Foghorn Therapeutics (FHTX) 10-Q 11 May 21 2021 Q1 Quarterly report Financial data

Cover Page

Cover Page - shares	3 Months Ended
	Mar. 31, 2021	Apr. 30, 2021
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2021
Document Transition Report	false
Entity File Number	001-39634
Entity Registrant Name	Foghorn Therapeutics Inc.
Entity Incorporation, State	DE
Entity Tax Identification Number	47-5271393
Entity Address, Street Name	500 Technology Square, Ste 700
Entity Address, City	Cambridge
Entity Address, State	MA
Entity Address, Postal Zip Code	02139
City Area Code	617
Local Phone Number	586-3100
Title of each class	Common Stock, $0.0001 par value per share
Trading Symbol(s)	FHTX
Name of each exchange on which registered	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		36,846,084
Amendment Flag	false
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q1
Entity Central Index Key	0001822462
Current Fiscal Year End Date	--12-31

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 66,449	$ 92,795
Marketable securities	94,468	92,975
Prepaid expenses and other current assets	4,398	4,917
Total current assets	165,315	190,687
Property and equipment, net	19,493	19,528
Restricted cash	1,733	1,733
Other assets	1,603	842
Operating lease right-of-use assets	41,742	42,804
Total assets	229,886	255,594
Current liabilities:
Accounts payable	2,911	3,680
Accrued expenses	5,126	9,161
Operating lease liabilities	5,783	3,981
Financing lease liability	105	0
Deferred revenue	2,407	2,024
Total current liabilities	16,332	18,846
Long-term Debt	19,739	19,654
Operating lease liabilities, net of current portion	56,548	58,361
Financing lease liability, net of current portion	225	0
Deferred revenue, net of current portion	11,878	12,546
Total liabilities	104,722	109,407
Commitments and contingencies (Note 11)
Stockholders’ equity:
Preferred stock, $0.0001 par value; 25,000,000 shares authorized at March 31, 2021 and December 31, 2020; no shares issued or outstanding	0	0
Common stock, $0.0001 par value; 175,000,000 shares authorized at March 31, 2021 and December 31, 2020; 36,826,775 shares issued and outstanding at March 31, 2021; 36,790,946 shares issued and outstanding at December 31, 2020	4	4
Additional paid-in capital	311,076	309,126
Accumulated other comprehensive income (loss)	6	(7)
Accumulated deficit	(185,922)	(162,936)
Total stockholders’ equity	125,164	146,187
Total liabilities and stockholders’ equity	$ 229,886	$ 255,594

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Mar. 31, 2021	Dec. 31, 2020
Statement of Financial Position [Abstract]
Preferred stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Preferred stock, shares authorized (in shares)	25,000,000	25,000,000
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Common stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Common stock, shares authorized (in shares)	175,000,000	175,000,000
Common stock, shares issued (in shares)	36,826,775	36,790,946
Common stock, shares outstanding (in shares)	36,826,775	36,790,946

Condensed Consolidated Statemen

Condensed Consolidated Statements Of Operations And Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Income Statement [Abstract]
Collaboration revenue	$ 286	$ 0
Operating expenses:
Research and development	18,726	11,503
General and administrative	4,690	2,221
Total operating expenses	23,416	13,724
Loss from operations	(23,130)	(13,724)
Other income (expense):
Interest expense	(486)	(258)
Interest income and other income (expense), net	630	29
Change in fair value of preferred stock warrant liability	0	1
Total other income (expense), net	144	(228)
Net loss	$ (22,986)	$ (13,952)
Net loss per share attributable to common stockholders—basic and diluted (in dollars per share)	$ (0.62)	$ (2.71)
Weighted average common shares outstanding—basic and diluted (in shares)	36,817,277	5,154,229
Comprehensive loss:
Net loss	$ (22,986)	$ (13,952)
Other comprehensive loss:
Unrealized losses on marketable securities	13	0
Total other comprehensive loss	13	0
Total comprehensive loss	$ (22,973)	$ (13,952)

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Convertible Preferred Stock and Stockholders’ Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit	Series A-1, A-2 and B Convertible Preferred Stock
Beginning balance at Dec. 31, 2019	$ (88,016)	$ 0	$ 6,120	$ 0	$ (94,136)	$ 86,544
Beginning balance (Shares) at Dec. 31, 2019		4,870,851				28,615,546
Increase (Decrease) in Stockholders' Equity
Issuance of common stock upon exercise of stock options	247		247
Issuance of common stock upon exercise of stock options (in shares)		97,034
Vesting of restricted stock (in shares)		222,973
Stock-based compensation expense	517		517
Net loss	(13,952)				(13,952)
Ending balance at Mar. 31, 2020	(101,204)	$ 0	6,884	0	(108,088)	$ 86,544
Ending balance (Shares) at Mar. 31, 2020		5,190,858				28,615,546
Beginning balance at Dec. 31, 2020	$ 146,187	$ 4	309,126	(7)	(162,936)	$ 0
Beginning balance (Shares) at Dec. 31, 2020	36,790,946	36,790,946				0
Increase (Decrease) in Stockholders' Equity
Issuance of common stock upon exercise of stock options	$ 62		62
Issuance of common stock upon exercise of stock options (in shares)		35,829
Stock-based compensation expense	1,888		1,888
Unrealized gains on marketable securities	13			13
Net loss	(22,986)				(22,986)
Ending balance at Mar. 31, 2021	$ 125,164	$ 4	$ 311,076	$ 6	$ (185,922)	$ 0
Ending balance (Shares) at Mar. 31, 2021	36,826,775	36,826,775				0

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Cash flows from operating activities:
Net loss	$ (22,986)	$ (13,952)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	1,888	517
Depreciation and amortization expense	772	255
Change in fair value of preferred stock warrant liability	0	(1)
Noncash lease expense	1,062	608
Noncash interest expense	85	64
Accretion of discount on marketable securities	(13)	0
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(295)	(64)
Accounts payable	(754)	969
Accrued expenses and other current liabilities	(2,609)	(17)
Operating lease liabilities	(11)	859
Deferred revenue	(286)	0
Net cash used in operating activities	(23,147)	(10,762)
Cash flows from investing activities:
Purchases of property and equipment	(1,794)	(1,021)
Purchases of marketable securities	(26,467)	0
Proceeds from the sale of marketable securities	25,000	0
Net cash used in investing activities	(3,261)	(1,021)
Cash flows from financing activities:
Proceeds from issuance of common stock upon exercise of stock options	62	247
Net cash provided by financing activities	62	247
Net decrease in cash, cash equivalents and restricted cash	(26,346)	(11,536)
Cash, cash equivalents and restricted cash at beginning of period	94,528	17,255
Cash, cash equivalents and restricted cash at end of period	68,182	5,719
Supplemental cash flow information:
Cash paid for interest	400	190
Supplemental disclosure of noncash investing and financing information:
Purchases of property and equipment included in accounts payable and accrued expenses	$ 959	$ 1,471

Condensed Consolidated Statem_4

Condensed Consolidated Statements of Cash Flows (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2021	Mar. 31, 2020
Reconciliation of cash, cash equivalents and restricted cash:
Cash and cash equivalents	$ 66,449	$ 3,443
Restricted cash (current and non-current)	1,733	2,276
Total cash, cash equivalents and restricted cash shown in the statement of cash flows	$ 68,182	$ 5,719

Nature of Business and Basis of

Nature of Business and Basis of Presentation	3 Months Ended
	Mar. 31, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Nature of Business and Basis of Presentation	Nature of Business and Basis of Presentation Foghorn Therapeutics Inc. (the “Company”) is a clinical-stage biopharmaceutical company discovering and developing a new class of medicines targeting genetically determined dependencies within the chromatin regulatory system. The Company uses its proprietary Gene Traffic Control platform to identify, validate and potentially drug targets within the system. The Company was founded in October 2015 as a Delaware corporation. The Company is headquartered in Cambridge, Massachusetts. The Company is subject to risks similar to those of other early-stage companies in the biopharmaceutical industry, including dependence on key individuals, the need to develop commercially viable products, competition from other companies, many of whom are larger and better capitalized, the impact of the COVID-19 pandemic and the need to obtain adequate additional financing to fund the development of its products. There can be no assurance that the Company’s research and development will be successfully completed, that adequate protection for the Company’s intellectual property will be maintained, that any products developed will obtain required regulatory approval or that any approved products will be commercially viable. Even if the Company’s development efforts are successful, it is uncertain when, if ever, the Company will generate significant revenue from the sale of its products. In March 2020, the World Health Organization declared the global novel coronavirus disease 2019 (“COVID-19”) outbreak a pandemic. The Company’s operations have not been significantly impacted by the COVID-19 pandemic. However, the Company cannot at this time predict the specific extent, duration, or full impact that the COVID-19 pandemic will have on its financial condition and operations, including ongoing and planned clinical trials. The impact of the COVID-19 outbreak on the Company’s financial performance will depend on future developments, including the duration and spread of the pandemic and related governmental advisories and restrictions. These developments and the impact of COVID-19 on the financial markets and the overall economy are highly uncertain and cannot be predicted. If the financial markets and/or the overall economy are impacted for an extended period, the Company’s results may be materially adversely affected. Going concern On October 27, 2020, the Company completed its initial public offering (“IPO”) pursuant to which it issued and sold 7,500,000 shares of its common stock at a public offering price of $16.00 per share, resulting in net proceeds of $108.0 million, after deducting underwriting discounts and commissions and other offering expenses. On November 19, 2020, the Company issued and sold an additional 951,837 shares of common stock at the IPO price of $16.00 per share pursuant to the underwriters’ partial exercise of their option to purchase additional shares of common stock, resulting in additional net proceeds of $14.2 million after deducting underwriting discounts and commissions. The accompanying condensed consolidated financial statements have been prepared on the basis of continuity of operations, realization of assets and the satisfaction of liabilities and commitments in the ordinary course of business. Since inception, the Company has funded its operations primarily with proceeds from sales of preferred stock, debt financing, an upfront payment of $15.0 million the Company received in July 2020 under a collaboration agreement with Merck Sharp & Dohme Corp. (see Note 9), and most recently, with proceeds from the sale of common stock in the IPO completed in October 2020. The Company has incurred losses since inception and as of March 31, 2021, the Company had an accumulated deficit of $185.9 million. The Company expects to continue to generate operating losses in the foreseeable future. As of the issuance date of these interim condensed consolidated financial statements the Company expects that its cash, cash equivalents and marketable securities will be sufficient to fund its operating expenses and capital expenditure requirements for at least 12 months. The Company will need to obtain additional funding through public or private equity offerings, debt financings, collaborations, strategic alliances and/or licensing arrangements. The Company may not be able to obtain financing on acceptable terms, or at all, and the Company may not be able to enter into collaborative or strategic alliances or licensing arrangements. The terms of any financing may adversely affect the holdings or the rights of the Company’s stockholders. Arrangements with collaborators or others may require the Company to relinquish rights to certain of its technologies or programs. If the Company is unable to obtain funding, the Company could be forced to delay, reduce or eliminate some or all of its research and development programs, pipeline expansion or commercialization efforts, which could adversely affect its business prospects. Although management will continue to pursue these plans, there is no assurance that the Company will be successful in obtaining sufficient funding on terms acceptable to the Company to fund continuing operations when needed or at all. Basis of presentation The Company’s condensed consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”) and pursuant to the rules and regulations of the Securities and Exchange Commission for interim financial statements. Certain information and footnote disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to such rules and regulations. The accompanying condensed consolidated financial statements include the accounts of the Company and its wholly-owned subsidiary. All intercompany accounts and transactions have been eliminated in consolidation. Any reference in these notes to applicable guidance is meant to refer to the authoritative GAAP as found in the Accounting Standards Codification (“ASC”) and Accounting Standards Update (“ASU”) of the Financial Accounting Standards Board (“FASB”). Unaudited interim financial information The accompanying condensed consolidated balance sheet as of March 31, 2021, the condensed consolidated statements of operations and comprehensive loss, convertible preferred stock and stockholders’ equity and cash flows for the three months ended March 31, 2021 and 2020 are unaudited. The unaudited interim condensed consolidated financial statements have been prepared on the same basis as the audited annual consolidated financial statements and, in the opinion of management, reflect all adjustments, which include only normal recurring adjustments, necessary for the fair statement of the Company’s financial position as of March 31, 2021 and the results of its operations and its cash flows for the three months ended March 31, 2021 and 2020. The results for the three months ended March 31, 2021 are not necessarily indicative of results to be expected for the year ending December 31, 2021, any other interim periods, or any future year or period.

Summary of Significant Accounti

Summary of Significant Accounting Policies	3 Months Ended
	Mar. 31, 2021
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies The accounting policies of the Company are set forth in Note 2 to the consolidated financial statements contained in the Company’s 2020 Annual Report on Form 10-K. The Company includes herein certain updates to those policies. Leases In accordance with ASC 842, Leases, the Company accounts for a contract as a lease when it has the right to control the asset for a period of time while obtaining substantially all of the asset’s economic benefits. The Company determines if an arrangement is a lease or contains an embedded lease at inception. For arrangements that meet the definition of a lease, the Company determines the initial classification and measurement of its right-of-use asset and lease liability at the lease commencement date and thereafter if modified. The lease term includes any renew al or purchase options that the Company is reasonably assured to exercise. The present value of lease payments is determined by using the interest rate implicit in the lease, if that rate is readily determinable; otherwise, the Company uses its estimated secured incremental borrowing rate for that lease term. The Company’s policy is to not record leases with an original term of twelve months or less on its consolidated balance sheets and recognizes those lease payments in the income statement on a straight-line basis over the lease term. The Company’s existing leases are for office and laboratory space and equipment leases. In addition to rent, the leases may require the Company to pay additional costs, such as utilities, maintenance and other operating costs, which are generally referred to as non-lease components. The Company has elected to not separate lease and non-lease components. Only the fixed costs for lease components and their associated non-lease components are accounted for as a single lease component and recognized as part of a right-of-use asset and liability. Rent expense for operating leases is recognized on a straight-line basis over the reasonably assured lease term based on the total lease payments and is included in operating expenses in the condensed consolidated statements of operations and comprehensive loss. For the Company's financing lease, amortization of the right-of-use asset is recognized on a straight-line basis over the shorter of the useful life of the asset or the lease term and is included in operating expenses on the condensed consolidated statements of operations and comprehensive loss. Interest on the finance lease liability is recognized in interest expense on the condensed consolidated statements of operations and comprehensive loss. Recently issued accounting pronouncements From time to time, new accounting pronouncements are issued by the FASB or other standard setting bodies that the Company adopts as of the specified effective date. The Company qualifies as an “emerging growth company” as defined in the Jumpstart Our Business Startups Act of 2012 and has elected not to “opt out” of the extended transition related to complying with new or

Marketable Securities and Fair

Marketable Securities and Fair Value Measurements	3 Months Ended
	Mar. 31, 2021
Fair Value Disclosures [Abstract]
Marketable Securities and Fair Value Measurements	Marketable Securities and Fair Value Measurements As of March 31, 2021, available for sale marketable securities by security type consisted of (in thousands): Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value U.S. treasury notes (due within one year) $ 94,463 $ 5 $ — $ 94,468 Total $ 94,463 $ 5 $ — $ 94,468 As of December 31, 2020, available for sale marketable securities by security type consisted of (in thousands): Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value U.S. treasury notes (due within one year) $ 92,982 $ — $ (7) $ 92,975 Total $ 92,982 $ — $ (7) $ 92,975 The following tables present the Company’s fair value hierarchy for its assets and liabilities, which are measured at fair value on a recurring basis (in thousands): Fair Value Measurements at March 31, 2021 Using: Level 1 Level 2 Level 3 Total Assets: Cash equivalents: Money market funds $ 66,423 $ — $ — $ 66,423 Marketable securities: U.S. treasury notes — 94,468 — 94,468 Total $ 66,423 $ 94,468 $ — $ 160,891 Fair Value Measurements at December 31, 2020 Using: Level 1 Level 2 Level 3 Total Assets: Cash equivalents: Money market funds $ 48,770 $ — $ — $ 48,770 U.S. treasury notes — 42,997 — 42,997 Marketable securities: U.S. treasury notes — 92,975 — 92,975 Total $ 48,770 $ 135,972 $ — $ 184,742 During the three months ended March 31, 2021 and 2020, there were no transfers between Level 1, Level 2 and Level 3.

Property and Equipment, Net

Property and Equipment, Net	3 Months Ended
	Mar. 31, 2021
Property, Plant and Equipment [Abstract]
Property and Equipment, Net	Property and Equipment, Net Property and equipment, net consisted of the following (in thousands): March 31, 2021 December 31, 2020 Laboratory equipment $ 3,998 $ 3,740 Furniture and fixtures 815 815 Computer equipment and software 100 100 Leasehold improvements 17,024 16,961 Financing lease right-of-use asset 384 — Assets not yet placed in service 47 15 22,368 21,631 Less: Accumulated depreciation and amortization (2,875) (2,103) 19,493 19,528 Depreciation and amortization expense, including amortization of financing lease right-of-use assets, was $0.8 million and $0.3 million for the three months ended March 31, 2021 and 2020, respectively.

Accrued Expenses

Accrued Expenses	3 Months Ended
	Mar. 31, 2021
Payables and Accruals [Abstract]
Accrued Expenses	Accrued Expenses Accrued expenses consisted of the following (in thousands): March 31, 2021 December 31, 2020 Accrued employee compensation and benefits $ 978 $ 3,513 Accrued tenant improvements 913 2,385 Accrued external research and development expenses 2,477 2,146 Accrued professional fees 620 979 Other 138 138 $ 5,126 $ 9,161

Notes Payable

Notes Payable	3 Months Ended
	Mar. 31, 2021
Debt Disclosure [Abstract]
Notes Payable	Notes Payable Long-term debt consisted of the following (in thousands): March 31, 2021 December 31, 2020 Principal amount of long-term debt $ 20,000 $ 20,000 Less: Current portion of long-term debt — — Long-term debt, net of current portion 20,000 20,000 Final payment fee 1,000 1,000 Debt discount, net of accretion (1,261) (1,346) Long-term debt, net of discount and current portion $ 19,739 $ 19,654 As of March 31, 2021, the Company had outstanding loans under its loan and security agreement of $20.0 million. On November 19, 2020, the Company entered into a loan and security agreement (the "Oxford Loan Agreement"), with Oxford Finance LLC, or Oxford, for an aggregate principal amount of $20.0 million (the "Oxford Term Loan A") and up to an additional $5.0 million (the "Oxford Term Loan B"). On November 19, 2020, the Company borrowed $20.0 million under the Oxford Term Loan A. The Term Loan bears interest at a floating per annum rate equal to the greater of (i) 8.0% and (ii) the sum of (a) thirty-day LIBOR rate plus (b) 7.84%. In addition, upon loan maturity or prepayment, the Company is required to make a final payment fee equal to 5.0% of the aggregate principal amount borrowed which is being amortized to interest expense over the term of the debt using the effective interest method. The Company is required to make monthly interest only payments under the Oxford Loan each month beginning on January 1, 2021. Beginning on December 1, 2023, the Company is required to make consecutive equal monthly payments of principal, together with applicable interest, in arrears, based upon a repayment schedule equal to 24 months, with a final maturity date of November 1, 2025 (the “Maturity Date”). At the Company’s option, the Company may elect to prepay the loans subject to a prepayment fee equal to the following percentage of the principal amount being prepaid: 2% if an advance is prepaid during the first 12 months following the applicable advance date, 1% if an advance is prepaid after 12 months but prior to 24 months following the applicable advance date, and 0.5% if an advance is prepaid any time after 24 months following the applicable advance date but prior to the Maturity Date. The Company's obligations under the Oxford Loan Agreement are secured by a security interest in all of its assets, other than its intellectual property. The Company is also subject to certain affirmative and negative covenants restricting the Company’s activities, including limitations on dispositions, mergers or acquisitions; encumbering its intellectual property; incurring indebtedness or liens; paying dividends; making certain investments; and engaging in certain other business transactions. The obligations under the Loan are subject to acceleration upon the occurrence of specified events of default, including a material adverse change in the Company’s business, operations or financial or other condition. Upon the occurrence of an event of default and until such event of default is no longer continuing, the annual interest rate will be 5.0% above the otherwise applicable rate. As of March 31, 2021 and December 31, 2020, the Company believes an event of default would be remote. In connection with the Oxford Loan Agreement, the Company granted warrants to purchase 18,445 shares of the Company’s common stock at $16.26 per share. The issued warrants are exercisable for 10 years. The Company valued the warrants using the Black-Scholes option pricing model and determined the fair value of the warrants to be $0.2 million. The Company determined the warrants met the criteria for equity classification, and, as such, the fair value of the warrants were recorded as additional paid-in capital and as a discount to the debt which is being amortized to interest expense over the term of the Oxford Loan of five years. In addition, the Company incurred debt issuance costs of $0.2 million. As of March 31, 2021, the interest rate applicable to outstanding borrowings under the Oxford Loan Agreement was 8.0%. During the three months ended March 31, 2021, the weighted average effective interest rate on outstanding borrowings was approximately 9.7%. As of March 31, 2021, future principal payments due are as follows (in thousands): Remainder of 2021 (nine months) $ — 2022 — 2023 833 2024 10,000 2025 $ 9,167 $ 20,000 As of March 31, 2020, the Company had outstanding loans under its amended loan and security agreement with Comerica Bank. In November 2020, the Company used a portion of the proceeds from its new loan and security agreement described above to repay the outstanding principal balances in full plus unpaid accrued interest and the final payment fee.

Common Stock and Net Loss Per S

Common Stock and Net Loss Per Share	3 Months Ended
	Mar. 31, 2021
Equity [Abstract]
Common Stock and Net Loss Per Share	Common Stock and Net Loss Per Share Common Stock Each share of common stock entitles the holder to one vote on all matters submitted to a vote of the Company’s stockholders. Common stockholders are not entitled to receive dividends, unless declared by the board of directors. Net Loss Per Share The following common stock equivalents presented based on amounts outstanding at each period end, have been excluded from the calculation of diluted net loss per share because including them would have had an anti-dilutive impact: March 31, 2021 2020 Stock options to purchase common stock 6,303,254 3,785,380 Warrants to purchase common stock 18,445 — Convertible preferred stock (as converted to common stock) — 15,467,863 Warrants to purchase convertible preferred stock — 14,076 Unvested restricted common stock — 668,920 6,321,699 19,936,239

Stock-Based Compensation

Stock-Based Compensation	3 Months Ended
	Mar. 31, 2021
Share-based Payment Arrangement [Abstract]
Stock-Based Compensation	Stock-Based Compensation 2016 Stock incentive plan The Company’s 2016 Stock Incentive Plan, (the “2016 Plan”) provided for the Company to grant incentive stock options or nonqualified stock options and other equity awards to employees, directors and consultants of the Company. Upon the effectiveness of the 2020 Equity Incentive Plan (the “2020 Plan”) in October 2020, the Company ceased granting additional awards under the 2016 Plan. 2020 Equity Incentive Plan On October 21, 2020, the Company’s board of directors adopted and its stockholders approved the 2020 Plan, which became effective on October 21, 2020. The 2020 Plan provides for the grant of incentive stock options, non-qualified options, stock appreciation rights, restricted stock awards, restricted stock units and other stock-based awards. The number of shares initially reserved for issuance under the 2020 Plan was (i) 2,200,000 shares (the “share pool”), plus (ii) the number of shares of common stock available for issuance under the 2016 Plan as of the effective date of the 2020 Plan, plus the number of shares of common stock underlying awards under the 2016 Plan that on or after the date of adoption expire or become unexercisable without delivery of shares, are forfeited to, or repurchased for cash, are settled in cash, or otherwise become available again for grant under the 2016 Plan, in each case, in accordance with its terms (up to an aggregate of 5,078,295 shares). As of March 31, 2021, 2,380,492 shares remained available for future grant under the 2020 Plan. The share pool will automatically increase on January 1 of each year from 2021 to 2030 by the lesser of (i) four percent of the number of shares of our common stock outstanding as of the close of business on the immediately preceding December 31 and (ii) the number of shares determined by the board of directors on or prior to such date for such year. The number of shares reserved for issuance under the 2020 Plan was increased by 1,471,576 shares effective January 1, 2021. The 2020 Plan is administered by the board of directors or, at the discretion of the board of directors, by a committee of the board of directors. The exercise prices, vesting and other restrictions are determined at the discretion of the board of directors, or its committee if so delegated. Stock options granted with service-based vesting conditions generally vest over four years and expire after ten years. The exercise price for stock options granted is not less than the fair value of common stock on the date of grant. The Company bases fair value of common stock on the quoted market price. Prior to the IPO, the board of directors determined the value the Company’s common stock, taking into consideration its most recently available valuation of common stock performed by third parties as well as additional relevant factors which may have changed since the date of the most recent contemporaneous valuation through the date of grant. 2020 Employee Stock Purchase Plan On October 21, 2020, the Company’s board of directors adopted and its stockholders approved the 2020 Employee Stock Purchase Plan (the “ESPP”), which became effective on October 21, 2020. The aggregate number of shares of common stock available for purchase pursuant to the exercise of options under the ESPP is 360,000 shares, plus an automatic annual increase, as of January 1 of each year from 2021 to 2030, equal to the lesser of one percent of the number of shares of common stock outstanding as of the close of business on the immediately preceding December 31 and (ii) the number of shares determined by the board of directors on or prior to such date for such year (up to a maximum of 3,220,520 shares). The number of shares reserved for issuance under the ESPP was increased by 367,894 shares effective January 1, 2021. As of March 31, 2021, no offering periods have commenced under the ESPP. Stock-based compensation Stock-based compensation expense was classified in the statements of operations and comprehensive loss as follows (in thousands): Three Months Ended March 31, 2021 2020 Research and development expenses $ 1,014 $ 327 General and administrative expenses 874 190 $ 1,888 $ 517 As of March 31, 2021, total unrecognized compensation cost related to unvested options was $26.3 million, which is expected to be recognized over a weighted average period of 3.3 years.

Collaboration Agreement

Collaboration Agreement	3 Months Ended
	Mar. 31, 2021
Collaboration Agreement [Abstract]
Collaboration Agreement	Collaboration Agreement In July 2020, the Company entered into a research collaboration and license agreement (the “Collaboration Agreement”) with Merck Sharp & Dohme Corp. (“Merck”). The Company and Merck will apply Foghorn’s proprietary Gene Traffic Control platform to discover and develop novel therapeutics. Under the Collaboration Agreement, the Company granted Merck exclusive global rights to develop, manufacture and commercialize drugs that target dysregulation of a single transcription factor. Under the terms of the Collaboration Agreement, the Company and Merck are each responsible to perform certain research activities in accordance with a mutually agreed upon research plan. Merck may substitute the selected transcription factor during certain stages of the research program, subject to certain limitations. Following completion of the research program, Merck is responsible for the development and commercialization of the compounds developed pursuant to the research program and any product containing such compounds. Pursuant to the Collaboration Agreement, the Company will also participate on a joint steering committee. Under the terms of the agreement, Foghorn received a nonrefundable upfront payment of $15.0 million from Merck and is eligible to receive up to $245.0 million upon achievement of specified research, development and regulatory milestones by any product candidate generated by the collaboration, and up to $165.0 million upon achievement of specified sales-based milestones per approved product from the collaboration, if any. The Company will be eligible to receive tiered royalties, calculated on a product-by-product and country-by-country basis, on net sales of approved products from the collaboration, if any, at royalty rates ranging from the mid single digits to low tens, depending on whether the products are covered by patent rights it licenses to Merck. Unless terminated earlier, the Collaboration Agreement will continue in full force and effect until one or more products has received marketing authorization and, thereafter, until expiration of all royalty obligations under the Collaboration Agreement. The Company or Merck may terminate the Collaboration Agreement upon an uncured material breach by the other party or insolvency of the other party. Merck may also terminate the Merck Collaboration Agreement for any reason upon certain notice to the Company. The Company determined that the (1) research, development, manufacture and commercialization licenses, (2) the research activities performed by the Company and (3) service on the joint committees represent a single performance obligation under the Collaboration Agreement. The Company determined that Merck cannot benefit from the licenses separately from the research activities and participation on the joint steering committee because these services are specialized and rely on the Company’s expertise such that these activities are highly interrelated and therefore not distinct. Accordingly, the promised goods and services represent one combined performance obligation, and the entire transaction price was allocated to that single combined performance obligation. The performance obligation will be satisfied over the research term as the Company performs the research activities and participates in a joint steering committee to oversee research activities. The upfront payment of $15.0 million was initially recorded as deferred revenue and is being recognized as revenue as the performance obligation is satisfied. The Company recognizes revenue using the cost-to-cost method, which it believes best depicts the transfer of control to the customer over time. Under the cost-to-cost method, the extent of progress towards completion is measured based on the ratio of actual costs incurred to the total estimated costs expected upon satisfying the identified performance obligation. Under this method, revenue is recorded as a percentage of the estimated transaction price based on the extent of progress towards completion. As of March 31, 2021, the potential research, development and regulatory milestone payments that the Company is eligible to receive were excluded from the transaction price as they were fully constrained by uncertain events. The Company will reevaluate the transaction price at the end of each reporting period and as uncertain events are resolved or other changes in circumstances occur, and if necessary, the Company will adjust its estimate of the transaction price. Any additions to the transaction price would be reflected in the period as a cumulative revenue catch-up based on the ratio of costs incurred to the total estimated costs expected applied to the revised transaction price. Sales-based royalties and milestone payments, which predominantly relate to the license, will be recognized if and when the related sales occur. As of March 31, 2021, the aggregate amount of the transaction price related to the unsatisfied portion of the performance obligation is $14.3 million, which is expected to be recognized as revenue through 2028. The Company does not expect collaboration revenue to be recognized evenly over this period as it will be recognized on a percentage of completion basis (using cost-to-cost method) as the Company performs the research activities and participates on the joint steering committee, which will likely vary from period to period. In estimating the total costs to satisfy its single performance obligation pursuant to the Collaboration Agreement, the Company is required to make significant estimates including an estimate of the number of transcription factor substitutions and the expected time and expected costs to fulfill the performance obligation. The cumulative effect of revisions to the total estimated costs to complete the Company’s single performance obligation will be recorded in the period in which the changes are identified, and amounts can be reasonably estimated. While such revisions will have no impact on the Company’s cash flows, a significant change in these assumptions and estimates could have a material impact on the timing and amount of revenue recognized in future periods. At inception, the Company assessed the Collaboration Agreement to determine whether a significant financing component exists and concluded that a significant financing component does not exist. For the three months ended March 31, 2021, the Company had recorded $0.3 million of revenue under the Collaboration Agreement, which was included in deferred revenue at the beginning of the period.

Leases

Leases	3 Months Ended
	Mar. 31, 2021
Leases [Abstract]
Leases	Leases In October 2019, the Company entered into a lease for 81,441 square feet of office and laboratory space in Cambridge, Massachusetts, commencing in January 2020 (the “New Lease”). The initial term of the New Lease was eight years with a five-year option to extend at fair-market rent at the time of the extension. The base rent payments escalate annually over the eight-year lease term and totaled approximately $60.3 million. In connection with the New Lease, the landlord agreed to fund up to $3.0 million in tenant improvements to the leased facility as well as up to an additional $16.3 million, which resulted in additional rent payments to the landlord over the lease term. During the three months ended March 31, 2021 and 2020, $1.5 million and $0.7 million, respectively, of leasehold improvements were reimbursed by the landlord, which resulted in an increase to operating lease liabilities. The Company will be obligated to pay its portion o f real estate taxes and costs related to the premises, including costs of operations and management of the leased premises. On January 1, 2020, the lease commencement date, the Company recorded an operating lease asset of $38.6 million and corresponding lease liability of $38.3 million. In June 2020, the Company amended the New Lease to defer payment of a portion of the base rent and operating expenses and to extend the lease term by nine months to September 2028. The amendment was accounted for as a lease modification and the right-of-use asset and lease liability were remeasured at the modification date of June 29, 2020 resulting in an increase of $7.4 million to both the right-of-use asset and lease liabilities. The Company had a lease for office and laboratory facilities in Cambridge, Massachusetts under a noncancellable operating lease that began in August 2017 and expired in March 2025. In April 2020, this lease was assigned and assumed by a related party which became effective in October 2020. The components of lease expense were as follows (in thousands): Three Months Ended March 31, 2021 2020 Operating lease cost $ 1,887 $ 1,258 Short-term lease cost — 27 Variable lease cost 763 236 $ 2,650 $ 1,521 Supplemental disclosure of cash flow information related to leases was as follows (in thousands): Three Months Ended March 31, 2021 2020 Cash paid for amounts included in the measurement of operating lease liabilities $ 2,371 $ 456 Operating lease liabilities arising from obtaining right-of-use assets $ — $ 38,306 Financing lease liabilities arising from obtaining right-of-use assets $ 330 $ — The weighted-average remaining lease term and discount rate as of period ends were as follows: March 31, 2021 December 31, 2020 Weighted-average remaining lease term - operating leases (in years) 7.4 7.7 Weighted-average discount rate - operating leases 5.35 % 5.35 % Future annual minimum lease payments under operating leases as of March 31, 2021 were as follows (in thousands): Remainder of 2021 (nine months) $ 7,391 2022 10,005 2023 10,115 2024 10,355 2025 10,603 Thereafter 30,521 Total future minimum lease payments 78,990 Less: imputed interest (14,261) Less: estimated lease incentives (2,398) Total operating lease liabilities $ 62,331 Included in the condensed consolidated balance sheet (in thousands): March 31, 2021 Current operating lease liabilities $ 5,783 Operating lease liabilities, net of current portion 56,548 Total operating lease liabilities $ 62,331 Sublease agreement In April 2020, the Company entered into a two-year sublease agreement to sublet approximately 16,843 square feet of office space under the New Lease, as amended, which began in July 2020. In February 2021, the Company entered into an amendment to the sublease to sublet approximately 2,980 square feet of additional office space to the sublessee for the remaining lease term. As of March 31, 2021, the remaining rent payments due to the Company under the amended sublease were $2.6 million. During the three months ended March 31, 2021, the Company recorded other income of $0.6 million related to this sublease. Financing lease I n October 2020, the Company entered into an equipment lease with a three-year term and an optional purchase option. The Company analyzed the terms of the lease and, due to the likelihood of the Company exercising a purchase option at the end of
Leases	Leases In October 2019, the Company entered into a lease for 81,441 square feet of office and laboratory space in Cambridge, Massachusetts, commencing in January 2020 (the “New Lease”). The initial term of the New Lease was eight years with a five-year option to extend at fair-market rent at the time of the extension. The base rent payments escalate annually over the eight-year lease term and totaled approximately $60.3 million. In connection with the New Lease, the landlord agreed to fund up to $3.0 million in tenant improvements to the leased facility as well as up to an additional $16.3 million, which resulted in additional rent payments to the landlord over the lease term. During the three months ended March 31, 2021 and 2020, $1.5 million and $0.7 million, respectively, of leasehold improvements were reimbursed by the landlord, which resulted in an increase to operating lease liabilities. The Company will be obligated to pay its portion o f real estate taxes and costs related to the premises, including costs of operations and management of the leased premises. On January 1, 2020, the lease commencement date, the Company recorded an operating lease asset of $38.6 million and corresponding lease liability of $38.3 million. In June 2020, the Company amended the New Lease to defer payment of a portion of the base rent and operating expenses and to extend the lease term by nine months to September 2028. The amendment was accounted for as a lease modification and the right-of-use asset and lease liability were remeasured at the modification date of June 29, 2020 resulting in an increase of $7.4 million to both the right-of-use asset and lease liabilities. The Company had a lease for office and laboratory facilities in Cambridge, Massachusetts under a noncancellable operating lease that began in August 2017 and expired in March 2025. In April 2020, this lease was assigned and assumed by a related party which became effective in October 2020. The components of lease expense were as follows (in thousands): Three Months Ended March 31, 2021 2020 Operating lease cost $ 1,887 $ 1,258 Short-term lease cost — 27 Variable lease cost 763 236 $ 2,650 $ 1,521 Supplemental disclosure of cash flow information related to leases was as follows (in thousands): Three Months Ended March 31, 2021 2020 Cash paid for amounts included in the measurement of operating lease liabilities $ 2,371 $ 456 Operating lease liabilities arising from obtaining right-of-use assets $ — $ 38,306 Financing lease liabilities arising from obtaining right-of-use assets $ 330 $ — The weighted-average remaining lease term and discount rate as of period ends were as follows: March 31, 2021 December 31, 2020 Weighted-average remaining lease term - operating leases (in years) 7.4 7.7 Weighted-average discount rate - operating leases 5.35 % 5.35 % Future annual minimum lease payments under operating leases as of March 31, 2021 were as follows (in thousands): Remainder of 2021 (nine months) $ 7,391 2022 10,005 2023 10,115 2024 10,355 2025 10,603 Thereafter 30,521 Total future minimum lease payments 78,990 Less: imputed interest (14,261) Less: estimated lease incentives (2,398) Total operating lease liabilities $ 62,331 Included in the condensed consolidated balance sheet (in thousands): March 31, 2021 Current operating lease liabilities $ 5,783 Operating lease liabilities, net of current portion 56,548 Total operating lease liabilities $ 62,331 Sublease agreement In April 2020, the Company entered into a two-year sublease agreement to sublet approximately 16,843 square feet of office space under the New Lease, as amended, which began in July 2020. In February 2021, the Company entered into an amendment to the sublease to sublet approximately 2,980 square feet of additional office space to the sublessee for the remaining lease term. As of March 31, 2021, the remaining rent payments due to the Company under the amended sublease were $2.6 million. During the three months ended March 31, 2021, the Company recorded other income of $0.6 million related to this sublease. Financing lease I n October 2020, the Company entered into an equipment lease with a three-year term and an optional purchase option. The Company analyzed the terms of the lease and, due to the likelihood of the Company exercising a purchase option at the end of

Commitments and Contingencies

Commitments and Contingencies	3 Months Ended
	Mar. 31, 2021
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies Leases The Company’s commitments under its leases are described in Note 10. License agreements The Company has entered into various exclusive and non-exclusive license agreements for certain technologies. Under the terms of these license agreements, the Company could be required to reimburse the licensors for patent expenses and remit amounts in the low single-digit as sales-based royalties upon the occurrence of specific events as outlined in the corresponding license agreements. The Company is also required to make annual license maintenance fees of less than $0.1 million and pay up to $1.1 million in regulatory milestones on each licensed product upon the occurrence of specific events as outlined in one of the license agreements. None of our product candidates utilize technologies covered by these licenses. Indemnification agreements In the ordinary course of business, the Company may provide indemnification of varying scope and terms to vendors, lessors, contract research organizations, business partners and other parties with respect to certain matters including, but not limited to, losses arising out of breach of such agreements or from intellectual property infringement claims made by third parties. In addition, the Company has entered into indemnification agreements with members of its board of directors and its executive officers that will require the Company, among other things, to indemnify them against certain liabilities that may arise by reason of their status or service as directors or officers. The maximum potential amount of future payments the Company could be required to make under these indemnification agreements is, in many cases, unlimited. The Company has not incurred any material costs as a result of such indemnifications and is not currently aware of any indemnification claims. Legal Proceedings From time to time, the Company may become involved in litigation or other legal proceedings. The Company is not currently a party to any material litigation or legal proceedings.

Defined Contribution Plan

Defined Contribution Plan	3 Months Ended
	Mar. 31, 2021
Retirement Benefits [Abstract]
Defined Contribution Plan	Defined Contribution PlanThe Company has a 401(k) defined contribution plan (the “401(k) Plan”) for its employees. Eligible employees may make pretax contributions to the 401(k) Plan up to statutory limits. There was no discretionary match made under the 401(k) Plan as of March 31, 2021.

Related Parties

Related Parties	3 Months Ended
	Mar. 31, 2021
Related Party Transactions [Abstract]
Related Parties	Related Parties In October 2015, the Company entered into a five-year service agreement with Flagship Pioneering (“Flagship”), an affiliate of one of its stockholders, Flagship Venture Funds, to provide general and administrative services to the Company, including certain consulting services and the provision of employee health and dental benefit plans for the Company’s employees. The Company made no cash payments to Flagship for services received under this during the three months ended March 31, 2021. The Company made cash payments to Flagship for services received under this agreement of $0.2 million during the three months ended March 31, 2020. As of March 31, 2021 and December 31, 2020, the Company had no accounts payable to Flagship. This agreement expired in 2020. In October 2015, the Company entered into a five-year consulting agreement with a scientific founder of the Company who is also a board member and a shareholder. In October 2020, this agreement was extended to January 1, 2022, with an option to renew. During the three months ended March 31, 2021 and 2020, the Company paid the scientific founder $0.1 million. As of March 31, 2021 and December 31, 2020, the Company had de minimis accounts payable to this scientific founder.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2021
Accounting Policies [Abstract]
Basis of presentation	Basis of presentation The Company’s condensed consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”) and pursuant to the rules and regulations of the Securities and Exchange Commission for interim financial statements. Certain information and footnote disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to such rules and regulations. The accompanying condensed consolidated financial statements include the accounts of the Company and its wholly-owned subsidiary. All intercompany accounts and transactions have been eliminated in consolidation. Any reference in these notes to applicable guidance is meant to refer to the authoritative GAAP as found in the Accounting Standards Codification (“ASC”) and Accounting Standards Update (“ASU”) of the Financial Accounting Standards Board (“FASB”).
Leases	Leases In accordance with ASC 842, Leases, the Company accounts for a contract as a lease when it has the right to control the asset for a period of time while obtaining substantially all of the asset’s economic benefits. The Company determines if an arrangement is a lease or contains an embedded lease at inception. For arrangements that meet the definition of a lease, the Company determines the initial classification and measurement of its right-of-use asset and lease liability at the lease commencement date and thereafter if modified. The lease term includes any renew al or purchase options that the Company is reasonably assured to exercise. The present value of lease payments is determined by using the interest rate implicit in the lease, if that rate is readily determinable; otherwise, the Company uses its estimated secured incremental borrowing rate for that lease term. The Company’s policy is to not record leases with an original term of twelve months or less on its consolidated balance sheets and recognizes those lease payments in the income statement on a straight-line basis over the lease term. The Company’s existing leases are for office and laboratory space and equipment leases. In addition to rent, the leases may require the Company to pay additional costs, such as utilities, maintenance and other operating costs, which are generally referred to as non-lease components. The Company has elected to not separate lease and non-lease components. Only the fixed costs for lease components and their associated non-lease components are accounted for as a single lease component and recognized as part of a right-of-use asset and liability. Rent expense for operating leases is recognized on a straight-line basis over the reasonably assured lease term based on the total lease payments and is included in operating expenses in the condensed consolidated statements of operations and comprehensive loss.
Recently issued accounting pronouncements	Recently issued accounting pronouncements From time to time, new accounting pronouncements are issued by the FASB or other standard setting bodies that the Company adopts as of the specified effective date. The Company qualifies as an “emerging growth company” as defined in the Jumpstart Our Business Startups Act of 2012 and has elected not to “opt out” of the extended transition related to complying with new or

Marketable Securities and Fai_2

Marketable Securities and Fair Value Measurements (Tables)	3 Months Ended
	Mar. 31, 2021
Fair Value Disclosures [Abstract]
Summary of Available for Sale Marketable Securities By Security Type	As of March 31, 2021, available for sale marketable securities by security type consisted of (in thousands): Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value U.S. treasury notes (due within one year) $ 94,463 $ 5 $ — $ 94,468 Total $ 94,463 $ 5 $ — $ 94,468 As of December 31, 2020, available for sale marketable securities by security type consisted of (in thousands): Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value U.S. treasury notes (due within one year) $ 92,982 $ — $ (7) $ 92,975 Total $ 92,982 $ — $ (7) $ 92,975
Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis	The following tables present the Company’s fair value hierarchy for its assets and liabilities, which are measured at fair value on a recurring basis (in thousands): Fair Value Measurements at March 31, 2021 Using: Level 1 Level 2 Level 3 Total Assets: Cash equivalents: Money market funds $ 66,423 $ — $ — $ 66,423 Marketable securities: U.S. treasury notes — 94,468 — 94,468 Total $ 66,423 $ 94,468 $ — $ 160,891 Fair Value Measurements at December 31, 2020 Using: Level 1 Level 2 Level 3 Total Assets: Cash equivalents: Money market funds $ 48,770 $ — $ — $ 48,770 U.S. treasury notes — 42,997 — 42,997 Marketable securities: U.S. treasury notes — 92,975 — 92,975 Total $ 48,770 $ 135,972 $ — $ 184,742

Property and Equipment, Net (Ta

Property and Equipment, Net (Tables)	3 Months Ended
	Mar. 31, 2021
Property, Plant and Equipment [Abstract]
Summary of Property and Equipment Net	Property and equipment, net consisted of the following (in thousands): March 31, 2021 December 31, 2020 Laboratory equipment $ 3,998 $ 3,740 Furniture and fixtures 815 815 Computer equipment and software 100 100 Leasehold improvements 17,024 16,961 Financing lease right-of-use asset 384 — Assets not yet placed in service 47 15 22,368 21,631 Less: Accumulated depreciation and amortization (2,875) (2,103) 19,493 19,528

Accrued Expenses (Tables)

Accrued Expenses (Tables)	3 Months Ended
	Mar. 31, 2021
Payables and Accruals [Abstract]
Accrued Expenses	Accrued expenses consisted of the following (in thousands): March 31, 2021 December 31, 2020 Accrued employee compensation and benefits $ 978 $ 3,513 Accrued tenant improvements 913 2,385 Accrued external research and development expenses 2,477 2,146 Accrued professional fees 620 979 Other 138 138 $ 5,126 $ 9,161

Notes Payable (Tables)

Notes Payable (Tables)	3 Months Ended
	Mar. 31, 2021
Debt Disclosure [Abstract]
Summary of Long Term Debt	Long-term debt consisted of the following (in thousands): March 31, 2021 December 31, 2020 Principal amount of long-term debt $ 20,000 $ 20,000 Less: Current portion of long-term debt — — Long-term debt, net of current portion 20,000 20,000 Final payment fee 1,000 1,000 Debt discount, net of accretion (1,261) (1,346) Long-term debt, net of discount and current portion $ 19,739 $ 19,654
Summary of Future Long Term Loan Principal Payments Due	As of March 31, 2021, future principal payments due are as follows (in thousands): Remainder of 2021 (nine months) $ — 2022 — 2023 833 2024 10,000 2025 $ 9,167 $ 20,000

Common Stock and Net Loss Per_2

Common Stock and Net Loss Per Share (Tables)	3 Months Ended
	Mar. 31, 2021
Equity [Abstract]
Summary of Earnings Per Share Diluted Anti Dilutive Impact	The following common stock equivalents presented based on amounts outstanding at each period end, have been excluded from the calculation of diluted net loss per share because including them would have had an anti-dilutive impact: March 31, 2021 2020 Stock options to purchase common stock 6,303,254 3,785,380 Warrants to purchase common stock 18,445 — Convertible preferred stock (as converted to common stock) — 15,467,863 Warrants to purchase convertible preferred stock — 14,076 Unvested restricted common stock — 668,920 6,321,699 19,936,239

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	3 Months Ended
	Mar. 31, 2021
Share-based Payment Arrangement [Abstract]
Summary of Stock-Based Compensation Expense	Stock-based compensation expense was classified in the statements of operations and comprehensive loss as follows (in thousands): Three Months Ended March 31, 2021 2020 Research and development expenses $ 1,014 $ 327 General and administrative expenses 874 190 $ 1,888 $ 517

Leases (Tables)

Leases (Tables)	3 Months Ended
	Mar. 31, 2021
Leases [Abstract]
Summary of Lease Cost	The components of lease expense were as follows (in thousands): Three Months Ended March 31, 2021 2020 Operating lease cost $ 1,887 $ 1,258 Short-term lease cost — 27 Variable lease cost 763 236 $ 2,650 $ 1,521
Summary of Supplemental Cash Flow Information Related to Leases	Supplemental disclosure of cash flow information related to leases was as follows (in thousands): Three Months Ended March 31, 2021 2020 Cash paid for amounts included in the measurement of operating lease liabilities $ 2,371 $ 456 Operating lease liabilities arising from obtaining right-of-use assets $ — $ 38,306 Financing lease liabilities arising from obtaining right-of-use assets $ 330 $ — The weighted-average remaining lease term and discount rate as of period ends were as follows: March 31, 2021 December 31, 2020 Weighted-average remaining lease term - operating leases (in years) 7.4 7.7 Weighted-average discount rate - operating leases 5.35 % 5.35 %
Summary of Minimum Lease Payments	Future annual minimum lease payments under operating leases as of March 31, 2021 were as follows (in thousands): Remainder of 2021 (nine months) $ 7,391 2022 10,005 2023 10,115 2024 10,355 2025 10,603 Thereafter 30,521 Total future minimum lease payments 78,990 Less: imputed interest (14,261) Less: estimated lease incentives (2,398) Total operating lease liabilities $ 62,331 Included in the condensed consolidated balance sheet (in thousands): March 31, 2021 Current operating lease liabilities $ 5,783 Operating lease liabilities, net of current portion 56,548 Total operating lease liabilities $ 62,331
Summary of Operating Lease Liabilities	Future annual minimum lease payments under operating leases as of March 31, 2021 were as follows (in thousands): Remainder of 2021 (nine months) $ 7,391 2022 10,005 2023 10,115 2024 10,355 2025 10,603 Thereafter 30,521 Total future minimum lease payments 78,990 Less: imputed interest (14,261) Less: estimated lease incentives (2,398) Total operating lease liabilities $ 62,331 Included in the condensed consolidated balance sheet (in thousands): March 31, 2021 Current operating lease liabilities $ 5,783 Operating lease liabilities, net of current portion 56,548 Total operating lease liabilities $ 62,331

Nature of Business and Basis _2

Nature of Business and Basis of Presentation (Details) - USD ($) $ / shares in Units, $ in Thousands	Nov. 19, 2020	Oct. 27, 2020	Jul. 31, 2020	Mar. 31, 2021	Dec. 31, 2020
Organization Consolidation And Presentation Of Financial Statements
Upfront payment received from Merck			$ 15,000	$ 15,000
Accumulated deficit				$ (185,922)	$ (162,936)
IPO
Organization Consolidation And Presentation Of Financial Statements
Stock issued during the period shares new issues shares (in shares)		7,500,000
Sale of stock issue price per share (in dollars per share)		$ 16
Sale of stock consideration received on the transaction		$ 108,000
Over-Allotment Option
Organization Consolidation And Presentation Of Financial Statements
Stock issued during the period shares new issues shares (in shares)	951,837
Sale of stock issue price per share (in dollars per share)	$ 16
Sale of stock consideration received on the transaction	$ 14,200

Marketable Securities and Fai_3

Marketable Securities and Fair Value Measurements - Summary of Available for Sale Marketable Securities By Security Type (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Amortized Cost	$ 94,463	$ 92,982
Gross Unrealized Gains	5	0
Gross Unrealized Losses	0	(7)
Estimated Fair Value	94,468	92,975
U.S. treasury notes (due within one year)
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Amortized Cost	94,463	92,982
Gross Unrealized Gains	5	0
Gross Unrealized Losses	0	(7)
Estimated Fair Value	$ 94,468	$ 92,975

Marketable Securities and Fai_4

Marketable Securities and Fair Value Measurements - Summary of Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Marketable securities	$ 94,468	$ 92,975
Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Total	160,891	184,742
Recurring | U.S. treasury notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Marketable securities	94,468	92,975
Recurring | Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Cash equivalents	66,423	48,770
Recurring | U.S. treasury notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Cash equivalents		42,997
Recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Total	66,423	48,770
Recurring | Level 1 | U.S. treasury notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Marketable securities	0	0
Recurring | Level 1 | Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Cash equivalents	66,423	48,770
Recurring | Level 1 | U.S. treasury notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Cash equivalents		0
Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Total	94,468	135,972
Recurring | Level 2 | U.S. treasury notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Marketable securities	94,468	92,975
Recurring | Level 2 | Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Cash equivalents	0	0
Recurring | Level 2 | U.S. treasury notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Cash equivalents		42,997
Recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Total	0	0
Recurring | Level 3 | U.S. treasury notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Marketable securities	0	0
Recurring | Level 3 | Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Cash equivalents	$ 0	0
Recurring | Level 3 | U.S. treasury notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Cash equivalents		$ 0

Property and Equipment, Net - S

Property and Equipment, Net - Summary of Property and Equipment Net (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Property, Plant, and Equipment and Finance Lease Right-of-Use Asset, after Accumulated Depreciation and Amortization
Financing lease right-of-use asset	$ 384	$ 0
Property plant and equipment including finance right of use assets, gross	22,368	21,631
Less: Accumulated depreciation and amortization	(2,875)	(2,103)
Property and equipment, net	19,493	19,528
Laboratory equipment
Property, Plant, and Equipment and Finance Lease Right-of-Use Asset, after Accumulated Depreciation and Amortization
Property, Plant and Equipment, Gross	3,998	3,740
Furniture and fixtures
Property, Plant, and Equipment and Finance Lease Right-of-Use Asset, after Accumulated Depreciation and Amortization
Property, Plant and Equipment, Gross	815	815
Computer equipment and software
Property, Plant, and Equipment and Finance Lease Right-of-Use Asset, after Accumulated Depreciation and Amortization
Property, Plant and Equipment, Gross	100	100
Leasehold improvements
Property, Plant, and Equipment and Finance Lease Right-of-Use Asset, after Accumulated Depreciation and Amortization
Property, Plant and Equipment, Gross	17,024	16,961
Assets not yet placed in service
Property, Plant, and Equipment and Finance Lease Right-of-Use Asset, after Accumulated Depreciation and Amortization
Property, Plant and Equipment, Gross	$ 47	$ 15

Property and Equipment, Net - A

Property and Equipment, Net - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Property, Plant and Equipment [Abstract]
Depreciation and amortization expense	$ 772	$ 255

Accrued Expenses (Details)

Accrued Expenses (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Payables and Accruals [Abstract]
Accrued employee compensation and benefits	$ 978	$ 3,513
Accrued tenant improvements	913	2,385
Accrued external research and development expenses	2,477	2,146
Accrued professional fees	620	979
Other	138	138
Accrued Liabilities, Current, Total	$ 5,126	$ 9,161

Notes Payable - Summary of Long

Notes Payable - Summary of Long Term Debt (Details) - USD ($)	Mar. 31, 2021	Dec. 31, 2020
Debt Disclosure [Abstract]
Principal amount of long-term debt	$ 20,000,000	$ 20,000,000
Less: Current portion of long-term debt	0	0
Long-term debt, net of current portion	20,000,000	20,000,000
Final payment fee	1,000,000	1,000,000
Debt discount, net of accretion	(1,261,000)	(1,346,000)
Long-term debt, net of discount and current portion	$ 19,739,000	$ 19,654,000

Notes Payable - Additional Info

Notes Payable - Additional Information (Details) - USD ($)	Nov. 19, 2020	Mar. 31, 2021	Dec. 31, 2020
Short-term Debt
Principal borrowing amount		$ 20,000,000	$ 20,000,000
Oxford Finance LLC
Short-term Debt
Debt instrument, interest rate, stated percentage	8.00%	8.00%
Debt, final payment fee percentage	5.00%	5.00%
Class of warrant or right, number of securities called by warrants or rights (shares)		18,445
Warrants issue price ( per share)		$ 16.26
Warrants exercisable term		10 years
Warrant fair value	$ 200,000
Debt instrument, term		5 years
Payment of notes payable issuance costs		$ 200,000
Debt, weighted average interest rate		9.70%
Oxford Finance LLC | Period One
Short-term Debt
Prepayment fee (percent)		2.00%
Oxford Finance LLC | Period One | Maximum
Short-term Debt
Prepayment period (months)		12 months
Oxford Finance LLC | Period Two
Short-term Debt
Prepayment fee (percent)		1.00%
Oxford Finance LLC | Period Two | Minimum
Short-term Debt
Prepayment period (months)		12 months
Oxford Finance LLC | Period Two | Maximum
Short-term Debt
Prepayment period (months)		24 months
Oxford Finance LLC | Period Three
Short-term Debt
Prepayment fee (percent)		0.50%
Oxford Finance LLC | Period Three | Minimum
Short-term Debt
Prepayment period (months)		24 months
Oxford Finance LLC | LIBOR
Short-term Debt
Debt instrument, basis spread on variable rate	7.84%
Term Loan A
Short-term Debt
Principal borrowing amount		$ 20,000,000
Term Loan B | Oxford Finance LLC
Short-term Debt
Additional borrowing capacity	$ 5,000,000

Notes Payable - Summary of Futu

Notes Payable - Summary of Future Principal Payments Due (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Long-term Debt, Fiscal Year Maturity
Remainder of 2021 (nine months)	$ 0
2022	0
2023	833
2024	10,000
2025	9,167
Long-term debt, net of current portion	$ 20,000	$ 20,000

Common Stock and Net Loss Per_3

Common Stock and Net Loss Per Share - Earnings Per Share Diluted Anti Dilutive Impact (Details)	3 Months Ended
	Mar. 31, 2021voteshares	Mar. 31, 2020shares
Antidilutive Securities Excluded from Computation of Earnings Per Share
Anti-dilutive shares excluded from the calculation of earnings per share (shares)	6,321,699	19,936,239
Voting rights per share (per share) | vote	1
Stock options to purchase common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share
Anti-dilutive shares excluded from the calculation of earnings per share (shares)	6,303,254	3,785,380
Warrants to purchase common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share
Anti-dilutive shares excluded from the calculation of earnings per share (shares)	18,445	0
Convertible preferred stock (as converted to common stock)
Antidilutive Securities Excluded from Computation of Earnings Per Share
Anti-dilutive shares excluded from the calculation of earnings per share (shares)	0	15,467,863
Warrants to purchase convertible preferred stock (as converted to common stock)
Antidilutive Securities Excluded from Computation of Earnings Per Share
Anti-dilutive shares excluded from the calculation of earnings per share (shares)	0	14,076
Unvested restricted common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share
Anti-dilutive shares excluded from the calculation of earnings per share (shares)	0	668,920

Stock-Based Compensation - Addi

Stock-Based Compensation - Additional Information (Details) - USD ($) $ in Millions	Jan. 01, 2021	Mar. 31, 2021	Oct. 21, 2020
Share-based Payment Arrangement
Unrecognized compensation costs related to unvested options and unvested restricted stock		$ 26.3
Weighted average period of unrecognized compensation costs		3 years 3 months 18 days
2020 Equity Incentive Plan
Share-based Payment Arrangement
Number of shares authorized		5,078,295	2,200,000
Common stock shares available for grant		2,380,492
Annual share percentage increase (percent)			4.00%
Number of additional shares authorized	1,471,576
Award vesting period		4 years
Expiration period		10 years
2020 Employee Stock Purchase Plan
Share-based Payment Arrangement
Number of shares authorized		3,220,520	360,000
Annual share percentage increase (percent)			1.00%
Number of additional shares authorized	367,894

Stock-Based Compensation - Summ

Stock-Based Compensation - Summary of Stock-based compensation expense (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Share-based Payment Arrangement
Stock-based compensation expense	$ 1,888	$ 517
Research and development expenses
Share-based Payment Arrangement
Stock-based compensation expense	1,014	327
General and administrative expenses
Share-based Payment Arrangement
Stock-based compensation expense	$ 874	$ 190

Collaboration Agreement - Addit

Collaboration Agreement - Additional Information (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended
	Jul. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Collaborative Arrangement and Arrangement Other than Collaborative
Upfront payment received from Merck	$ 15,000	$ 15,000
Deferred revenue		15,000
Unsatisfied portion of the performance obligation		14,300
Revenue		286	$ 0
Maximum | Sales based
Collaborative Arrangement and Arrangement Other than Collaborative
Amount receivable for achievement of milestones		165,000
Research Development And Regulatory | Maximum
Collaborative Arrangement and Arrangement Other than Collaborative
Amount receivable for achievement of milestones		245,000
Merck Collaboration Agreement
Collaborative Arrangement and Arrangement Other than Collaborative
Revenue		$ 300

Leases - Additional Information

Leases - Additional Information (Details) $ in Thousands	3 Months Ended		96 Months Ended
	Mar. 31, 2021USD ($)	Mar. 31, 2020USD ($)	Dec. 31, 2027USD ($)	Feb. 28, 2021ft²	Dec. 31, 2020USD ($)	Jun. 29, 2020USD ($)	Apr. 30, 2020ft²	Jan. 01, 2020USD ($)	Oct. 31, 2019USD ($)ft²
Lessee, Lease, Description
Operating lease right-of-use assets	$ 41,742				$ 42,804
Operating lease liability	62,331
Future sublease income outstanding	2,600
Sublease income recorded as other income	$ 600
Finance lease contract term (years)	3 years
Financing lease right-of-use asset	$ 400
Finance lease liability	300
Office and Laboratory Space In Cambridge, Massachusetts
Lessee, Lease, Description
Area of leased property | ft²									81,441
Operating lease term (years)									8 years
Operating lease term extension (years)									5 years
Reimbursements from lessor	$ 1,500	$ 700
Operating lease right-of-use assets								$ 38,600
Operating lease liability								$ 38,300
Office Space In Cambridge, Massachusetts
Lessee, Lease, Description
Area of leased property | ft²							16,843
Term of property subleased under operating lease							2 years
Additional Office Space In Cambridge, Massachusetts
Lessee, Lease, Description
Area of leased property | ft²				2,980
Maximum | Office and Laboratory Space In Cambridge, Massachusetts
Lessee, Lease, Description
Leasehold improvements landlord allowance									$ 3,000
Leasehold improvements landlord allowance to be repaid									$ 16,300
Forecast | Office and Laboratory Space In Cambridge, Massachusetts
Lessee, Lease, Description
Operating lease rent payments			$ 60,300
Adjustments | Office and Laboratory Space In Cambridge, Massachusetts
Lessee, Lease, Description
Operating lease right-of-use assets						$ 7,400
Operating lease liability						$ 7,400

Leases - Summary of Lease Cost

Leases - Summary of Lease Cost (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Leases [Abstract]
Operating lease cost	$ 1,887	$ 1,258
Short-term lease cost	0	27
Variable lease cost	763	236
Total	$ 2,650	$ 1,521

Leases - Summary of Supplementa

Leases - Summary of Supplemental Cash Flow Information Related to Leases (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Leases [Abstract]
Cash paid for amounts included in the measurement of operating lease liabilities	$ 2,371	$ 456
Operating lease liabilities arising from obtaining right-of-use assets	0	38,306
Financing lease liabilities arising from obtaining right-of-use assets	$ 330	$ 0

Leases - Summary of Weighted-Av

Leases - Summary of Weighted-Average Remaining Lease Term and Discount Rate Leases (Details)	Mar. 31, 2021	Dec. 31, 2020
Leases [Abstract]
Weighted-average remaining lease term - operating leases (in years)	7 years 4 months 24 days	7 years 8 months 12 days
Weighted-average discount rate - operating leases	5.35%	5.35%

Leases - Summary of Minimum Lea

Leases - Summary of Minimum Lease Payment (Details) $ in Thousands	Mar. 31, 2021USD ($)
Leases [Abstract]
Remainder of 2021 (nine months)	$ 7,391
2022	10,005
2023	10,115
2024	10,355
2025	10,603
Thereafter	30,521
Total future minimum lease payments	78,990
Less: imputed interest	(14,261)
Less: estimated lease incentives	(2,398)
Total operating lease liabilities	$ 62,331

Leases - Summary of Operating L

Leases - Summary of Operating Lease Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Leases [Abstract]
Current operating lease liabilities	$ 5,783	$ 3,981
Operating lease liabilities, net of current portion	56,548	$ 58,361
Total operating lease liabilities	$ 62,331

Commitments and Contingencies (

Commitments and Contingencies (Details) - Stanford - Maximum $ in Millions	3 Months Ended
	Mar. 31, 2021USD ($)
Commitments And Contingencies
Annual license maintenance fees	$ 0.1
Milestones payable upon event	$ 1.1

Related Parties (Details)

Related Parties (Details) - USD ($)	1 Months Ended	3 Months Ended
	Oct. 31, 2015	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Related Party Transaction
Accounts payable		$ 2,911,000		$ 3,680,000
Flagship Pioneering
Related Party Transaction
Service agreement term	5 years
Payments made to related party under service agreement		0	$ 200,000
Accounts payable		0		$ 0
Scientific Founder
Related Party Transaction
Service agreement term	5 years
Payments made to related party under service agreement		$ 100,000	$ 100,000