Biomea Fusion (BMEA) 10-Q 3 Nov 21 2021 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2021	Oct. 26, 2021
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2021
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q3
Document Quarterly Report	true
Document Transition Report	false
Entity Registrant Name	Biomea Fusion, Inc.
Entity Central Index Key	0001840439
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Trading Symbol	BMEA
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity Small Business	true
Entity Common Stock, Shares Outstanding		29,044,784
Entity Interactive Data Current	Yes
Title of 12(b) Security	Common Stock, $0.0001 par value
Security Exchange Name	NASDAQ
Entity Current Reporting Status	No
Entity Shell Company	false
Entity File Number	001-40335
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	82-2520134
Entity Address, Address Line One	650 Main Street
Entity Address, City or Town	Redwood City
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	94063
City Area Code	650
Local Phone Number	980-9099

Condensed Balance Sheets

Condensed Balance Sheets - USD ($)	Sep. 30, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 156,974,000	$ 61,695,000
Short-term investments	32,431,000
Prepaid expenses and other current assets	1,698,000	528,000
Total current assets	191,103,000	62,223,000
Property and equipment, net	2,963,000	81,000
Restricted cash	216,000	0
Prepaid and other long-term assets	23,000	12,000
Long-term investments	2,238,000
Right-of-use assets	2,860,000	210,000
Total assets	199,403,000	62,526,000
Current liabilities:
Accounts payable	1,249,000	727,000
Accrued expenses and other current liabilities	3,838,000	633,000
Loan payable		36,000
Short-term operating lease liabilities	554,000	223,000
Total current liabilities	5,641,000	1,619,000
Long-term operating lease liabilities	2,431,000
Total liabilities	8,072,000	1,619,000
Commitments and contingencies (Note 9)
Stockholders' equity
Preferred stock, $0.0001 par value; 10,000,000 and 0 shares authorized as of September 30, 2021 and December 31, 2020; 0 and 0 shares issued and outstanding as of September 30, 2021 and December 31, 2020, respectively
Common stock, $0.0001 par value; 300,000,000 and 25,300,080 shares authorized as of September 30, 2021 and December 31, 2020, respectively; 29,041,708 and 11,953,107 shares issued and outstanding as of September 30, 2021 and December 31, 2020, respectively	2,000	1,000
Additional paid-in capital	226,359,000	13,343,000
Accumulated other comprehensive income	2,000
Accumulated deficit	(35,032,000)	(8,175,000)
Total stockholders' equity	191,331,000	5,169,000
Total liabilities and stockholders' equity	$ 199,403,000	62,526,000
Series A Convertible Preferred Stock
Current liabilities:
Series A convertible preferred stock, $0.0001 par value; 0 and 7,064,925 shares authorized as of September 30, 2021 and December 31, 2020; 0 and 7,064,925 shares issued and outstanding as of September 30, 2021 and December 31, 2020, respectively		$ 55,738,000

Condensed Balance Sheets (Paren

Condensed Balance Sheets (Parenthetical) - $ / shares	Sep. 30, 2021	Dec. 31, 2020
Preferred stock, shares outstanding	0
Preferred stock, par value	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	10,000,000	0
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	300,000,000	25,300,080
Common stock, shares issued	29,041,708	11,953,107
Common stock, shares outstanding	29,041,708	11,953,107
Series A Convertible Preferred Stock
Preferred stock, par value	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	0	7,064,925
Preferred stock, shares issued	0	7,064,925
Preferred stock, shares outstanding	0	7,064,925

Condensed Statements of Operati

Condensed Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Operating expenses:
Research and development	$ 7,886	$ 789	$ 16,908	$ 1,339
General and administrative	4,752	346	10,022	489
Total operating expenses	12,638	1,135	26,930	1,828
Loss from operations	(12,638)	(1,135)	(26,930)	(1,828)
Interest and other income, net	32		73	2
Net loss	(12,606)	(1,135)	(26,857)	(1,826)
Other comprehensive loss:
Unrealized gain on investments, net			2
Comprehensive loss	$ (12,606)	$ (1,135)	$ (26,855)	$ (1,826)
Net loss per common share, basic and diluted	$ (0.43)	$ (0.10)	$ (1.21)	$ (0.18)
Weighted-average number of common shares used to compute basic and diluted net loss per common share	29,001,213	11,724,100	22,105,321	10,082,667

Condensed Statements of Convert

Condensed Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	IPO	Series A Convertible Preferred Stock	Common Stock	Common StockIPO	Additional Paid-In Capital	Additional Paid-In CapitalIPO	Accumulated Other Comprehensive Gain (Loss)	Accumulated Deficit
Balance at Dec. 31, 2019	$ (21)			$ 1		$ 2,829			$ (2,851)
Balance (in shares) at Dec. 31, 2019				8,703,234
Issuance of common stock, net of offering costs	50					50
Issuance of common stock, net of offering costs (in shares)				230,650
Net loss and comprehensive loss	(398)								(398)
Balance at Mar. 31, 2020	(369)			$ 1		2,879			(3,249)
Balance (in shares) at Mar. 31, 2020				8,933,884
Balance at Dec. 31, 2019	(21)			$ 1		2,829			(2,851)
Balance (in shares) at Dec. 31, 2019				8,703,234
Net loss and comprehensive loss	(1,826)
Balance at Sep. 30, 2020	7,695			$ 1		12,371			(4,677)
Balance (in shares) at Sep. 30, 2020				11,724,100
Balance at Mar. 31, 2020	(369)			$ 1		2,879			(3,249)
Balance (in shares) at Mar. 31, 2020				8,933,884
Issuance of common stock, net of offering costs	9,492					9,492
Issuance of common stock, net of offering costs (in shares)				2,790,216
Net loss and comprehensive loss	(293)								(293)
Balance at Jun. 30, 2020	8,830			$ 1		12,371			(3,542)
Balance (in shares) at Jun. 30, 2020				11,724,100
Net loss and comprehensive loss	(1,135)								(1,135)
Balance at Sep. 30, 2020	7,695			$ 1		12,371			(4,677)
Balance (in shares) at Sep. 30, 2020				11,724,100
Balance at Dec. 31, 2020	5,169			$ 1		13,343			(8,175)
Balance (in shares) at Dec. 31, 2020			7,064,925
Balance at Dec. 31, 2020			$ 55,738
Balance (in shares) at Dec. 31, 2020				11,953,107
Series A financing costs			$ (3)
Issuance of restricted stock (in shares)				51,526
Stock-based compensation expense	919					919
Unrealized gain (loss) on investments	(15)							$ (15)
Net loss and comprehensive loss	(5,852)								(5,852)
Balance at Mar. 31, 2021	221			$ 1		14,262		(15)	(14,027)
Balance (in shares) at Mar. 31, 2021			7,064,925
Balance at Mar. 31, 2021			$ 55,735
Balance (in shares) at Mar. 31, 2021				12,004,633
Balance at Dec. 31, 2020	$ 5,169			$ 1		13,343			(8,175)
Balance (in shares) at Dec. 31, 2020			7,064,925
Balance at Dec. 31, 2020			$ 55,738
Balance (in shares) at Dec. 31, 2020				11,953,107
Exercise of stock options, (in shares)	43,850
Unrealized gain (loss) on investments	$ 2
Net loss and comprehensive loss	(26,857)
Balance at Sep. 30, 2021	$ 191,331			$ 2		226,359		2	(35,032)
Balance (in shares) at Sep. 30, 2021	0		0
Balance (in shares) at Sep. 30, 2021				29,041,708
Balance at Mar. 31, 2021	$ 221			$ 1		14,262		(15)	(14,027)
Balance (in shares) at Mar. 31, 2021			7,064,925
Balance at Mar. 31, 2021			$ 55,735
Balance (in shares) at Mar. 31, 2021				12,004,633
Issuance of common stock, net of offering costs		$ 152,754			$ 1		$ 152,753
Issuance of common stock, net of offering costs (in shares)					9,823,532
Issuance of restricted stock (in shares)				53,240
Stock-based compensation expense	1,463					1,463
Exercise of stock options	225					225
Exercise of stock options, (in shares)				43,850
Conversion of preferred stock to common stock	55,735					55,735
Conversion of preferred stock to common stock (in shares)			(7,064,925)
Conversion of convertible preferred stock into common stock			$ (55,735)
Conversion of preferred stock to common stock (in shares)				7,064,925
Unrealized gain (loss) on investments	17							17
Net loss and comprehensive loss	(8,399)								(8,399)
Balance at Jun. 30, 2021	202,016			$ 2		224,438		2	(22,426)
Balance (in shares) at Jun. 30, 2021				28,990,180
Issuance of restricted stock (in shares)				51,528
Stock-based compensation expense	1,921					1,921
Net loss and comprehensive loss	(12,606)								(12,606)
Balance at Sep. 30, 2021	$ 191,331			$ 2		$ 226,359		$ 2	$ (35,032)
Balance (in shares) at Sep. 30, 2021	0		0
Balance (in shares) at Sep. 30, 2021				29,041,708

Condensed Statements of Cash Fl

Condensed Statements of Cash Flows	3 Months Ended	9 Months Ended
	Sep. 30, 2021USD ($)	Sep. 30, 2021USD ($)	Sep. 30, 2020USD ($)
Operating Activities
Net loss		$ (26,857,000)	$ (1,826,000)
Adjustments to reconcile net loss to net cash used in operating activities
Depreciation	$ 65,000	99,000	2,300
Non-cash operating lease expense		566,000	42,000
Stock-based compensation expense		4,303,000
Net amortization of premiums and accretion of discounts on investments		361,000
Changes in operating assets and liabilities:
Prepaid expenses and other current assets		(1,170,000)	(147,000)
Other assets		(11,000)
Accounts payable		419,000	118,000
Accrued expenses and other current liabilities		3,205,000	112,000
Lease liabilities		(454,000)	(24,000)
Net cash used in operating activities		(19,539,000)	(1,723,000)
Investing Activities
Purchase of property and equipment		(2,878,000)	(12,000)
Purchase of investments		(38,492,000)
Maturities of investments		3,465,000
Net cash used in investing activities		(37,905,000)	(12,000)
Financing Activities
Proceeds from issuance of common stock from seed series			9,542,000
Series A financing costs incurred		(3,000)
Net proceeds from issuance of common stock from initial public offering		152,753,000
Proceeds from stock option exercise		225,000
Proceeds (payment) from Paycheck Protection Program loan		(36,000)	36,000
Net cash provided by financing activities		152,939,000	9,578,000
Net increase in cash, cash equivalents, and restricted cash		95,495,000	7,843,000
Cash, cash equivalents, and restricted cash at the beginning of the period		61,695,000	239,000
Cash, cash equivalents, and restricted cash at the end of the period	157,190,000	157,190,000	8,082,000
Non-cash financing and investing activities:
Conversion of convertible preferred stock into common stock		55,735,000
Acquisition of right of use asset		3,216,000	334,000
Acquisition of fixed assets in accounts payable and accrued liabilities		103,000	12,000
Change in unrealized gain on investments		2,000
Reconciliation of cash and cash equivalents and restricted cash:
Cash and cash equivalents	156,974,000	156,974,000	8,082,000
Restricted cash	216,000	216,000
Cash, cash equivalents, and restricted cash at the end of the period	$ 157,190,000	$ 157,190,000	$ 8,082,000

Organization

Organization	9 Months Ended
	Sep. 30, 2021
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Organization	Note 1. Organization Organization Biomea Fusion, Inc., (the “Company”), was established in the state of Delaware in August 2017 as Biomea Fusion, LLC. In December 2020, all outstanding membership interests in Biomea Fusion, LLC were converted into equity interests in the Company. The capitalization information included in these financial statements is consistently presented as if it is that of Biomea Fusion, Inc., even during the prior period when investors held their equity interests in Biomea Fusion, LLC. The Company is a biopharmaceutical company focused on the discovery and development of irreversible small molecules to treat patients with genetically defined cancers. Since its inception in 2017, the Company has built its proprietary FUSION System platform to design and develop a pipeline of novel irreversible therapies. Basis of Presentation The accompanying interim condensed financial statements as of September 30, 2021 and for the three and nine months ended September 30, 2021, and the related interim information contained within the notes to the financial statements, are unaudited. The unaudited interim condensed financial statements have been prepared in accordance with generally accepted accounting principles in the United States (“U.S. GAAP”) for interim financial information and on the same basis as the audited financial statements included on the Company’s annual financial statements filed with the Securities and Exchange Commission (“SEC”) within the Company’s Prospectus dated April 15, 2021 (the “Prospectus”). In the opinion of management, the accompanying unaudited interim condensed financial statements contain all adjustments (consisting of normal recurring adjustments) necessary to state fairly the Company’s financial position as of September 30, 2021, and the results of its operations and cash flows for the three and nine months ended September 30, 2021. All such adjustments are of a normal and recurring nature. The interim financial data as of September 30, 2021 is not necessarily indicative of the results to be expected for the year ending December 31, 2021, or for any future period. The accompanying condensed financial statements and related financial information should be read in conjunction with the audited financial statements and the related notes thereto for the year ended December 31, 2020. Forward Stock Split In April 2021, the Company’s board of directors approved an amended and restated certificate of incorporation to effect a split of shares of the Company’s outstanding capital at a ratio of 8.84-for-1 (the “Forward Stock Split”) effective as of April 12, 2021. The number of authorized shares and the par values of the common stock and convertible preferred stock were not adjusted as a result of the Forward Stock Split. All references to common stock, options to purchase common stock, convertible preferred stock, share data, per share data and related information contained in the financial statements have been retrospectively adjusted to reflect the effect of the Forward Stock Split for all periods presented. Initial Public Offering On April 16, 2021, the Company’s registration statement on Form S-1 (File No. 333-254793) relating to its initial public offering (“IPO”) of common stock became effective. The IPO closed on April 20, 2021 at which time the Company issued an aggregate of 9,000,000 shares of its common stock at a price of $17.00 per share. Subsequent to the close, an additional 823,532 shares were issued in connection with the partial exercise by the underwriters of their option to purchase additional shares of common stock. In addition, immediately prior to the closing of the IPO, all outstanding shares of the Company’s convertible preferred stock automatically converted into 7,064,925 shares of common stock. In connection with the completion of its IPO, on April 20, 2021, the Company’s certificate of incorporation was amended and restated to provide for 300,000,000 authorized shares of common stock with a par value of $0.0001 per share and 10,000,000 authorized shares of preferred stock with a par value of $0.0001 per share. Liquidity and Capital Resources The Company has incurred net operating losses and negative cash flows from operations since its inception and had an accumulated deficit of $35.0 million at September 30, 2021. As of September 30, 2021, the Company had cash, cash equivalents, restricted cash, and investments of $191.9 million. To date, none of the Company’s product candidates have been approved for sale, and the Company has not generated any revenue since inception. Management expects operating losses to continue and increase for the foreseeable future, as the Company progresses into clinical development activities for its lead product candidate. The Company’s prospects are subject to risks, expenses and uncertainties frequently encountered by companies in the biotechnology industry as discussed below. While the Company has been able to raise multiple rounds of financing, there can be no assurance that in the event the Company requires additional financing, such financing will be available on terms which are favorable or at all. Failure to generate sufficient cash flows from operations, raise additional capital or reduce certain discretionary spending would have a material adverse effect on the Company’s ability to achieve its intended business objectives .

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2021
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Note 2. Summary of Significant Accounting Policies Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. On an ongoing basis, the Company evaluates its estimates, including, but not limited to, those related to investments, manufacturing accruals, accrued research and development expenses, fair value of common stock, stock-based compensation, operating lease right-of-use (ROU) assets and liabilities, income tax uncertainties and the valuation of deferred tax assets. The Company bases its estimates on its historical experience and also on assumptions that it believes are reasonable; however, actual results could significantly differ from those estimates . Segments The Company operates and manages its business as one reportable and operating segment, which is the business of developing clinical product candidates for the treatment of cancer patients. The Company’s chief executive officer, who is the chief operating decision maker, reviews financial information on an aggregate basis for allocating resources and evaluating financial performance. All long-lived assets are maintained in, and all losses are attributable to, the United States. Cash, Cash Equivalents, and Restricted Cash The Company considers all highly liquid investments with original maturities of three months or less from the date of purchase to be cash and cash equivalents. Cash equivalents consist of amounts invested in money market accounts and are stated at fair value. Restricted cash as of September 30, 2021 included a $216,000 stand-by letter of credit issued in favor of the landlord in connection with a lease of lab space located in San Carlos, California, which is classified in noncurrent assets. There was no restricted cash as of December 31, 2020. Investments The Company’s investments have been classified and accounted for as available-for-sale securities. Fixed income securities consist of U.S. Treasury securities, U.S. government agency securities, corporate debt, and commercial paper. The specific identification method is used to determine the cost basis of fixed income securities sold. These securities are recorded on the condensed balance sheets at fair value. Unrealized gains and losses on these securities are included as a separate component of accumulated other comprehensive loss. The cost of investment securities is adjusted for amortization of premiums and accretion of discounts to maturity. Such amortization and accretion are included in other income (expense), net. Realized gains and losses and declines in fair value judged to be other-than-temporary, if any, are also included in other income (expense), net. The Company evaluates securities for other-than-temporary impairment at the balance sheet date. Declines in fair value determined to be other-than-temporary are also included in other income (expense), net. The Company classifies its investments as short or long-term primarily based on the remaining contractual maturity of the securities. Long term investments consist of asset backed securities and corporate debt. There have been no significant realized gains or losses on the Company’s investments for the periods presented. There were no securities that have been in a continuous unrealized loss position for more than 12 months. Concentration of Credit Risk and Other Risks and Uncertainties Financial instruments that potentially subject the Company to a concentration of credit risk, consist primarily of cash and cash equivalents. The Company maintains bank deposits in federally insured financial institutions and these deposits may exceed federally insured limits. The Company is exposed to credit risk in the event of default by the financial institutions holding its cash and cash equivalents to the extent recorded in the balance sheet. The Company has not experienced any losses on its deposits of cash and cash equivalents. The Company’s future results of operations involve a number of other risks and uncertainties. Factors that could affect the Company’s future operating results and cause actual results to vary materially from expectations include, but are not limited to, uncertainty of results of clinical trials and reaching milestones, uncertainty of regulatory approval of the Company’s potential product candidates, uncertainty of market acceptance of the Company’s product candidates, competition from substitute products and larger companies, securing and protecting proprietary technology, strategic relationships and dependence on key individuals or sole source suppliers. The Company’s product candidates require approvals from the U.S. Food and Drug Administration and comparable foreign regulatory agencies prior to commercial sales in their respective jurisdictions. There can be no assurance that any product candidates will receive the necessary approvals. If the Company is denied approval, approval is delayed or the Company is unable to maintain approval for any product candidate, it could have a materially adverse impact on the Company. Property and Equipment, Net Property and equipment are recorded at cost, net of accumulated depreciation and amortization. Property and equipment are depreciated using the straight-line method over the estimated useful lives of the assets. The useful lives of property and equipment are as follows: Laboratory equipment 3-5 years Furniture and fixtures 5 years Leasehold improvements Shorter of remaining lease term or estimated useful life Computer equipment 3 years Upon retirement or sale of the assets, the cost and related accumulated depreciation and amortization are removed from the balance sheet and the resulting gain or loss is recorded to the statements of operations. Repairs and maintenance are expensed as incurred. Impairment of Long-lived Assets Long-lived assets are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. Recoverability of assets to be held and used is measured by a comparison of the carrying amount of an asset to future net cash flows expected to be generated by the asset. If the carrying amount of an asset exceeds its estimated future cash flows, an impairment charge is recognized by the amount by which the carrying amount of the asset exceeds the fair value of the asset. There have been no such impairments of long-lived assets for any of the periods presented. Convertible Preferred Stock The Company records shares of convertible preferred stock at fair value on the dates of issuances, net of issuance costs. The Company classifies convertible preferred stock outside of stockholders’ equity (deficit) because the shares contain liquidation features that are not solely within the Company’s control. The Company analyzed all embedded derivatives and beneficial conversion features for its convertible preferred stock and concluded that none requires bifurcation. The Company has elected not to adjust the carrying values of the convertible preferred stock to the liquidation preferences of such shares because it is uncertain whether or when an event would occur that would obligate the Company to pay the liquidation preferences to holders of convertible preferred stock. Subsequent adjustments to the carrying values to the liquidation preferences will be made only when it becomes probable that such a liquidation event will occur. Research and Development Expenses The Company’s research and development expenses consist primarily of external and internal costs incurred in connection with the research and development of its research programs and product candidates. External costs include: • expenses incurred under agreements with third-party contract manufacturing organizations (“CMOs”), contract research organizations (“CROs”), research and development service providers, academic research institutions and consulting costs; and • laboratory expenses, including supplies and services. Internal costs include: • personnel-related expenses, including salaries, benefits and stock-based compensation for personnel in research and product development roles; and • facilities and other allocated expenses, including expenses for rent and facilities maintenance, and amortization. The Company expenses research and development costs in the periods in which they are incurred. Nonrefundable advance payments for goods or services to be received in future periods for use in research and development activities are deferred and capitalized. The capitalized amounts are then expensed as the related goods are delivered and as services are performed. The Company tracks direct costs by stage of program, clinical or preclinical. However, the Company does not track indirect costs on a stage of program basis because these costs are deployed across multiple programs and, as such, are not separately classified. Accrued Research and Development Expenses The Company records accruals for estimated costs of research, preclinical, and manufacturing development, which are significant components of research and development expenses. A substantial portion of the Company’s ongoing research and development activities is conducted by third-party service providers, CROs and CMOs. The Company’s contracts with the CROs and CMOs generally include fees such as initiation fees, reservation fees, costs related to animal studies and safety tests, verification run costs, materials and reagents expenses, taxes, etc. The financial terms of these contracts are subject to negotiation, which vary from contract to contract and may result in payment flows that do not match the periods over which materials or services are provided to the Company under such contracts. The Company accrues the costs incurred under agreements with these third parties based on estimates of actual work completed in accordance with the respective agreements. The Company determines the estimated costs through discussions with internal personnel and external service providers as to the progress, or stage of completion and actual timeline (start- date and end-date) of the services and the agreed-upon fees to be paid for such services. Through September 30, 2021, there have been no material differences from the Company’s estimated accrued research and development expenses to actual expenses. Patent Costs All patent-related costs incurred in connection with filing and prosecuting patent applications are expensed as incurred due to the uncertainty about the recovery of the expenditure. Amounts incurred are classified as general and administrative expenses in the accompanying statements of operations . Stock-based Compensation The Company’s measures stock options and other stock-based awards granted to directors, employees and non-employees based on their fair value on the date of the grant and recognizes the corresponding compensation expense of those awards over the requisite service period, which is generally the vesting period of the respective award, and estimates the fair value of share-based awards to employees and directors using the Black-Scholes option-pricing valuation model. The Company has only issued stock options and restricted share awards with service-based vesting conditions and records the expense for these awards using the straight-line method. The Company accounts for the forfeitures as they occur. Leases On January 1, 2020, the Company early adopted ASC 842, Leases Under ASC 842, the Company determines if an arrangement is a lease at inception. Lease liabilities and their corresponding right-of-use assets are recorded based on the present value of lease payments over the expected lease term. In determining the present value of lease payments, the Company uses its incremental borrowing rate based on the information available at the lease commencement date. The Company’s operating leases have one single component. The lease component results in a right-of-use asset being recorded on the balance sheet and expensed as lease expense on a straight-line basis in the Company’s statements of operations. Building improvements are paid for by the tenant and are capitalized as leasehold improvements and included in property and equipment, net in the balance sheet. Income Taxes The Company began providing for income taxes under the asset and liability method in December 2020 upon conversion from a limited liability company into a corporation. Current income tax expense or benefit represents the amount of income taxes expected to be payable or refundable for the current year. Deferred income tax assets and liabilities are determined based on differences between the financial statement reporting and tax basis of assets and liabilities and net operating loss and credit carryforwards and are measured using the enacted tax rates and laws that will be in effect when such items are expected to reverse. Deferred income tax assets are reduced, as necessary, by a valuation allowance when management determines it is more likely than not that some or all the tax benefits will not be realized. The Company accounts for uncertain tax positions in accordance with ASC No. 740 Income Taxes The Company includes any penalties and interest expense related to income taxes as a component of income tax expense, as necessary. Comprehensive Loss Other comprehensive loss represents the changes in stockholders’ equity except those resulting from distributions to stockholders. The Company’s unrealized losses on available-for-sale investment securities represent components of other comprehensive loss that are excluded from the reported net loss and are presented in the consolidated statements of operations and comprehensive loss. Net Loss Per Share Basic net loss per share is calculated by dividing the net loss by the weighted-average number of shares of common stock outstanding during the periods, without consideration for common stock equivalents. Diluted net loss per share is the same as basic net loss per share, since the effects of potentially dilutive securities are antidilutive given the net loss for the periods presented. Recent Accounting Pronouncements The Company is an emerging growth company (“EGC”), as defined in the Jumpstart Our Business Startups Act of 2012 (“JOBS Act”), and may take advantage of reduced reporting requirements that are otherwise applicable to public companies. Section 107 of the JOBS Act exempts emerging growth companies from being required to comply with new or revised financial accounting standards until private companies are required to comply with those standards. The Company has elected to use the extended transition period for complying with new or revised accounting standards; and as a result of this election, its financial statements may not be comparable to companies that comply with public company effective dates. The JOBS Act also exempts the Company from having to provide an auditor attestation of internal controls over financial reporting under Sarbanes-Oxley Act Section 404(b). The Company will remain an EGC until the earliest of (i) the last day of the fiscal year in which it has total annual gross revenues of $1.07 billion or more, (ii) the last day of the fiscal year following the fifth anniversary of the completion of its IPO, (iii) the date on which it has issued more than $1.0 billion in nonconvertible debt during the previous three years or (iv) the date on which it is deemed to be a large accelerated filer under the rules of the Securities and Exchange Commission (“SEC”), which generally is when it has more than $700 million in market value of its stock held by non-affiliates, has been a public company for at least 12 months and has filed one annual report on Form 10-K. From time to time, new accounting pronouncements are issued by the Financial Accounting Standards Board (FASB), or other standard setting bodies and adopted by the Company as of the specified effective date. Unless otherwise discussed, the impact of recently issued standards that are not yet effective will not have a material impact on the Company’s financial position or results of operations upon adoption. In June 2016, the FASB issued ASU 2016-13, Financial Instruments – Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments , which requires that financial assets measured at amortized cost be presented at the net amount expected to be collected. The measurement of expected credit losses is based on historical experience, current conditions, and reasonable and supportable forecasts that affect collectability. This ASU also eliminates the concept of “other-than-temporary” impairment when evaluating available-for-sale debt securities and instead focuses on determining whether any impairment is a result of a credit loss or other factors. An entity will recognize an allowance for credit losses on available-for-sale debt securities rather than an other-than-temporary impairment that reduces the cost basis of the investment. This ASU is effective for fiscal years beginning after December 15, 2022 and interim periods within those fiscal years. Early adoption is permitted. The Company is currently assessing the impact of this standard on its financial statements and related disclosures. In December 2019, the Financial Accounting Standards Board issued ASU No 2019-12, “Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes” (“ASU 2019-12”). ASU 2019-12 removes certain exceptions to the general principles in Topic 740 in Generally Accepted Accounting Principles. ASU 2019-12 is effective for public entities for fiscal years beginning after December 15, 2020, with early adoption permitted. The Company does not expect ASU 2019-12 to have a material effect on the Company’s current financial position, results of operations or financial statement disclosures.

Fair Value Measurement

Fair Value Measurement	9 Months Ended
	Sep. 30, 2021
Fair Value Disclosures [Abstract]
Fair Value Measurement	Note 3. Fair Value Measurement The Company applies fair value accounting for all financial assets and liabilities and non-financial assets and liabilities that are recognized or disclosed at fair value in the financial statements on a recurring basis. Fair value is an exit price, representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. As such, fair value is a market-based measurement that should be determined based on assumptions that market participants would use in pricing an asset or liability. As a basis for considering such assumptions, a three-tier fair value hierarchy has been established, which prioritizes the inputs used in measuring fair value as follows: Level 1—Observable inputs, such as quoted prices in active markets for identical assets or liabilities at the measurement date. Level 2—Observable inputs other than Level 1 prices such as quoted prices for similar assets or liabilities, quoted prices in markets that are not active, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. Level 3—Unobservable inputs which reflect management’s best estimate of what market participants would use in pricing the asset or liability at the measurement date. Consideration is given to the risk inherent in the valuation technique and the risk inherent in the inputs to the model. In determining fair value, the Company utilizes valuation techniques that maximize the use of observable inputs and minimize the use of unobservable inputs to the extent possible as well as considers counterparty credit risk in its assessment of fair value. The Company’s cash equivalents includes investments in money market funds that are classified as Level 1 of the fair value hierarchy. The Company values the funds at $1 stable net asset value, which is the quoted price in active markets for identical assets that the Company has the ability to access. The Company’s cash equivalents and available-for-sale securities also include commercial paper, asset backed securities, and corporate notes, which have been classified within Level 2 of the fair value of the hierarchy because of the sufficient observable inputs for revaluation. Financial instruments classified within Level 2 of the fair value hierarchy are valued based on other observable inputs, including broker or dealer quotations or alternative pricing sources. When quoted prices in active markets for identical assets or liabilities are not available, the Company relies on non-binding quotes from its investment managers, which are based on proprietary valuation models of independent pricing services. These models generally use inputs such as observable market data, quoted market prices for similar instruments, or historical pricing trends of a security relative to its peers. To validate the fair value determination provided by its investment managers, the Company reviews the pricing movement in the context of overall market trends and trading information from its investment managers. In addition, the Company assesses the inputs and methods used in determining the fair value in order to determine the classification of securities in the fair value hierarchy. As of September 30, 2021, there were no financial instruments classified as Level 3. The fair value of the Company’s cash equivalents and short-term investments approximates their respective carrying amounts due to their short-term maturity. The following tables set forth the fair value of the Company’s financial assets, which consist of investments measured and recognized at fair value (in thousands): September 30, 2021 Fair Value Hierarchy Level Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Money market funds ( 1) Level 1 $ 116,259 $ — $ — $ 116,259 Investments Corporate notes Level 2 20,573 5 (3 ) 20,575 Commercial paper Level 2 8,995 — — 8,995 Asset backed securities Level 2 5,098 1 (1 ) 5,098 Total $ 150,925 $ 6 $ (4 ) $ 150,927 (1) Included in cash and cash equivalents on the balance sheets . The Company did not have any investments as of December 31, 2020. Realized gains or losses from the sale of investments and other-than-temporary impairments, if any, on available-for-sale securities are reported in other income (expense), net as incurred. The cost of securities sold was determined based on the specific identification method. The amount of realized gains and realized losses on investments for the periods presented have not been material.

Property and Equipment, Net

Property and Equipment, Net	9 Months Ended
	Sep. 30, 2021
Property Plant And Equipment [Abstract]
Property and Equipment, Net	Note 4. Property and Equipment, Net Property and equipment, net consisted of the following (in thousands): September 30, 2021 December 31, 2020 Computers $ 96 $ — Furniture and fixtures 315 7 Lab equipment 1,366 — Leasehold improvements 296 24 Construction in progress 997 58 Total property and equipment, gross 3,070 89 Less: accumulated depreciation (107 ) (8 ) Total property and equipment, net $ 2,963 $ 81 Depreciation expense was $65,000 and $99,000, respectively, for the three and nine months September 30, 2021 and was $2,300 for the three and nine months ended September 30, 2020.

Leases

Leases	9 Months Ended
	Sep. 30, 2021
Leases [Abstract]
Leases	Note 5. Leases The Company early adopted Accounting Standards Update ASU 842 on January 1, 2020. There was no cumulative-effect adjustment recorded to accumulated deficit upon adoption. Under ASC 842, the Company determines if an arrangement is a lease at inception. In addition, the Company determines whether leases meet the classification criteria of a finance or operating lease at the lease commencement date. As of December 31, 2020, the Company’s lease population consisted of real estate. As of the date of adoption of ASC 842 and December 31, 2020, the Company did not have finance leases. Operating leases are included in operating lease right-of-use (“ROU”) assets, short-term lease liabilities, and long-term lease liabilities in the Company’s balance sheet. ROU assets represent the Company’s right to use an underlying asset for the lease term and lease liabilities represent the Company’s obligation to make lease payments arising from the lease. Operating lease ROU assets and liabilities are recognized at the lease commencement date based on the present value of lease payments over the lease term. In determining the present value of lease payments, the Company uses its incremental borrowing rate based on the information available at the lease commencement date if the rate implicit in the lease is not readily determinable. The Company determines the incremental borrowing rate base on an analysis of corporate bond yields with a credit rating similar to the Company. The determination of the Company’s incremental borrowing rate requires management judgment including the development of a synthetic credit rating and cost of debt as the Company currently does not carry any debt. The Company believes that the estimates used in determining the incremental borrowing rate are reasonable based upon current facts and circumstances. Applying different judgments to the same facts and circumstances could result in the estimated amounts to vary. The operating lease ROU assets also include adjustments for prepayments and accrued lease payments and exclude lease incentives. The Company’s lease terms may include options to extend or terminate the lease when it is reasonably certain that the Company will exercise such options. Operating lease cost is recognized on a straight-line basis over the expected lease term. Lease agreements entered into after the adoption of ASC 842 that include lease and non-lease components are accounted for as a single lease component. Lease agreements with a noncancelable term of less than 12 months are not recorded on the Company’s balance sheet. Operating Leases The Company leased its original office and lab space in Redwood City, California and San Carlos, California respectively. Both of the 12.5 month leases were entered into in August 2020 and ended in August 2021. The lab lease was extended on a month-to-month basis starting in September 2021. In February 2021, the Company entered into an 8-month sublease agreement with Level Home, Inc. for additional office space located in Redwood City, California. Rent is $38,766 per month with an abatement of base rent for the first month. This lease will be treated as a short-term lease in accordance with ASC 842 and therefore, is excluded from the right-of -use asset and liability. In September 2021, the Company renewed the lease agreement on a month-to-month basis. In March 2021, the Company signed a 5-year lease for new lab space located in San Carlos, California. The lease commenced on May 1, 2021 with monthly lease payments of $57,638 with annual increases of 3%. This lease is accounted for under ASC 842. Upon initiation, the Company recognized a right-of-use asset and liability of $3.2 million, discounted at 5.4%, the Company’s estimated incremental borrowing rate over the 5 year expected remaining term. In September 2021, the Company entered into a 12-month sublease for additional office space located in Redwood City, California. The lease is expected to commence in January 2022 and rent payments under the agreement amount to approximately $2.7 million. This lease will be treated as a short-term lease in accordance with ASC 842 and therefore, is excluded from the right-of -use asset and liability. Lease expense was $0.4 million and $0.8 million, respectively, for the three and nine months ended September 30, 2021 and $63,000 and The undiscounted future non-cancellable lease payments under the Company’s operating leases as of September 30, 2021 is as follows (in thousands): Operating Lease Year Ending December Commitments 2021 (remaining three months) $ 175 2022 705 2023 727 2024 748 2025 771 Thereafter 259 Total undiscounted lease payments 3,385 Less: Present value adjustments (400 ) Present value of lease payments $ 2,985

Balance Sheet Components

Balance Sheet Components	9 Months Ended
	Sep. 30, 2021
Balance Sheet Related Disclosures [Abstract]
Balance Sheet Components	Note 6. Balance Sheet Components Prepaid Expenses and Other Current Assets Prepaid expenses and other current assets consisted of the following (in thousands): September 30, December 31, 2021 2020 Prepaid expenses $ 1,528 $ 463 Other current asset — 29 Interest receivable 115 — Security deposits 55 36 Total prepaid expenses and other current assets $ 1,698 $ 528 Accrued Expenses and Other Current Liabilities Accrued expense and other current liabilities consisted of the following (in thousands): September 30, December 31, 2021 2020 Accrued research and development materials and services $ 1,773 $ 519 Accrued professional services 262 67 Accrued personnel expenses 1,601 47 Other liabilities 202 — Total accrued expenses and other current liabilities $ 3,838 $ 633

Capital Structure

Capital Structure	9 Months Ended
	Sep. 30, 2021
Equity [Abstract]
Capital Structure	Note 7. Capital Structure In December 2020, all of the outstanding membership interests in Biomea Fusion LLC were exchanged for equity interests in Biomea Fusion, Inc. in a statutory conversion under Delaware law. All of the share information referenced throughout the financial statements and notes to the financial statements have been retroactively adjusted to reflect the change in capital structure. In connection with the completion of its IPO, on April 20, 2021, the Company’s certificate of incorporation was amended and restated to authorize 300,000,000 shares of common stock with a par value of $0.0001 per share and 10,000,000 shares of preferred stock with a par value of $0.0001 per share. Common Stock The Company is authorized to issue 300,000,000 shares of common stock, par value $0.0001 per share. As of December 31, 2020, there were 12,702,942 shares of common stock outstanding, including 749,835 unvested restricted shares of common stock subject to repurchase. There were no options to purchase common stock outstanding as of December 31, 2020. As of September 30, 2021, there were 29,635,250 shares of common stock outstanding, including 593,542 unvested restricted shares of common stock subject to repurchase. There were 2,966,518 options to purchase common stock outstanding as of September 30, 2021. Common stockholders are entitled to dividends when and if declared by the Company’s Board of Directors and after any preferred share dividends are fully paid. The holder of each share of common stock is entitled to one vote. As of September 30, 2021 and December 31, 2020, no dividends have been declared. Series A Convertible Preferred Stock In December 2020, the Company issued 7,064,925 shares of its convertible preferred stock, par value $0.0001, raising $55.7 million in net proceeds. Prior to the December 2020 convertible preferred stock financing, there were no shares of convertible preferred stock outstanding. Preferred stock consisted of the following as of December 31, 2020 (in thousands, except share numbers): Shares authorized Shares issued and outstanding Original issue price Carrying value Liquidation preference Series A convertible preferred stock 7,064,925 7,064,925 $ 7.93 $ 55,738 $ 56,000 Immediately prior to the closing of the IPO, all outstanding shares of the Company’s convertible preferred stock converted into 7,064,925 shares of common stock and the related carrying value was reclassified to common stock and additional paid-in capital. There were no shares of convertible preferred stock outstanding as of September 30, 2021.

Stock-Based Compensation

Stock-Based Compensation	9 Months Ended
	Sep. 30, 2021
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-Based Compensation	Note 8. Stock-Based Compensation 2020 Equity Incentive Plan The Company adopted the 2020 Equity Incentive Plan (the “2020 Plan”) on December 18, 2020. The 2020 Plan reserved 4,327,799 shares of common stock to grant stock-based compensation awards, including stock options and restricted stock awards, to employees and non-employees. 2021 Equity Incentive Plan In April 2021, the Company adopted the 2021 Equity Incentive Plan (the “2021 Plan”). Options granted under the 2021 Plan expire no later than 10 years from the date of grant. The exercise price of options granted under the 2021 Plan must at least be equal to the fair market value of the Company’s common stock on the date of grant. Subject to adjustment in the case of certain capitalization events as provided in the 2021 Plan, the Company initially reserved 3,370,000 shares of the Company’s common stock for issuance pursuant to awards under the 2021 Plan. The 2021 Plan is administered by the Compensation Committee of the Company’s Board of Directors. The number of shares of the Company’s common stock available for issuance under the 2021 Plan will also include an annual increase on the first day of each fiscal year beginning in 2022 and ending in 2031, equal to the lesser of (i) 5% of the Company’s common stock outstanding at December 31 of the immediately preceding year, or (ii) such number of shares as determined by the Company’s Board of Directors. As of September 30, 2021, 2,427,743 shares of common stock remained available for issuance under the 2021 Plan. 2021 Employee Stock Purchase Plan The Company adopted a 2021 Employee Stock Purchase Plan (“ESPP”) in April 2021. The ESPP enables eligible employees of the Company and designated affiliates to purchase shares of common stock at a discount of 15%. , 2021, 306,000 shares of common stock remained available for issuance under the ESPP. Stock Options The Company’s measures stock options and other stock-based awards granted to directors, employees and non-employees based on their fair value on the date of the grant and recognizes the corresponding compensation expense of those awards over the requisite service period, which is generally the vesting period of the respective award. The Company has only issued stock options and restricted share awards with service-based vesting conditions and records the expense for these awards using the straight-line method. Forfeitures are accounted for as they occur. The Company granted its first restricted stock awards in the fourth quarter of 2020. The Company has determined the fair value of restricted stock awards granted based on the fair value of its common stock. There were no stock options outstanding as of December 31, 2020. The Company issued its first stock options in the first quarter of 2021. The Company estimates the fair value of each stock option grant using the Black-Scholes option pricing model, which uses as inputs the following assumptions: Expected term —The expected term represents the period that the stock-based awards are expected to be outstanding. The Company uses the simplified method to determine the expected term, which is based on the average of the time-to-vesting and the contractual life of the options. Expected volatility —Because the Company has been privately held and does not have any trading history for its common stock, the expected volatility was estimated based on the average volatility for comparable publicly traded biotechnology companies over a period equal to the expected term of the stock option grants. The comparable companies were chosen based on the similar size, stage in life cycle or area of specialty. The Company will continue to take this approach until a sufficient amount of historical information regarding the volatility of its own stock price becomes available. Risk-free interest rate —The risk-free interest rate is based on the yield of the U.S. Treasury notes as of the grant date with terms commensurate with the expected term of the awards. Dividend yield —The Company has never paid dividends on its common stock and has no plans to pay dividends on its common stock. Therefore, the Company used an expected dividend yield of zero. Total stock-based compensation expense recorded in the condensed statements of operations and allocated as follows (in thousands): Three Months Ended Nine Months Ended September 30, September 30, 2021 2020 2021 2020 Research and development $ 766 $ — $ 1,690 $ — General and administrative 1,155 — 2,613 — Total stock-based compensation expense $ 1,921 $ — $ 4,303 $ — The following table summarizes stock option activity Outstanding Options Shares Weighted- Average Exercise Weighted- Average Remaining Contractual Term (Years) Balance—December 31, 2020 — $ — — Granted 3,113,099 $ 9.79 Exercised (43,850 ) $ 5.14 Cancelled (102,731 ) $ 6.60 Balance—September 30, 2021 2,966,518 $ 9.96 9.4 Exercisable 446,210 $ 8.46 9.1 The fair value of stock options was estimated using the following weighted-average assumptions: Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Expected term in years 6.0 — 6.0 — Expected volatility 91 % — 91 % — Risk-free interest rate 0.9 % — 0.9 % — Dividend yield — — — — Weighted average fair value of share-based awards granted $ 10.33 $ — $ 7.26 $ — Restricted Stock The Company granted 824,429 restricted stock awards to employees and non-employees during the fourth quarter of 2020 that vest quarterly over four years. Restricted stock awards are share awards that entitle the holder to receive freely tradeable shares of the Company’s common stock. The underlying shares are outstanding as of the issuance date. Any unvested shares are subject to forfeiture in the case that the grantee’s service terminates prior to vesting of the restricted stock. As of September 30, 2021 and December 31, 2020, a total of 593,542 and 749,835 restricted common stock shares remained unvested subject to repurchase, respectively. There were no restricted shares issued during the nine months ended September 30, 2021.

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2021
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	Note 9. Commitments and Contingencies Legal Proceedings From time to time, the Company may become involved in legal proceedings arising from the ordinary course of business. The Company records a liability for such matters when it is probable that future losses will be incurred and that such losses can be reasonably estimated. Significant judgment by the Company is required to determine both probability and the estimated amount. Management is currently not aware of any legal matters that could have a material adverse effect on its financial position, results of operations or cash flows. Indemnification In the ordinary course of business, the Company enters into agreements that may include indemnification provisions. Pursuant to such agreements, the Company may indemnify, hold harmless and defend an indemnified party for losses suffered or incurred by the indemnified party. Some of the provisions will limit losses to those arising from third party actions. In some cases, the indemnification will continue after the termination of the agreement. The maximum potential amount of future payments the Company could be required to make under these provisions is not determinable. The Company has never incurred material costs to defend lawsuits or settle claims related to these indemnification provisions. The Company has also entered into indemnification agreements with its directors and officers that may require the Company to indemnify its directors and officers against liabilities that may arise by reason of their status or service as directors or officers to the fullest extent permitted by Delaware corporate law. The Company currently has directors’ and officers’ insurance.

Debt

Debt	9 Months Ended
	Sep. 30, 2021
Debt Disclosure [Abstract]
Debt	Note 10. Debt On May 5, 2020, the Company entered into a promissory note with City National Bank, which provided a loan in the amount of $36,000 (“PPP Loan”) pursuant to the Paycheck Protection Program (“PPP”), administered by the Small Business Administration under the CARES Act. The PPP Loan has a two-year

Related Party Transactions

Related Party Transactions	9 Months Ended
	Sep. 30, 2021
Related Party Transactions [Abstract]
Related Party Transactions	Note 11. Related Party Transactions During the year ended December 31, 2019, A2A Pharmaceuticals and Biomea Health, LLC invested a combined $1.4 million in the Company in exchange for 4,428,500 shares of the Company’s common stock. Biomea Health, LLC’s initial investment of $0.2 million was in the form of expenses paid by Biomea Health, LLC on behalf of the Company. During the nine months ended September 30, 2021, A2A Pharmaceuticals and Biomea Health, LLC invested a combined $0.3 million in the Company in exchange for 799,569 shares of the Company’s common stock. As of September 30, 2021 and December 31, 2020, the Company had an outstanding receivable balance from Biomea Health LLC of approximately $0 and $8,000, respectively. This receivable balance as of December 31, 2020 is related to operating expenses paid for by the Company on behalf of Biomea Health LLC.

Net Loss and Net Loss Per Share

Net Loss and Net Loss Per Share	9 Months Ended
	Sep. 30, 2021
Earnings Per Share [Abstract]
Net Loss and Net Loss Per Share	Note 12. Net Loss and Net Loss Per Share The following table sets forth the computation of the basic and diluted net loss per share: Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Numerator: Net loss attributable to common stockholders, basic and diluted $ (12,606 ) $ (1,135 ) $ (26,857 ) $ (1,826 ) Denominator: Weighted-average common shares outstanding 29,001,213 11,724,100 22,105,321 10,082,667 Net loss per share attributable to common stockholders: Basic and diluted $ (0.43 ) $ (0.10 ) $ (1.21 ) $ (0.18 ) Since the Company was in a loss position for all periods presented, basic net loss per share is the same as diluted net loss per share for all periods as the inclusion of all common stock equivalents outstanding would have been anti-dilutive. Potentially dilutive securities that were not included in the diluted per share calculations because they would be anti-dilutive were as follows:

Subsequent Events

Subsequent Events	9 Months Ended
	Sep. 30, 2021
Subsequent Events [Abstract]
Subsequent Events	Note 13. Subsequent Events The Company did not have any subsequent events as of the filing date of this Quarterly Report on Form 10-Q.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2021
Accounting Policies [Abstract]
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. On an ongoing basis, the Company evaluates its estimates, including, but not limited to, those related to investments, manufacturing accruals, accrued research and development expenses, fair value of common stock, stock-based compensation, operating lease right-of-use (ROU) assets and liabilities, income tax uncertainties and the valuation of deferred tax assets. The Company bases its estimates on its historical experience and also on assumptions that it believes are reasonable; however, actual results could significantly differ from those estimates .
Segments	Segments The Company operates and manages its business as one reportable and operating segment, which is the business of developing clinical product candidates for the treatment of cancer patients. The Company’s chief executive officer, who is the chief operating decision maker, reviews financial information on an aggregate basis for allocating resources and evaluating financial performance. All long-lived assets are maintained in, and all losses are attributable to, the United States.
Cash, Cash Equivalents, and Restricted Cash	Cash, Cash Equivalents, and Restricted Cash The Company considers all highly liquid investments with original maturities of three months or less from the date of purchase to be cash and cash equivalents. Cash equivalents consist of amounts invested in money market accounts and are stated at fair value. Restricted cash as of September 30, 2021 included a $216,000 stand-by letter of credit issued in favor of the landlord in connection with a lease of lab space located in San Carlos, California, which is classified in noncurrent assets. There was no restricted cash as of December 31, 2020.
Investments	Investments The Company’s investments have been classified and accounted for as available-for-sale securities. Fixed income securities consist of U.S. Treasury securities, U.S. government agency securities, corporate debt, and commercial paper. The specific identification method is used to determine the cost basis of fixed income securities sold. These securities are recorded on the condensed balance sheets at fair value. Unrealized gains and losses on these securities are included as a separate component of accumulated other comprehensive loss. The cost of investment securities is adjusted for amortization of premiums and accretion of discounts to maturity. Such amortization and accretion are included in other income (expense), net. Realized gains and losses and declines in fair value judged to be other-than-temporary, if any, are also included in other income (expense), net. The Company evaluates securities for other-than-temporary impairment at the balance sheet date. Declines in fair value determined to be other-than-temporary are also included in other income (expense), net. The Company classifies its investments as short or long-term primarily based on the remaining contractual maturity of the securities. Long term investments consist of asset backed securities and corporate debt. There have been no significant realized gains or losses on the Company’s investments for the periods presented. There were no securities that have been in a continuous unrealized loss position for more than 12 months.
Concentration of Credit Risk and Other Risks and Uncertainties	Concentration of Credit Risk and Other Risks and Uncertainties Financial instruments that potentially subject the Company to a concentration of credit risk, consist primarily of cash and cash equivalents. The Company maintains bank deposits in federally insured financial institutions and these deposits may exceed federally insured limits. The Company is exposed to credit risk in the event of default by the financial institutions holding its cash and cash equivalents to the extent recorded in the balance sheet. The Company has not experienced any losses on its deposits of cash and cash equivalents. The Company’s future results of operations involve a number of other risks and uncertainties. Factors that could affect the Company’s future operating results and cause actual results to vary materially from expectations include, but are not limited to, uncertainty of results of clinical trials and reaching milestones, uncertainty of regulatory approval of the Company’s potential product candidates, uncertainty of market acceptance of the Company’s product candidates, competition from substitute products and larger companies, securing and protecting proprietary technology, strategic relationships and dependence on key individuals or sole source suppliers. The Company’s product candidates require approvals from the U.S. Food and Drug Administration and comparable foreign regulatory agencies prior to commercial sales in their respective jurisdictions. There can be no assurance that any product candidates will receive the necessary approvals. If the Company is denied approval, approval is delayed or the Company is unable to maintain approval for any product candidate, it could have a materially adverse impact on the Company.
Property and Equipment, Net	Property and Equipment, Net Property and equipment are recorded at cost, net of accumulated depreciation and amortization. Property and equipment are depreciated using the straight-line method over the estimated useful lives of the assets. The useful lives of property and equipment are as follows: Laboratory equipment 3-5 years Furniture and fixtures 5 years Leasehold improvements Shorter of remaining lease term or estimated useful life Computer equipment 3 years Upon retirement or sale of the assets, the cost and related accumulated depreciation and amortization are removed from the balance sheet and the resulting gain or loss is recorded to the statements of operations. Repairs and maintenance are expensed as incurred.
Impairment of Long-Lived Assets	Impairment of Long-lived Assets Long-lived assets are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. Recoverability of assets to be held and used is measured by a comparison of the carrying amount of an asset to future net cash flows expected to be generated by the asset. If the carrying amount of an asset exceeds its estimated future cash flows, an impairment charge is recognized by the amount by which the carrying amount of the asset exceeds the fair value of the asset. There have been no such impairments of long-lived assets for any of the periods presented.
Convertible Preferred Stock	Convertible Preferred Stock The Company records shares of convertible preferred stock at fair value on the dates of issuances, net of issuance costs. The Company classifies convertible preferred stock outside of stockholders’ equity (deficit) because the shares contain liquidation features that are not solely within the Company’s control. The Company analyzed all embedded derivatives and beneficial conversion features for its convertible preferred stock and concluded that none requires bifurcation. The Company has elected not to adjust the carrying values of the convertible preferred stock to the liquidation preferences of such shares because it is uncertain whether or when an event would occur that would obligate the Company to pay the liquidation preferences to holders of convertible preferred stock. Subsequent adjustments to the carrying values to the liquidation preferences will be made only when it becomes probable that such a liquidation event will occur.
Research and Development Expenses	Research and Development Expenses The Company’s research and development expenses consist primarily of external and internal costs incurred in connection with the research and development of its research programs and product candidates. External costs include: • expenses incurred under agreements with third-party contract manufacturing organizations (“CMOs”), contract research organizations (“CROs”), research and development service providers, academic research institutions and consulting costs; and • laboratory expenses, including supplies and services. Internal costs include: • personnel-related expenses, including salaries, benefits and stock-based compensation for personnel in research and product development roles; and • facilities and other allocated expenses, including expenses for rent and facilities maintenance, and amortization. The Company expenses research and development costs in the periods in which they are incurred. Nonrefundable advance payments for goods or services to be received in future periods for use in research and development activities are deferred and capitalized. The capitalized amounts are then expensed as the related goods are delivered and as services are performed. The Company tracks direct costs by stage of program, clinical or preclinical. However, the Company does not track indirect costs on a stage of program basis because these costs are deployed across multiple programs and, as such, are not separately classified.
Accrued Research and Development Expenses	Accrued Research and Development Expenses The Company records accruals for estimated costs of research, preclinical, and manufacturing development, which are significant components of research and development expenses. A substantial portion of the Company’s ongoing research and development activities is conducted by third-party service providers, CROs and CMOs. The Company’s contracts with the CROs and CMOs generally include fees such as initiation fees, reservation fees, costs related to animal studies and safety tests, verification run costs, materials and reagents expenses, taxes, etc. The financial terms of these contracts are subject to negotiation, which vary from contract to contract and may result in payment flows that do not match the periods over which materials or services are provided to the Company under such contracts. The Company accrues the costs incurred under agreements with these third parties based on estimates of actual work completed in accordance with the respective agreements. The Company determines the estimated costs through discussions with internal personnel and external service providers as to the progress, or stage of completion and actual timeline (start- date and end-date) of the services and the agreed-upon fees to be paid for such services. Through September 30, 2021, there have been no material differences from the Company’s estimated accrued research and development expenses to actual expenses.
Patent Costs	Patent Costs All patent-related costs incurred in connection with filing and prosecuting patent applications are expensed as incurred due to the uncertainty about the recovery of the expenditure. Amounts incurred are classified as general and administrative expenses in the accompanying statements of operations .
Stock-based compensation	Stock-based Compensation The Company’s measures stock options and other stock-based awards granted to directors, employees and non-employees based on their fair value on the date of the grant and recognizes the corresponding compensation expense of those awards over the requisite service period, which is generally the vesting period of the respective award, and estimates the fair value of share-based awards to employees and directors using the Black-Scholes option-pricing valuation model. The Company has only issued stock options and restricted share awards with service-based vesting conditions and records the expense for these awards using the straight-line method. The Company accounts for the forfeitures as they occur.
Leases	Leases On January 1, 2020, the Company early adopted ASC 842, Leases Under ASC 842, the Company determines if an arrangement is a lease at inception. Lease liabilities and their corresponding right-of-use assets are recorded based on the present value of lease payments over the expected lease term. In determining the present value of lease payments, the Company uses its incremental borrowing rate based on the information available at the lease commencement date. The Company’s operating leases have one single component. The lease component results in a right-of-use asset being recorded on the balance sheet and expensed as lease expense on a straight-line basis in the Company’s statements of operations. Building improvements are paid for by the tenant and are capitalized as leasehold improvements and included in property and equipment, net in the balance sheet.
Income Taxes	Income Taxes The Company began providing for income taxes under the asset and liability method in December 2020 upon conversion from a limited liability company into a corporation. Current income tax expense or benefit represents the amount of income taxes expected to be payable or refundable for the current year. Deferred income tax assets and liabilities are determined based on differences between the financial statement reporting and tax basis of assets and liabilities and net operating loss and credit carryforwards and are measured using the enacted tax rates and laws that will be in effect when such items are expected to reverse. Deferred income tax assets are reduced, as necessary, by a valuation allowance when management determines it is more likely than not that some or all the tax benefits will not be realized. The Company accounts for uncertain tax positions in accordance with ASC No. 740 Income Taxes The Company includes any penalties and interest expense related to income taxes as a component of income tax expense, as necessary.
Comprehensive Loss	Comprehensive Loss Other comprehensive loss represents the changes in stockholders’ equity except those resulting from distributions to stockholders. The Company’s unrealized losses on available-for-sale investment securities represent components of other comprehensive loss that are excluded from the reported net loss and are presented in the consolidated statements of operations and comprehensive loss.
Net Loss Per Share	Net Loss Per Share Basic net loss per share is calculated by dividing the net loss by the weighted-average number of shares of common stock outstanding during the periods, without consideration for common stock equivalents. Diluted net loss per share is the same as basic net loss per share, since the effects of potentially dilutive securities are antidilutive given the net loss for the periods presented.
Recent Accounting Pronouncements	Recent Accounting Pronouncements The Company is an emerging growth company (“EGC”), as defined in the Jumpstart Our Business Startups Act of 2012 (“JOBS Act”), and may take advantage of reduced reporting requirements that are otherwise applicable to public companies. Section 107 of the JOBS Act exempts emerging growth companies from being required to comply with new or revised financial accounting standards until private companies are required to comply with those standards. The Company has elected to use the extended transition period for complying with new or revised accounting standards; and as a result of this election, its financial statements may not be comparable to companies that comply with public company effective dates. The JOBS Act also exempts the Company from having to provide an auditor attestation of internal controls over financial reporting under Sarbanes-Oxley Act Section 404(b). The Company will remain an EGC until the earliest of (i) the last day of the fiscal year in which it has total annual gross revenues of $1.07 billion or more, (ii) the last day of the fiscal year following the fifth anniversary of the completion of its IPO, (iii) the date on which it has issued more than $1.0 billion in nonconvertible debt during the previous three years or (iv) the date on which it is deemed to be a large accelerated filer under the rules of the Securities and Exchange Commission (“SEC”), which generally is when it has more than $700 million in market value of its stock held by non-affiliates, has been a public company for at least 12 months and has filed one annual report on Form 10-K. From time to time, new accounting pronouncements are issued by the Financial Accounting Standards Board (FASB), or other standard setting bodies and adopted by the Company as of the specified effective date. Unless otherwise discussed, the impact of recently issued standards that are not yet effective will not have a material impact on the Company’s financial position or results of operations upon adoption. In June 2016, the FASB issued ASU 2016-13, Financial Instruments – Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments , which requires that financial assets measured at amortized cost be presented at the net amount expected to be collected. The measurement of expected credit losses is based on historical experience, current conditions, and reasonable and supportable forecasts that affect collectability. This ASU also eliminates the concept of “other-than-temporary” impairment when evaluating available-for-sale debt securities and instead focuses on determining whether any impairment is a result of a credit loss or other factors. An entity will recognize an allowance for credit losses on available-for-sale debt securities rather than an other-than-temporary impairment that reduces the cost basis of the investment. This ASU is effective for fiscal years beginning after December 15, 2022 and interim periods within those fiscal years. Early adoption is permitted. The Company is currently assessing the impact of this standard on its financial statements and related disclosures. In December 2019, the Financial Accounting Standards Board issued ASU No 2019-12, “Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes” (“ASU 2019-12”). ASU 2019-12 removes certain exceptions to the general principles in Topic 740 in Generally Accepted Accounting Principles. ASU 2019-12 is effective for public entities for fiscal years beginning after December 15, 2020, with early adoption permitted. The Company does not expect ASU 2019-12 to have a material effect on the Company’s current financial position, results of operations or financial statement disclosures.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	9 Months Ended
	Sep. 30, 2021
Property Plant And Equipment [Abstract]
Summary of Useful Lives of Property and Equipment	The useful lives of property and equipment are as follows: Laboratory equipment 3-5 years Furniture and fixtures 5 years Leasehold improvements Shorter of remaining lease term or estimated useful life Computer equipment 3 years

Fair Value Measurement (Tables)

Fair Value Measurement (Tables)	9 Months Ended
	Sep. 30, 2021
Fair Value Disclosures [Abstract]
Summary of Fair Value of Financial Assets Consist of Investments Measured and Recognized at Fair Value	The following tables set forth the fair value of the Company’s financial assets, which consist of investments measured and recognized at fair value (in thousands): September 30, 2021 Fair Value Hierarchy Level Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Money market funds ( 1) Level 1 $ 116,259 $ — $ — $ 116,259 Investments Corporate notes Level 2 20,573 5 (3 ) 20,575 Commercial paper Level 2 8,995 — — 8,995 Asset backed securities Level 2 5,098 1 (1 ) 5,098 Total $ 150,925 $ 6 $ (4 ) $ 150,927 (1) Included in cash and cash equivalents on the balance sheets .

Property and Equipment, Net (Ta

Property and Equipment, Net (Tables)	9 Months Ended
	Sep. 30, 2021
Property Plant And Equipment [Abstract]
Summary of Property and Equipment, Net	Property and equipment, net consisted of the following (in thousands): September 30, 2021 December 31, 2020 Computers $ 96 $ — Furniture and fixtures 315 7 Lab equipment 1,366 — Leasehold improvements 296 24 Construction in progress 997 58 Total property and equipment, gross 3,070 89 Less: accumulated depreciation (107 ) (8 ) Total property and equipment, net $ 2,963 $ 81

Leases (Tables)

Leases (Tables)	9 Months Ended
	Sep. 30, 2021
Leases [Abstract]
Schedule of Undiscounted Future Non-cancellable Lease Payments Under Operating Leases	The undiscounted future non-cancellable lease payments under the Company’s operating leases as of September 30, 2021 is as follows (in thousands): Operating Lease Year Ending December Commitments 2021 (remaining three months) $ 175 2022 705 2023 727 2024 748 2025 771 Thereafter 259 Total undiscounted lease payments 3,385 Less: Present value adjustments (400 ) Present value of lease payments $ 2,985

Balance Sheet Components (Table

Balance Sheet Components (Tables)	9 Months Ended
	Sep. 30, 2021
Balance Sheet Related Disclosures [Abstract]
Summary of Prepaid Expenses and Other Current Assets	Prepaid expenses and other current assets consisted of the following (in thousands): September 30, December 31, 2021 2020 Prepaid expenses $ 1,528 $ 463 Other current asset — 29 Interest receivable 115 — Security deposits 55 36 Total prepaid expenses and other current assets $ 1,698 $ 528
Summary of Accrued Expense and Other Current Liabilities	Accrued expense and other current liabilities consisted of the following (in thousands): September 30, December 31, 2021 2020 Accrued research and development materials and services $ 1,773 $ 519 Accrued professional services 262 67 Accrued personnel expenses 1,601 47 Other liabilities 202 — Total accrued expenses and other current liabilities $ 3,838 $ 633

Capital Structure (Tables)

Capital Structure (Tables)	9 Months Ended
	Sep. 30, 2021
Equity [Abstract]
Schedule of Series A Convertible Preferred Stock	Preferred stock consisted of the following as of December 31, 2020 (in thousands, except share numbers): Shares authorized Shares issued and outstanding Original issue price Carrying value Liquidation preference Series A convertible preferred stock 7,064,925 7,064,925 $ 7.93 $ 55,738 $ 56,000

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	9 Months Ended
	Sep. 30, 2021
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Summary of Stock-Based Compensation Expense Recorded in Condensed Statements of Operations and Allocated	Total stock-based compensation expense recorded in the condensed statements of operations and allocated as follows (in thousands): Three Months Ended Nine Months Ended September 30, September 30, 2021 2020 2021 2020 Research and development $ 766 $ — $ 1,690 $ — General and administrative 1,155 — 2,613 — Total stock-based compensation expense $ 1,921 $ — $ 4,303 $ —
Summary of Stock Option Activity	The following table summarizes stock option activity Outstanding Options Shares Weighted- Average Exercise Weighted- Average Remaining Contractual Term (Years) Balance—December 31, 2020 — $ — — Granted 3,113,099 $ 9.79 Exercised (43,850 ) $ 5.14 Cancelled (102,731 ) $ 6.60 Balance—September 30, 2021 2,966,518 $ 9.96 9.4 Exercisable 446,210 $ 8.46 9.1
Summary of Fair Value of Stock Options Estimated using Weighted-Average Assumptions	The fair value of stock options was estimated using the following weighted-average assumptions: Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Expected term in years 6.0 — 6.0 — Expected volatility 91 % — 91 % — Risk-free interest rate 0.9 % — 0.9 % — Dividend yield — — — — Weighted average fair value of share-based awards granted $ 10.33 $ — $ 7.26 $ —

Net Loss and Net Loss Per Sha_2

Net Loss and Net Loss Per Share (Tables)	9 Months Ended
	Sep. 30, 2021
Earnings Per Share [Abstract]
Summary of Computation of Basic and Diluted Net Loss Per Share	The following table sets forth the computation of the basic and diluted net loss per share: Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Numerator: Net loss attributable to common stockholders, basic and diluted $ (12,606 ) $ (1,135 ) $ (26,857 ) $ (1,826 ) Denominator: Weighted-average common shares outstanding 29,001,213 11,724,100 22,105,321 10,082,667 Net loss per share attributable to common stockholders: Basic and diluted $ (0.43 ) $ (0.10 ) $ (1.21 ) $ (0.18 )

Organization - Additional Infor

Organization - Additional Information (Detail) $ / shares in Units, $ in Thousands	Apr. 21, 2021shares	Apr. 20, 2021USD ($)$ / sharesshares	Apr. 19, 2021shares	Apr. 12, 2021	Sep. 30, 2021USD ($)$ / sharesshares	Dec. 31, 2020USD ($)$ / sharesshares
Class Of Stock [Line Items]
Forward stock split ratio				8.84
Preferred stock converted to common stock			7,064,925
Proceeds from IPO net of underwriting discounts and commissions and offering costs | $					$ 152,753
Common stock, shares authorized					300,000,000	25,300,080
Common stock, par value | $ / shares					$ 0.0001	$ 0.0001
Preferred stock, shares authorized					10,000,000	0
Preferred stock, par value | $ / shares					$ 0.0001	$ 0.0001
Accumulated deficit | $					$ (35,032)	$ (8,175)
Cash, cash equivalents, restricted cash, and investments | $					$ 191,900
IPO
Class Of Stock [Line Items]
Issuance of common stock, net of offering costs (in shares)		9,000,000
Initial public offering, price per share | $ / shares		$ 17
Shares issued in connection with underwriters exercise of option to purchase additional shares	823,532
Preferred stock converted to common stock		7,064,925
Proceeds from IPO net of underwriting discounts and commissions and offering costs | $		$ 152,800
Common stock, shares authorized		300,000,000
Common stock, par value | $ / shares		$ 0.0001
Preferred stock, shares authorized		10,000,000
Preferred stock, par value | $ / shares		$ 0.0001

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Additional Information (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2021USD ($)	Sep. 30, 2020USD ($)	Sep. 30, 2021USD ($)Segment	Sep. 30, 2020USD ($)	Dec. 31, 2020USD ($)	Jan. 01, 2020USD ($)
Summary Of Significant Accounting Policies [Line Items]
Number of reportable segments | Segment			1
Number of operating segments | Segment			1
Restricted cash	$ 216,000		$ 216,000		$ 0
Debt securities, realized gain (loss)			0
Debt securities, continuous unrealized loss position, 12 months or longer	0		0
Impairment of long-lived assets	0	$ 0	0	$ 0
Right-of-use asset	2,860,000		2,860,000		210,000	$ 300,000
Lease liabilities	554,000		554,000		$ 223,000	$ 300,000
Total annual gross revenues			1,070,000,000
Minimum
Summary Of Significant Accounting Policies [Line Items]
Issued nonconvertible debt			1,000,000,000
Market value of its stock held by non-affiliates			700,000,000
Stand-by Letter of Credit
Summary Of Significant Accounting Policies [Line Items]
Restricted cash	$ 216,000		$ 216,000

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Summary of Useful Lives of Property and Equipment (Details)	9 Months Ended
	Sep. 30, 2021
Laboratory Equipment | Minimum
Property Plant And Equipment [Line Items]
Useful lives of property and equipment	3 years
Laboratory Equipment | Maximum
Property Plant And Equipment [Line Items]
Useful lives of property and equipment	5 years
Furniture and Fixtures
Property Plant And Equipment [Line Items]
Useful lives of property and equipment	5 years
Leasehold Improvements
Property Plant And Equipment [Line Items]
Useful lives of property and equipment	Shorter of remaining lease term or estimated useful life
Computer Equipment
Property Plant And Equipment [Line Items]
Useful lives of property and equipment	3 years

Fair Value Measurement - Additi

Fair Value Measurement - Additional Information (Details) - USD ($)	Sep. 30, 2021	Dec. 31, 2020
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Stable net asset value	$ 1
Financial instruments classified as Level 3	150,927,000
Investments		$ 0
Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial instruments classified as Level 3	$ 0

Fair Value Measurement - Summar

Fair Value Measurement - Summary of Fair Value of Financial Assets Consist of Investments Measured and Recognized at Fair Value (Details) $ in Thousands	Sep. 30, 2021USD ($)
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 150,925
Gross Unrealized Gains	6
Gross Unrealized Losses	(4)
Fair Value	150,927
Money Market Funds | Level 1
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	116,259	[1]
Fair Value	116,259	[1]
Corporate Notes | Level 2
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	20,573
Gross Unrealized Gains	5
Gross Unrealized Losses	(3)
Fair Value	20,575
Commercial Paper | Level 2
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	8,995
Fair Value	8,995
Asset Backed Securities | Level 2
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	5,098
Gross Unrealized Gains	1
Gross Unrealized Losses	(1)
Fair Value	$ 5,098
[1]	Included in cash and cash equivalents on the balance sheets

Property and Equipment Net - Su

Property and Equipment Net - Summary of Property and Equipment, Net (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Property Plant And Equipment [Line Items]
Total property and equipment, gross	$ 3,070	$ 89
Less: accumulated depreciation	(107)	(8)
Total property and equipment, net	2,963	81
Computers
Property Plant And Equipment [Line Items]
Total property and equipment, gross	96
Furniture and Fixtures
Property Plant And Equipment [Line Items]
Total property and equipment, gross	315	7
Lab Equipment
Property Plant And Equipment [Line Items]
Total property and equipment, gross	1,366
Leasehold Improvements
Property Plant And Equipment [Line Items]
Total property and equipment, gross	296	24
Construction in Progress
Property Plant And Equipment [Line Items]
Total property and equipment, gross	$ 997	$ 58

Property and Equipment Net - Ad

Property and Equipment Net - Additional Information (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Property Plant And Equipment [Abstract]
Depreciation expense	$ 65,000	$ 2,300	$ 99,000	$ 2,300

Leases - Additional Information

Leases - Additional Information (Details) - USD ($)	1 Months Ended		3 Months Ended		9 Months Ended
	Sep. 30, 2021	Feb. 28, 2021	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Mar. 31, 2021	Dec. 31, 2020	Jan. 01, 2020
Lessee Lease Description [Line Items]
Right-of-use asset	$ 2,860,000		$ 2,860,000		$ 2,860,000			$ 210,000	$ 300,000
Operating lease, liability	$ 2,985,000		2,985,000		2,985,000
Operating lease expense			$ 400,000	$ 63,000	$ 800,000	$ 91,000
California
Lessee Lease Description [Line Items]
Operating lease, term of contract	12 months 15 days		12 months 15 days		12 months 15 days
Operating sublease, term of contract	12 months
Operating lease, lease not yet commenced, term of contract							5 years
Operating lease, lease not yet commenced, monthly lease payments					$ 57,638
Operating lease, lease not yet commenced, rate of annual increases to rent	3.00%		3.00%		3.00%
Right-of-use asset	$ 3,200,000		$ 3,200,000		$ 3,200,000
Operating lease, liability	$ 3,200,000		$ 3,200,000		$ 3,200,000
Operating lease, weighted average discount rate	5.40%		5.40%		5.40%
Operating lease, weighted average remaining lease term	5 years		5 years		5 years
Total rent payment	$ 2,700,000
California | Level Home, Inc.
Lessee Lease Description [Line Items]
Operating sublease, term of contract		8 months
Monthly rental payment		$ 38,766

Leases - Schedule of Undiscount

Leases - Schedule of Undiscounted Future Non-cancellable Lease Payments Under Operating Leases (Details) $ in Thousands	Sep. 30, 2021USD ($)
Operating Lease Liabilities Payments Due [Abstract]
2021 (remaining three months)	$ 175
2022	705
2023	727
2024	748
2025	771
Thereafter	259
Total undiscounted lease payments	3,385
Less: Present value adjustments	(400)
Present value of lease payments	$ 2,985

Balance Sheet Components - Summ

Balance Sheet Components - Summary of Prepaid Expenses and Other Current Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Prepaid Expense And Other Assets Current [Abstract]
Prepaid expenses	$ 1,528	$ 463
Other current asset		29
Interest receivable	115
Security deposits	55	36
Total prepaid expenses and other current assets	$ 1,698	$ 528

Balance Sheet Components - Su_2

Balance Sheet Components - Summary of Accrued Expense and Other Current Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Accrued Liabilities Current [Abstract]
Accrued research and development materials and services	$ 1,773	$ 519
Accrued professional services	262	67
Accrued personnel expenses	1,601	47
Other liabilities	202
Total accrued expenses and other current liabilities	$ 3,838	$ 633

Capital Structure - Additional

Capital Structure - Additional Information (Details) - USD ($)	Apr. 20, 2021	Apr. 19, 2021	Dec. 31, 2020	Sep. 30, 2021	Mar. 31, 2021	Nov. 30, 2020
Class Of Stock [Line Items]
Preferred stock, shares authorized			0	10,000,000
Preferred stock, par value			$ 0.0001	$ 0.0001
Common stock, par value			$ 0.0001	$ 0.0001
Common stock, shares authorized			25,300,080	300,000,000
Common stock, shares outstanding			12,702,942	29,635,250
Options to purchase common stock outstanding			0	2,966,518
Dividends declared			$ 0	$ 0
Convertible preferred stock, shares outstanding				0
Preferred stock converted to common stock		7,064,925
Series A Convertible Preferred Stock
Class Of Stock [Line Items]
Convertible preferred stock, shares issued			7,064,925	0
Convertible preferred stock par value			$ 0.0001	$ 0.0001
Proceeds from issuance of convertible preferred stock			$ 55,700,000
Convertible preferred stock, shares outstanding			7,064,925	0	7,064,925	0
Restricted Stock
Class Of Stock [Line Items]
Unvested restricted shares of common stock			749,835	593,542
IPO
Class Of Stock [Line Items]
Preferred stock, shares authorized	10,000,000
Preferred stock, par value	$ 0.0001
Common stock, par value	$ 0.0001
Common stock, shares authorized	300,000,000
Preferred stock converted to common stock	7,064,925

Capital Structure - Schedule of

Capital Structure - Schedule of Series A Convertible Preferred Stock (Details) - USD ($) $ / shares in Units, $ in Thousands	Sep. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Nov. 30, 2020
Class Of Stock [Line Items]
Preferred stock, shares outstanding	0
Series A Convertible Preferred Stock
Class Of Stock [Line Items]
Preferred stock, shares authorized	0		7,064,925
Preferred stock, shares issued	0		7,064,925
Preferred stock, shares outstanding	0	7,064,925	7,064,925	0
Original issue price			$ 7.93
Carrying value		$ 55,735	$ 55,738
Liquidation preference			$ 56,000

Stock-Based Compensation - Addi

Stock-Based Compensation - Additional Information (Details) - shares	1 Months Ended	3 Months Ended	9 Months Ended	12 Months Ended
	Apr. 30, 2021	Dec. 31, 2020	Sep. 30, 2021	Dec. 31, 2022	Dec. 18, 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock options outstanding		0	2,966,518
Expected dividend yield			0.00%
2020 Equity Incentive Plan | Employees and Non-Employees
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Reserved shares of common stock to grant stock-based compensation awards					4,327,799
2021 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Reserved shares of common stock to grant stock-based compensation awards	3,370,000		2,427,743
Options granted expiration period	10 years
2021 Equity Incentive Plan | Forecast
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation arrangement by share-based payment award, percentage of increment based on prior year				5.00%
2021 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Reserved shares of common stock to grant stock-based compensation awards			306,000
Discounted percentage for employees and designated affiliates to purchase common stock	15.00%
Common shares available for purchase	306,000
2021 Employee Stock Purchase Plan | Forecast
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation arrangement by share-based payment award, percentage of increment based on prior year				1.00%
Restricted Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Restricted stock awards granted			0
Unvested restricted awards		749,835	593,542
Restricted Stock | Employees and Non-Employees
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Restricted stock awards granted		824,429
Vesting period		4 years

Stock-Based Compensation - Summ

Stock-Based Compensation - Summary of Stock-Based Compensation Expense Recorded in Condensed Statements of Operations and Allocated (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2021
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation expense	$ 1,921	$ 4,303
Research and Development
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation expense	766	1,690
General and Administrative
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation expense	$ 1,155	$ 2,613

Stock-Based Compensation - Su_2

Stock-Based Compensation - Summary of Stock Option Activity (Details)	9 Months Ended
	Sep. 30, 2021$ / sharesshares
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Shares, Beginning Balance	0
Shares, Granted	3,113,099
Shares, Exercised	(43,850)
Shares, Cancelled	(102,731)
Shares, Ending Balance	2,966,518
Shares, Exercisable	446,210
Weighted Average Exercise Price, Granted | $ / shares	$ 9.79
Weighted Average Exercise Price, Exercised | $ / shares	5.14
Weighted Average Exercise Price, Cancelled | $ / shares	6.60
Weighted Average Exercise Price, Ending Balance | $ / shares	9.96
Weighted Average Exercise Price, Exercisable | $ / shares	$ 8.46
Weighted Average Remaining Contract Term	9 years 4 months 24 days
Weighted Average Remaining Contract Term, Exercisable	9 years 1 month 6 days

Stock-Based Compensation - Su_3

Stock-Based Compensation - Summary of Fair Value of Stock Options Estimated using Weighted-Average Assumptions (Details) - $ / shares	3 Months Ended	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2021
Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions And Methodology [Abstract]
Expected term in years	6 years	6 years
Expected volatility	91.00%	91.00%
Risk-free interest rate	0.90%	0.90%
Expected dividend yield		0.00%
Weighted average fair value of share-based awards granted	$ 10.33	$ 7.26

Debt - Additional Information (

Debt - Additional Information (Details) - Promissory Note - City National Bank - PPP Loan - CARES Act	May 05, 2020USD ($)
Debt Instrument [Line Items]
Loan amount	$ 36,000
Loan term	2 years
Interest rate	1.00%
Monthly principal and interest payments deferral period	7 months
Prepayment penalties	$ 0

Related Party Transactions - Ad

Related Party Transactions - Additional Information (Details) - USD ($)	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2019	Dec. 31, 2020
A2A Pharmaceuticals and Biomea Health, LLC
Related Party Transaction [Line Items]
Amount invested in exchange of common stock shares	$ 300,000	$ 1,400,000
Number of common stock shares exchanged	799,569	4,428,500
Biomea Health, LLC
Related Party Transaction [Line Items]
Expenses paid		$ 200,000
Outstanding receivable balance	$ 0		$ 8,000

Net Loss and Net Loss Per Sha_3

Net Loss and Net Loss Per Share - Summary of Computation of Basic and Diluted Net Loss Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020
Numerator:
Net loss attributable to common stockholders, basic and diluted	$ (12,606)	$ (8,399)	$ (5,852)	$ (1,135)	$ (293)	$ (398)	$ (26,857)	$ (1,826)
Denominator:
Weighted-average common shares outstanding	29,001,213			11,724,100			22,105,321	10,082,667
Net loss per share attributable to common stockholders:
Basic and diluted	$ (0.43)			$ (0.10)			$ (1.21)	$ (0.18)