Cullinan Oncology (CGEM) 10-Q 15 May 24 2024 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2024	May 08, 2024
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2024
Document Fiscal Year Focus	2024
Document Fiscal Period Focus	Q1
Entity Registrant Name	CULLINAN THERAPEUTICS, 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		57,634,234

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Current assets:
Cash and cash equivalents	$ 74,228	$ 98,434
Short-term investments	358,783	368,633
Prepaid expenses and other current assets	12,710	13,124
Total current assets	445,721	480,191
Property and equipment, net	913	989
Operating lease right-of-use assets	2,336	2,543
Other assets	460	459
Total assets	449,430	484,182
Current liabilities:
Accounts payable	3,707	2,493
Accrued expenses and other current liabilities	16,889	24,204
Operating lease liabilities, current	1,329	1,440
Total current liabilities	21,925	28,137
Long-term liabilities:
Operating lease liabilities, net of current portion	1,840	2,150
Total liabilities	23,765	30,287
Commitments and contingencies (Note 11)
Stockholders' equity:
Preferred stock, $0.0001 par value, 10,000,000 shares authorized as of March 31, 2024 and December 31, 2023; 647,500 shares issued and outstanding as of March 31, 2024 and December 31, 2023	0	0
Common stock, $0.0001 par value, 150,000,000 shares authorized as of March 31, 2024 and December 31, 2023; 43,065,645 and 42,900,083 shares issued and outstanding as of March 31, 2024 and December 31, 2023, respectively	4	4
Additional paid-in capital	663,997	654,685
Accumulated other comprehensive loss	(331)	(129)
Accumulated deficit	(238,005)	(200,857)
Total Cullinan stockholders' equity	425,665	453,703
Noncontrolling interests	0	192
Total stockholders' equity	425,665	453,895
Total liabilities and stockholders' equity	$ 449,430	$ 484,182

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Mar. 31, 2024	Dec. 31, 2023
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, Share Outstanding	647,500	647,500
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	150,000,000	150,000,000
Common Stock, Shares Issued	43,065,645	42,900,083
Common stock, shares outstanding	43,065,645	42,900,083

CONSOLIDATED STATEMENTS OF OPER

CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE INCOME (LOSS) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Operating expenses:
Research and development	$ 30,646	$ 52,096
General and administrative	12,343	10,660
Total operating expenses	42,989	62,756
Loss from operations	(42,989)	(62,756)
Other income (expense):
Interest income	5,693	4,508
Other income (expense), net	(44)	107
Net loss	(37,340)	(58,141)
Net loss attributable to noncontrolling interests	(192)	(179)
Net loss attributable to common stockholders of Cullinan	(37,148)	(57,962)
Comprehensive income (loss):
Net loss	(37,340)	(58,141)
Unrealized gain (loss) on investments	(202)	1,359
Comprehensive loss	(37,542)	(56,782)
Comprehensive loss attributable to noncontrolling interests	(192)	(179)
Comprehensive loss attributable to Cullinan	$ (37,350)	$ (56,603)
Net loss per share attributable to common stockholders of Cullinan:
Net loss per share, basic	$ (0.86)	$ (1.42)
Net income loss per share, diluted	$ (0.86)	$ (1.42)
Weighted-average shares used in computing net income (loss) per share attributable to common stockholders of Cullinan
Weighted-average common stock outstanding - basic	43,011	40,682
Weighted-average common stock outstanding - diluted	43,011	40,682

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
Balances at Dec. 31, 2022	$ 535,029		$ 5	$ 585,320	$ (2,601)	$ (47,695)
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
Net Loss	(58,141)					(57,962)	(179)
Balances at Mar. 31, 2023	485,649		$ 4	592,544	(1,242)	(105,657)
Balances, shares at Mar. 31, 2023		647,500	39,343,601
Balances at Dec. 31, 2023	453,895		$ 4	654,685	(129)	(200,857)	192
Balances, shares at Dec. 31, 2023		647,500	42,900,083
Net issuance of common stock under equity-based compensation plans	(1,085)			(1,085)
Net issuance of common stock under equity-based compensation plans, shares			165,562
Equity-based compensation	8,227			8,227
Unrealized gain (loss) on investments	(202)				(202)
Net Loss	(37,340)					(37,148)	$ (192)
Balances at Mar. 31, 2024	$ 425,665		$ 4	$ 663,997	$ (331)	$ (238,005)
Balances, shares at Mar. 31, 2024		647,500	43,065,645

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Operating activities:
Net loss	$ (37,340)	$ (58,141)
Adjustments to reconcile net loss to net cash used in operating activities:
Equity-based compensation expense	8,227	7,259
Accretion on marketable securities	(3,306)	(1,371)
Depreciation and amortization	76	72
Non-cash contributions from noncontrolling interests	0	4
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	411	(755)
Accounts payable	1,214	(630)
Accrued expenses and other current liabilities	(7,529)	2,640
Income tax payable	0	(75)
Net cash used in operating activities	(38,247)	(50,997)
Investing activities:
Purchase of marketable securities	(131,369)	(89,139)
Proceeds from maturities of marketable securities	144,325	104,482
Purchase of property and equipment	0	(159)
Net cash provided by investing activities	12,956	15,184
Financing activities:
Proceeds from issuance of convertible notes	0	1,825
Proceeds from (payments related to) net issuance of common stock under equity-based compensation plans	1,085	(36)
Net cash provided by financing activities	1,085	1,789
Net decrease in cash and cash equivalents	(24,206)	(34,024)
Cash and cash equivalents at beginning of period	98,434	156,152
Cash and cash equivalents at end of period	74,228	122,128
Non-cash financing activities and supplemental cash flow information
Purchases of property and equipment included in accounts payable and accrued expenses and other liabilities	0	49
Conversion of convertible note into noncontrolling interest	0	175
Cash paid (refunded) for income taxes	$ (3,870)	$ 75

Pay vs Performance Disclosure

Pay vs Performance Disclosure - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Pay vs Performance Disclosure
Net Income (Loss)	$ (37,148)	$ (57,962)

Insider Trading Arrangements

Insider Trading Arrangements	3 Months Ended
	Mar. 31, 2024 shares
Trading Arrangements, by Individual
Material Terms of Trading Arrangement	Adoption of 10b5-1 Trading Plans by Our Officers and Directors During our fiscal quarter ended March 31, 2024, one of our officers (as defined in Rule 16a-1(f) under the Securities Exchange Act of 1934, as amended (the “Exchange Act”)) entered into contracts, instructions or written plans for the purchase or sale of our securities that are intended to satisfy the conditions specified in Rule 10b5-1(c) under the Exchange Act for an affirmative defense against liability for trading in securities on the basis of material nonpublic information. We refer to these contracts, instructions, and written plans as “Rule 10b5-1 trading plans” and each one as a “Rule 10b5-1 trading plan.” We describe the material terms of the Rule 10b5-1 trading plan below. Jennifer Michaelson, Chief Scientific Officer On January 5, 2024 , Jennifer Michaelson , our Chief Scientific Officer , entered into a Rule 10b5-1 trading plan that provides that Dr. Michaelson, acting through a broker, may sell up to an aggregate of 212,000 shares of our common stock. Sales of shares under the plan will begin no earlier than the later of (a) April 5, 2024 (the 91st day after the plan’s adoption) or (b) the earlier of (x) the third business day after our Quarterly Report on Form 10-Q for our fiscal quarter ended March 31, 2024 is filed with the SEC or (y) May 5, 2024 (the 121st day after the plan’s adoption). The plan is scheduled to terminate on November 1, 2025 , subject to earlier termination upon the sale of all shares subject to the plan, or upon termination by Dr. Michaelson or the broker, or as otherwise provided in the plan.
Jennifer Michaelson [Member]
Trading Arrangements, by Individual
Name	Jennifer Michaelson
Title	Chief Scientific Officer
Rule 10b5-1 Arrangement Adopted	true
Adoption Date	January 5, 2024
Termination Date	November 1, 2025
Aggregate Available	212,000

Nature of Business and Basis of

Nature of Business and Basis of Presentation	3 Months Ended
	Mar. 31, 2024
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 Therapeutics, Inc., together with its consolidated subsidiaries ("Cullinan" or the "Company"), is a clinical-stage biopharmaceutical company dedicated to creating new standards of care for patients that was incorporated in September 2016 and has a principal place of business in Cambridge, Massachusetts. In April 2024, the Company changed its name from Cullinan Oncology, Inc. to Cullinan Therapeutics, Inc. Liquidity The Company has a history of significant operating losses and has had negative cash flows from operations since its inception and expects to continue to generate operating losses for the foreseeable future. Cullinan’s ultimate success depends on the outcome of its research and development activities as well as its ability to commercialize the Company’s product candidates. Cullinan 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 Cullinan’s expectations for a number of reasons, including reasons beyond the Company’s control. Since inception, Cullinan 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, short-term investments, and interest receivable of $ 434.8 million as of March 31, 2024 , will be sufficient to fund its operating expenses and capital expenditure requirements through the next twelve months from the date of issuance of these consolidated financial statements. In April 2024, Cullinan sold shares of its common stock and pre-funded warrants for shares of its common stock in a private placement (the “2024 Private Placement”) for gross proceeds of $ 280.0 million, before deducting offering expenses. Refer to Note 13 for additional detail regarding the 2024 Private Placement.

Summary of Significant Accounti

Summary of Significant Accounting Policies	3 Months Ended
	Mar. 31, 2024
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, 2023 (the “2023 10-K”). Basis of Presentation The accompanying 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 and Exchange Commission (the "SEC") for interim financial reporting and include the accounts of the Company and its consolidated subsidiaries. Intercompany balances and transactions have been eliminated in consolidation. The Company operates as one segment, which is developing early-stage therapeutics. In the opinion of Cullinan’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 2023 10-K. Recently Adopted Accounting Pronouncements In November 2023, the Financial Accounting Standards Board (the “FASB”) issued an accounting standards update to improve reportable segment disclosure requirements, primarily through enhanced disclosures about significant segment expenses. The main provisions of this update require companies to disclose, on an annual and interim basis, significant segment expenses, segment profit and loss, and other segments items that are regularly provided to the Company's Chief Operating Decision Maker (the "CODM"). This update also requires companies to disclose the title and position of the CODM and to explain how the CODM uses the reported segment measures in assessing segment performance and deciding how to allocate resources. The update also requires companies with a single reportable segment to provide all required segment reporting disclosures. This new standard will be effective for fiscal years beginning after December 15, 2023, and interim periods within fiscal years beginning after December 15, 2024. Early adoption is permitted. Cullinan adopted this standard on January 1, 2024 for 2024 annual reporting and interim periods beginning in 2025. Recently Issued Accounting Pronouncements In December 2023, the FASB issued an accounting standards update to enhance transparency about income tax information through improvements to income tax disclosures primarily related to the rate reconciliation and income taxes paid information. The main provisions in this update will require companies to disclose, on an annual basis, specific categories in the rate reconciliation and provide additional information for reconciling items that meet a quantitative threshold. This update will also require companies to disclose, on an annual basis, the amount of income taxes paid, income (or loss) from continuing operations before income tax expense (or benefit), and income tax expense (or benefit) from continuing operations, disaggregated by federal, state, and foreign jurisdictions. This new standard will be effective beginning for fiscal years beginning after December 15, 2025, and early adoption is permitted. The Company expects that it will adopt this new standard on January 1, 2026. The Company is evaluating the impact this new standard will have on its consolidated financial statements and associated disclosures.

Financial Instruments

Financial Instruments	3 Months Ended
	Mar. 31, 2024
Financial Instruments Pledged as Collateral [Abstract]
Financial Instruments	(3) Financial Instruments Investments Cullinan recognized its investments by security type at March 31, 2024 as follows (in thousands): Amortized Gross Gross Estimated Short-term investments U.S. government notes $ 182,022 $ 14 $ ( 128 ) $ 181,908 Corporate notes 138,235 2 ( 180 ) 138,057 Asset-backed securities 38,857 — ( 39 ) 38,818 Total short-term investments 359,114 16 ( 347 ) 358,783 Total investments $ 359,114 $ 16 $ ( 347 ) $ 358,783 Cullinan recognized its investments by security type at December 31, 2023 as follows (in thousands): Amortized Gross Gross Estimated Short-term investments U.S. government notes $ 208,289 $ 221 $ ( 16 ) $ 208,494 Corporate notes 99,359 27 ( 275 ) 99,111 Asset-backed securities 61,114 3 ( 89 ) 61,028 Total short-term investments 368,762 251 ( 380 ) 368,633 Total investments $ 368,762 $ 251 $ ( 380 ) $ 368,633 Fair Value of Financial Instruments The following table sets forth the fair value of Cullinan’s financial assets that were measured at fair value on a recurring basis as of March 31, 2024 (in thousands): Level 1 Level 2 Level 3 Total Short-term investments U.S. government notes $ — $ 181,908 $ — $ 181,908 Corporate notes — 138,057 — 138,057 Asset-backed securities — 38,818 — 38,818 Total short-term investments — 358,783 — 358,783 Total investments $ — $ 358,783 $ — $ 358,783 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, 2023 (in thousands): Level 1 Level 2 Level 3 Total Short-term investments U.S. government notes $ — $ 208,494 $ — $ 208,494 Corporate notes — 99,111 — 99,111 Asset-backed securities — 61,028 — 61,028 Total short-term investments — 368,633 — 368,633 Total investments $ — $ 368,633 $ — $ 368,633 As of March 31, 2024 and December 31, 2023 , the fair values of Cullinan's 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, 2024
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, 2024 and December 31, 2023 (in thousands): March 31, 2024 December 31, 2023 Contracted research and development expenses $ 8,879 $ 8,434 Due to Taiho under collaboration agreement, net 4,033 7,869 Employee compensation 2,458 6,987 Other current liabilities 1,519 914 Total accrued expenses and other current liabilities $ 16,889 $ 24,204

License and Collaboration Agree

License and Collaboration Agreements	3 Months Ended
	Mar. 31, 2024
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 Cullinan 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, Cullinan paid Harbour an upfront license fee of $ 25.0 million at signing. Harbour is eligible to receive up to $ 148.0 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 $ 415.0 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 Cullinan certain intellectual property rights to enable the Company to perform its obligations and exercise its rights under the Harbour License Agreement. As of March 31, 2024, no milestones have been achieved under the Harbour License Agreement. Unless earlier terminated, the Harbour License Agreement will continue in effect until the expiration of Cullinan’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. Cullinan 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. Cullinan 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 for the three months ended March 31, 2023. Co-Development Agreement with Taiho Cullinan has a co-development agreement with an affiliate of Taiho, pursuant to which the Company is collaborating to develop zipalertinib and has the option to co-commercialize zipalertinib in the U.S. Development costs for zipalertinib are 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 Cullinan 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, 2024 and 2023 , the Company recorded research and development expense of $ 6.0 million and $ 4.7 million, respectively, related to its share of costs incurred by Taiho. Cullinan incurred $ 1.9 million and $ 1.0 million of costs that were reimbursable by Taiho in the three months ended March 31, 2024 and 2023 , respectively, which were recorded as a reduction to research and development expenses. The net amounts of $ 4.0 million and $ 7.9 million due to Taiho were recorded within accrued expenses and other current liabilities as of March 31, 2024 and December 31, 2023, respectively. Other License and Collaboration Agreements During the three months ended March 31, 2024 , Cullinan recorded less than $ 0.1 million in research and development expenses relating to its other license and collaboration agreements. During the three months ended March 31, 2023 , Cullinan recorded $ 0.2 million relating to the license agreement with the Massachusetts Institute of Technology for CLN-617 within research and development expenses.

Stockholders' Equity

Stockholders' Equity	3 Months Ended
	Mar. 31, 2024
Stockholders' Equity Note [Abstract]
Stockholders' Equity	(6) Stockholders' Equity 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 March 31, 2024. At-the-Market Equity Offering Program In May 2023, Cullinan entered into an agreement with Cowen and Company, LLC (“Cowen”) to establish an at-the-market equity offering program (the “ATM") pursuant to which the Company may offer and sell up to $ 125.0 million of its common stock from time to time through Cowen, acting as its sales agent. The Company made no sales under the ATM in the three months ended March 31, 2024. Through March 31, 2024 , the Company has sold approximately 3.3 million shares under the ATM and received net proceeds of $ 38.4 million after deducting commissions. As of March 31, 2024 , Cullinan had $ 85.6 million in shares of its common stock remaining under the ATM. Preferred Stock In January 2023, the Company entered into an exchange agreement with Biotechnology Value Fund, L.P., Biotechnology Value Fund II, L.P., Biotechnology Value Trading Fund OS LP, and MSI BVF SPV, LLC (the “Stockholders”), pursuant to which the Stockholders exchanged 6.5 million shares of Cullinan’s common stock for 0.6 million shares of newly designated Series A convertible preferred stock, a “toothless” preferred stock, par value $ 0.0001 per share. Each share of the preferred stock will be convertible into ten shares of common stock at the option of the holder at any time, subject to certain limitations, including that the holder will be prohibited from converting preferred stock into common stock if, as a result of such conversion, the holder, together with its affiliates, would beneficially own a number of shares of common stock more than 9.99 % of the total common stock then issued and outstanding immediately following the conversion of such shares of preferred stock. Holders of the preferred stock are permitted to increase this percentage to an amount not to exceed 19.99 % upon 60 days notice. Shares of preferred stock will generally have no voting rights, except as required by law and except that the consent of a majority of the holders of the outstanding preferred stock will be required to amend the terms of the preferred stock. In the event of the Company’s liquidation, dissolution or winding up, holders of preferred stock will participate pari passu with any distribution of proceeds to holders of common stock. Holders of preferred stock are entitled to receive when, as, and if dividends are declared and paid on the common stock, an equivalent dividend, calculated on an as-converted basis. Shares of preferred stock are otherwise not entitled to dividends. The preferred stock ranks (i) senior to any class or series of capital stock of Cullinan hereafter created specifically ranking by its terms junior to the preferred stock; (ii) on parity with the common stock and any class or series of capital stock of the Company created specifically ranking by its terms on parity with the preferred stock; and (iii) junior to any class or series of capital stock of Cullinan created specifically ranking by its terms senior to any preferred stock, in each case, as to distributions of assets upon liquidation, dissolution or winding up of the Company, whether voluntarily or involuntarily. The Company evaluated the preferred stock for liability or equity classification. Cullinan determined that the preferred stock should be classified as permanent equity as it is not redeemable for cash or other assets (i) on a fixed or determinable date, (ii) at the option of the holder, or (iii) upon the occurrence of an event that is not solely within control of the Company. Noncontrolling Interests Certain of the Company's development subsidiaries have issued common stock and preferred stock to the Company and to third parties. The holders of subsidiary common stock and preferred stock are generally 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. The following table shows the Company’s ownership interest as of March 31, 2024 and December 31, 2023, respectively, in its development subsidiaries and their product candidates: Ownership as of Development Subsidiary (Product Candidate) March 31, 2024 December 31, 2023 Cullinan MICA Corp. (CLN-619) 95 % 95 % Cullinan Florentine Corp. (CLN-049) 96 % 96 % Cullinan Amber Corp. (CLN-617) 94 % 94 %

Equity-Based Compensation

Equity-Based Compensation	3 Months Ended
	Mar. 31, 2024
Share-Based Payment Arrangement [Abstract]
Equity-Based Compensation	(8) Equity-Based Compensation Cullinan 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, 2024 and 2023 (in thousands): Three Months Ended March 31, 2024 2023 General and administrative $ 5,092 $ 4,205 Research and development 3,135 3,054 Total equity-based compensation $ 8,227 $ 7,259

Related Party Transactions

Related Party Transactions	3 Months Ended
	Mar. 31, 2024
Related Party Transactions [Abstract]
Related Party Transactions	(9) Related Party Transactions Royalty Transfer Agreements The Company's CLN-619, CLN-049, and CLN-617 development subsidiaries are each party to royalty transfer agreements with two charitable foundations that are affiliated with an investor which beneficially owns more than five percent of the Company's common stock. Under these royalty transfer agreements, the charitable 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. Cullinan 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. Cullinan 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, 2024. 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, 2024 and December 31, 2023 .

Commitments and Contingencies

Commitments and Contingencies	3 Months Ended
	Mar. 31, 2024
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, Cullinan 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 Cullinan, 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, Cullinan 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, 2024 and December 31, 2023. Legal Proceedings Cullinan 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. Cullinan expenses as incurred the costs related to such legal proceedings.

Leases

Leases	3 Months Ended
	Mar. 31, 2024
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 . Cullinan has an additional operating lease for approximately 14,000 square feet of office space in a multi-tenant building in Cambridge, Massachusetts, which commenced in August 2022 and goes through July 2026. Lease expense consisted of operating lease costs of $ 0.3 million and $ 0.4 million for the three months ended March 31, 2024 and 2023, respectively. The following table summarizes supplemental cash flow information for the three months ended March 31, 2024 and 2023 (in thousands): Three Months Ended March 31, 2024 2023 Cash paid for amounts included in measurement of lease liabilities: Operating cash flows from operating leases $ 510 $ 416 The following table summarizes the Company’s future minimum lease payments as of March 31, 2024 (in thousands): March 31, 2024 Remainder of 2024 $ 1,228 2025 1,461 2026 871 Total future minimum lease payments 3,560 Less: imputed interest ( 391 ) Total lease liabilities at present value $ 3,169 The following table summarizes the weighted-average remaining lease term and discount rate as of March 31, 2024 and December 31, 2023: March 31, 2024 December 31, 2023 Weighted-average remaining lease term (in years) 2.2 2.4 Weighted-average discount rate 10.9 % 10.9 % As Cullinan’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. Cullinan’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.

Net Loss per Share Attributable

Net Loss per Share Attributable to Common Stockholders of Cullinan	3 Months Ended
	Mar. 31, 2024
Earnings Per Share [Abstract]
Net Loss per Share Attributable to Common Stockholders of Cullinan	(12) Net Loss per Share Attributable to Common Stockholders of Cullinan The following table sets forth the calculation of basic and diluted net loss per share attributable to common stockholders of Cullinan for the three months ended March 31, 2024 and 2023 (in thousands, except per share data): Three Months Ended March 31, 2024 2023 Numerator: Net loss attributable to common stockholders of Cullinan $ ( 37,148 ) $ ( 57,962 ) Denominator: Weighted-average common stock outstanding — basic and diluted 43,011 40,682 Net loss per share attributable to common stockholders of Cullinan: Basic and diluted $ ( 0.86 ) $ ( 1.42 ) Cullinan used the treasury stock method for equity awards and the if-converted method for preferred stock 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 attributable to common stockholders of Cullinan for the three months ended March 31, 2024 and 2023 because their effect would have been anti-dilutive (in thousands): Three Months Ended March 31, 2024 2023 Stock options 10,155 8,835 Restricted stock awards and units 520 408 Employee stock purchase plan 4 — Preferred stock 6,475 5,108 Total 17,154 14,351

Subsequent Events

Subsequent Events	3 Months Ended
	Mar. 31, 2024
Subsequent Events [Abstract]
Subsequent Events	(13) Subsequent Events 2024 Private Placement In April 2024, Cullinan completed the 2024 Private Placement in which Cullinan issued approximately 14.4 million shares of its common stock and pre-funded warrants to purchase approximately 0.3 million additional shares of its common stock. Cullinan received gross proceeds of $ 280.0 million from the 2024 Private Placement, before deducting offering expenses.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2024
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying 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 and Exchange Commission (the "SEC") for interim financial reporting and include the accounts of the Company and its consolidated subsidiaries. Intercompany balances and transactions have been eliminated in consolidation. The Company operates as one segment, which is developing early-stage therapeutics. In the opinion of Cullinan’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 2023 10-K.
Recently Adopted Accounting Pronouncements	Recently Adopted Accounting Pronouncements In November 2023, the Financial Accounting Standards Board (the “FASB”) issued an accounting standards update to improve reportable segment disclosure requirements, primarily through enhanced disclosures about significant segment expenses. The main provisions of this update require companies to disclose, on an annual and interim basis, significant segment expenses, segment profit and loss, and other segments items that are regularly provided to the Company's Chief Operating Decision Maker (the "CODM"). This update also requires companies to disclose the title and position of the CODM and to explain how the CODM uses the reported segment measures in assessing segment performance and deciding how to allocate resources. The update also requires companies with a single reportable segment to provide all required segment reporting disclosures. This new standard will be effective for fiscal years beginning after December 15, 2023, and interim periods within fiscal years beginning after December 15, 2024. Early adoption is permitted. Cullinan adopted this standard on January 1, 2024 for 2024 annual reporting and interim periods beginning in 2025.
Recently Issued Accounting Pronouncements	Recently Issued Accounting Pronouncements In December 2023, the FASB issued an accounting standards update to enhance transparency about income tax information through improvements to income tax disclosures primarily related to the rate reconciliation and income taxes paid information. The main provisions in this update will require companies to disclose, on an annual basis, specific categories in the rate reconciliation and provide additional information for reconciling items that meet a quantitative threshold. This update will also require companies to disclose, on an annual basis, the amount of income taxes paid, income (or loss) from continuing operations before income tax expense (or benefit), and income tax expense (or benefit) from continuing operations, disaggregated by federal, state, and foreign jurisdictions. This new standard will be effective beginning for fiscal years beginning after December 15, 2025, and early adoption is permitted. The Company expects that it will adopt this new standard on January 1, 2026. The Company is evaluating the impact this new standard will have on its consolidated financial statements and associated disclosures.

Financial Instruments (Tables)

Financial Instruments (Tables)	3 Months Ended
	Mar. 31, 2024
Financial Instruments Pledged as Collateral [Abstract]
Schedule of Short-term and Long-term Investment Marketable Securities by Security Type	Investments Cullinan recognized its investments by security type at March 31, 2024 as follows (in thousands): Amortized Gross Gross Estimated Short-term investments U.S. government notes $ 182,022 $ 14 $ ( 128 ) $ 181,908 Corporate notes 138,235 2 ( 180 ) 138,057 Asset-backed securities 38,857 — ( 39 ) 38,818 Total short-term investments 359,114 16 ( 347 ) 358,783 Total investments $ 359,114 $ 16 $ ( 347 ) $ 358,783 Cullinan recognized its investments by security type at December 31, 2023 as follows (in thousands): Amortized Gross Gross Estimated Short-term investments U.S. government notes $ 208,289 $ 221 $ ( 16 ) $ 208,494 Corporate notes 99,359 27 ( 275 ) 99,111 Asset-backed securities 61,114 3 ( 89 ) 61,028 Total short-term investments 368,762 251 ( 380 ) 368,633 Total investments $ 368,762 $ 251 $ ( 380 ) $ 368,633
Summary of Fair Value of Financial Assets Measured on Recurring Basis	The following table sets forth the fair value of Cullinan’s financial assets that were measured at fair value on a recurring basis as of March 31, 2024 (in thousands): Level 1 Level 2 Level 3 Total Short-term investments U.S. government notes $ — $ 181,908 $ — $ 181,908 Corporate notes — 138,057 — 138,057 Asset-backed securities — 38,818 — 38,818 Total short-term investments — 358,783 — 358,783 Total investments $ — $ 358,783 $ — $ 358,783 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, 2023 (in thousands): Level 1 Level 2 Level 3 Total Short-term investments U.S. government notes $ — $ 208,494 $ — $ 208,494 Corporate notes — 99,111 — 99,111 Asset-backed securities — 61,028 — 61,028 Total short-term investments — 368,633 — 368,633 Total investments $ — $ 368,633 $ — $ 368,633

Accrued Expenses and Other Cu_2

Accrued Expenses and Other Current Liabilities (Tables)	3 Months Ended
	Mar. 31, 2024
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, 2024 and December 31, 2023 (in thousands): March 31, 2024 December 31, 2023 Contracted research and development expenses $ 8,879 $ 8,434 Due to Taiho under collaboration agreement, net 4,033 7,869 Employee compensation 2,458 6,987 Other current liabilities 1,519 914 Total accrued expenses and other current liabilities $ 16,889 $ 24,204

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	3 Months Ended
	Mar. 31, 2024
Common Stock And Noncontrolling Interest In Subsidiaries [Abstract]
Schedule of Development Subsidiaries and Their Product Candidates	The following table shows the Company’s ownership interest as of March 31, 2024 and December 31, 2023, respectively, in its development subsidiaries and their product candidates: Ownership as of Development Subsidiary (Product Candidate) March 31, 2024 December 31, 2023 Cullinan MICA Corp. (CLN-619) 95 % 95 % Cullinan Florentine Corp. (CLN-049) 96 % 96 % Cullinan Amber Corp. (CLN-617) 94 % 94 %

Equity-Based Compensation (Tabl

Equity-Based Compensation (Tables)	3 Months Ended
	Mar. 31, 2024
Share-Based Payment Arrangement [Abstract]
Schedule of Equity-based Compensation Expense Categories In Consolidated Statements of Operations and Comprehensive Income (Loss)	Cullinan 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, 2024 and 2023 (in thousands): Three Months Ended March 31, 2024 2023 General and administrative $ 5,092 $ 4,205 Research and development 3,135 3,054 Total equity-based compensation $ 8,227 $ 7,259

Leases (Tables)

Leases (Tables)	3 Months Ended
	Mar. 31, 2024
Leases [Abstract]
Supplemental Cash Flow Information Relating to Leases	The following table summarizes supplemental cash flow information for the three months ended March 31, 2024 and 2023 (in thousands): Three Months Ended March 31, 2024 2023 Cash paid for amounts included in measurement of lease liabilities: Operating cash flows from operating leases $ 510 $ 416
Summarizes of Future Minimum Lease Payments	The following table summarizes the Company’s future minimum lease payments as of March 31, 2024 (in thousands): March 31, 2024 Remainder of 2024 $ 1,228 2025 1,461 2026 871 Total future minimum lease payments 3,560 Less: imputed interest ( 391 ) Total lease liabilities at present value $ 3,169
Summarizes Lease Term and Discount Rate	The following table summarizes the weighted-average remaining lease term and discount rate as of March 31, 2024 and December 31, 2023: March 31, 2024 December 31, 2023 Weighted-average remaining lease term (in years) 2.2 2.4 Weighted-average discount rate 10.9 % 10.9 %

Net Loss per Share (Tables)

Net Loss per Share (Tables)	3 Months Ended
	Mar. 31, 2024
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 attributable to common stockholders of Cullinan for the three months ended March 31, 2024 and 2023 (in thousands, except per share data): Three Months Ended March 31, 2024 2023 Numerator: Net loss attributable to common stockholders of Cullinan $ ( 37,148 ) $ ( 57,962 ) Denominator: Weighted-average common stock outstanding — basic and diluted 43,011 40,682 Net loss per share attributable to common stockholders of Cullinan: Basic and diluted $ ( 0.86 ) $ ( 1.42 )
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 attributable to common stockholders of Cullinan for the three months ended March 31, 2024 and 2023 because their effect would have been anti-dilutive (in thousands): Three Months Ended March 31, 2024 2023 Stock options 10,155 8,835 Restricted stock awards and units 520 408 Employee stock purchase plan 4 — Preferred stock 6,475 5,108 Total 17,154 14,351

Nature of Business and Basis _2

Nature of Business and Basis of Presentation - Additional Information (Details) - USD ($) $ in Millions	4 Months Ended
	Apr. 30, 2024	Mar. 31, 2024
Nature Of Business And Basis Of Presentation [Line Items]
Cash equivalents short term investments and interest recivable		$ 434.8
2024 Private Placement | Subsequent Event [Member]
Nature Of Business And Basis Of Presentation [Line Items]
Net Cash Proceeds from 2024 Private Placement	$ 280

Summary of Significant Accoun_3

Summary of Significant Accounting Policies - Additional Information (Details)	3 Months Ended
	Mar. 31, 2024 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, 2024	Dec. 31, 2023
Operating lease right-of-use assets	$ 2,336	$ 2,543
Operating lease liabilities, current	1,329	1,440
Noncurrent portion of operating lease liabilities	$ 1,840	$ 2,150

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, 2024	Dec. 31, 2023	Mar. 31, 2023	Dec. 31, 2022
Stockholders' Equity (Members' Deficit)
Common Stock	$ 4	$ 4
Additional paid-in capital	663,997	654,685
Accumulated other comprehensive loss	(331)	(129)
Accumulated deficit	(238,005)	(200,857)
Total Cullinan Stockholders' Equity (Members' Deficit)	425,665	453,703
Non-controlling interests in subsidiaries	0	192
Total Stockholders' Equity (Members' Deficit)	$ 425,665	$ 453,895	$ 485,649	$ 535,029

Financial Instruments - Schedul

Financial Instruments - Schedule of Short-term and Long-term Investment Marketable Securities by Security Type (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Available For Sale Securities Fair Value To Amortized Cost Basis [Line Items]
Amortized Cost	$ 359,114	$ 368,762
Gross Unrealized Gains	16	251
Gross Unrealized Losses	(347)	(380)
Estimated Fair Value	358,783	368,633
Short Term Investments
Available For Sale Securities Fair Value To Amortized Cost Basis [Line Items]
Amortized Cost	359,114	368,762
Gross Unrealized Gains	16	251
Gross Unrealized Losses	(347)	(380)
Estimated Fair Value	358,783	368,633
Short Term Investments | U.S. Government Notes
Available For Sale Securities Fair Value To Amortized Cost Basis [Line Items]
Amortized Cost	182,022	208,289
Gross Unrealized Gains	14	221
Gross Unrealized Losses	(128)	(16)
Estimated Fair Value	181,908	208,494
Short Term Investments | Asset-backed Securities
Available For Sale Securities Fair Value To Amortized Cost Basis [Line Items]
Amortized Cost	38,857	61,114
Gross Unrealized Gains	0	3
Gross Unrealized Losses	(39)	(89)
Estimated Fair Value	38,818	61,028
Short Term Investments | Corporate Note Securities
Available For Sale Securities Fair Value To Amortized Cost Basis [Line Items]
Amortized Cost	138,235	99,359
Gross Unrealized Gains	2	27
Gross Unrealized Losses	(180)	(275)
Estimated Fair Value	$ 138,057	$ 99,111

Financial Instruments - Summary

Financial Instruments - Summary of Fair Value of Financial Assets Measured on Recurring Basis (Details) - Recurring - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total short-term investments	$ 358,783	$ 368,633
Assets Fair Value Disclosure, Total	358,783	368,633
Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total short-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	358,783	368,633
Assets Fair Value Disclosure, Total	358,783	368,633
Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total short-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	181,908	208,494
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
U.S. Government Notes | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total short-term investments	181,908	208,494
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	38,818	61,028
Asset-backed Securities | Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total short-term investments	0	0
Asset-backed Securities | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total short-term investments	38,818	61,028
Asset-backed Securities | 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	138,057	99,111
Corporate Note Securities | Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total short-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	138,057	99,111
Corporate Note Securities | Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total short-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, 2024	Dec. 31, 2023
Accounts Payable and Accrued Liabilities, Current [Abstract]
Contracted research and development expenses	$ 8,879	$ 8,434
Due to Taiho under collaboration agreement, net	4,033	7,869
Employee compensation	2,458	6,987
Other current liabilities	1,519	914
Total accrued expenses and other current liabilities	$ 16,889	$ 24,204

License and Collaboration Agr_2

License and Collaboration Agreements - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
License And Collaboration Agreements [Line Items]
Research and development costs	$ 30,646	$ 52,096
Harbour License Agreement [Member]
License And Collaboration Agreements [Line Items]
Upfront license fee		25,000
Collaboration Agreements [Member]
License And Collaboration Agreements [Line Items]
Research and development costs	100
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	$ 6,000	4,700
Accrued expenses and other current liabilities	4,000		$ 7,900
Research and development costs	$ 1,900	1,000
MIT | Collaboration Agreements [Member]
License And Collaboration Agreements [Line Items]
Research and development costs		$ 200

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information (Details) - USD ($)	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023	Jan. 31, 2023
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 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	43,065,645		42,900,083
Losses attributed to noncontrolling interests	$ (192,000)	$ (179,000)
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				6,500,000
In May 2023
Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]
Offer and sell companys common stock	125,000,000
At-the-Market Equity Offering Program | In May 2023
Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]
Net proceeds	$ 38,400,000
Shares sold/issued	3,300,000
Treasury Stock, Common, Shares	85,600,000

Stockholders' Equity - Schedule

Stockholders' Equity - Schedule of Development Subsidiaries and Their Product Candidates (Details) - Subsidiaries [Member]	Mar. 31, 2024	Dec. 31, 2023
Cullinan M I C A Corp [Member]
Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]
Subsidiary, Ownership Percentage	95%	95%
Cullinan Florentine Corp [Member]
Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]
Subsidiary, Ownership Percentage	96%	96%
Cullinan Amber Corp [Member]
Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]
Subsidiary, Ownership Percentage	94%	94%

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, 2024	Mar. 31, 2023
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total equity-based compensation	$ 8,227	$ 7,259
General and Administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total equity-based compensation	5,092	4,205
Research and Development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total equity-based compensation	$ 3,135	$ 3,054

Related Party Transactions - Ad

Related Party Transactions - Additional Information (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2024 USD ($)
Related Party Transaction [Line Items]
Royalties under obligation	$ 0

Commitment and Contingencies (A

Commitment and Contingencies (Additional Information) (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
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
	Aug. 31, 2022 ft²	Mar. 31, 2024 USD ($) ft²	Mar. 31, 2023 USD ($)
Lessee Lease Description [Line Items]
Operating Lease expense | $		$ 0.3	$ 0.4
Operating lease commence date		Feb. 01, 2018
Operating lease expiration date		Jun. 30, 2024
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, 2024	Mar. 31, 2023
Leases [Abstract]
Operating cash flows from operating leases	$ 510	$ 416

Leases - Summary of Future Mini

Leases - Summary of Future Minimum Payments Due Under Operating Lease (Details) $ in Thousands	Mar. 31, 2024 USD ($)
Lessee, Operating Lease, Liability, to be Paid, Fiscal Year Maturity [Abstract]
Remainder of 2024	$ 1,228
2025	1,461
2026	871
Total future minimum lease payments	3,560
Less: imputed interest	(391)
Total lease liabilities at present value	$ 3,169

Leases - Summary of Weighted Av

Leases - Summary of Weighted Average Remaining Lease Terms and Discount Rates (Details)	Mar. 31, 2024	Dec. 31, 2023
Leases [Abstract]
Weighted-average remaining lease term (years)	2 years 2 months 12 days	2 years 4 months 24 days
Weighted-average discount rate	10.90%	10.90%

Net Loss per Share Attributab_2

Net Loss per Share Attributable to Common Stockholders of Cullinan (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Numerator:
Net Income (Loss)	$ (37,148)	$ (57,962)
Denominator
Weighted-average common stock outstanding - basic	43,011	40,682
Weighted-average common stock outstanding - diluted	43,011	40,682
Net loss per share attributable to common stockholders of Cullinan:
Basic	$ (0.86)	$ (1.42)
Diluted	$ (0.86)	$ (1.42)

Net Loss per Share - Summary of

Net Loss 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, 2024	Mar. 31, 2023
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Shares excluded from computation of diluted net loss per share (in shares)	17,154	14,351
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)	6,475	5,108
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)	10,155	8,835
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)	520	408
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)	4	0

Subsequent Events (Additional I

Subsequent Events (Additional Information) (Details) - USD ($) $ in Millions	4 Months Ended
	Apr. 30, 2024	Mar. 31, 2024	Dec. 31, 2023
Subsequent Event [Line Items]
Common Stock, Shares Issued		43,065,645	42,900,083
Subsequent Event [Member] | 2024 Private Placement
Subsequent Event [Line Items]
Net Cash Proceeds from 2024 Private Placement	$ 280
Common Stock, Shares Issued	14,400,000
Subsequent Event [Member] | 2024 Private Placement | Pre-Funded Warrants [Member]
Subsequent Event [Line Items]
Warrants Issued to Purchase Additional Common Shares	300,000