Stoke Therapeutics (STOK) 10-K 9 Mar 21 2020 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Mar. 01, 2021	Jun. 30, 2020
Cover [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Entity Registrant Name	Stoke Therapeutics, Inc.
Entity Central Index Key	0001623526
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Interactive Data Current	Yes
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Well Known Seasoned Issuer	No
Entity Public Float			$ 385
Entity Common Stock, Shares Outstanding		36,664,429
Entity Shell Company	false
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity File Number	001-38938
Entity Incorporation State Country Code	DE
Entity Tax Identification Number	47-1144582
Entity Address, Address Line One	45 Wiggins Ave
Entity Address City Or Town	Bedford
Entity Address State Or Province	MA
Entity Address Postal Zip Code	01730
City Area Code	781
Local Phone Number	430-8200
Document Annual Report	true
Document Transition Report	false
ICFR Auditor Attestation Flag	false
Title of 12(b) Security	Common Stock, $0.0001 par value per share
Trading Symbol	STOK
Security Exchange Name	NASDAQ
Documents Incorporated by Reference	Portions of the registrant’s Definitive Proxy Statement relating to the 2021 Annual Meeting of Shareholders, scheduled to be held on June 8, 2021, are incorporated by reference into Part III of this Annual Report on Form 10-K to the extent stated herein. The Definitive Proxy Statement will be filed within 120 days of the Registrant’s fiscal year ended December 31, 2020. Except with respect to information specifically incorporated by reference in this Form 10-K, the Proxy Statement is not deemed to be filed as part of this Form 10-K.

Consolidated balance sheets

Consolidated balance sheets - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 287,308	$ 222,471
Prepaid expenses and other current assets	6,435	3,281
Deferred financing costs	181
Interest receivable	6	281
Total current assets	293,930	226,033
Restricted cash	205	205
Operating lease right-of-use assets	1,115
Property and equipment, net	2,675	2,512
Total assets	297,925	228,750
Current liabilities:
Accounts payable	1,495	751
Accrued and other current liabilities	9,930	3,350
Total current liabilities	11,425	4,101
Long term liabilities	422	221
Total liabilities	11,847	4,322
Commitments and contingencies (Note 6)
Stockholders’ equity
Common stock, par value of $0.0001 per share; 300,000,000 shares authorized, 36,577,149 and 32,861,842 shares issued and outstanding as of December 31, 2020 and 2019, respectively	4	3
Additional paid-in capital	396,352	282,460
Accumulated deficit	(110,278)	(58,035)
Total stockholders’ equity	286,078	224,428
Total liabilities and stockholders’ equity	$ 297,925	$ 228,750

Consolidated balance sheets (Pa

Consolidated balance sheets (Parenthetical) - $ / shares	Dec. 31, 2020	Dec. 31, 2019
Statement Of Financial Position [Abstract]
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	300,000,000	300,000,000
Common stock, shares issued	36,577,149	32,861,842
Common stock, shares outstanding	36,577,149	32,861,842

Consolidated statements of oper

Consolidated statements of operations and comprehensive loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Operating expenses:
Research and development	$ 32,197	$ 23,764
General and administrative	20,847	11,914
Total operating expenses	53,044	35,678
Loss from operations	(53,044)	(35,678)
Other income (expense):
Interest income	744	3,351
Other income, net	57	2
Total other income (expense)	801	3,353
Net loss and comprehensive loss	$ (52,243)	$ (32,325)
Net loss per share—basic and diluted	$ (1.56)	$ (1.80)
Weighted average common shares outstanding—basic and diluted	33,488,456	17,971,443

Consolidated statements of stoc

Consolidated statements of stockholders' equity - USD ($) $ in Thousands	Total	Initial Public Offering	Follow-on Offering	Convertible Preferred Stock	Common Stock	Common StockInitial Public Offering	Common StockFollow-on Offering	Additional Paid-in Capital	Additional Paid-in CapitalInitial Public Offering	Additional Paid-in CapitalFollow-on Offering	Accumulated Deficit
Balance at Dec. 31, 2018	$ 105,068			$ 2				$ 130,776			$ (25,710)
Balance, Shares at Dec. 31, 2018				22,677,585	727,413
Stock-based compensation	1,922							1,922
Issuance of common stock upon exercise of stock options	$ 314							314
Issuance of common stock upon exercise of stock options, Shares	382,068				382,068
Issuance of common stock		$ 149,449				$ 1			$ 149,448
Issuance of common stock, Shares						9,074,776
Conversion of preferred stock to common stock				$ (2)	$ 2
Conversion of preferred stock to common stock, Shares				(22,677,585)	22,677,585
Net loss	$ (32,325)										(32,325)
Balance at Dec. 31, 2019	224,428				$ 3			282,460			(58,035)
Balance, Shares at Dec. 31, 2019					32,861,842
Stock-based compensation	5,768							5,768
Issuance of common stock upon exercise of stock options	$ 2,843							2,843
Issuance of common stock upon exercise of stock options, Shares	841,463				822,916
Issuance of common stock related to employee stock purchase plan	$ 352							352
Issuance of common stock related to employee stock purchase plan, Shares					17,391
Issuance of common stock			$ 104,930				$ 1			$ 104,929
Issuance of common stock, Shares							2,875,000
Net loss	(52,243)										(52,243)
Balance at Dec. 31, 2020	$ 286,078				$ 4			$ 396,352			$ (110,278)
Balance, Shares at Dec. 31, 2020					36,577,149

Consolidated statements of cash

Consolidated statements of cash flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Cash flows from operating activities:
Net loss	$ (52,243)	$ (32,325)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	888	450
Stock-based compensation	5,768	1,922
Loss on disposal of property and equipment	3	3
Reduction in the carrying amount of right of use assets	1,038
Changes in assets and liabilities:
Prepaid expenses and other current assets	(2,878)	(2,024)
Accounts payable and accrued liabilities	5,203	891
Deferred rent		28
Net cash used in operating activities	(42,221)	(31,055)
Cash flows from investing activities:
Purchases of property and equipment	(1,050)	(1,635)
Proceeds from sale of property and equipment		1
Net cash used in investing activities	(1,050)	(1,634)
Cash flows from financing activities:
Proceeds from issuance of common stock upon public offerings	105,398	151,912
Payment of offering costs	(306)	(2,463)
Proceeds from issuance of common stock upon exercise of stock options	2,843	315
Proceeds from Employee Stock Purchase Plan	352
Deferred financing costs	(179)
Other		(2)
Net cash provided by financing activities	108,108	149,762
Net increase in cash, cash equivalents and restricted cash	64,837	117,073
Cash, cash equivalents and restricted cash—beginning of year	222,676	105,603
Cash, cash equivalents and restricted cash—end of year	287,513	222,676
Supplemental Disclosure of Non-Cash Investing and Financing Activities:
Right-of-use assets recognized in exchange for operating leases upon adoption of Topic 842	2,153
Property and equipment included in accrued expense and accounts payable	6	$ 140
Deferred offering costs not yet paid	$ 162

Nature of the Business and Basi

Nature of the Business and Basis of Presentation	12 Months Ended
	Dec. 31, 2020
Accounting Policies [Abstract]
Nature of the business and basis of presentation	1. Nature of the business and basis of presentation Organization Stoke Therapeutics, Inc. (the Company) was founded in June 2014 and was incorporated under the laws of the State of Delaware. The Company is an early-stage biopharmaceutical company pioneering a new way to treat the underlying causes of severe genetic diseases by precisely upregulating protein expression. Shelf Registration In July 2020, the Company filed a universal Shelf Registration statement on Form S-3 (the “Registration Statement”) with the Securities and Exchange Commission (the “SEC”). The Registration Statement was declared effective by the SEC on July 20, 2020, and contains two prospectuses: a base prospectus, which covers the offering, issuance and sale by the Company of up to a maximum aggregate offering price of $400,000,000 of our common stock, preferred stock, debt securities, warrants to purchase our common stock, preferred stock or debt securities, subscription rights to purchase our common stock, preferred stock or debt securities and/or units consisting of some or all of these securities; and a sales agreement prospectus covering the offering, issuance and sale by us of up to a maximum aggregate offering price of $150,000,000 of our common stock that may be issued and sold under a Controlled Equity Offering Sales Agreement. The specific terms of any securities to be offered pursuant to the base prospectus will be specified in a prospectus supplement to the base prospectus. The $150,000,000 of common stock that may be offered, issued and sold under the sales agreement prospectus is included in the $400,000,000 of securities that may be offered, issued and sold by the Company under the base prospectus. As of December 31, 2020, the Company has not issued any securities in connection with the Controlled Equity Offering Sales Agreement. Follow-on public offering On November 24, 2020, pursuant to a prospectus supplement to the Registration Statement, we completed an underwritten public offering, of our common stock and issued and sold 2,875,000 shares of common stock at a public offering price of $39.00 per share, which included 375,000 shares sold upon full exercise of the underwriters’ option to purchase additional shares of common stock resulting in net proceeds of $104.9 million after deducting underwriting discounts and commissions and estimated offering expenses. Initial public offering On June 21, 2019, the Company completed an initial public offering (“IPO”) of its common stock and issued and sold 9,074,776 shares of common stock at a public offering price of $18.00 per share, which included 1,183,666 shares sold upon full exercise of the underwriters’ option to purchase additional shares, resulting in net proceeds of approximately $149.4 million after deducting underwriting discounts, commissions and offering costs of $13.9 million. Upon closing of the IPO, the Company’s outstanding convertible preferred stock automatically converted into shares of common stock (see Note 7). Upon conversion of the convertible preferred stock, the Company reclassified the carrying value of the convertible preferred stock to common stock and additional paid-in capital. On June 6, 2019, the Company effected a one-for-9.95 reverse split of the Company’s issued and outstanding common and convertible preferred stock. Upon the effectiveness of the reverse stock split, (i) all shares of outstanding common stock and convertible preferred stock were adjusted; (ii) the number of shares of common stock for which each outstanding option to purchase common stock is exercisable were adjusted; and (iii) the exercise price of each outstanding option to purchase common stock were adjusted. All of the outstanding common stock share numbers (including shares of common stock subject to the Company’s options and as converted for the outstanding convertible preferred stock shares), share prices, exercise prices and per share amounts contained in the consolidated financial statements have been retroactively adjusted in the consolidated financial statements to reflect this reverse stock split for all periods presented. The par value per share and the authorized number of shares of common stock and convertible preferred stock were not adjusted as a result of the reverse stock split. On June 21, 2019, the Company filed an amended and restate certificate of incorporation with the Secretary of State of the State of Delaware to authorize the issuance of up to 300 million shares of common stock. $0.0001 par value, and 10 million shares of undesignated preferred stock, $0.0001 par value per share. Uncertainties The Company is subject to risks and uncertainties common to early-stage companies in the biotechnology industry including, but not limited to, development by competitors of new technological innovations, dependence on key personnel, protection of proprietary technology, compliance with government regulations and ability to secure additional capital to fund operations. Product candidates currently under development will require significant additional research and development efforts, including extensive preclinical and clinical testing and regulatory approval prior to commercialization. These efforts require significant amounts of additional capital, adequate personnel and infrastructure and extensive compliance-reporting capabilities. Even if the Company’s product development efforts are successful, it is uncertain when, if ever, the Company will realize significant revenue from product sales. Liquidity The Company expects that its operating losses and negative cash flows will continue for the foreseeable future. As of the issuance date of its consolidated financial statements for the year ended December 31, 2020, the Company expects that its cash and cash equivalents will be sufficient to fund its operating expenses and capital expenditure requirements into 2024. The Company plans to seek additional funding through public or private equity offerings, debt financings, other collaborations, strategic alliances and 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 strategic alliances or other arrangements on favorable terms, or at all. The terms of any financing may adversely affect the holdings or the rights of the Company’s stockholders. If the Company is unable to obtain funding, the Company could be required to delay, reduce or eliminate research and development programs, product portfolio expansion or future commercialization efforts, which could adversely affect its business prospects.

Summary of Significant Accounti

Summary of Significant Accounting Policies and Recent Accounting Pronouncements	12 Months Ended
	Dec. 31, 2020
Accounting Policies [Abstract]
Summary of significant accounting policies and recent accounting pronouncements	2. Summary of significant accounting policies and recent accounting pronouncements Basis of presentation and consolidation The accompanying consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles (GAAP), and include the accounts of Stoke Therapeutics, Inc. and its wholly-owned subsidiary. Any reference in these notes to applicable guidance is meant to refer to GAAP as found in the Accounting Standards Codification (“ASC”) and Accounting Standards Update (“ASU”) of the Financial Accounting Standards Board (“FASB”). All intercompany transactions between and among the Company and its’ consolidated subsidiary have been eliminated. Use of estimates The preparation of consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities, equity, expenses and disclosure of contingent assets and liabilities. Estimates are periodically reviewed in light of changes in circumstances, facts and experience. Actual results could differ from those estimates. Cash and cash equivalents The Company considers all highly liquid investments with an original maturity of three months or less at the date of purchase to be cash equivalents. The Company deposits its cash in checking, sweep and money market accounts. Restricted cash At December 31, 2020, restricted cash consisted of money market accounts collateralizing letters of credit issued as security deposits in connection with the Company’s leases of its corporate facilities. The following table reconciles cash and cash equivalents and restricted cash per the consolidated balance sheet to the statement of cash flows: As of December 31, 2020 2019 Cash and cash equivalents $ 287,308 $ 222,471 Restricted cash 205 205 $ 287,513 $ 222,676 Concentration of credit risk Financial instruments that potentially expose the Company to concentrations of credit risk primarily consist of cash and cash equivalents. The Company maintains its cash and cash equivalents at an accredited financial institution in amounts that exceed federally insured limits. The Company does not believe that it is subject to unusual credit risk beyond the normal credit risk associated with commercial banking relationships. Fair value of financial instruments ASC Topic 820, Fair Value Measurement Level 1—Quoted market prices in active markets for identical assets or liabilities. Level 2—Inputs other than Level 1 inputs that are either directly or indirectly observable, such as quoted market prices, interest rates and yield curves. Level 3—Unobservable inputs developed using estimates of assumptions developed by the Company, which reflect those that a market participant would use. To the extent the valuation is based on models or inputs that are less observable or unobservable in the market, the determination of fair values requires more judgment. Accordingly, the degree of judgment exercised by the Company in determining fair value is greatest for instruments categorized as Level 3. A financial instrument’s level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement. Deferred offering costs The Company capitalizes certain legal, professional accounting and other third-party fees that are directly associated with in-process equity financings as deferred offering costs until such financings are consummated. After consummation of the equity financing, these costs are recorded in the consolidated statement of stockholders’ equity as a reduction of additional paid-in capital. Property and equipment Property and equipment are initially recorded at cost less accumulated depreciation. Cost includes the acquisition costs and all costs necessary to bring the asset to the location and working condition necessary for its intended use. Depreciation expense is recognized using the straight-line method over the estimated useful life of each asset. Upon retirement or sale, the cost of assets disposed of and the related accumulated depreciation are removed from the accounts and any resulting gain or loss is included in the accompanying consolidated statements of operations and comprehensive loss. Expenditures for normal, recurring or periodic repairs and maintenance related to property and equipment are charged to expense as incurred. The cost for planned major maintenance activities, including the related acquisition or construction of assets, is capitalized if it will result in future economic benefits. Estimated useful lives for property and equipment are as follows: Property and equipment Estimated useful life Computer and office equipment 3-5 years Laboratory equipment and Furniture and fixtures 5-7 years Leasehold improvements Lesser of estimated useful life or remaining lease term Impairment of long-lived assets The Company reviews the recoverability of its long-lived assets when events or changes in circumstances occur that indicate that the carrying value of the assets may not be recoverable. The assessment of possible impairment is based on the ability to recover the carrying value of the assets from the expected future cash flows (undiscounted and without interest expense) of the related operations. If these cash flows are less than the carrying value of such assets, an impairment loss for the difference between the estimated fair value and carrying value is recorded. There were no impairment losses recognized during the years ended December 31, 2020 and 2019. Research and development costs Research and development costs are expensed as incurred. Research and development expenses are comprised of costs incurred in performing research and development activities, including salaries and benefits, facilities costs, depreciation, third-party license fees, and costs related to third parties engaged to conduct preclinical research development activities. The Company has entered into various research and development contracts with research institutions and other companies to conduct research on its behalf. These agreements are generally cancellable. The Company records accruals for estimated ongoing research costs. When evaluating the adequacy of the accrued liabilities, the Company analyzes progress of the studies, including the phase or completion of events, invoices received and contracted costs. Significant judgments and estimates may be made in determining the accrued balances at the end of any reporting period. Actual results could differ from the Company’s estimates. The Company’s historical accrual estimates have not been materially different from the actual costs. Stock options The Company measures its stock-based awards granted based on the estimated fair values of the awards and recognizes the compensation for employees and nonemployees over the requisite service period. The Company uses the Black-Scholes option-pricing model to estimate the fair value of its stock-based awards. The Company has elected the practical expedient to use the midpoint between vesting date and the contractual term as the expected term for certain awards with service or performance conditions. Stock-based compensation is recognized using the straight-line method. Forfeitures of unvested stock-based awards are accounted for when they occur. 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 consolidated statements of operations and comprehensive loss. Leases In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842). This standard established a right-of-use model that requires all lessees to recognize right-of-use assets and lease liabilities on their balance sheet that arise from leases as well as provide disclosures with respect to certain qualitative and quantitative information related to a company's leasing arrangements. The Company adopted Topic 842 on January 1, 2020 using the modified retrospective approach and elected to apply the transition method that allows companies to continue applying guidance under the lease standard in effect at that time in the comparative period financial statements and recognize a cumulative-effect adjustment to the balance sheet on the date of adoption. The Company has also elected the package of practical expedients to not reassess its prior conclusions about lease identification, lease classification and indirect costs and to not separate lease and non-lease components. Upon adoption of Topic 842 on January 1, 2020, the Company recorded right-of-use assets of $2.2 million, operating lease liabilities of $2.2 million and the elimination of deferred rent of $0.03 million. Adoption of the standard did not result in the Company recording a cumulative effect adjustment. The Company determines whether an arrangement is a lease at inception. The Company accounts for a lease when it has the right to control the leased asset for a period of time while obtaining substantially all of the assets’ economic benefits. The Company determined that it held operating leases for office and laboratory space as of January 1, 2020. Operating lease right-of-use assets and operating lease liabilities are recognized based on the present value of the future minimum lease payments over the lease term at the lease commencement date. The discount rate used to determine the present value of the lease payments is the Company’s incremental borrowing rate based on the information available at lease inception, as the Company did not have information to determine the rate implicit in the leases. Lease expense for operating leases is recognized on a straight-line basis over the reasonably assured lease term based on the total lease payments (which include initial direct costs and lease incentives). The expense is included in operating expenses in the consolidated statements of operations. The Company’s lease agreements also contain variable payments, primarily maintenance-related costs, which are expensed as incurred and not included in the measurement of the right-of-use assets and lease liabilities. Income taxes The Company accounts for income taxes using the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the estimated future tax consequences attributable to temporary differences between the consolidated financial statement carrying amounts of existing assets and liabilities and their respective tax base. Deferred tax assets and liabilities are determined on the basis of the differences between the consolidated financial statements and tax basis of assets and liabilities using enacted tax rates in effect for the year in which the temporary differences are expected to be settled or recovered. Changes in deferred tax assets and liabilities are recorded in the provision for income taxes. The Company assesses the likelihood that its deferred tax assets will be recovered from future taxable income and, to the extent it believes, based upon the weight of available evidence that it is more likely than not that all or a portion of the deferred tax assets will not be realized, a valuation allowance is established through a charge to income tax expense. Potential for recovery of deferred tax assets is evaluated by estimating the future taxable profits expected and considering prudent and feasible tax planning strategies. At December 31, 2020 and 2019, the Company has recorded a full valuation allowance. Reserves are provided for tax benefits for which realization is uncertain. Such benefits are only recognized when the underlying tax position is considered more-likely-than-not to be sustained on examination by a taxing authority, assuming they possess full knowledge of the position and facts. Interest and penalties related to uncertain tax positions are recognized in the provision of income taxes; however, the Company currently has no interest or penalties related to uncertain income tax benefits. The Tax Cuts and Jobs Act (the TCJA) was enacted on December 22, 2017. The TCJA reduced the U.S. federal corporate tax rate from a top rate of 35% to a flat rate of 21%. The Company continues to monitor for legislative developments, issuance of regulations and technical memorandum to provide further clarification and/or interpretations of the TCJA and will adjust its consolidated financial statements as needed. Segment and geographic information Operating segments are defined as components of an entity about which separate discrete information is available for evaluation by the chief operating decision maker, or decision-making group, in deciding how to allocate resources and in assessing performance. The Company operates in one segment in the United States. The Company’s chief executive officer, as the chief operating decision-maker, manages and allocates resources to the operations of the Company on a total company basis using consolidated financial information. Emerging growth company and smaller reporting company status The Company is an emerging growth company, as defined in the Jumpstart Our Business Startups Act of 2012 (the JOBS Act). Under the JOBS Act, emerging growth companies can delay adopting new or revised accounting standards issued subsequent to the enactment of the JOBS Act, until such time as those standards apply to private companies. The Company has elected to use this extended transition period for complying with new or revised accounting standards that have different effective dates for public and private companies until the earlier of the date that it is (i) no longer an emerging growth company or (ii) affirmatively and irrevocably opt out of the extended transition period provided in the JOBS Act. As a result, the Company’s consolidated financial statements may not be comparable to companies that comply with the new or revised accounting pronouncements as of public company effective dates. The Company will remain an emerging growth company until the earliest of (i) the last day of the Company’s first fiscal year (a) following the fifth anniversary of the completion of our IPO, (b) in which the Company has total annual gross revenues of at least $1.07 billion, or (c) when the Company is deemed to be a large accelerated filer, which means the market value of the Company’s common stock that is held by non-affiliates exceeds $700.0 million as of the prior June 30 th The Company is also a “smaller reporting company,” meaning that in the event of an initial public offering the market value of its stock held by non-affiliates plus the proposed aggregate amount of gross proceeds to the Company as a result of such offering is less than $700 million and its annual revenue is less than $100 million during the most recently completed fiscal year. The Company may continue to be a smaller reporting company as long as either (i) the market value of its stock held by non-affiliates is less than $250 million or (ii) its annual revenue is less than $100 million during the most recently completed fiscal year and the market value of its stock held by non-affiliates is less than $700 million. If the Company is a smaller reporting company at the time it ceases to be an emerging growth company, the Company may continue to rely on exemptions from certain disclosure requirements that are available to smaller reporting companies. Specifically, as a smaller reporting company, the Company may choose to present only the two most recent fiscal years of audited financial statements in its Annual Report on Form 10-K and, similar to emerging growth companies, smaller reporting companies have reduced disclosure obligations regarding executive compensation. Recently issued accounting pronouncements In July 2017, the FASB issued ASU 2017-11, Earnings Per Share I. Accounting for Certain Financial Instruments with Down Round Features; II. Replacement of the Indefinite Deferral for Mandatorily Redeemable Financial Instruments of Certain Nonpublic Entities and Certain Mandatorily Redeemable Noncontrolling Interests with a Scope Exception In August 2018, the FASB issued ASU 2018-13, “Fair Value Measurement (Topic 820), Disclosure Framework—Changes to the Disclosure Requirements for Fair Value Measurement”. In December 2019, the FASB issued ASU 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes. This guidance removes certain exceptions for recognizing deferred taxes for investments, performing intraperiod allocation and calculating income taxes in interim periods. It also adds guidance to reduce complexity in certain areas, including recognizing deferred taxes for tax goodwill and allocating taxes to members of a consolidated group. This ASU is effective for interim and annual periods beginning after December 15, 2020, and early adoption is permitted. The Company is

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2020
Fair Value Disclosures [Abstract]
Fair value measurements	3. Fair value measurements The following tables present information about the Company’s financial assets measured at fair value on a recurring basis and indicate the level of the fair value hierarchy utilized to determine such fair values: Fair value measurements as of December 31, 2020 Level 1 Level 2 Level 3 Total Cash equivalents: Money market funds $ 287,308 $ — $ — $ 287,308 Total $ 287,308 $ — $ — $ 287,308 Fair value measurements as of December 31, 2019 Level 1 Level 2 Level 3 Total Cash equivalents: Money market funds $ 222,471 $ — $ — $ 222,471 Total $ 222,471 $ — $ — $ 222,471 The Company’s assets with fair value categorized as Level 1 within the fair value hierarchy include money market funds. Money market funds are publicly traded mutual funds and are presented as cash equivalents on the consolidated balance sheets as of December 31, 2020 and 2019. There were no transfers among Level 1, Level 2, or Level 3 categories in the periods presented. The carrying value of cash, cash equivalents, accounts payable and accrued expenses that are reported on the consolidated balance sheets approximate their fair value due to the short-term nature of these assets and liabilities.

Property and Equipment, Net

Property and Equipment, Net	12 Months Ended
	Dec. 31, 2020
Property Plant And Equipment [Abstract]
Property and equipment, net	4. Property and equipment, net Property and equipment, net consisted of the following: As of December 31, 2020 2019 Laboratory equipment $ 3,936 $ 2,489 Furniture and fixtures 108 108 Leasehold improvements 210 40 Office equipment 108 79 Construction in progress 5 611 4,367 3,327 Less accumulated depreciation (1,692 ) (815 ) $ 2,675 $ 2,512 Depreciation expense was $0.9 million and $0.5 million for the years ended December 31, 2020 and 2019, respectively.

Accrued and Other Current Liabi

Accrued and Other Current Liabilities	12 Months Ended
	Dec. 31, 2020
Payables And Accruals [Abstract]
Accrued and other current liabilities	5. Accrued and other current liabilities Accrued and other current liabilities consisted of the following: As of December 31, 2020 2019 Accrued employee compensation costs $ 4,123 2,053 Accrued professional 593 228 Accrued research and development costs 3,689 959 Accrued other 82 56 Other current liabilities 1,443 54 $ 9,930 $ 3,350

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2020
Commitments And Contingencies Disclosure [Abstract]
Commitments and contingencies	6. In August 2018, the Company entered into an agreement to lease approximately 23,000 square feet of space for a term of three years. Lease terms are triple net lease commencing at $0.9 million per year, then with 3% annual base rent increases plus operating expenses, real estate taxes, utilities and janitorial fees. The lease commencement date was December 10, 2018. In December 2018, the Company entered into an agreement to lease 2,485 square feet of space for an initial term of three years. The lease includes one renewal option for an additional two years, however, any time after the initial term the landlord may relocate the Company from the premises to a space reasonably comparable in size and utility. As the Company does not have the right to control the use of the identified asset after the initial term, the renewal option was excluded from the lease liability calculation. Lease terms commence at $0.2 million per annum, with 2.5% annual base rent increases plus operating expenses, real estate taxes, utilities and janitorial fees. The lease commencement date was May 1, 2019. Future minimum lease payments under non-cancellable leases as of December 31, 2020 are as follows (in thousands): 2021 $ 1,102 2022 81 Total lease payments 1,183 Less imputed interest (37) Present value of lease liabilities $ 1,146 Lease balances as of December 31, 2020 are as follows (in thousands): Operating right-of-use assets $ 1,115 Current Portion of operating lease liabilities $ 1,066 Non-current portion of operating lease liabilities 80 Total operating lease liabilities $ 1,146 The weighted average remaining lease term and weighted average discount rate of our operating leases as of December 31, 2020 are as follows: Weighted average remaining lease term in years 1.0 Weighted average discount rate 7.02 % 2021 1,102 2022 81 Thereafter — $ 1,183 In accordance with Topic 842, lease expense incurred under operating leases was approximately $1.1 million for the year ended December 31, 2020. For the year ended December 31, 2019, rent expense incurred was approximately $1.1 million. Consulting Agreement In October 2014, the Company entered into a consulting agreement with a member of the Company’s board of directors, who is also an employee of Cold Spring Harbor Laboratory (“CSHL”), to provide consulting services related to scientific research related to the development of antisense-based drugs, therapies, diagnostic and research tools, products, services and intellectual property. The Company recognized expenses of $0.02 million each for the years ended December 31, 2020 and 2019. The initial term of this agreement was five years and the parties mutually agreed not to extend the consulting agreement in April 2020. Scientific Advisory Board Agreement In June 2020, the Company entered into a scientific advisory board agreement with a member of the Company’s board of directors, who is also an employee of CSHL, to provide scientific advisory services related to the Company’s Targeted Augmentation of Nuclear Gene Output (“TANGO”) antisense oligonucleotide technology and other antisense oligonucleotide technologies, as well as current and future therapeutic targets and programs. The Company recognized expense of $0.05 million in the year ended December 31, 2020, for such scientific advisory services. The term of this agreement is 12 months. License and research agreements In July 2015, the Company entered into a worldwide license agreement, or the CSHL Agreement, with CSHL, with respect to TANGO patents. Under the CSHL Agreement, the Company receives an exclusive (except with respect to certain government rights and non-exclusive licenses), worldwide license under certain patents and applications relating to TANGO. As part of the CSHL Agreement, the Company granted CSHL 164,927 shares of common stock valued based on an independent appraisal at approximately $0.07 million. The CSHL Agreement obligates the Company to make additional payments that are contingent upon certain milestones being achieved. The Company is also required to pay royalties, tiered based on the scope of patent coverage for each licensed product, ranging from a low-single digit percentage to a mid-single digit percentage on annual net sales. These royalty obligations apply on a licensed product-by-licensed product and country-by-country basis until the latest of (i) the expiration of the last valid claim of a CSHL patent covering the applicable licensed product or (ii) the expiration of any regulatory exclusivity for the applicable licensed product. In addition, if the Company sublicenses the rights under the CSHL Agreement, the Company is required to pay a maximum of twenty percent of the sublicense revenue to CSHL, which may be reduced to a mid-teens or a mid-single digit percentage upon achievement of certain clinical milestones for the applicable licensed product. Finally, the Company is required to pay an annual license maintenance fee of $0.01 million, which amount is creditable against any owed royalty or milestone payments. The maximum aggregate potential milestone payments payable total approximately $0.9 million. Additionally, certain licenses under the CSHL Agreement require the Company to reimburse CSHL for certain past and ongoing patent related expenses, however there were no expenses related to these reimbursable patent costs during the years ended December 31, 2020 and 2019. In April 2016, the Company entered into an exclusive, worldwide license agreement with the University of Southampton, or the Southampton Agreement, whereby the Company acquired rights to foundational technologies related to the Company’s TANGO technology. Under the Southampton Agreement, the Company receives an exclusive, worldwide license under certain licensed patents and applications relating to TANGO. Under the Southampton Agreement, the Company may be obligated to make additional payments that are contingent upon certain milestones being achieved, as well as royalties on future product sales. These royalty obligations survive until the latest of (i) the expiration of the last valid claim of a licensed patent covering a subject product or (ii) the expiration of any regulatory exclusivity for the subject product in a country. In addition, if the Company sublicenses its rights under the Southampton Agreement, the Company is required to pay a mid-single digit percentage of the sublicense revenue to the University of Southampton. The maximum aggregate potential milestone payments payable by the Company total approximately 0.4 million pounds sterling (approximately $0.5 million as of December 31, 2020). As of December 31, 2020, and 2019, the Company has recorded no liabilities under the Southampton Agreement. Litigation The Company may periodically become subject to legal proceedings and claims arising in connection with ongoing business activities, including claims or disputes related to patents that have been issued or that are pending in the field of research on which it is focused. As of December 31, 2020, the Company had no legal proceedings to which it was a party or to which its property was subject.

Convertible Preferred Stock

Convertible Preferred Stock	12 Months Ended
	Dec. 31, 2020
Stockholders Equity Note [Abstract]
Convertible preferred stock	7. Convertible preferred stock On June 6, 2019, the Company’s stockholders approved an amendment to the Company’s Amended and Restated Certificate of Incorporation which became effective on June 21, 2019 upon which the authorized capital stock of the Corporation consisted of 300 million shares of common stock, $0.0001 per share par value, and 10 million shares of undesignated preferred stock, $0.0001 per share par value. On June 21, 2019, the Company completed its IPO and in conjunction therewith, all outstanding convertible preferred stock was converted into common stock. Accordingly, as of December 31, 2020 and 2019, there was no preferred stock outstanding. The following table summarizes the Company’s issued and outstanding Preferred Stock: Series A Preferred Series A-2 Preferred Series B Preferred Total convertible Preferred Shares Amount Shares Amount Shares Amount Shares Amount Balance, December 31, 2018 4,980,168 $ 11,725 7,617,746 $ 28,880 10,079,671 $ 89,742 22,677,585 $ 130,347 Conversion to Common Stock upon initial public offering (4,980,168 ) $ (11,725 ) (7,617,746 ) $ (28,880 ) (10,079,671 ) $ (89,742 ) (22,677,585 ) $ (130,347 ) Balance, December 31, 2019 — — — — — — — —

Share-Based Compensation

Share-Based Compensation	12 Months Ended
	Dec. 31, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Share-Based Compensation	8. Share-Based Compensation In June 2019, the Company’s board of directors and stockholders approved the 2019 Equity Incentive Plan (the “2019 Plan”) which became effective on June 17, 2019 and replaced the Company’s 2014 Equity Incentive Plan (the “2014 Plan”). In addition to the shares of common stock reserved for future issuance under the 2014 Plan that were added to the 2019 Plan upon its effective date, the Company initially reserved 2,200,000 shares of common stock for issuance under the 2019 Plan. The number of shares reserved for issuance under the Company’s 2019 Plan will increase automatically on January 1 of each of 2020 through 2029 by the number of shares equal to 4% of the aggregate number of outstanding shares of the Company’s common stock as of the immediately preceding December 31, or a lesser number as may be determined by the Company’s board of directors. As of December 31, 2020 there were no shares available for future issuance under the 2014 Plan and 2,431,303 shares were available under the 2019 Plan. During the years ended December 31, 2020 and December 31, 2019, the Company granted options to purchase 1,231,532 and 1,234,569 shares of common stock to certain of its employees, and directors, respectively. The options vest over four years except for certain options granted to members of our board of directors which vest over one or three years and are exercisable at a per share price equal to the fair value of the common stock on the grant date. A summary of stock option activity for awards is presented below: Number of shares Weighted average exercise price Weighted average remaining contractual life (years) Aggregate intrinsic value ( 1) Outstanding as of January 1, 2019 3,484,628 $ 1.20 8.9 $ 3,436 Granted 1,234,569 10.39 Exercised (382,068 ) 0.91 Forfeited or expired (94,772 ) 1.24 Outstanding as of December 31, 2019 4,242,357 3.91 8.8 106,138 Granted 1,231,532 23.72 Exercised (841,463 ) 3.38 Forfeited or expired (178,004 ) 21.15 Outstanding as of December 31, 2020 4,454,422 $ 8.80 8.0 $ 236,685 Exercisable as of December 31, 2020 1,918,281 $ 4.40 7.4 $ 110,350 (1) The aggregate intrinsic value is calculated as the difference between the exercise price of the underlying options and the estimated fair value of the common stock for the options that were in the money at December 31, 2020 and 2019. The weighted average grant date fair value per share of stock options granted during the years ended December 31, 2020 and 2019 was $14.75 and $6.06, respectively. The aggregate grant date fair value of stock options granted during the years ended December 31, 2020 and 2019 was approximately $18.2 million and $7.5 million, respectively. The aggregate intrinsic value of stock options exercised during the year ended December 31, 2020 and 2019 was approximately $27.3 million and $10.5 million, respectively. Stock-based compensation and stock options The Company recorded stock-based compensation expense of $5.8 million and $1.9 million during the years ended December 31, 2020 and 2019, respectively. As of December 31, 2020, there was $17.6 million of unrecognized compensation cost related to unvested stock-based compensation arrangements granted under the 2014 and the 2019 Plans. The compensation is expected to be recognized over a weighted average period of 2.9 years as of December 31, 2020. Stock-based compensation expense recorded as research and development and general and administrative expenses in the accompanying consolidated statements of operations is as follows: Year ended December 31, 2020 2019 Research and development $ 1,875 $ 499 General and administrative 3,893 1,423 $ 5,768 $ 1,922 The Company uses the Black-Scholes option pricing model to calculate the grant-date fair value of an award. The fair values of the options granted to employees and directors were calculated using the following assumptions for the years ended December 31, 2020 and 2019: Year ended December 31, 2020 2019 Risk-free interest rate 0.38-1.48% 1.42-2.81% Expected dividend yield 0 % 0 % Expected life 5.5-6.25 years 5.5-6.375 years Expected volatility 70 % 60-68% 2019 Employee stock purchase plan In June 2019, the Company adopted the 2019 Employee Stock Purchase Plan (“ESPP”), which became effective on June 18, 2019. The Company initially reserved 315,000 shares of common stock for sale under the ESPP. At December 31, 2020, the Company had 288,808 shares available for issuance under the plan. The average grant date fair value per share under the plan was $25.46 for 2020. The total ESPP stock-based compensation expense for the year ended December 31, 2020 was $0.3 million. The number of shares reserved for issuance under the ESPP will increase automatically on January 1st of each of the first ten calendar years following the first offering date by the number of shares equal to the lesser of 1% of the total outstanding shares of the Company’s common stock as of the immediately preceding December 31 or a lower amount determined by the Company’s board of directors. The aggregate number of shares issued over the term of the ESPP will not exceed 3,150,000 shares of the Company’s common stock.

Net Loss Per Share Attributable

Net Loss Per Share Attributable to Common Stockholders	12 Months Ended
	Dec. 31, 2020
Earnings Per Share [Abstract]
Net loss per share attributable to common stockholders	9. Net loss per share attributable to common stockholders The following table summarizes the computation of basic and diluted net loss per share attributable to common stockholders of the Company: Year ended December 31, 2020 2019 Numerator: Net loss $ (52,243 ) $ (32,325 ) Denominator: Weighted-average number of common shares, basic and diluted 33,488,456 17,971,443 Net loss per share, basic and diluted $ (1.56 ) $ (1.80 ) The Company’s potential dilutive securities, which include common stock options and ESPP purchase rights, have been excluded from the computation of diluted net loss per share as the effect would be anti-dilutive. Therefore, the weighted average number of common shares outstanding used to calculate both basic and diluted net loss per share is the same. The Company excluded the following potential common shares, presented based on amounts outstanding at period end, from the computation of diluted net loss per share for the periods indicated because including them would have had an anti-dilutive effect: December 31, 2020 2019 Outstanding options to purchase common stock 4,454,424 4,242,357

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Income taxes	10. Income taxes A reconciliation of the expected income tax expense (benefit) computed using the federal statutory income tax rate to the Company’s effective income tax rate is as follows: Year ended December 31, 2020 2019 Expected income tax benefit at the federal statutory rate 21.0 % 21.0 % State income taxes, net of federal benefit 8.3 6.7 Non-deductible items 6.2 (0.4 ) Research and development credit, net 1.2 4.3 Other 0.2 0.3 Change in valuation allowance (36.9 ) (31.9 ) Total 0.0 % 0.0 % The principal components of the Company’s deferred tax assets and liabilities consist of the following: As of December 31, 2020 2019 Deferred tax assets: Federal and state net operating loss carryforwards $ 32,097 $ 14,999 Research and development tax credits 2,816 2,171 Other 2,293 761 Gross deferred tax assets 37,206 17,931 Less: valuation allowance (37,206 ) (17,931 ) Net deferred tax assets $ — $ — As of December 31, 2020 and 2019, the Company had federal net operating loss carryforwards of $116.9 million and $54.5 million, respectively, which may be available to reduce future taxable income, and expire at various dates beginning in 2034, for those net operating loss carryforwards generated prior to 2018. Net operating losses generated in 2018 and beyond have no expiration. As of December 31, 2020 and 2019, the Company had state net operating loss carry forwards of $118.8 million and $56.3 million, respectively, which may be available to reduce future taxable income and expire at various dates beginning in 2034. In addition, at December 31, 2020 and 2019, the Company had federal research and development tax credit carryforwards of $2.0 million and $1.5 million, respectively, and state research and development tax credit carry forwards of $1.0 million and $0.8 million, respectively. Both federal and state research and development tax credit carry forwards may be available to reduce future tax liabilities and expire at various dates beginning in 2030. In accordance with ASC 740, Accounting for Income Taxes The CARES Act temporarily repealed the 80% taxable income limitation for tax years beginning before January 1, 2021. Federal NOL carry forwards generated from 2018 or later and Federal NOL carryforwards to taxable years beginning after December 31, 2020 will be subject to the 80% limitation. Also, under the CARES Act, federal NOLs arising in 2018, 2019 and 2020 can be carried back 5 years. New legislation or regulation which could affect our tax burden could be enacted by any governmental authority. The Company cannot predict the timing or extent of such tax-related developments which could have a negative impact on our financial results. Additionally, the Company uses its best judgment in attempting to quantify and reserve for these tax obligations. However, a challenge by a taxing authority, the Company’s ability to utilize tax benefits such as carryforwards or tax credits, or a deviation from other tax-related assumptions could have a material adverse effect on our business, results of operations, or financial condition. Utilization of the net operating loss carryforwards and research and development tax credit carryforwards may be subject to a substantial annual limitation under Sections 382 and 383 of the Internal Revenue Code of 1986, as amended (the Code) due to ownership changes that have occurred previously or that could occur in the future. These ownership changes may limit the amount of carryforwards that can be utilized annually to offset future taxable income. The Company has not conducted a formal study to assess whether a change of control has occurred or whether there have been multiple changes of control since inception due to the significant complexity and cost associated with such a study. If the Company has experienced a change of control, as defined for purposes of Section 382 and 383 of the Code, at any time since inception, utilization of the net operating loss carryforwards or research and development tax credit carryforwards may be subject to an annual limitation under Section 382 and 383 of the Code, which is determined by first multiplying the value of the Company’s stock at the time of the ownership change by the applicable long-term tax-exempt rate, and then could be subject to additional adjustments, as required. Any limitation may result in expiration of a portion of the net operating loss carryforwards or research and development tax credit carryforwards before utilization. The Company applies ASC 740 related to accounting for uncertainty in income taxes. The Company’s reserves related to income taxes are based on a determination of whether, and how much of, a tax benefit taken by the Company in its tax filings or positions is more likely than not to be realized following resolution of any potential contingencies present related to the tax benefit. At December 31, 2020, and 2019 the Company had no unrecognized tax benefits. Interest and penalty charges, if any, related to unrecognized tax benefits would be classified as income tax expense in the accompanying consolidated statements of operations and comprehensive loss.

Employee Benefits

Employee Benefits	12 Months Ended
	Dec. 31, 2020
Compensation And Retirement Disclosure [Abstract]
Employee benefits	11. Employee benefits In 2016, the Company established a defined-contribution savings plan under Section 401(k) of the Internal Revenue Code (the “401(k) Plan”). The 401(k) Plan covers all employees who meet defined minimum age and service requirements and allows participants to defer a portion of their annual compensation on a pretax basis. On January 1, 2020, the Company began to make matching contributions up to 4% of annual salary for those employees who are participating in the 401(k) Plan. For the year ended December 31, 2020, the Company made matching contributions of $0.02 million. The Company was not required to make and did not make any contributions to the 401(k) Plan for the year ended December 31, 2019.

Selected Quarterly Financial In

Selected Quarterly Financial Information (Unaudited)	12 Months Ended
	Dec. 31, 2020
Quarterly Financial Information Disclosure [Abstract]
Selected Quarterly Financial Information (Unaudited)	12. Selected Quarterly Financial Information (Unaudited) Selected quarterly results from operations for the years ended December 31, 2020 and 2019 are as follows: (in thousands, except for per share data) 2020 Quarter End March 31 June 30 September 30 December 31 Revenue — — — — Operating expenses $ 11,735 $ 13,012 $ 13,711 $ 14,586 Loss from operations (11,735 ) (13,012 ) (13,711 ) (14,586 ) Net loss (11,039 ) (12,959 ) (13,684 ) (14,561 ) Net loss per share, basic and diluted $ (0.34 ) $ (0.39 ) $ (0.41 ) $ (0.42 ) 2019 Quarter End March 31 June 30 September 30 December 31 Revenue — — — — Operating expenses $ 6,322 $ 8,445 $ 9,842 $ 11,069 Loss from operations (6,322 ) (8,445 ) (9,842 ) (11,069 ) Net loss (5,742 ) (7,819 ) (8,604 ) (10,160 ) Net loss per share, basic and diluted $ (6.89 ) $ (1.54 ) $ (0.26 ) $ (0.31 )

Subsequent Events

Subsequent Events	12 Months Ended
	Dec. 31, 2020
Subsequent Events [Abstract]
Subsequent events	13. Subsequent events The Company has evaluated subsequent events through the issuance date of these consolidated financial statements. The Company has concluded that no events or transactions have occurred that require disclosure in the accompanying consolidated financial statements.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies and Recent Accounting Pronouncements (Policies)	12 Months Ended
	Dec. 31, 2020
Accounting Policies [Abstract]
Basis of Presentation and Consolidation	Basis of presentation and consolidation The accompanying consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles (GAAP), and include the accounts of Stoke Therapeutics, Inc. and its wholly-owned subsidiary. Any reference in these notes to applicable guidance is meant to refer to GAAP as found in the Accounting Standards Codification (“ASC”) and Accounting Standards Update (“ASU”) of the Financial Accounting Standards Board (“FASB”). All intercompany transactions between and among the Company and its’ consolidated subsidiary have been eliminated.
Use of Estimates	Use of estimates The preparation of consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities, equity, expenses and disclosure of contingent assets and liabilities. Estimates are periodically reviewed in light of changes in circumstances, facts and experience. Actual results could differ from those estimates.
Cash and Cash Equivalents	Cash and cash equivalents The Company considers all highly liquid investments with an original maturity of three months or less at the date of purchase to be cash equivalents. The Company deposits its cash in checking, sweep and money market accounts.
Restricted Cash	Restricted cash At December 31, 2020, restricted cash consisted of money market accounts collateralizing letters of credit issued as security deposits in connection with the Company’s leases of its corporate facilities. The following table reconciles cash and cash equivalents and restricted cash per the consolidated balance sheet to the statement of cash flows: As of December 31, 2020 2019 Cash and cash equivalents $ 287,308 $ 222,471 Restricted cash 205 205 $ 287,513 $ 222,676
Concentration of Credit Risk	Concentration of credit risk Financial instruments that potentially expose the Company to concentrations of credit risk primarily consist of cash and cash equivalents. The Company maintains its cash and cash equivalents at an accredited financial institution in amounts that exceed federally insured limits. The Company does not believe that it is subject to unusual credit risk beyond the normal credit risk associated with commercial banking relationships.
Fair Value of Financial Instruments	Fair value of financial instruments ASC Topic 820, Fair Value Measurement Level 1—Quoted market prices in active markets for identical assets or liabilities. Level 2—Inputs other than Level 1 inputs that are either directly or indirectly observable, such as quoted market prices, interest rates and yield curves. Level 3—Unobservable inputs developed using estimates of assumptions developed by the Company, which reflect those that a market participant would use. To the extent the valuation is based on models or inputs that are less observable or unobservable in the market, the determination of fair values requires more judgment. Accordingly, the degree of judgment exercised by the Company in determining fair value is greatest for instruments categorized as Level 3. A financial instrument’s level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement.
Deferred Offering Costs	Deferred offering costs The Company capitalizes certain legal, professional accounting and other third-party fees that are directly associated with in-process equity financings as deferred offering costs until such financings are consummated. After consummation of the equity financing, these costs are recorded in the consolidated statement of stockholders’ equity as a reduction of additional paid-in capital.
Property and Equipment	Property and equipment Property and equipment are initially recorded at cost less accumulated depreciation. Cost includes the acquisition costs and all costs necessary to bring the asset to the location and working condition necessary for its intended use. Depreciation expense is recognized using the straight-line method over the estimated useful life of each asset. Upon retirement or sale, the cost of assets disposed of and the related accumulated depreciation are removed from the accounts and any resulting gain or loss is included in the accompanying consolidated statements of operations and comprehensive loss. Expenditures for normal, recurring or periodic repairs and maintenance related to property and equipment are charged to expense as incurred. The cost for planned major maintenance activities, including the related acquisition or construction of assets, is capitalized if it will result in future economic benefits. Estimated useful lives for property and equipment are as follows: Property and equipment Estimated useful life Computer and office equipment 3-5 years Laboratory equipment and Furniture and fixtures 5-7 years Leasehold improvements Lesser of estimated useful life or remaining lease term
Impairment of Long-Lived Assets	Impairment of long-lived assets The Company reviews the recoverability of its long-lived assets when events or changes in circumstances occur that indicate that the carrying value of the assets may not be recoverable. The assessment of possible impairment is based on the ability to recover the carrying value of the assets from the expected future cash flows (undiscounted and without interest expense) of the related operations. If these cash flows are less than the carrying value of such assets, an impairment loss for the difference between the estimated fair value and carrying value is recorded. There were no impairment losses recognized during the years ended December 31, 2020 and 2019.
Research and Development Costs	Research and development costs Research and development costs are expensed as incurred. Research and development expenses are comprised of costs incurred in performing research and development activities, including salaries and benefits, facilities costs, depreciation, third-party license fees, and costs related to third parties engaged to conduct preclinical research development activities. The Company has entered into various research and development contracts with research institutions and other companies to conduct research on its behalf. These agreements are generally cancellable. The Company records accruals for estimated ongoing research costs. When evaluating the adequacy of the accrued liabilities, the Company analyzes progress of the studies, including the phase or completion of events, invoices received and contracted costs. Significant judgments and estimates may be made in determining the accrued balances at the end of any reporting period. Actual results could differ from the Company’s estimates. The Company’s historical accrual estimates have not been materially different from the actual costs.
Stock Options	Stock options The Company measures its stock-based awards granted based on the estimated fair values of the awards and recognizes the compensation for employees and nonemployees over the requisite service period. The Company uses the Black-Scholes option-pricing model to estimate the fair value of its stock-based awards. The Company has elected the practical expedient to use the midpoint between vesting date and the contractual term as the expected term for certain awards with service or performance conditions. Stock-based compensation is recognized using the straight-line method. Forfeitures of unvested stock-based awards are accounted for when they occur.
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 consolidated statements of operations and comprehensive loss.
Leases	Leases In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842). This standard established a right-of-use model that requires all lessees to recognize right-of-use assets and lease liabilities on their balance sheet that arise from leases as well as provide disclosures with respect to certain qualitative and quantitative information related to a company's leasing arrangements. The Company adopted Topic 842 on January 1, 2020 using the modified retrospective approach and elected to apply the transition method that allows companies to continue applying guidance under the lease standard in effect at that time in the comparative period financial statements and recognize a cumulative-effect adjustment to the balance sheet on the date of adoption. The Company has also elected the package of practical expedients to not reassess its prior conclusions about lease identification, lease classification and indirect costs and to not separate lease and non-lease components. Upon adoption of Topic 842 on January 1, 2020, the Company recorded right-of-use assets of $2.2 million, operating lease liabilities of $2.2 million and the elimination of deferred rent of $0.03 million. Adoption of the standard did not result in the Company recording a cumulative effect adjustment. The Company determines whether an arrangement is a lease at inception. The Company accounts for a lease when it has the right to control the leased asset for a period of time while obtaining substantially all of the assets’ economic benefits. The Company determined that it held operating leases for office and laboratory space as of January 1, 2020. Operating lease right-of-use assets and operating lease liabilities are recognized based on the present value of the future minimum lease payments over the lease term at the lease commencement date. The discount rate used to determine the present value of the lease payments is the Company’s incremental borrowing rate based on the information available at lease inception, as the Company did not have information to determine the rate implicit in the leases. Lease expense for operating leases is recognized on a straight-line basis over the reasonably assured lease term based on the total lease payments (which include initial direct costs and lease incentives). The expense is included in operating expenses in the consolidated statements of operations. The Company’s lease agreements also contain variable payments, primarily maintenance-related costs, which are expensed as incurred and not included in the measurement of the right-of-use assets and lease liabilities.
Income Taxes	Income taxes The Company accounts for income taxes using the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the estimated future tax consequences attributable to temporary differences between the consolidated financial statement carrying amounts of existing assets and liabilities and their respective tax base. Deferred tax assets and liabilities are determined on the basis of the differences between the consolidated financial statements and tax basis of assets and liabilities using enacted tax rates in effect for the year in which the temporary differences are expected to be settled or recovered. Changes in deferred tax assets and liabilities are recorded in the provision for income taxes. The Company assesses the likelihood that its deferred tax assets will be recovered from future taxable income and, to the extent it believes, based upon the weight of available evidence that it is more likely than not that all or a portion of the deferred tax assets will not be realized, a valuation allowance is established through a charge to income tax expense. Potential for recovery of deferred tax assets is evaluated by estimating the future taxable profits expected and considering prudent and feasible tax planning strategies. At December 31, 2020 and 2019, the Company has recorded a full valuation allowance. Reserves are provided for tax benefits for which realization is uncertain. Such benefits are only recognized when the underlying tax position is considered more-likely-than-not to be sustained on examination by a taxing authority, assuming they possess full knowledge of the position and facts. Interest and penalties related to uncertain tax positions are recognized in the provision of income taxes; however, the Company currently has no interest or penalties related to uncertain income tax benefits. The Tax Cuts and Jobs Act (the TCJA) was enacted on December 22, 2017. The TCJA reduced the U.S. federal corporate tax rate from a top rate of 35% to a flat rate of 21%. The Company continues to monitor for legislative developments, issuance of regulations and technical memorandum to provide further clarification and/or interpretations of the TCJA and will adjust its consolidated financial statements as needed.
Segment and Geographic Information	Segment and geographic information Operating segments are defined as components of an entity about which separate discrete information is available for evaluation by the chief operating decision maker, or decision-making group, in deciding how to allocate resources and in assessing performance. The Company operates in one segment in the United States. The Company’s chief executive officer, as the chief operating decision-maker, manages and allocates resources to the operations of the Company on a total company basis using consolidated financial information.
Emerging Growth Company and Smaller Reporting Company Status	Emerging growth company and smaller reporting company status The Company is an emerging growth company, as defined in the Jumpstart Our Business Startups Act of 2012 (the JOBS Act). Under the JOBS Act, emerging growth companies can delay adopting new or revised accounting standards issued subsequent to the enactment of the JOBS Act, until such time as those standards apply to private companies. The Company has elected to use this extended transition period for complying with new or revised accounting standards that have different effective dates for public and private companies until the earlier of the date that it is (i) no longer an emerging growth company or (ii) affirmatively and irrevocably opt out of the extended transition period provided in the JOBS Act. As a result, the Company’s consolidated financial statements may not be comparable to companies that comply with the new or revised accounting pronouncements as of public company effective dates. The Company will remain an emerging growth company until the earliest of (i) the last day of the Company’s first fiscal year (a) following the fifth anniversary of the completion of our IPO, (b) in which the Company has total annual gross revenues of at least $1.07 billion, or (c) when the Company is deemed to be a large accelerated filer, which means the market value of the Company’s common stock that is held by non-affiliates exceeds $700.0 million as of the prior June 30 th The Company is also a “smaller reporting company,” meaning that in the event of an initial public offering the market value of its stock held by non-affiliates plus the proposed aggregate amount of gross proceeds to the Company as a result of such offering is less than $700 million and its annual revenue is less than $100 million during the most recently completed fiscal year. The Company may continue to be a smaller reporting company as long as either (i) the market value of its stock held by non-affiliates is less than $250 million or (ii) its annual revenue is less than $100 million during the most recently completed fiscal year and the market value of its stock held by non-affiliates is less than $700 million. If the Company is a smaller reporting company at the time it ceases to be an emerging growth company, the Company may continue to rely on exemptions from certain disclosure requirements that are available to smaller reporting companies. Specifically, as a smaller reporting company, the Company may choose to present only the two most recent fiscal years of audited financial statements in its Annual Report on Form 10-K and, similar to emerging growth companies, smaller reporting companies have reduced disclosure obligations regarding executive compensation.
Recently Issued Accounting Pronouncements	Recently issued accounting pronouncements In July 2017, the FASB issued ASU 2017-11, Earnings Per Share I. Accounting for Certain Financial Instruments with Down Round Features; II. Replacement of the Indefinite Deferral for Mandatorily Redeemable Financial Instruments of Certain Nonpublic Entities and Certain Mandatorily Redeemable Noncontrolling Interests with a Scope Exception In August 2018, the FASB issued ASU 2018-13, “Fair Value Measurement (Topic 820), Disclosure Framework—Changes to the Disclosure Requirements for Fair Value Measurement”. In December 2019, the FASB issued ASU 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes. This guidance removes certain exceptions for recognizing deferred taxes for investments, performing intraperiod allocation and calculating income taxes in interim periods. It also adds guidance to reduce complexity in certain areas, including recognizing deferred taxes for tax goodwill and allocating taxes to members of a consolidated group. This ASU is effective for interim and annual periods beginning after December 15, 2020, and early adoption is permitted. The Company is

Summary of Significant Accoun_3

Summary of Significant Accounting Policies and Recent Accounting Pronouncements (Tables)	12 Months Ended
	Dec. 31, 2020
Accounting Policies [Abstract]
Schedule of Cash and Cash Equivalents and Restricted Cash	The following table reconciles cash and cash equivalents and restricted cash per the consolidated balance sheet to the statement of cash flows: As of December 31, 2020 2019 Cash and cash equivalents $ 287,308 $ 222,471 Restricted cash 205 205 $ 287,513 $ 222,676
Schedule of Estimated Useful Lives for Property and Equipment	Estimated useful lives for property and equipment are as follows: Property and equipment Estimated useful life Computer and office equipment 3-5 years Laboratory equipment and Furniture and fixtures 5-7 years Leasehold improvements Lesser of estimated useful life or remaining lease term

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2020
Fair Value Disclosures [Abstract]
Schedule of Financial Assets Measured at Fair Value on Recurring Basis and Level of Fair Value Hierarchy Utilized	The following tables present information about the Company’s financial assets measured at fair value on a recurring basis and indicate the level of the fair value hierarchy utilized to determine such fair values: Fair value measurements as of December 31, 2020 Level 1 Level 2 Level 3 Total Cash equivalents: Money market funds $ 287,308 $ — $ — $ 287,308 Total $ 287,308 $ — $ — $ 287,308 Fair value measurements as of December 31, 2019 Level 1 Level 2 Level 3 Total Cash equivalents: Money market funds $ 222,471 $ — $ — $ 222,471 Total $ 222,471 $ — $ — $ 222,471

Property and Equipment, Net (Ta

Property and Equipment, Net (Tables)	12 Months Ended
	Dec. 31, 2020
Property Plant And Equipment [Abstract]
Summary of Property, and Equipment, Net	Property and equipment, net consisted of the following: As of December 31, 2020 2019 Laboratory equipment $ 3,936 $ 2,489 Furniture and fixtures 108 108 Leasehold improvements 210 40 Office equipment 108 79 Construction in progress 5 611 4,367 3,327 Less accumulated depreciation (1,692 ) (815 ) $ 2,675 $ 2,512

Accrued and Other Current Lia_2

Accrued and Other Current Liabilities (Tables)	12 Months Ended
	Dec. 31, 2020
Payables And Accruals [Abstract]
Schedule of Accrued and Other Current Liabilities	Accrued and other current liabilities consisted of the following: As of December 31, 2020 2019 Accrued employee compensation costs $ 4,123 2,053 Accrued professional 593 228 Accrued research and development costs 3,689 959 Accrued other 82 56 Other current liabilities 1,443 54 $ 9,930 $ 3,350

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2020
Commitments And Contingencies Disclosure [Abstract]
Schedule of Future Minimum Lease Payments Under Non-Cancellable Leases	Future minimum lease payments under non-cancellable leases as of December 31, 2020 are as follows (in thousands): 2021 $ 1,102 2022 81 Total lease payments 1,183 Less imputed interest (37) Present value of lease liabilities $ 1,146
Summary of Lease Balances	Lease balances as of December 31, 2020 are as follows (in thousands): Operating right-of-use assets $ 1,115 Current Portion of operating lease liabilities $ 1,066 Non-current portion of operating lease liabilities 80 Total operating lease liabilities $ 1,146
Summary of Weighted Average Remaining Lease Term and Weighted Average Discount Rate of Operating Leases	The weighted average remaining lease term and weighted average discount rate of our operating leases as of December 31, 2020 are as follows: Weighted average remaining lease term in years 1.0 Weighted average discount rate 7.02 %
Schedule of Future Minimum Lease Payments Under Non-Cancellable Leases	2021 1,102 2022 81 Thereafter — $ 1,183

Convertible Preferred Stock (Ta

Convertible Preferred Stock (Tables)	12 Months Ended
	Dec. 31, 2020
Stockholders Equity Note [Abstract]
Summary of Issued and Outstanding Preferred Stock	The following table summarizes the Company’s issued and outstanding Preferred Stock: Series A Preferred Series A-2 Preferred Series B Preferred Total convertible Preferred Shares Amount Shares Amount Shares Amount Shares Amount Balance, December 31, 2018 4,980,168 $ 11,725 7,617,746 $ 28,880 10,079,671 $ 89,742 22,677,585 $ 130,347 Conversion to Common Stock upon initial public offering (4,980,168 ) $ (11,725 ) (7,617,746 ) $ (28,880 ) (10,079,671 ) $ (89,742 ) (22,677,585 ) $ (130,347 ) Balance, December 31, 2019 — — — — — — — —

Share-Based Compensation (Table

Share-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Summary of Stock Option Activity for Awards	A summary of stock option activity for awards is presented below: Number of shares Weighted average exercise price Weighted average remaining contractual life (years) Aggregate intrinsic value ( 1) Outstanding as of January 1, 2019 3,484,628 $ 1.20 8.9 $ 3,436 Granted 1,234,569 10.39 Exercised (382,068 ) 0.91 Forfeited or expired (94,772 ) 1.24 Outstanding as of December 31, 2019 4,242,357 3.91 8.8 106,138 Granted 1,231,532 23.72 Exercised (841,463 ) 3.38 Forfeited or expired (178,004 ) 21.15 Outstanding as of December 31, 2020 4,454,422 $ 8.80 8.0 $ 236,685 Exercisable as of December 31, 2020 1,918,281 $ 4.40 7.4 $ 110,350
Summary of Stock-based Compensation Expense	Stock-based compensation expense recorded as research and development and general and administrative expenses in the accompanying consolidated statements of operations is as follows: Year ended December 31, 2020 2019 Research and development $ 1,875 $ 499 General and administrative 3,893 1,423 $ 5,768 $ 1,922
Summary of Fair Values of Options Granted to Employees and Directors	The Company uses the Black-Scholes option pricing model to calculate the grant-date fair value of an award. The fair values of the options granted to employees and directors were calculated using the following assumptions for the years ended December 31, 2020 and 2019: Year ended December 31, 2020 2019 Risk-free interest rate 0.38-1.48% 1.42-2.81% Expected dividend yield 0 % 0 % Expected life 5.5-6.25 years 5.5-6.375 years Expected volatility 70 % 60-68%

Net Loss Per Share Attributab_2

Net Loss Per Share Attributable to Common Stockholders (Tables)	12 Months Ended
	Dec. 31, 2020
Earnings Per Share [Abstract]
Schedule of Computation of Basic and Diluted Net Loss Per Share Attributable to Common Stockholders	The following table summarizes the computation of basic and diluted net loss per share attributable to common stockholders of the Company: Year ended December 31, 2020 2019 Numerator: Net loss $ (52,243 ) $ (32,325 ) Denominator: Weighted-average number of common shares, basic and diluted 33,488,456 17,971,443 Net loss per share, basic and diluted $ (1.56 ) $ (1.80 )
Schedule of Antidilutive Securities Excluded from Computation of Diluted Net Loss Per Share	The Company excluded the following potential common shares, presented based on amounts outstanding at period end, from the computation of diluted net loss per share for the periods indicated because including them would have had an anti-dilutive effect: December 31, 2020 2019 Outstanding options to purchase common stock 4,454,424 4,242,357

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Reconciliation of Expected Income Tax Expense (Benefit) using Federal Statutory Income Tax Rate to Effective Income Tax Rate	A reconciliation of the expected income tax expense (benefit) computed using the federal statutory income tax rate to the Company’s effective income tax rate is as follows: Year ended December 31, 2020 2019 Expected income tax benefit at the federal statutory rate 21.0 % 21.0 % State income taxes, net of federal benefit 8.3 6.7 Non-deductible items 6.2 (0.4 ) Research and development credit, net 1.2 4.3 Other 0.2 0.3 Change in valuation allowance (36.9 ) (31.9 ) Total 0.0 % 0.0 %
Schedule of Deferred Tax Assets and Liabilities	The principal components of the Company’s deferred tax assets and liabilities consist of the following: As of December 31, 2020 2019 Deferred tax assets: Federal and state net operating loss carryforwards $ 32,097 $ 14,999 Research and development tax credits 2,816 2,171 Other 2,293 761 Gross deferred tax assets 37,206 17,931 Less: valuation allowance (37,206 ) (17,931 ) Net deferred tax assets $ — $ —

Selected Quarterly Financial _2

Selected Quarterly Financial Information (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2020
Quarterly Financial Information Disclosure [Abstract]
Selected Quarterly Results from Operations	Selected quarterly results from operations for the years ended December 31, 2020 and 2019 are as follows: (in thousands, except for per share data) 2020 Quarter End March 31 June 30 September 30 December 31 Revenue — — — — Operating expenses $ 11,735 $ 13,012 $ 13,711 $ 14,586 Loss from operations (11,735 ) (13,012 ) (13,711 ) (14,586 ) Net loss (11,039 ) (12,959 ) (13,684 ) (14,561 ) Net loss per share, basic and diluted $ (0.34 ) $ (0.39 ) $ (0.41 ) $ (0.42 ) 2019 Quarter End March 31 June 30 September 30 December 31 Revenue — — — — Operating expenses $ 6,322 $ 8,445 $ 9,842 $ 11,069 Loss from operations (6,322 ) (8,445 ) (9,842 ) (11,069 ) Net loss (5,742 ) (7,819 ) (8,604 ) (10,160 ) Net loss per share, basic and diluted $ (6.89 ) $ (1.54 ) $ (0.26 ) $ (0.31 )

Nature of the Business and Ba_2

Nature of the Business and Basis of Presentation - Additional Information (Details)	Nov. 24, 2020USD ($)$ / sharesshares	Jun. 21, 2019USD ($)$ / sharesshares	Jun. 06, 2019	Jul. 31, 2020USD ($)	Dec. 31, 2020USD ($)$ / sharesshares	Dec. 31, 2019$ / sharesshares
Nature Of Business And Basis Of Presentation [Line Items]
Entity incorporation state name					DE
Securities issued in connection with shelf registration					$ 0
Reverse stock split, description					On June 6, 2019, the Company effected a one-for-9.95 reverse split of the Company’s issued and outstanding common and convertible preferred stock.
Reverse stock split			0.1005
Common stock, shares authorized | shares		300,000,000			300,000,000	300,000,000
Common stock, per share par value | $ / shares		$ 0.0001			$ 0.0001	$ 0.0001
Undesignated preferred stock, shares authorized | shares		10,000,000
Undesignated preferred stock, per share par value | $ / shares		$ 0.0001
Common Stock
Nature Of Business And Basis Of Presentation [Line Items]
Net proceeds from underwritten public offering	$ 104,900,000
Net proceeds from initial public offering		$ 149,400,000
Base Prospectus
Nature Of Business And Basis Of Presentation [Line Items]
Maximum aggregate offering price				$ 400,000,000
Sales Agreement Prospectus
Nature Of Business And Basis Of Presentation [Line Items]
Maximum aggregate offering price				$ 150,000,000
Underwritten Public Offering | Common Stock
Nature Of Business And Basis Of Presentation [Line Items]
Stock issued during period, shares | shares	2,875,000
Stock issued, price per share | $ / shares	$ 39
Underwriters' Option | Common Stock
Nature Of Business And Basis Of Presentation [Line Items]
Stock issued during period, shares | shares	375,000	1,183,666
Initial Public Offering | Common Stock
Nature Of Business And Basis Of Presentation [Line Items]
Stock issued during period, shares | shares		9,074,776				9,074,776
Stock issued, price per share | $ / shares		$ 18
Offering costs		$ 13,900,000

Summary of Significant Accoun_4

Summary of Significant Accounting Policies and Recent Accounting Pronouncements - Schedule of Cash and Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accounting Policies [Abstract]
Cash and cash equivalents	$ 287,308	$ 222,471
Restricted cash	205	205
Total cash, cash equivalents and restricted cash	$ 287,513	$ 222,676	$ 105,603

Summary of Significant Accoun_5

Summary of Significant Accounting Policies and Recent Accounting Pronouncements - Schedule of Estimated Useful Lives for Property and Equipment (Details)	12 Months Ended
	Dec. 31, 2020
Computer and Office Equipment | Minimum
Property Plant And Equipment [Line Items]
Estimated useful life	3 years
Computer and Office Equipment | Maximum
Property Plant And Equipment [Line Items]
Estimated useful life	5 years
Laboratory Equipment and Furniture and Fixtures | Minimum
Property Plant And Equipment [Line Items]
Estimated useful life	5 years
Laboratory Equipment and Furniture and Fixtures | Maximum
Property Plant And Equipment [Line Items]
Estimated useful life	7 years
Leasehold Improvements
Property Plant And Equipment [Line Items]
Estimated useful life	Lesser of estimated useful life or remaining lease term

Summary of Significant Accoun_6

Summary of Significant Accounting Policies and Recent Accounting Pronouncements - Additional Information (Details)	12 Months Ended
	Dec. 31, 2020USD ($)Segment	Dec. 31, 2019USD ($)	Dec. 31, 2017	Jan. 01, 2020USD ($)	Dec. 31, 2018USD ($)
Accounting Policies [Line Items]
Impairment losses recognized	$ 0	$ 0
Operating lease right-of-use assets	1,115,000
Operating lease liabilities	1,146,000
Cumulative effect adjustment	286,078,000	$ 224,428,000			$ 105,068,000
Unrecognized income tax benefits, interest or penalties	$ 0
Federal corporate tax rate	21.00%	21.00%	35.00%
Number of operating segments | Segment	1
ASU 2016-02
Accounting Policies [Line Items]
Change in accounting principle, accounting standards update, adopted	true
Change in accounting principle, accounting standards update, adoption date	Jan. 1, 2020
Operating lease right-of-use assets				$ 2,200,000
Operating lease liabilities				2,200,000
Deferred rent				30,000
ASU 2016-02 | Cumulative Effect, Period of Adoption, Adjustment
Accounting Policies [Line Items]
Cumulative effect adjustment				$ 0
ASU 2017-11
Accounting Policies [Line Items]
Change in accounting principle, accounting standards update, adopted	true
Change in accounting principle, accounting standards update, adoption date	Jan. 1, 2020
Change in accounting principle, accounting standards update, immaterial effect	true
ASU 2018-13
Accounting Policies [Line Items]
Change in accounting principle, accounting standards update, adopted	true
Change in accounting principle, accounting standards update, adoption date	Jan. 1, 2020
Change in accounting principle, accounting standards update, immaterial effect	true

Fair Value Measurements - Sched

Fair Value Measurements - Schedule of Financial Assets Measured at Fair Value on Recurring Basis and Level of Fair Value Hierarchy Utilized (Details) - Fair Value, Recurring - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents	$ 287,308	$ 222,471
Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents	287,308	222,471
Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents	287,308	222,471
Level 1 | Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents	$ 287,308	$ 222,471

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Fair Value Disclosures [Abstract]
Fair value assets, transfers between level 1, level 2 and level 3, amount	$ 0	$ 0
Fair value liabilities, transfers between level 1, level 2 and level 3, amount	$ 0	$ 0

Property and Equipment, Net - S

Property and Equipment, Net - Summary of Property, and Equipment, Net (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Property Plant And Equipment [Line Items]
Property, and equipment, gross	$ 4,367	$ 3,327
Less accumulated depreciation	(1,692)	(815)
Property, and equipment, net	2,675	2,512
Laboratory Equipment
Property Plant And Equipment [Line Items]
Property, and equipment, gross	3,936	2,489
Furniture and Fixtures
Property Plant And Equipment [Line Items]
Property, and equipment, gross	108	108
Leasehold Improvements
Property Plant And Equipment [Line Items]
Property, and equipment, gross	210	40
Office Equipment
Property Plant And Equipment [Line Items]
Property, and equipment, gross	108	79
Construction in Progress
Property Plant And Equipment [Line Items]
Property, and equipment, gross	$ 5	$ 611

Property and Equipment, Net - A

Property and Equipment, Net - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Property Plant And Equipment [Abstract]
Depreciation	$ 888	$ 450

Accrued and Other Current Lia_3

Accrued and Other Current Liabilities - Schedule of Accrued and Other Current Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Payables And Accruals [Abstract]
Accrued employee compensation costs	$ 4,123	$ 2,053
Accrued professional	593	228
Accrued research and development costs	3,689	959
Accrued other	82	56
Other current liabilities	1,443	54
Total accrued and other current liabilities	$ 9,930	$ 3,350

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Details)	1 Months Ended			12 Months Ended
	Dec. 31, 2018USD ($)ft²Option	Aug. 31, 2018USD ($)ft²	Jul. 31, 2015USD ($)shares	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)	Dec. 31, 2020GBP (£)
Commitments And Contingencies [Line Items]
Area of space subject to operating lease | ft²	2,485	23,000
Operating lease term	3 years	3 years
Operating lease cost per year	$ 200,000	$ 900,000
Annual base rent increase percentage for operating lease	2.50%	3.00%
Operating lease commencement date	May 1, 2019	Dec. 10, 2018
Number of options to renewal operating lease term | Option	1
Operating lease, renewal term	2 years
Liabilities recorded under agreement				$ 11,847,000	$ 4,322,000
CSHL Agreement
Commitments And Contingencies [Line Items]
Stock issued during period, shares | shares			164,927
Shares of common stock granted, value			$ 70,000
Percentage of maximum required payment of sublicense revenue			20.00%
Annual license maintenance fee				10,000
Maximum aggregate potential milestone payments payable				900,000
Expenses related to reimbursable patent costs				0	0
Southampton Agreement
Commitments And Contingencies [Line Items]
Maximum aggregate potential milestone payments payable				500,000		£ 400,000
Liabilities recorded under agreement				0	0
Member of Board of Directors
Commitments And Contingencies [Line Items]
Consulting services expenses				$ 20,000	20,000
Consulting services agreement term				5 years
Scientific advisory services expenses				$ 50,000
Scientific advisory services agreement term				12 months
ASU 2016-02
Commitments And Contingencies [Line Items]
Operating leases expense				$ 1,100,000	$ 1,100,000

Commitments and Contingencies_2

Commitments and Contingencies - Schedule of Future Minimum Lease Payments Under Non-Cancellable Leases (Details) $ in Thousands	Dec. 31, 2020USD ($)
Future minimum lease payments under non-cancellable leases
2021	$ 1,102
2022	81
Total lease payments	1,183
Less imputed interest	(37)
Present value of lease liabilities	$ 1,146

Commitments and Contingencies_3

Commitments and Contingencies - Summary of Lease Balances (Details) $ in Thousands	Dec. 31, 2020USD ($)
Commitments And Contingencies Disclosure [Abstract]
Operating lease right-of-use assets	$ 1,115
Current Portion of operating lease liabilities	$ 1,066
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	stok:AccruedAndOtherCurrentLiabilities
Non-current portion of operating lease liabilities	$ 80
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	us-gaap:LiabilitiesNoncurrent
Total operating lease liabilities	$ 1,146

Commitments and Contingencies_4

Commitments and Contingencies - Summary of Weighted Average Remaining Lease Term and Weighted Average Discount Rate of Operating Leases (Details)	Dec. 31, 2020
Commitments And Contingencies Disclosure [Abstract]
Weighted average remaining lease term in years	1 year
Weighted average discount rate	7.02%

Commitments and Contingencies_5

Commitments and Contingencies - Schedule of Future Minimum Lease Payments Under Non-Cancellable Leases Before the Adoption of Topic 842 (Details) $ in Thousands	Dec. 31, 2020USD ($)
Future minimum payments for operating leases
2021	$ 1,102
2022	81
Total	$ 1,183

Convertible Preferred Stock - A

Convertible Preferred Stock - Additional Information (Details) - $ / shares	Dec. 31, 2020	Dec. 31, 2019	Jun. 21, 2019
Stockholders Equity Note [Abstract]
Common stock, shares authorized	300,000,000	300,000,000	300,000,000
Common stock, par value	$ 0.0001	$ 0.0001	$ 0.0001
Preferred stock, shares authorized			10,000,000
Preferred stock, par value			$ 0.0001
Preferred stock, shares outstanding	0	0

Convertible Preferred Stock - S

Convertible Preferred Stock - Summary of Issued and Outstanding Preferred Stock (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019USD ($)shares
Class Of Stock [Line Items]
Balance, Shares	0
Series A Convertible Preferred Stock
Class Of Stock [Line Items]
Balance | $	$ 11,725
Conversion to Common Stock upon initial public offering | $	$ (11,725)
Conversion to Common Stock upon initial public offering, Shares	(4,980,168)
Balance, Shares	4,980,168
Series A-2 Convertible Preferred Stock
Class Of Stock [Line Items]
Balance | $	$ 28,880
Conversion to Common Stock upon initial public offering | $	$ (28,880)
Conversion to Common Stock upon initial public offering, Shares	(7,617,746)
Balance, Shares	7,617,746
Series B Convertible Preferred Stock
Class Of Stock [Line Items]
Balance | $	$ 89,742
Conversion to Common Stock upon initial public offering | $	$ (89,742)
Conversion to Common Stock upon initial public offering, Shares	(10,079,671)
Balance, Shares	10,079,671
Convertible Preferred Stock
Class Of Stock [Line Items]
Balance | $	$ 130,347
Conversion of preferred stock to common stock | $	$ (2)
Conversion of preferred stock to common stock, Shares	(22,677,585)
Conversion to Common Stock upon initial public offering | $	$ (130,347)
Conversion to Common Stock upon initial public offering, Shares	(22,677,585)
Balance, Shares	22,677,585

Share-Based Compensation - Addi

Share-Based Compensation - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	12 Months Ended
	Jun. 30, 2019	Dec. 31, 2020	Dec. 31, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Option granted to purchase shares		1,231,532	1,234,569
Options vest over period		4 years
Weighted average grant date fair value per share of stock options granted		$ 14.75	$ 6.06
Aggregate grant date fair value of stock options granted		$ 18,200	$ 7,500
Aggregate intrinsic value of stock options exercised		27,300	10,500
Stock based compensation expense		5,768	$ 1,922
Unrecognized compensation cost		$ 17,600
Expected weighted average period		2 years 10 months 24 days
Member of Board of Directors | Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options vest over period		1 year
Member of Board of Directors | Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options vest over period		3 years
2019 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares of common stock reserved for issuance	2,200,000
Percentage of increase in reserved common shares	4.00%
Number of common shares available for future issuance		2,431,303
2014 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of common shares available for future issuance		0
2019 ESPP
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares of common stock reserved for issuance	315,000
Number of common shares available for future issuance		288,808
Weighted average grant date fair value per share of stock options granted		$ 25.46
Stock based compensation expense		$ 300
2019 ESPP | Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares of common stock reserved for issuance	3,150,000
Percentage of increase in reserved common shares	1.00%

Share-Based Compensation - Summ

Share-Based Compensation - Summary of Stock Option Activity for Awards (Details) - USD ($) $ / shares in Units, $ in Thousands		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of shares, Outstanding balance		4,242,357	3,484,628
Number of shares, Granted		1,231,532	1,234,569
Number of shares, Exercised		(841,463)	(382,068)
Number of shares, Forfeited or expired		(178,004)	(94,772)
Number of shares, Outstanding balance		4,454,422	4,242,357	3,484,628
Number of shares, Exercisable as of December 31, 2019		1,918,281
Weighted average exercise price, Outstanding balance		$ 3.91	$ 1.20
Weighted average exercise price, Granted		23.72	10.39
Weighted average exercise price, Exercised		3.38	0.91
Weighted average exercise price, Forfeited or expired		21.15	1.24
Weighted average exercise price, Outstanding balance		8.80	$ 3.91	$ 1.20
Weighted average exercise price, Exercisable as of December 31, 2019		$ 4.40
Weighted average remaining contractual life, Outstanding		8 years	8 years 9 months 18 days	8 years 10 months 24 days
Weighted average remaining contractual life, Exercisable		7 years 4 months 24 days
Aggregate intrinsic value, Outstanding value	[1]	$ 236,685	$ 106,138	$ 3,436
Aggregate intrinsic value, Exercisable as of December 31, 2019	[1]	$ 110,350
[1]	The aggregate intrinsic value is calculated as the difference between the exercise price of the underlying options and the estimated fair value of the common stock for the options that were in the money at December 31, 2020 and 2019.

Share-Based Compensation - Su_2

Share-Based Compensation - Summary of Stock-based Compensation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock based compensation expense	$ 5,768	$ 1,922
Research and Development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock based compensation expense	1,875	499
General and Administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock based compensation expense	$ 3,893	$ 1,423

Share-Based Compensation - Su_3

Share-Based Compensation - Summary of Fair Values of Options Granted to Employees and Directors (Details)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Risk-free interest rate, minimum	0.38%	1.42%
Risk-free interest rate, maximum	1.48%	2.81%
Expected dividend yield	0.00%	0.00%
Expected volatility, minimum		60.00%
Expected volatility	70.00%
Expected volatility, maximum		68.00%
Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected life	5 years 6 months	5 years 6 months
Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected life	6 years 3 months	6 years 4 months 15 days

Net Loss Per Share Attributab_3

Net Loss Per Share Attributable to Common Stockholders - Schedule of Computation of Basic and Diluted Net Loss Per Share Attributable to Common Stockholders (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019
Numerator:
Net loss	$ (14,561)	$ (13,684)	$ (12,959)	$ (11,039)	$ (10,160)	$ (8,604)	$ (7,819)	$ (5,742)	$ (52,243)	$ (32,325)
Denominator:
Weighted-average number of common shares, basic and diluted									33,488,456	17,971,443
Net loss per share, basic and diluted	$ (0.42)	$ (0.41)	$ (0.39)	$ (0.34)	$ (0.31)	$ (0.26)	$ (1.54)	$ (6.89)	$ (1.56)	$ (1.80)

Net Loss Per Share Attributab_4

Net Loss Per Share Attributable to Common Stockholders - Schedule of Antidilutive Securities Excluded from Computation of Diluted Net Loss Per Share (Details) - shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Outstanding Options to Purchase Common Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of earnings per share, amount	4,454,424	4,242,357

Income Taxes - Reconciliation o

Income Taxes - Reconciliation of Expected Income Tax Expense (Benefit) using Federal Statutory Income Tax Rate to Effective Income Tax Rate (Details)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Expected income tax benefit at the federal statutory rate	21.00%	21.00%	35.00%
State income taxes, net of federal benefit	8.30%	6.70%
Non-deductible items	6.20%	(0.40%)
Research and development credit, net	1.20%	4.30%
Other	0.20%	0.30%
Change in valuation allowance	(36.90%)	(31.90%)
Total	0.00%	0.00%

Income Taxes - Schedule of Defe

Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Deferred tax assets:
Federal and state net operating loss carryforwards	$ 32,097	$ 14,999
Research and development tax credits	2,816	2,171
Other	2,293	761
Gross deferred tax assets	37,206	17,931
Less: valuation allowance	$ (37,206)	$ (17,931)

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Income Taxes [Line Items]
Valuation allowance	$ 37,206,000	$ 17,931,000
Change in valuation allowance	$ 19,300,000	10,300,000
Percentage of taxable income, limitation repealed under CARES act	80.00%
Percentage of federal NOL carry forwards subject to limitation under CARES act	80.00%
Federal NOL carry back period under CARES act	5 years
Unrecognized tax benefits	$ 0	0
Federal
Income Taxes [Line Items]
Operating loss carryforwards	$ 116,900,000	$ 54,500,000
Operating loss carryforwards, expiration beginning year	2034	2034
Federal | Research and Development Tax Credit
Income Taxes [Line Items]
Tax credit carryforwards	$ 2,000,000	$ 1,500,000
Tax credit carryforwards, expiration beginning year	2030	2030
State
Income Taxes [Line Items]
Operating loss carryforwards	$ 118,800,000	$ 56,300,000
Operating loss carryforwards, expiration beginning year	2034	2034
State | Research and Development Tax Credit
Income Taxes [Line Items]
Tax credit carryforwards	$ 1,000,000	$ 800,000
Tax credit carryforwards, expiration beginning year	2030	2030

Employee Benefits - Additional

Employee Benefits - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Defined Contribution Plan Disclosure [Line Items]
Contributions to 401(k) Plan	$ 20,000	$ 0
Maximum
Defined Contribution Plan Disclosure [Line Items]
Maximum matching contribution percentage of employees salary	4.00%

Selected Quarterly Financial _3

Selected Quarterly Financial Information (Unaudited) - Selected Quarterly Results from Operations (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019
Quarterly Financial Information Disclosure [Abstract]
Operating expenses	$ 14,586	$ 13,711	$ 13,012	$ 11,735	$ 11,069	$ 9,842	$ 8,445	$ 6,322	$ 53,044	$ 35,678
Loss from operations	(14,586)	(13,711)	(13,012)	(11,735)	(11,069)	(9,842)	(8,445)	(6,322)	(53,044)	(35,678)
Net loss	$ (14,561)	$ (13,684)	$ (12,959)	$ (11,039)	$ (10,160)	$ (8,604)	$ (7,819)	$ (5,742)	$ (52,243)	$ (32,325)
Net loss per share—basic and diluted	$ (0.42)	$ (0.41)	$ (0.39)	$ (0.34)	$ (0.31)	$ (0.26)	$ (1.54)	$ (6.89)	$ (1.56)	$ (1.80)