Cullinan Oncology (CGEM) 10-Q 11 May 23 2023 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2023	May 01, 2023
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2023
Document Fiscal Year Focus	2023
Document Fiscal Period Focus	Q1
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		39,360,916

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Current assets:
Cash and cash equivalents	$ 122,128	$ 156,152
Short-term investments	268,572	311,140
Prepaid expenses and other current assets	8,331	7,180
Total current assets	399,031	474,472
Property and equipment, net	1,239	1,174
Operating lease right-of-use assets	3,819	4,130
Other assets	459	459
Long-term investments	110,442	80,882
Total assets	514,990	561,117
Current liabilities:
Accounts payable	2,031	2,660
Accrued expenses and other current liabilities	18,379	14,135
Income tax payable	4,207	4,282
Operating lease liabilities, current	1,554	1,421
Total current liabilities	26,171	22,498
Long-term liabilities:
Operating lease liabilities, net of current portion	3,170	3,590
Total liabilities	29,341	26,088
Commitments and contingencies (Note 11)
Stockholders' equity:
Preferred stock, $0.0001 par value, 10,000,000 shares authorized as of March 31, 2023 and December 31, 2022; 647,500 and no shares issued and outstanding as of March 31, 2023 and December 31, 2022, respectively	0	0
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	4	5
Additional paid-in capital	592,544	585,320
Accumulated other comprehensive loss	(1,242)	(2,601)
Accumulated deficit	(105,657)	(47,695)
Total Cullinan stockholders' equity	485,649	535,029
Noncontrolling interests	0	0
Total stockholders' equity	485,649	535,029
Total liabilities and stockholders' equity	$ 514,990	$ 561,117

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Mar. 31, 2023	Dec. 31, 2022
Statement of Financial Position [Abstract]
Preferred Stock par value	$ 0.0001	$ 0.0001
Preferred Stock, shares authorized	10,000,000	10,000,000
Preferred Stock, Share issued	647,500	647,500
Preferred Stock, Shares Outstanding	0	0
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	150,000,000	150,000,000
Common stock, shares issued	39,343,601	45,796,449
Common stock, shares outstanding	39,343,601	45,796,449

CONSOLIDATED STATEMENTS OF OPER

CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE INCOME (LOSS) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Income Statement [Abstract]
Loss from operations	$ (62,756)	$ (32,657)
Type of revenue [Extensible List]	us-gaap:LicenseMember	us-gaap:LicenseMember
Operating expenses:
Research and development	$ 52,096	$ 24,536
General and administrative	10,660	8,121
Total operating expenses	62,756	32,657
Other income (expense):
Interest income	4,508	197
Other income (expense), net	107	0
Net income (loss) before income taxes	(58,141)	(32,460)
Income tax benefit	0	(19,568)
Net loss	(58,141)	(12,892)
Net loss attributable to noncontrolling interests	(179)	(794)
Net loss attributable to common stockholders of Cullinan	(57,962)	(12,098)
Comprehensive loss:
Net loss	(58,141)	(12,892)
Unrealized gain (loss) on investments	1,359	(2,296)
Comprehensive loss	(56,782)	(15,188)
Comprehensive loss attributable to noncontrolling interests	(179)	(794)
Comprehensive loss attributable to Cullinan	$ (56,603)	$ (14,394)
Net loss per share:
Basic	$ (1.42)	$ (0.27)
Diluted	$ (1.42)	$ (0.27)
Weighted-average shares used in computing net loss per share:
Basic	40,682	44,432
Diluted	40,682	44,432

CONSOLIDATED STATEMENTS OF STOC

CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Preferred Stock	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Loss	Accumulated Deficit	Noncontrolling Interest in Subsidiaries
Balances at Dec. 31, 2021	$ 425,374		$ 4	$ 584,714	$ (838)	$ (158,909)	$ 403
Balances, shares at Dec. 31, 2021			44,292,102
Net issuance of common stock under equity-based compensation plans	1,566			1,566
Contributions from noncontrolling interests	1,153						1,153
Net issuance of common stock under equity-based compensation plans, shares			367,924
Equity-based compensation	6,565			6,559			6
Unrealized gain (loss) on investments	(2,296)				(2,296)
Shares tendered for withholding taxes	(22)
Net 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, 2022	535,029		$ 5	585,320	(2,601)	(47,695)	0
Balances, shares at Dec. 31, 2022			45,796,449
Issuance of preferred stock in exchange for common stock, Share		647,500	6,475,000
Issuance of preferred stock in exchange for common stock			$ (1)	1
Net issuance of common stock under equity-based compensation plans	36			(36)
Contributions from noncontrolling interests	179						179
Net issuance of common stock under equity-based compensation plans, shares			22,152
Equity-based compensation	7,259			7,259
Unrealized gain (loss) on investments	1,359				1,359
Shares tendered for withholding taxes	0
Net loss	(58,141)					(57,962)	(179)
Balances at Mar. 31, 2023	$ 485,649		$ 4	$ 592,544	$ (1,242)	$ (105,657)	$ 0
Balances, shares at Mar. 31, 2023		647,500	39,343,601

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Operating activities:
Net loss	$ (58,141)	$ (12,892)
Adjustments to reconcile net income (loss) to net cash used in operating activities:
Equity-based compensation expense	7,259	6,565
Depreciation and amortization	72	13
Amortization or accretion on marketable securities	(1,371)	946
Non Cash Contributions From Noncontrolling Interests	4	0
Deferred Income Tax Benefit	0	(19,568)
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(755)	(1,140)
Accounts payable	(630)	3,137
Accrued expenses and other current liabilities	2,640	1,031
Income tax payable	(75)	0
Net cash used in operating activities	(50,997)	(21,908)
Investing activities:
Proceeds from sales and maturities of marketable securities	104,482	91,731
Purchase of marketable securities	(89,139)	(57,020)
Purchase of property and equipment	(159)	0
Net cash provided by (used in) investing activities	15,184	34,711
Financing activities:
Contributions From Noncontrolling Interests	0	1,153
Issuance Of Convertible Notes	1,825	800
Proceeds from net issuance of common stock under equity-based compensation plans	(36)	1,588
Net cash provided by financing activities	1,789	3,541
Net increase (decrease) in cash and cash equivalents	(34,024)	16,344
Cash and cash equivalents at beginning of period	156,152	59,774
Cash and cash equivalents at end of period	122,128	76,118
Non-cash financing activities and supplemental cash flow information
Conversion Of Convertible Note Into Noncontrolling Interest	175	0
Purchases of property and equipment included in accounts payable and accrued expenses and other liabilities	49	0
Cash paid for income taxes	75	0
Tax Withholding On Stock Awards Not Yet Paid	$ 0	$ 22

Nature of Business and Basis of

Nature of Business and Basis of Presentation	3 Months Ended
	Mar. 31, 2023
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 clinical-stage biopharmaceutical company focused on modality-agnostic targeted oncology that was incorporated in September 2016 and has a principal place of business in Cambridge, Massachusetts. Liquidity The Company has incurred significant operating losses, with the exception of 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. 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 $ 390.7 million and long-term investments and interest receivable of $ 112.8 million as of March 31, 2023, 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	3 Months Ended
	Mar. 31, 2023
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 its Annual Report on Form 10-K for the fiscal year ended December 31, 2022 (the “2022 10-K”), except for its accounting policy for equity-based compensation. Basis of Presentation The unaudited consolidated financial statements of the Company have been prepared in conformity with accounting principles generally accepted in the United States ("U.S. GAAP") and in accordance with applicable rules and regulations of the Securities Exchange Commission (the "SEC") for interim financial reporting and include the accounts of the Company and its consolidated 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 2022 10-K. Equity-Based Compensation The fair value of equity-based awards is measured at the grant date and is recognized as expense over the requisite service period, which is generally the vesting period. Forfeitures are recognized as they occur. The Company classifies equity-based compensation in its consolidated statements of operations and comprehensive income (loss) in the same manner in which the award recipient’s payroll costs or service payments are classified. The fair value of service-based restricted stock units ("RSUs") is the closing market price of the Company's common stock on the grant date. The Company measures the fair value of market-based RSUs on the grant date using a Monte Carlo simulation model. The Company estimates the fair value of stock options using the Black-Scholes option pricing model. Both the Monte Carlo simulation model and the Black-Scholes option pricing model require the input of objective and subjective assumptions. Certain assumptions used, including the Company's expected stock price volatility, 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. Prior to 2023, the expected volatility used in the Black-Scholes option pricing model for new options was based on historical volatilities of the stock prices of similar entities within the Company’s industry over a period of time commensurate with the expected term assumption. In 2023, the Company determined that a sufficient amount of historical information was available regarding the volatility of its stock price to begin using a blended rate that combines our historical volatility with the historical volatilities of the stock prices of similar entities within the Company’s industry over a period of time commensurate with the expected term assumption. Recently Issued Accounting Pronouncements There are no recently issued accounting pronouncements that will have a material impact on the Company's consolidated financial statements.

Financial Instruments

Financial Instruments	3 Months Ended
	Mar. 31, 2023
Financial Instruments Pledged as Collateral [Abstract]
Financial Instruments	(3) Financial Instruments Investments The Company recognized its short-term and long-term investments by security type at March 31, 2023 as follows: Amortized Gross Gross Estimated (in thousands) Short-term investments Corporate notes $ 211,915 $ 7 $ ( 1,268 ) $ 210,654 Asset-backed securities 36,025 2 ( 9 ) 36,018 Commercial paper 12,932 1 ( 3 ) 12,930 U.S. government notes 8,996 — ( 26 ) 8,970 Total short-term investments 269,868 10 ( 1,306 ) 268,572 Long-term investments Corporate notes 79,501 132 ( 96 ) 79,537 Asset-backed securities 30,887 18 — 30,905 Total long-term investments 110,388 150 ( 96 ) 110,442 Total investments $ 380,256 $ 160 $ ( 1,402 ) $ 379,014 The Company recognized its short-term and long-term investments by security type at December 31, 2022 as follows: Amortized Gross Gross Estimated (in thousands) Short-term investments Corporate notes $ 244,498 $ 11 $ ( 1,743 ) $ 242,766 Asset-backed securities 16,625 — ( 15 ) 16,610 Commercial paper 18,035 3 ( 13 ) 18,025 U.S. government notes 34,029 — ( 290 ) 33,739 Total short-term investments 313,187 14 ( 2,061 ) 311,140 Long-term investments Corporate notes 81,436 18 ( 572 ) 80,882 Total long-term investments 81,436 18 ( 572 ) 80,882 Total investments $ 394,623 $ 32 $ ( 2,633 ) $ 392,022 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 March 31, 2023: Level 1 Level 2 Level 3 Total (in thousands) Short-term investments Corporate notes $ — $ 210,654 $ — $ 210,654 Asset-backed securities — 36,018 — 36,018 Commercial paper — 12,930 — 12,930 U.S. government notes — 8,970 — 8,970 Total short-term investments — 268,572 — 268,572 Long-term investments Corporate notes — 79,537 — 79,537 Asset-backed securities — 30,905 — 30,905 Total long-term investments — 110,442 — 110,442 Total investments $ — $ 379,014 $ — $ 379,014 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, 2022: Level 1 Level 2 Level 3 Total (in thousands) Short-term investments Corporate notes $ — $ 242,766 $ — $ 242,766 Asset-backed securities — 16,610 — 16,610 Commercial paper — 18,025 — 18,025 U.S. government notes — 33,739 — 33,739 Total short-term investments — 311,140 — 311,140 Long-term investments Corporate notes — 80,882 — 80,882 Total long-term investments — 80,882 — 80,882 Total investments $ — $ 392,022 $ — $ 392,022 As of March 31, 2023 and December 31, 2022, the fair values of cash and cash equivalents, prepaid expenses and other current assets, accounts payable, accrued expenses and other current liabilities approximated their carrying values due to the short-term nature of these instruments.

Accrued Expenses and Other Curr

Accrued Expenses and Other Current Liabilities	3 Months Ended
	Mar. 31, 2023
Accrued Expenses And Other Current Liabilities [Abstract]
Accrued Expenses and Other Current Liabilities	(4) Accrued Expenses and Other Current Liabilities Accrued expenses and other current liabilities consisted of the following as of March 31, 2023 and December 31, 2022: March 31, 2023 December 31, 2022 (in thousands) Accrued research and development expenses $ 10,031 $ 7,486 Accrued bonus 1,389 4,516 Other current liabilities 5,110 1,955 Convertible note and accrued interest 1,849 178 Total accrued expenses and other current liabilities $ 18,379 $ 14,135

License and Collaboration Agree

License and Collaboration Agreements	3 Months Ended
	Mar. 31, 2023
License And Collaboration Agreements [Abstract]
License and Collaboration Agreements	(5) License and Collaboration Agreements Harbour License Agreement In February 2023, the Company and Harbour BioMed US Inc. (“Harbour”) entered into a license and collaboration agreement (the “Harbour License Agreement”), pursuant to which Harbour granted to the Company an exclusive license for the development, manufacturing and commercialization of HBM7008 (CLN-418) in the U.S. Under the terms of the Harbour License Agreement, the Company paid Harbour an upfront license fee of $ 25.0 million at signing. Harbour will be eligible to receive up to $ 148 million in milestone payments based on the achievement of pre-specified development and regulatory milestones. Harbour is also eligible to receive up to an additional $ 415 million in sales-based milestones as well as tiered royalties up to the high teens on a licensed product-by-licensed product basis, as a percentage of U.S. commercial sales. In addition, under the Harbour License Agreement, Harbour granted the Company certain intellectual property rights to enable the Company to perform its obligations and exercise its rights under the Harbour License Agreement. Unless earlier terminated, the Harbour License Agreement will continue in effect until the expiration of the Company’s royalty obligations. The Harbour License Agreement may be terminated by either party for a material breach by the other party, subject to notice and cure provisions, or in the event of the other party’s insolvency. The Company may terminate the Harbour License Agreement for convenience by providing 90 days written notice to Harbour. In the Harbour License Agreement, each party made customary representations and warranties and agreed to customary covenants, including, without limitation, with respect to indemnification, for transactions of this type. The Company evaluated the Harbour License Agreement and determined that the exclusive license for the development, manufacturing and commercialization of HBM7008 (CLN-418) in the U.S represented an asset acquisition of in-process research and development. The Company also determined that the asset had no alternative future use at the time of acquisition, and therefore the upfront license fee of $ 25.0 million was recorded within research and development expenses during the three months ended March 31, 2023. Co-Development Agreement with Taiho In June 2022, the Company and an affiliate of Taiho Pharmaceutical Co., Ltd (“Taiho”) entered into a co-development agreement, pursuant to which the Company will collaborate to develop zipalertinib and will retain the option to co-commercialize zipalertinib in the U.S. Under the co-development agreement, development costs for zipalertinib 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. 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. Payments made to or received from Taiho for zipalertinib development activities after the execution of the co-development agreement are recorded within research and development expenses. For the three months ended March 31, 2023, the Company recorded research and development expense of $ 4.7 million related to its share of costs incurred by Taiho. Cullinan incurred $ 1.0 million of costs that were reimbursable by Taiho during the three months ended March 31, 2023, which were recorded as a reduction to research and development expenses. The cumulative net amount of $ 2.7 million due to Taiho was recorded within accrued expenses and other current liabilities as of March 31, 2023. Other License and Collaboration Expenses During the three months ended March 31, 2023, the Company recorded $ 0.2 million in research and development expenses relating to the license agreement with Massachusetts Institute of Technology relating to CLN-617. During the three months ended March 31, 2022, the Company recorded $ 0.5 million in research and development expenses relating to a collaboration agreement with Adimab, LLC.

Equity-Based Compensation

Equity-Based Compensation	3 Months Ended
	Mar. 31, 2023
Share-Based Payment Arrangement [Abstract]
Equity-Based Compensation	(7) Equity-Based Compensation The Company recorded equity-based compensation in the following expense categories in the consolidated statements of operations and comprehensive income (loss) for the three months ended March 31, 2023 and 2022: Three Months Ended March 31, 2023 2022 (in thousands) Research and development $ 3,054 $ 2,660 General and administrative 4,205 3,905 Total equity-based compensation $ 7,259 $ 6,565 Determining Fair Value of Options 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 three months ended March 31, 2023 and 2022 were determined using the methods and assumptions discussed below: • The expected term of options is determined using the “simplified” method, as prescribed in the SEC Staff Accounting Bulletin 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 risk-free interest rate is based on implied yields available from U.S. Treasury securities with a remaining term equal to the expected term assumed at the grant date. • Prior to 2023, the expected volatility used in the Black-Scholes option pricing model for new options was based on historical volatilities of the stock prices of similar entities within the Company’s industry over a period of time commensurate with the expected term assumption. In 2023, the Company determined that a sufficient amount of historical information was available regarding the volatility of its stock price to begin using a blended rate that combines its historical volatility with the historical volatilities of the stock prices of similar entities within the Company’s industry over a period of time commensurate with the expected term assumption. • The estimated annual dividend yield was based on the Company’s expectation of not paying dividends on its common stock in the foreseeable future. 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 in the three months ended March 31, 2023 and 2022: Three Months Ended March 31, 2023 2022 Risk-free interest rate 4.0 % 1.8 % Expected term (in years) 6.0 6.0 Expected volatility 79.3 % 77.3 % Expected dividend yield 0.0 % 0.0 %

Related Party Transactions

Related Party Transactions	3 Months Ended
	Mar. 31, 2023
Related Party Transactions [Abstract]
Related Party Transactions	(8) 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, the Foundations are collectively entitled to receive a low single digit royalty percentage 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 concluded that these instruments had no value at the inception of the agreements. The Company has not had any applicable net sales from its products and as a result, has no t paid or incurred any royalties under these agreements as of March 31, 2023. 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 March 31, 2023 and December 31, 2022.

Income Taxes

Income Taxes	3 Months Ended
	Mar. 31, 2023
Income Tax Disclosure [Abstract]
Income Taxes	(9) Income Taxes During the three months ended March 31, 2023, the Company did no t record an income tax expense or benefit. During the three months ended March 31, 2022, the Company recorded an income tax benefit of $ 19.6 million. The tax benefit recorded for the three months ended March 31, 2022 was driven by the expected utilization of net operating losses ("NOLs") generated during the quarter based on the Company's effective tax rate and the release of valuation allowance for certain historical tax losses against the expected gain from the sale of its entire equity interest in Cullinan Pearl. The Company has evaluated the positive and negative evidence bearing upon its ability to realize its deferred tax assets, which primarily consist of capitalized research and development costs, temporary differences on equity-based compensation, and NOL carryforwards. The Company has considered its history of cumulative net losses and its estimated future taxable income and has concluded that it is more likely than not that the Company will not realize the benefits of its deferred tax assets. As a result, the Company has maintained a full valuation allowance against its remaining net deferred tax assets as of March 31, 2023.

Commitments and Contingencies

Commitments and Contingencies	3 Months Ended
	Mar. 31, 2023
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	(10) 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 March 31, 2023 and December 31, 2022. 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	3 Months Ended
	Mar. 31, 2023
Leases [Abstract]
Leases	(11) 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 (the "Suite 520 Lease") . In August 2022, the Company entered into an additional operating 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 $ 0.4 million and $ 0.1 million for the three months ended March 31, 2023 and 2022, respectively. The following table summarizes supplemental cash flow information for the three months ended March 31, 2023 and 2022: Three Months Ended March 31, 2023 2022 (in thousands) Cash paid for amounts included in measurement of lease liabilities: Operating cash flows from operating leases $ 416 $ 151 Right-of-use asset obtained in exchange for an operating lease liability $ — $ 1,311 The following table summarizes the Company’s future minimum lease payments and reconciliation of lease liabilities as of March 31, 2023 (in thousands): March 31, 2023 Remainder of 2023 $ 1,465 2024 1,738 2025 1,461 2026 872 Total future minimum lease payments 5,536 Less: imputed interest ( 812 ) Total lease liabilities at present value $ 4,724 The following table summarizes the weighted-average remaining lease term and discount rate as of March 31, 2023 and December 31, 2022: March 31, 2023 December 31, 2022 Weighted-average remaining lease term (in years) 3.0 3.2 Weighted-average discount rate 10.8 % 10.8 % 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. Sublease Agreement In September 2022, the Company entered into a sublease agreement through May 2024 for the Suite 520 Lease. For the three months ended March 31, 2023, the Company recorded sublease income of $ 0.2 million within other income (expense), net. The Company expects to receive sublease payments of approximately $ 0.5 million for the remainder of 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 the Suite 520 lease during the term of the sublease.

Earnings per Share

Earnings per Share	3 Months Ended
	Mar. 31, 2023
Earnings Per Share [Abstract]
Earnings per Share	(12) Loss per Share The following table sets forth the calculation of basic and diluted net loss per share for the three months ended March 31, 2023 and 2022: Three Months Ended March 31, 2023 2022 (in thousands, except per share data) Numerator: Net loss attributable to common stockholders of Cullinan $ ( 57,962 ) $ ( 12,098 ) Denominator: Weighted-average common stock outstanding - basic and diluted 40,682 44,432 Net loss per share: Basic and diluted $ ( 1.42 ) $ ( 0.27 ) The Company used the treasury stock and if-converted methods to determine the number of dilutive shares. The following table sets forth potential common shares that were excluded from the computation of diluted net loss per share for the three months ended March 31, 2023 and 2022 because their effect would have been anti-dilutive: Three Months Ended March 31, 2023 2022 (in thousands) Stock options 8,835 9,985 Preferred stock 5,108 — Restricted stock awards and RSUs 408 74 Employee stock purchase plan — 7 Total 14,351 10,066

Subsequent Events

Subsequent Events	3 Months Ended
	Mar. 31, 2023
Subsequent Events [Abstract]
Subsequent Events	(13) Subsequent Events In May 2023, the Company entered into an agreement with Cowen and Company, LLC (“Cowen”) to establish an at-the-market equity offering program, pursuant to which Cowen can offer and sell up to $ 125.0 million of the Company’s common stock at prevailing market prices .

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2023
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The unaudited consolidated financial statements of the Company have been prepared in conformity with accounting principles generally accepted in the United States ("U.S. GAAP") and in accordance with applicable rules and regulations of the Securities Exchange Commission (the "SEC") for interim financial reporting and include the accounts of the Company and its consolidated 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 2022 10-K.
Equity-based Compensation	Equity-Based Compensation The fair value of equity-based awards is measured at the grant date and is recognized as expense over the requisite service period, which is generally the vesting period. Forfeitures are recognized as they occur. The Company classifies equity-based compensation in its consolidated statements of operations and comprehensive income (loss) in the same manner in which the award recipient’s payroll costs or service payments are classified. The fair value of service-based restricted stock units ("RSUs") is the closing market price of the Company's common stock on the grant date. The Company measures the fair value of market-based RSUs on the grant date using a Monte Carlo simulation model. The Company estimates the fair value of stock options using the Black-Scholes option pricing model. Both the Monte Carlo simulation model and the Black-Scholes option pricing model require the input of objective and subjective assumptions. Certain assumptions used, including the Company's expected stock price volatility, 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. Prior to 2023, the expected volatility used in the Black-Scholes option pricing model for new options was based on historical volatilities of the stock prices of similar entities within the Company’s industry over a period of time commensurate with the expected term assumption. In 2023, the Company determined that a sufficient amount of historical information was available regarding the volatility of its stock price to begin using a blended rate that combines our historical volatility with the historical volatilities of the stock prices of similar entities within the Company’s industry over a period of time commensurate with the expected term assumption.
Recently Adopted Accounting Pronouncements	Recently Issued Accounting Pronouncements There are no recently issued accounting pronouncements that will have a material impact on the Company's consolidated financial statements.

Financial Instruments (Tables)

Financial Instruments (Tables)	3 Months Ended
	Mar. 31, 2023
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 March 31, 2023 as follows: Amortized Gross Gross Estimated (in thousands) Short-term investments Corporate notes $ 211,915 $ 7 $ ( 1,268 ) $ 210,654 Asset-backed securities 36,025 2 ( 9 ) 36,018 Commercial paper 12,932 1 ( 3 ) 12,930 U.S. government notes 8,996 — ( 26 ) 8,970 Total short-term investments 269,868 10 ( 1,306 ) 268,572 Long-term investments Corporate notes 79,501 132 ( 96 ) 79,537 Asset-backed securities 30,887 18 — 30,905 Total long-term investments 110,388 150 ( 96 ) 110,442 Total investments $ 380,256 $ 160 $ ( 1,402 ) $ 379,014 The Company recognized its short-term and long-term investments by security type at December 31, 2022 as follows: Amortized Gross Gross Estimated (in thousands) Short-term investments Corporate notes $ 244,498 $ 11 $ ( 1,743 ) $ 242,766 Asset-backed securities 16,625 — ( 15 ) 16,610 Commercial paper 18,035 3 ( 13 ) 18,025 U.S. government notes 34,029 — ( 290 ) 33,739 Total short-term investments 313,187 14 ( 2,061 ) 311,140 Long-term investments Corporate notes 81,436 18 ( 572 ) 80,882 Total long-term investments 81,436 18 ( 572 ) 80,882 Total investments $ 394,623 $ 32 $ ( 2,633 ) $ 392,022
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 March 31, 2023: Level 1 Level 2 Level 3 Total (in thousands) Short-term investments Corporate notes $ — $ 210,654 $ — $ 210,654 Asset-backed securities — 36,018 — 36,018 Commercial paper — 12,930 — 12,930 U.S. government notes — 8,970 — 8,970 Total short-term investments — 268,572 — 268,572 Long-term investments Corporate notes — 79,537 — 79,537 Asset-backed securities — 30,905 — 30,905 Total long-term investments — 110,442 — 110,442 Total investments $ — $ 379,014 $ — $ 379,014 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, 2022: Level 1 Level 2 Level 3 Total (in thousands) Short-term investments Corporate notes $ — $ 242,766 $ — $ 242,766 Asset-backed securities — 16,610 — 16,610 Commercial paper — 18,025 — 18,025 U.S. government notes — 33,739 — 33,739 Total short-term investments — 311,140 — 311,140 Long-term investments Corporate notes — 80,882 — 80,882 Total long-term investments — 80,882 — 80,882 Total investments $ — $ 392,022 $ — $ 392,022 As of March 31, 2023 and December 31, 2022, the fair values of cash and cash equivalents, prepaid expenses and other current assets, accounts payable, accrued expenses and other current liabilities approximated their carrying values due to the short-term nature of these instruments.

Accrued Expenses and Other Cu_2

Accrued Expenses and Other Current Liabilities (Tables)	3 Months Ended
	Mar. 31, 2023
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 as of March 31, 2023 and December 31, 2022: March 31, 2023 December 31, 2022 (in thousands) Accrued research and development expenses $ 10,031 $ 7,486 Accrued bonus 1,389 4,516 Other current liabilities 5,110 1,955 Convertible note and accrued interest 1,849 178 Total accrued expenses and other current liabilities $ 18,379 $ 14,135

Equity-Based Compensation (Tabl

Equity-Based Compensation (Tables)	3 Months Ended
	Mar. 31, 2023
Share-Based Payment Arrangement [Abstract]
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) for the three months ended March 31, 2023 and 2022: Three Months Ended March 31, 2023 2022 (in thousands) Research and development $ 3,054 $ 2,660 General and administrative 4,205 3,905 Total equity-based compensation $ 7,259 $ 6,565
Schedule of Assumptions Used to Estimate Fair value of Market-Based RSUs Granted	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 in the three months ended March 31, 2023 and 2022: Three Months Ended March 31, 2023 2022 Risk-free interest rate 4.0 % 1.8 % Expected term (in years) 6.0 6.0 Expected volatility 79.3 % 77.3 % Expected dividend yield 0.0 % 0.0 %

Leases (Tables)

Leases (Tables)	3 Months Ended
	Mar. 31, 2023
Leases [Abstract]
Supplemental Cash Flow Information Relating to Leases	The following table summarizes supplemental cash flow information for the three months ended March 31, 2023 and 2022: Three Months Ended March 31, 2023 2022 (in thousands) Cash paid for amounts included in measurement of lease liabilities: Operating cash flows from operating leases $ 416 $ 151 Right-of-use asset obtained in exchange for an operating lease liability $ — $ 1,311
Summarizes of future minimum lease payments	The following table summarizes the Company’s future minimum lease payments and reconciliation of lease liabilities as of March 31, 2023 (in thousands): March 31, 2023 Remainder of 2023 $ 1,465 2024 1,738 2025 1,461 2026 872 Total future minimum lease payments 5,536 Less: imputed interest ( 812 ) Total lease liabilities at present value $ 4,724
Summarizes Lease Term and Discount Rate	The following table summarizes the weighted-average remaining lease term and discount rate as of March 31, 2023 and December 31, 2022: March 31, 2023 December 31, 2022 Weighted-average remaining lease term (in years) 3.0 3.2 Weighted-average discount rate 10.8 % 10.8 %

Earnings per Share (Tables)

Earnings per Share (Tables)	3 Months Ended
	Mar. 31, 2023
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 for the three months ended March 31, 2023 and 2022: Three Months Ended March 31, 2023 2022 (in thousands, except per share data) Numerator: Net loss attributable to common stockholders of Cullinan $ ( 57,962 ) $ ( 12,098 ) Denominator: Weighted-average common stock outstanding - basic and diluted 40,682 44,432 Net loss per share: Basic and diluted $ ( 1.42 ) $ ( 0.27 )
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 diluted net loss per share for the three months ended March 31, 2023 and 2022 because their effect would have been anti-dilutive: Three Months Ended March 31, 2023 2022 (in thousands) Stock options 8,835 9,985 Preferred stock 5,108 — Restricted stock awards and RSUs 408 74 Employee stock purchase plan — 7 Total 14,351 10,066

Nature of Business and Basis _2

Nature of Business and Basis of Presentation - Additional Information (Details) $ in Millions	Mar. 31, 2023 USD ($)
Nature Of Business And Basis Of Presentation [Line Items]
Long-term investments and interest receivables	$ 112.8
Cash, cash equivalents, short-term investments and long-term investments	$ 390.7

Summary of Significant Accoun_3

Summary of Significant Accounting Policies - Additional Information (Details)	3 Months Ended
	Mar. 31, 2023 Segment
Accounting Policies [Abstract]
Number of operating segments	1

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Supplemental Balance Sheet Information Related to Operating Leases (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Operating lease right-of-use assets	$ 3,819	$ 4,130
Operating lease liabilities, current	1,554	1,421
Noncurrent portion of operating lease liabilities	$ 3,170	$ 3,590

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	Mar. 31, 2023	Dec. 31, 2022	Mar. 31, 2022	Dec. 31, 2021
Stockholders' Equity (Members' Deficit)
Common Stock	$ 4	$ 5
Additional paid-in capital	592,544	585,320
Accumulated other comprehensive loss	(1,242)	(2,601)
Accumulated deficit	(105,657)	(47,695)
Total Cullinan Stockholders' Equity (Members' Deficit)	485,649	535,029
Non-controlling interests in subsidiaries	0	0
Total Stockholders' Equity (Members' Deficit)	$ 485,649	$ 535,029	$ 419,470	$ 425,374

Sale of Cullinan Pearl and Co-D

Sale of Cullinan Pearl and Co-Development Agreement with Taiho - Additional Information (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended
	Jun. 30, 2022	Mar. 31, 2023	Mar. 31, 2022
Defined Benefit Plan Disclosure [Line Items]
Research and development		$ 52,096	$ 24,536
Pearl - Taiho
Defined Benefit Plan Disclosure [Line Items]
Percentage of profits from potential sales	50%
Research and development		1,000
Research and development expense related to share of costs		$ 4,700

Financial Instruments - Schedul

Financial Instruments - Schedule of Short-term and Long-term Investment Marketable Securities by Security Type (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Available For Sale Securities Fair Value To Amortized Cost Basis [Line Items]
Amortized Cost	$ 380,256	$ 394,623
Gross Unrealized Gains	160	32
Gross Unrealized Losses	(1,402)	(2,633)
Estimated Fair Value	379,014	392,022
Long Term Investment
Available For Sale Securities Fair Value To Amortized Cost Basis [Line Items]
Amortized Cost	110,388	81,436
Gross Unrealized Gains	150	18
Gross Unrealized Losses	(96)	(572)
Estimated Fair Value	110,442	80,882
Long Term Investment | Asset-backed Securities
Available For Sale Securities Fair Value To Amortized Cost Basis [Line Items]
Amortized Cost	30,887
Gross Unrealized Gains	18
Gross Unrealized Losses	0
Estimated Fair Value	30,905
Long Term Investment | Corporate Note Securities
Available For Sale Securities Fair Value To Amortized Cost Basis [Line Items]
Amortized Cost	79,501	81,436
Gross Unrealized Gains	132	18
Gross Unrealized Losses	(96)	(572)
Estimated Fair Value	79,537	80,882
Short Term Investments
Available For Sale Securities Fair Value To Amortized Cost Basis [Line Items]
Amortized Cost	269,868	313,187
Gross Unrealized Gains	10	14
Gross Unrealized Losses	(1,306)	(2,061)
Estimated Fair Value	268,572	311,140
Short Term Investments | U.S. Government Notes
Available For Sale Securities Fair Value To Amortized Cost Basis [Line Items]
Amortized Cost	8,996	34,029
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(26)	(290)
Estimated Fair Value	8,970	33,739
Short Term Investments | Asset-backed Securities
Available For Sale Securities Fair Value To Amortized Cost Basis [Line Items]
Amortized Cost	36,025	16,625
Gross Unrealized Gains	2	0
Gross Unrealized Losses	(9)	(15)
Estimated Fair Value	36,018	16,610
Short Term Investments | Commercial Paper
Available For Sale Securities Fair Value To Amortized Cost Basis [Line Items]
Amortized Cost	12,932	18,035
Gross Unrealized Gains	1	3
Gross Unrealized Losses	(3)	(13)
Estimated Fair Value	12,930	18,025
Short Term Investments | Corporate Note Securities
Available For Sale Securities Fair Value To Amortized Cost Basis [Line Items]
Amortized Cost	211,915	244,498
Gross Unrealized Gains	7	11
Gross Unrealized Losses	(1,268)	(1,743)
Estimated Fair Value	$ 210,654	$ 242,766

Financial Instruments - Summary

Financial Instruments - Summary of Fair Value of Financial Assets Measured on Recurring Basis (Details) - Recurring - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total short-term investments	$ 268,572	$ 311,140
Total long-term investments	110,442	80,882
Assets Fair Value Disclosure, Total	379,014	392,022
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	0
Assets Fair Value Disclosure, Total	0	0
Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total short-term investments	268,572	311,140
Total long-term investments	110,442	80,882
Assets Fair Value Disclosure, Total	379,014	392,022
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	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	8,970	33,739
U.S. Government Notes | Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total short-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	8,970	33,739
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
Asset-backed Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total short-term investments	36,018	16,610
Total long-term investments	30,905
Asset-backed Securities | 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
Asset-backed Securities | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total short-term investments	36,018	16,610
Total long-term investments	30,905
Asset-backed Securities | 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
Commercial Paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total short-term investments	12,930	18,025
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	12,930	18,025
Commercial Paper | Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total short-term investments	0	0
Corporate Note Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total short-term investments	210,654	242,766
Total long-term investments	79,537	80,882
Corporate Note Securities | 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	0
Corporate Note Securities | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total short-term investments	210,654	242,766
Total long-term investments	79,537	80,882
Corporate Note Securities | 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	$ 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	Mar. 31, 2023	Dec. 31, 2022
Accounts Payable and Accrued Liabilities, Current [Abstract]
Accrued research and development expenses	$ 10,031	$ 7,486
Accrued bonus	1,389	4,516
Other current liabilities	5,110	1,955
Convertible note and accrued interest	1,849	178
Total accrued expenses and other current liabilities	$ 18,379	$ 14,135

License and Collaboration Agr_2

License and Collaboration Agreements - Additional Information (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended
	Jun. 30, 2022	Mar. 31, 2023	Mar. 31, 2022
License And Collaboration Agreements [Line Items]
Research and development costs		$ 52,096	$ 24,536
Harbour License Agreement [Member]
License And Collaboration Agreements [Line Items]
Upfront license fee		25,000
Harbour BioMed US Inc. [Member] | Harbour License Agreement [Member]
License And Collaboration Agreements [Line Items]
Upfront license fee		25,000
Harbour BioMed US Inc. [Member] | Maximum | Harbour License Agreement [Member] | Achievement Based [Member]
License And Collaboration Agreements [Line Items]
Aggregate amount of milestone payment		148,000
Harbour BioMed US Inc. [Member] | Maximum | Harbour License Agreement [Member] | Sales Based [Member]
License And Collaboration Agreements [Line Items]
Aggregate amount of milestone payment		415,000
Pearl - Taiho
License And Collaboration Agreements [Line Items]
Percentage of profits from potential sales	50%
Research and development expense related to share of costs		4,700
Accrued expenses and other current liabilities		2,700
Research and development costs		1,000
Adimab
License And Collaboration Agreements [Line Items]
Research and development costs			$ 500
MIT
License And Collaboration Agreements [Line Items]
Research and development costs		$ 200

Common Stock and Noncontrolling

Common Stock and Noncontrolling Interest in Subsidiaries - Additional Information (Details) - USD ($)	1 Months Ended		3 Months Ended
	Jan. 31, 2023	Mar. 31, 2022	Mar. 31, 2023	Mar. 31, 2022	Dec. 31, 2022
Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]
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.
Preferred Stock, Par or Stated Value Per Share			$ 0.0001		$ 0.0001
Number of common stock exchange					200,000
Number of shares of common stock, percentage			9.99%
Increase in number of shares of preferred stock, percentage			19.99%
Shares issued			647,500		647,500
Shares sold/issued			39,343,601		45,796,449
Losses attributed to noncontrolling interests			$ (179,000)	$ (794,000)
Biotechnology Value Fund, L.P exchange agreement [Member]
Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]
Newly designated Series A preferred stock	600,000
Preferred Stock, Par or Stated Value Per Share	$ 0.0001
Number of common stock exchange	6.5
Cullinan Amber Corp | Noncontrolling Interest in Subsidiaries
Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]
Losses attributed to noncontrolling interests			$ 0	0
Cullinan Amber Corp | Series A Preferred Stock
Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]
Percentage of share purchased as part of asset acquisition			94%
Ownership interest percentage			6%
Cullinan Florentine Corp | HLBV
Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]
Losses attributed to noncontrolling interests			$ 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			96%
Ownership interest percentage			4%
MICA
Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]
Purchase of convertible notes	$ 1,800,000
MICA | HLBV
Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]
Losses attributed to noncontrolling interests			$ 200,000	500,000
MICA | Series A Preferred Stock
Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]
Shares issued	100,000
Additional shares issued	3,800,000
Percentage of share purchased as part of asset acquisition			96%
Ownership interest percentage			4%
MICA | Series A Senior Preferred Stock
Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]
Purchase of shares		6,700,000
MICA | Series A Senior Preferred Stock | Other Existing Investors
Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]
Gross proceeds		$ 1,200,000
Purchase of shares		900,000
Cullinan Pearl Corp | HLBV
Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]
Losses attributed to noncontrolling interests				(300,000)
Cullinan Pearl Corp | Note Purchase Agreement
Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]
Convertible note purchased		$ 800,000		$ 800,000

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	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total equity-based compensation	$ 7,259	$ 6,565
Research and Development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total equity-based compensation	3,054	2,660
General and Administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total equity-based compensation	$ 4,205	$ 3,905

Equity-Based Compensation - S_2

Equity-Based Compensation - Schedule of Assumptions Used to Estimate Fair value of Market-Based RSUs Granted (Details)	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Share-Based Payment Arrangement, Recognized Amount [Abstract]
Risk-free interest rate	4%	1.80%
Expected term (in years)	6 years	6 years
Expected volatility	79.30%	77.30%
Expected dividend yield	0%	0%

Related Party Transactions - Ad

Related Party Transactions - Additional Information (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2023 USD ($)
Related Party Transaction [Line Items]
Royalties under obligation	$ 0

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Income Tax Disclosure [Abstract]
Income tax expense/(benefit)	$ 0	$ 19,568

Commitment and Contingencies (A

Commitment and Contingencies (Additional Information) (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
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
	Sep. 30, 2024 USD ($)	Sep. 30, 2023 USD ($)	Sep. 30, 2022 USD ($)	Aug. 31, 2022 ft²	Dec. 31, 2017 ft²	Mar. 31, 2023 USD ($)	Mar. 31, 2022 USD ($)
Lessee Lease Description [Line Items]
Operating Lease expense						$ 0.4	$ 0.1
Sublease payment			$ 0.2
Operating lease commence date					Feb. 01, 2018
Operating lease expiration date						Jun. 30, 2024
Scenario, Adjustment [Member]
Lessee Lease Description [Line Items]
Sublease payment	$ 0.3	$ 0.5
Massachusetts
Lessee Lease Description [Line Items]
Operating lease rentable area | ft²				14,000	8,000

Leases - Supplemental Cash Flow

Leases - Supplemental Cash Flow Information Relating to Leases (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Leases [Abstract]
Operating cash flows from operating leases	$ 416	$ 151
Right-of-use asset obtained in exchange for an operating lease liability	$ 0	$ 1,311

Leases - Summary of Future Mini

Leases - Summary of Future Minimum Payments Due Under Operating Lease (Details) $ in Thousands	Mar. 31, 2023 USD ($)
Lessee, Operating Lease, Liability, to be Paid [Abstract]
Remainder of 2023	$ 1,465
2024	1,738
2025	1,461
2026	872
Total future minimum lease payments	5,536
Less: imputed interest	(812)
Total lease liabilities at present value	$ 4,724

Leases - Summary of Weighted Av

Leases - Summary of Weighted Average Remaining Lease Terms and Discount Rates (Details)	Mar. 31, 2023	Dec. 31, 2022
Leases [Abstract]
Weighted-average remaining lease term (years)	3 years	3 years 2 months 12 days
Weighted-average discount rate	10.80%	10.80%

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
	Mar. 31, 2023	Mar. 31, 2022
Numerator:
Net loss attributable to common stockholders of Cullinan	$ (57,962)	$ (12,098)
Denominator
Weighted-average common stock outstanding - basic	40,682	44,432
Weighted-average common stock outstanding - diluted	40,682	44,432
Net loss per share:
Basic	$ (1.42)	$ (0.27)
Diluted	$ (1.42)	$ (0.27)

Earnings per Share - Summary _2

Earnings per Share - Summary of Outstanding Equity Instruments Excluded from Computation of Diluted Net Loss Per Share (Details) - shares shares in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Shares excluded from computation of diluted net loss per share (in shares)	14,351	10,066
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)	8,835	9,985
Preferred Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Shares excluded from computation of diluted net loss per share (in shares)	5,108	0
Restricted Stock Awards and RSUs
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Shares excluded from computation of diluted net loss per share (in shares)	408	74
Employee Stock Purchase Plan
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Shares excluded from computation of diluted net loss per share (in shares)	0	7

Subsequent Events (Additional I

Subsequent Events (Additional Information) (Details) $ in Millions	May 31, 2023 USD ($)
Subsequent Event [Member]
Subsequent Event [Line Items]
Offer and sell companys common stock	$ 125