	(300,000)			$ 1,200,000	(800,000)
MICA | Series A Senior Preferred Stock
Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]
Gross proceeds			$ 8,800,000		$ 7,100,000
Percentage of share purchased as part of asset acquisition										53.50%
Ownership interest percentage										46.50%
Purchase of shares			6,700,000		5,400,000
MICA | Series A Senior Preferred Stock | Other Existing Investors
Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]
Gross proceeds			$ 1,200,000		$ 900,000
Purchase of shares			900,000		700,000
Cullinan Pearl Corp | HLBV
Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]
Losses attributed to noncontrolling interests							$ (600,000)			$ (300,000)	$ 700,000

Equity-Based Compensation - Sch

Equity-Based Compensation - Schedule of Assumptions Used to Estimate Fair value of Market-Based RSUs Granted (Details)	9 Months Ended
	Sep. 30, 2022 $ / shares
Share-Based Payment Arrangement, Recognized Amount [Abstract]
Stock price	$ 12.98
Volatility	82.50%
Remaining term (in years)	2 years 8 months 12 days
Risk-free rate	2.90%
Expected dividend yield	0%

Equity-Based Compensation - S_2

Equity-Based Compensation - Schedule of Equity-based Compensation Expense Categories In Consolidated Statements of Operations and Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total equity-based compensation	$ 5,271	$ 4,557	$ 20,444	$ 12,230
Research and Development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total equity-based compensation	1,108	2,458	8,147	6,320
General and Administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total equity-based compensation	$ 4,163	$ 2,099	$ 12,297	$ 5,910

Related Party Transactions - Ad

Related Party Transactions - Additional Information (Details) - USD ($)	9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021
Related Party Transaction [Line Items]
Royalty percentage	1%
Royalties under obligation	$ 0
MPM Oncology Charitable Foundation, Inc.
Related Party Transaction [Line Items]
Royalty percentage	0.50%
UBS Optimus Foundation
Related Party Transaction [Line Items]
Royalty percentage		0.50%

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Income Tax Disclosure [Abstract]
Income tax benefit	$ (2,523)	$ 0	$ 43,979	$ 0

Commitment and Contingencies (A

Commitment and Contingencies (Additional Information) (Details) - USD ($) $ in Thousands	Sep. 30, 2022	Dec. 31, 2021
Indemnification Agreement [Member]
Loss Contingencies [Line Items]
Accrued Liabilities	$ 0	$ 0

Leases - Additional Information

Leases - Additional Information (Details) $ in Millions	1 Months Ended					3 Months Ended			9 Months Ended
	Sep. 30, 2024 USD ($)	Sep. 30, 2023 USD ($)	Sep. 30, 2022 USD ($) ft²	Aug. 31, 2022 ft²	Dec. 31, 2017 ft²	Dec. 31, 2022 USD ($)	Sep. 30, 2022 USD ($)	Sep. 30, 2021 USD ($)	Sep. 30, 2022 USD ($)	Sep. 30, 2021 USD ($)
Lessee Lease Description [Line Items]
Operating Lease expense							$ 0.3		$ 0.6
Rent expense under the prior lease accounting standard								$ 0.2		$ 0.5
Operating lease commence date					Feb. 01, 2018
Operating lease expiration date									Jun. 30, 2024
Lease Payments						$ 0.3
Scenario, Adjustment [Member]
Lessee Lease Description [Line Items]
Sublease payment	$ 0.3	$ 0.6	$ 0.1
Massachusetts
Lessee Lease Description [Line Items]
Operating lease rentable area | ft²			8,000	14,000	8,000

Leases - Supplemental Cash Flow

Leases - Supplemental Cash Flow Information Relating to Leases (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2022 USD ($)
Leases [Abstract]
Operating cash flows from operating leases	$ 456
ROU asset obtained in exchange for an operating lease liability	$ 4,931

Leases - Summary of Future Mini

Leases - Summary of Future Minimum Payments Due Under Operating Lease (Details) - USD ($) $ in Thousands		Sep. 30, 2022	Dec. 31, 2021
Lessee, Operating Lease, Liability, to be Paid [Abstract]
Remainder of 2022	[1]	$ (196)
2023		1,881
2024		1,738
2025		1,461
2026		872
Future minimum payments due under operating lease		5,756
Less: imputed interest		(1,068)
Total lease liabilities at present value		4,688
Lease liabilities, current		696	$ 0
Noncurrent portion of operating lease liabilities		$ 3,992	$ 0
[1] The Company's negative future lease payments for the remainder of 2022 represent a net cash inflow, which includes required lease payments in the fourth quarter and $ 0.3 million to be reimbursed by the lessor for improvements made to the newly leased office space pursuant the terms of the August 2022 lease.

Leases - Summary of Weighted Av

Leases - Summary of Weighted Average Remaining Lease Terms and Discount Rates (Details)	Sep. 30, 2022
Leases [Abstract]
Weighted-average remaining lease term (years)	3 years 4 months 24 days
Weighted-average discount rate	10.70%

Earnings per Share - Summary of

Earnings per Share - Summary of Calculation of Basic and Diluted Net Loss Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Numerator:
Net loss attributable to common stockholders of Cullinan	$ (24,804)	$ (17,350)	$ 137,996	$ (33,056)
Denominator
Weighted Average Number of Shares Outstanding, Basic	45,611	43,439	44,966	43,254
Dilutive effect of common stock issuable from assumed exercise of equity awards		0	1,614	0
Weighted Average Number of Shares Outstanding, Diluted	45,611	43,439	46,580	43,254
Earnings (net loss) per share
Earnings Per Share, Basic	$ (0.54)	$ (0.40)	$ 3.07	$ (0.76)
Earnings Per Share, Diluted	$ (0.54)	$ (0.40)	$ 2.96	$ (0.76)

Earnings per Share - Summary _2

Earnings per Share - Summary of Outstanding Equity Instruments Excluded from Computation of Diluted Net Loss Per Share (Details) - shares	9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Shares excluded from computation of diluted net loss per share (in shares)	6.679	7.334
Restricted Stock Awards
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Shares excluded from computation of diluted net loss per share (in shares)	0.024	0.132
Stock Options
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Shares excluded from computation of diluted net loss per share (in shares)	6.643	7.200
Estimated Shares Issuable Under The ESPP
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Shares excluded from computation of diluted net loss per share (in shares)	0.012	0.002

Subsequent Events (Additional I

Subsequent Events (Additional Information) (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended
	Oct. 31, 2022	Sep. 30, 2022
Subsequent Event [Line Items]
Share purchase price		$ 12.98
Subsequent Event [Member] | Cullinan MICA
Subsequent Event [Line Items]
Ownership percentage	92%
Subsequent Event [Member] | StockPurchaseAndTransferAgreements | Cullinan MICA
Subsequent Event [Line Items]
Share purchase price	$ 2.05
Aggregate purchase price	$ 30.7
Subsequent Event [Member] | StockPurchaseAndTransferAgreements | Cullinan MICA | Series A Preferred Stock
Subsequent Event [Line Items]
Stock Issued During Period Shares Purchase Of Assets	1,522,072
Subsequent Event [Member] | StockPurchaseAndTransferAgreements | Cullinan MICA | Series A Junior Preferred Stock
Subsequent Event [Line Items]
Stock Issued During Period Shares Purchase Of Assets	1,999,998
Subsequent Event [Member] | StockPurchaseAndTransferAgreements | Cullinan MICA | Series A-2 Junior Preferred Stock
Subsequent Event [Line Items]
Stock Issued During Period Shares Purchase Of Assets	11,451,514