RAPT Therapeutics (RAPT) 10-K 10 Mar 22 2021 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Mar. 04, 2022	Jun. 30, 2021
Cover [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2021
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	FY
Trading Symbol	RAPT
Entity Registrant Name	RAPT THERAPEUTICS, INC.
Entity Central Index Key	0001673772
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity Current Reporting Status	Yes
Entity Shell Company	false
Entity File Number	001-38997
Entity Tax Identification Number	47-3313701
Entity Address, Address Line One	561 Eccles Avenue
Entity Address, City or Town	South San Francisco
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	94080
City Area Code	650
Local Phone Number	489-9000
Entity Common Stock, Shares Outstanding		29,573,318
Entity Interactive Data Current	Yes
Title of 12(b) Security	Common Stock, par value $0.0001 per share
Security Exchange Name	NASDAQ
Entity Incorporation, State or Country Code	DE
Document Annual Report	true
Document Transition Report	false
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
ICFR Auditor Attestation Flag	false
Entity Public Float			$ 622
Auditor Firm ID	42
Auditor Name	Ernst & Young LLP
Auditor Location	Redwood City, California
Documents Incorporated by Reference	DOCUMENTS INCORPORATED BY REFERENCE Portions of the Registrant’s Definitive Proxy Statement for the 2022 Annual Meeting of Stockholders to be filed with the U.S. Securities and Exchange Commission pursuant to Regulation 14A within 120 days after the end of the fiscal year covered by this Annual Report on Form 10-K are incorporated by reference in Part III, Items 10-14 of this Annual Report on Form 10-K.

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 24,027	$ 24,918
Marketable securities	165,627	86,592
Prepaid expenses and other current assets	3,319	4,088
Total current assets	192,973	115,598
Property and equipment, net	2,741	2,982
Other assets	2,922	389
Total assets	198,636	118,969
Current liabilities:
Accounts payable	1,999	2,383
Accrued expenses	6,326	4,935
Deferred revenue, current	1,016	4,096
Other current liabilities	254	328
Total current liabilities	9,595	11,742
Deferred revenue, net of current portion	511	863
Deferred rent, net of current portion	2,150	2,185
Total liabilities	12,256	14,790
Commitments (see note 6)
Stockholders' equity:
Preferred stock, $0.0001 par value: 50,000,000 shares authorized; no shares issued and outstanding at December 31, 2021 and 2020
Common stock, $0.0001 par value; 500,000,000 shares authorized; 29,555,119 and 24,773,361 shares issued and outstanding at December 31, 2021 and 2020, respectively	3	2
Additional paid-in capital	470,629	319,196
Accumulated other comprehensive loss	(206)	(177)
Accumulated deficit	(284,046)	(214,842)
Total stockholders' equity	186,380	104,179
Total liabilities and stockholders' equity	$ 198,636	$ 118,969

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Dec. 31, 2021	Dec. 31, 2020
Statement Of Financial Position [Abstract]
Preferred stock, par value	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	50,000,000	50,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	500,000,000	500,000,000
Common stock, shares issued	29,555,119	24,773,361
Common stock, shares outstanding	29,555,119	24,773,361

CONSOLIDATED STATEMENTS OF OPER

CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Income Statement [Abstract]
Revenue	$ 3,813	$ 5,042
Operating expenses:
Research and development	56,985	45,485
General and administrative	16,037	12,771
Total operating expenses	73,022	58,256
Loss from operations	(69,209)	(53,214)
Other income, net	5	1,312
Net loss before taxes	(69,204)	(51,902)
Provision for income taxes		990
Net loss	(69,204)	(52,892)
Other comprehensive income (loss):
Foreign currency translation gain (loss)	258	(249)
Unrealized gain (loss) on marketable securities	(287)	52
Total comprehensive loss	$ (69,233)	$ (53,089)
Net loss per share, basic and diluted	$ (2.53)	$ (2.19)
Weighted average number of shares used in computing net loss per share, basic and diluted	27,390,326	24,134,305

CONSOLIDATED STATEMENTS OF STOC

CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	At The Market	Common Stock	Common StockAt The Market	Additional Paid-In Capital	Additional Paid-In CapitalAt The Market	Accumulated Deficit	Accumulated Other Comprehensive Income (Loss)
Beginning balance at Dec. 31, 2019	$ 73,121		$ 2		$ 235,049		$ (161,950)	$ 20
Beginning balance, shares at Dec. 31, 2019			21,833,037
Issuance of common stock, net of issuance costs	69,842	$ 3,768			69,842	$ 3,768
Issuance of common stock, net of issuance costs, shares			2,500,000	188,700
Issuances of common stock from employee stock plans	1,851				1,851
Issuances of common stock from employee stock plans, shares			251,624
Stock-based compensation	8,686				8,686
Foreign currency translation gain (loss)	(249)							(249)
Unrealized gain (loss) on marketable securities	52							52
Net loss	(52,892)						(52,892)
Ending balance at Dec. 31, 2020	$ 104,179		$ 2		319,196		(214,842)	(177)
Ending balance, shares at Dec. 31, 2020	24,773,361		24,773,361
Issuance of common stock, net of issuance costs	$ 134,770	$ 4,690	$ 1		134,769	$ 4,690
Issuance of common stock, net of issuance costs, shares			4,356,060	214,971
Issuances of common stock from employee stock plans	2,022				2,022
Issuances of common stock from employee stock plans, shares			210,727
Stock-based compensation	9,952				9,952
Foreign currency translation gain (loss)	258							258
Unrealized gain (loss) on marketable securities	(287)							(287)
Net loss	(69,204)						(69,204)
Ending balance at Dec. 31, 2021	$ 186,380		$ 3		$ 470,629		$ (284,046)	$ (206)
Ending balance, shares at Dec. 31, 2021	29,555,119		29,555,119

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Operating activities
Net loss	$ (69,204)	$ (52,892)
Adjustments to reconcile net loss to net cash used in operating activities:
Amortization of premium on marketable securities	1,270	497
Depreciation and amortization	996	1,123
Stock-based compensation expense	9,952	8,686
Loss on disposal of capital equipment	0	0
Gain (loss) on foreign currency translation	258	(249)
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(1,764)	(965)
Accounts payable, accrued expenses, and other current liabilities	933	2,390
Deferred revenue	(3,432)	959
Deferred rent, net of current portion	(35)	(40)
Net cash used in operating activities	(61,026)	(40,491)
Investing activities
Purchase of marketable securities	(164,977)	(139,334)
Proceeds from maturities of marketable securities	84,385	52,297
Proceeds from sale of equipment	0	0
Purchase of property and equipment	(755)	(398)
Net cash used in investing activities	(81,347)	(87,435)
Financing activities
Proceeds from issuances of common stock under employee stock plans	2,022	1,851
Net cash provided by financing activities	141,482	75,461
Net increase in cash and cash equivalents	(891)	(52,465)
Cash and cash equivalents at beginning of year	24,918	77,383
Cash and cash equivalents at end of year	24,027	24,918
Supplemental disclosures of cash flow information:
Cash paid for income taxes	0	990
Supplemental disclosures of non-cash investing and financing information
Offering costs included in accounts payable and accrued expenses	20	208
Public Offering
Financing activities
Proceeds from issuance of common stock, net of issuance costs	134,770	73,610
At The Market
Financing activities
Proceeds from issuance of common stock, net of issuance costs	$ 4,690	$ 0

Organization

Organization	12 Months Ended
	Dec. 31, 2021
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Organization	1. Organization Description of the Business RAPT Therapeutics, Inc. ( “ ” “ ” Equity Financings In June 2021, pursuant to the shelf registration statement on Form S-3 that was declared effective by the Securities and Exchange Commission (“SEC”) on November 16, 2020, the Company completed an underwritten public offering (“2021 Public Offering”) of 4,356,060 shares of common stock, including 568,181 shares of common stock issued in connection with the exercise of the over-allotment option by the underwriters, at a public offering price of $33.00 per share. The Company received approximately $134.8 million in net proceeds from the 2021 Public Offering, after deducting underwriting discounts and other offering-related costs. In February 2020, the Company completed an underwritten follow-on public offering (“Follow‑on Offering”) of 2,500,000 shares of its common stock issued at an offering price of $30.00 per share. The Follow-on Offering generated approximately $69.8 million in net proceeds after deducting underwriting discounts and other offering related costs. In November 2020, the Company filed a shelf registration statement on Form S-3 with the SEC covering (a) up to $350 million of the Company’s securities, including up to $100 million of shares of common stock that may be offered and sold from time to time in one or more “at-the-market” offerings pursuant to a Controlled Equity Offering SM Liquidity and Management Plans The accompanying consolidated financial statements have been prepared assuming that the Company will continue as a going concern. Since inception, the Company has incurred net losses and negative cash flows from operations. During the year ended December 31, 2021, the Company incurred a net loss of $69.2 million and used $61.0 million of cash in operations. At December 31, 2021, the Company had cash and cash equivalents and marketable securities of $189.7 million and working capital of $183.4 million. Management plans to continue to incur substantial costs in order to conduct research and development activities and additional capital will be needed to undertake these activities. The Company intends to raise such capital through the issuance of additional equity, borrowings and strategic alliances with other companies. However, if such arrangements are not available at adequate levels or on acceptable terms, the Company would be required to significantly reduce operating expenses and delay or reduce the scope of or eliminate some of its development programs. Management believes that the Company’s current cash and cash equivalents and marketable securities will provide sufficient funds to enable the Company to meet its obligations for at least 12 months from the filing date of this report.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2021
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Basis of Presentation The accompanying consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles (“U.S. GAAP”) and include the consolidated accounts of the Company and its wholly-owned subsidiary, RAPT Therapeutics Australia Pty Ltd., which was established in 2018. All intercompany balances and transactions have been eliminated in consolidation. Use of Estimates The preparation of the consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. On an ongoing basis, management evaluates its critical accounting policies or estimates related to revenue recognition, clinical trial accruals, fair value of assets and liabilities and stock-based compensation. The Company bases its estimates on historical experience and market-specific or other relevant assumptions that it believes are reasonable under the circumstances. The amounts of assets and liabilities reported in the Company’s balance sheets and the amounts of expenses and revenue reported for each of the periods presented are affected by estimates and assumptions. Actual results could differ from such estimates or assumptions. Concentration of Credit Risk and Other Risks and Uncertainties The Company is subject to a number of risks similar to other biopharmaceutical companies in the early stage, including, but not limited to, the need to obtain adequate additional funding, possible failure of preclinical testing or clinical trials, the need to obtain marketing approval for its product candidates, competitors developing new technological innovations, the need to successfully commercialize and gain market acceptance of the Company’s products and protection of proprietary technology. If the Company does not successfully obtain regulatory approval, commercialize or partner any of its product candidates, it will be unable to generate revenue from product sales or achieve profitability. Financial instruments that potentially subject the Company to a concentration of credit risk consist of cash and cash equivalents and marketable securities. Substantially all the Company’s cash is held by two financial institutions. Such deposits may, at times, exceed federally insured limits. The Company invests its cash equivalents in highly rated money market funds and short-term marketable securities comprising commercial paper, corporate bonds and U.S. government agency securities. Segments The Company operates as a single operating segment. The Company’s chief operating decision maker, its President and Chief Executive Officer, manages the Company’s operations on a consolidated basis for the purposes of allocating resources, making operating decisions and evaluating financial performance. Fair Value of Financial Instruments The carrying amount of the Company’s financial instruments, including certain prepaid and accrued expenses, approximates fair value due to their short-term maturities. Cash Equivalents The Company considers all highly liquid investments with original maturities of 90 days or less from the date of purchase to be cash equivalents. Marketable Securities Marketable securities primarily consist of commercial paper, corporate bonds and U.S. government agency securities Property and Equipment Property and equipment consist of computer equipment, laboratory equipment, leasehold improvements and furniture and fixtures, and is recorded at cost, less accumulated depreciation and amortization. Depreciation and amortization are calculated using the straight-line method over the estimated useful lives of the respective assets, generally three to five years. Leasehold improvements are amortized over the shorter of the lease term or the estimated useful life of the improvements. Depreciation and amortization begin at the time the asset is placed in service. Maintenance and repairs are charged to expense as incurred. Upon sale or retirement of assets, the cost and related accumulated depreciation and amortization are removed from the balance sheet and the resulting gain or loss is reflected in the results of operations. Impairment of Long-Lived Assets The Company evaluates its long-lived assets for impairment annually or more frequently whenever events or changes in circumstances indicate that the carrying value of these assets may not be recoverable. Recoverability of these assets is measured by comparing the carrying amount of each asset to the future undiscounted cash flows the asset is expected to generate over its remaining life. If the asset is considered to be impaired, the amount of any impairment is measured as the difference between the carrying value and the fair value of the impaired asset. For the years ended December 31, 2021 and 2020, the Company did not record any impairment losses on long-lived assets. Leases The Company leases office space and laboratory facilities under non-cancelable operating lease agreements and recognizes related rent expense on a straight-line basis over the term of the lease. Funding of leasehold improvements by the Company’s landlord is accounted for as a tenant improvement allowance and recorded as current and non-current deferred rent liabilities and amortized on a straight-line basis as a reduction of rent expense over the term of the lease. Revenue License and collaborative agreements consist of license, milestone and royalty payments generated through agreements with strategic partners for the development and commercialization of certain product candidates. The terms of an agreement may include a non-refundable upfront fee, payments based upon achievement of milestones and royalties on net product sales. If a portion of the nonrefundable upfront fee or other payments received is allocated to continuing performance obligations under the terms of an agreement, such portion is recorded as deferred revenue and recognized as revenue when (or as) the underlying performance obligation is satisfied. The Company recognizes revenue when it transfers promised goods or services to customers or counterparties in an amount that reflects the consideration to which the Company expects to be entitled in exchange for those goods or services. In determining the appropriate amount of revenue to be recognized, the Company performs the following steps: (i) identification of the promised goods or services in the agreement; (ii) determination of whether the promised goods or services are performance obligations, including whether they are distinct in the context of the agreement; (iii) measurement of the transaction price, including any constraint on variable consideration; (iv) allocation of the transaction price to performance obligations based on estimated selling prices; and (v) recognition of revenue when (or as) the Company satisfies each performance obligation. Licenses : If a license to the Company’s intellectual property is determined to be distinct from the other performance obligations identified in an agreement, the Company will recognize revenue from the nonrefundable, upfront fee allocated to the license when the license is transferred to the licensee and the licensee is able to use and benefit from the license. If a license is bundled with other performance obligations, the Company utilizes judgment to assess the nature of the combined performance obligations to determine whether the combined performance obligations are satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition. Milestone payments : If an agreement includes event-based or milestone payments, the Company evaluates whether the events or milestones are considered likely to be achieved and estimates the amount to be included in the transaction price using the most likely amount method. If it is unlikely that a significant revenue reversal of cumulative revenue recognized would occur, the value of the associated event-based or milestone payments is included in the transaction price. Event-based or milestone payments that are not within the control of the Company are not included in the transaction price until they become likely to be achieved. Royalties : If an agreement includes sales-based royalties and the license is deemed to be the predominant item to which the royalties relate, the Company will recognize revenue at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied (or partially satisfied). Research and Development Costs Research and development costs are expensed as incurred. Research and development costs consist primarily of salaries and benefits of research and development personnel, costs related to research activities, preclinical studies, clinical trials, drug manufacturing and allocated overhead and facility-related expenses. The Company accounts for non-refundable advance payments for goods or services that will be used in future research and development activities as expenses when the goods have been received or when the service has been performed rather than when the payment is made. Clinical trial costs are a component of research and development expenses. The Company expenses costs for its clinical trial activities performed by third parties, including clinical research organizations (“CROs”) and other service providers, as they are incurred, based upon estimates of the work completed over the life of the individual study in accordance with associated agreements. The Company uses information it receives from internal personnel and outside service providers to estimate the clinical trial costs incurred. Stock-Based Compensation The Company measures employee and director stock-based compensation expense for all stock-based awards based on their grant date fair value using the Black-Scholes option-pricing model. For stock-based awards with service conditions only, stock-based compensation expense is recognized over the requisite service period using the straight-line method. Forfeitures are recognized as they occur. Stock-based compensation expense for nonemployee stock-based awards is measured at fair value using the Black-Scholes option-pricing model. The Company recognizes stock-based compensation expense for the estimated fair value of the vested portion of nonemployee awards in its consolidated statements of operations and comprehensive loss. Stock-based compensation expense related to stock-based awards to nonemployees is subject to re-measurement over the service period, which approximates the vesting period. Stock-based compensation expense related to restricted stock awards is determined using the estimated fair value of the Company’s common stock on the date of grant for the period prior to the IPO. The fair value of restricted stock awards granted after the IPO is determined based on the stock price on the date of grant. The estimated fair value is amortized as compensation expense over the service period of the award. Foreign Currency Transactions The functional currency of RAPT Therapeutics Australia Pty Ltd., the Company’s wholly-owned subsidiary, is the Australian dollar. Accordingly, all monetary assets and liabilities of the subsidiary are translated into U.S. dollars at the current period-end exchange rates and non-monetary assets are translated using historical exchange rates. Income and expense elements are remeasured to U.S. dollars using the average exchange rates in effect during the period. Remeasurement gains and losses are recorded as other income (expense), net. The Company is subject to foreign currency risk with respect to its clinical contracts denominated in currencies other than the U.S. dollar. Payments on contracts denominated in foreign currencies are made at the spot rate on the day of payment. The cumulative adjustment resulting from the translation of financial statements to the reporting currency is recorded in other comprehensive income (loss). Income Taxes Income taxes are accounted for under the asset and liability method. Deferred tax assets and liabilities are recognized for the future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases and operating loss and tax credit carryforwards. Deferred tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the years in which those temporary differences are expected to be recovered or settled. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in income in the period such tax rate changes are enacted. The Company recognizes the effect of income tax positions only if those positions are more likely than not to be sustained. Recognized income tax positions are measured at the largest amount that is greater than 50% likely to be realized. Changes in recognition or measurement are reflected in the period in which the change in judgment occurs. Valuation allowances are established when necessary to reduce deferred tax assets to amounts more likely than not to be realized. Interest and penalties related to unrecognized tax benefits are recognized as a component of income tax expense. Comprehensive Loss Comprehensive loss includes net loss and certain changes in stockholders’ deficit that are excluded from net loss, primarily unrealized gains and losses from marketable securities and foreign currency translation adjustments. Net Loss Per Share Basic net loss per share is computed by dividing the net loss by the weighted average number of common shares outstanding during the period, without consideration of potential dilutive securities. Diluted net loss per common share is computed by dividing the net loss by the sum of the weighted average number of common shares outstanding during the period plus the number of potential dilutive securities outstanding during the period calculated in accordance with the treasury stock method. Diluted net loss per share is the same as basic net loss per share since the effect of potentially dilutive securities is anti-dilutive. Recent Accounting Pronouncements From time to time, new accounting pronouncements are issued by the Financial Accounting Standards Board (“FASB”) or other standard setting bodies and adopted by the Company as of the specified effective date. Under the Jumpstart Our Business Startups Act of 2012, as amended (the “JOBS Act”), the Company meets the definition of an emerging growth company and has elected the extended transition period for complying with new or revised accounting standards pursuant to Section 107(b) of the JOBS Act. Recent Accounting Pronouncements Not Yet Adopted In February 2016, the FASB issued ASU No. 2016-02, Leases The adoption of the new standard will have a material impact on the Company’s consolidated balance sheet as of January 1, 2022, as we will recognize the right-of-use assets and liabilities for our operating leases. We expect to record lease liabilities of approximately $8 - $9 million based on the present value of the remaining minimum rental payments using discount rates as of the effective date. We also expect to record corresponding right-of-use assets of approximately $6 - 7 million, based on the operating lease liabilities adjusted for unamortized deferred rent and lease incentives. The Company, however, does not expect a material impact to its consolidated statements of operations and consolidated statements of cash flow. In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments – Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments Codification Improvements to Topic 326, Financial Instruments—Credit Losses, Topic 815, Derivatives and Hedging, and Topic 825, Financial Instruments Financial Instruments—Credit Losses, Topic 326 Financial Instruments—Credit Losses (Topic 326), Derivatives and Hedging (Topic 815), and Leases (Topic 842): Effective Dates Codification Improvements to Topic 326, Financial Instruments—Credit Losses .

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2021
Fair Value Disclosures [Abstract]
Fair Value Measurements	3. Fair Value Measurements Fair value accounting is applied for all financial assets and liabilities that are recognized or disclosed at fair value in the financial statements on a recurring basis (at least annually). Financial instruments include cash and cash equivalents, marketable securities, accounts payable and accrued expenses that approximate fair value due to their relatively short maturities. Assets and liabilities recorded at fair value on a recurring basis in the balance sheet are categorized based upon the level of judgment associated with the inputs used to measure their fair values. Fair value is defined as the exchange price that would be received for an asset or an exit price that would be paid to transfer a liability in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. The authoritative guidance on fair value measurements establishes a three-tier fair value hierarchy for disclosure of fair value measurements as follows: Level 1—Inputs are unadjusted, quoted prices in active markets for identical assets or liabilities at the measurement date; Level 2—Inputs are observable, unadjusted quoted prices in active markets for similar assets or liabilities, unadjusted quoted prices for identical or similar assets or liabilities in markets that are not active or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the related assets or liabilities; and Level 3—Unobservable inputs that are significant to the measurement of the fair value of the assets or liabilities that are supported by little or no market data. To date, the Company has not recorded any impairment charges on its marketable securities due to other-than-temporary declines in market value. In determining whether a decline is other than temporary, the Company considers various factors, including the length of time and extent to which the market value has been less than amortized cost, the financial condition and near-term prospects of the issuer and the Company’s intent and ability to retain its investment in the issuer for a period of time sufficient to allow for any anticipated recovery in market value. The Company estimates the fair values of investments in corporate debt securities, commercial paper and U.S. government agency securities Cash equivalents and marketable securities, all of which are classified as available-for-sale securities and measured at fair value on a recurring basis, consisted of the following (in thousands): As of December 31, 2021 Fair Value Hierarchy Level Amortized Cost Unrealized Gains Unrealized Losses Fair Value Financial assets: Money market funds— classified as cash equivalents Level 1 $ 22,658 $ — $ — $ 22,658 Corporate debt Level 2 52,704 — (139 ) 52,565 Asset-backed securities Level 2 23,882 — (21 ) 23,861 Commercial paper Level 2 59,532 — — 59,532 U.S. government agency securities Level 2 29,744 — (75 ) 29,669 Total $ 188,520 $ — $ (235 ) $ 188,285 As of December 31, 2020 Fair Value Hierarchy Level Amortized Cost Unrealized Gains Unrealized Losses Fair Value Financial assets: Money market funds— classified as cash equivalents Level 1 $ 21,333 $ — $ — $ 21,333 Corporate debt Level 2 32,164 48 — 32,212 Asset-backed securities Level 2 12,367 2 (1 ) 12,368 Commercial paper Level 2 28,962 — — 28,962 U.S. government agency securities Level 2 13,047 3 — 13,050 Total $ 107,873 $ 53 $ (1 ) $ 107,925 The Company does not intend to sell the securities that are in an unrealized loss position and the Company believes it is more likely than not that the investments will be held until recovery of the amortized cost bases. The Company has determined that the gross unrealized losses on marketable securities as of December 31, 2021 were temporary in nature. The following table presents the remaining contractual maturities of the Company’s marketable securities as of December 31, 2021 (in thousands): December 31, 2021 Due in less than one year $ 132,804 Due in more than one year 55,481 Total $ 188,285

Property and Equipment

Property and Equipment	12 Months Ended
	Dec. 31, 2021
Property Plant And Equipment [Abstract]
Property and Equipment	4. Property and Equipment Property and equipment consisted of the following (in thousands): December 31, 2021 2020 Laboratory equipment $ 6,291 $ 5,966 Leasehold improvements 3,295 3,294 Computer equipment 482 447 Furniture and fixtures 357 357 Total property and equipment 10,425 10,064 Less accumulated depreciation and amortization (7,684 ) (7,082 ) Property and equipment, net $ 2,741 $ 2,982 Depreciation and amortization expenses were $1.0 million and $1.1 million for the years ended December 31, 2021 and 2020, respectively.

Accrued Expenses

Accrued Expenses	12 Months Ended
	Dec. 31, 2021
Payables And Accruals [Abstract]
Accrued Expenses	5. Accrued Expenses Accrued expenses consisted of the following (in thousands): December 31, 2021 2020 Accrued research and development expenses $ 2,205 $ 1,576 Accrued compensation 3,652 2,967 Accrued professional and consulting services 415 129 Other 54 263 Total accrued expenses $ 6,326 $ 4,935

Commitments

Commitments	12 Months Ended
	Dec. 31, 2021
Commitments And Contingencies Disclosure [Abstract]
Commitments	6. Commitments The Company enters into contracts in the normal course of business with CROs for preclinical studies and clinical trials. These agreements provide for notice of termination by either party and are, therefore, cancelable contracts. In May 2015, the Company entered into an operating lease for 30,376 square feet of laboratory and office facilities in South San Francisco, California, which expires in May 2022. In April 2018, the Company amended the lease agreement to include an additional 6,378 square feet of laboratory and office space increasing the total leased premises to 36,754 square feet. The lease amendment extended the lease term to November 2026 and contained scheduled rent increases over the lease term and an option for the Company to extend the lease for an additional five-year In February 2019, the Company entered into an agreement to sublease its facility lease of 6,378 square feet of laboratory and office space, which terminated in July 2020. As of December 31, 2021, future minimum non-cancelable lease payments, are as follows (in thousands): Year ending December 31: 2022 $ 2,037 2023 2,109 2024 2,183 2025 2,259 2026 2,137 Thereafter — Total minimum lease payments $ 10,725 The terms of the lease agreement provide for rental payments on a monthly basis and on a graduated scale. The Company recognizes rent expense on a straight-line basis over the lease period and has accrued for rent expense incurred but not paid. Rent expense includes certain monthly charges that do not represent non-cancelable obligations, as defined. These costs are determined based on actual charges incurred. In addition, tenant improvement allowances recorded are amortized as a reduction to rent expense on a straight-line basis over the lease term. Rent expense was $2.3 million and $2.1 million in the years ended December 31, 2021 and 2020, respectively. From time to time, the Company may be subject to various legal proceedings and claims arising in the ordinary course of business. The Company assesses contingencies to determine the degree of probability and range of possible loss for potential accrual in its financial statements. An estimated loss contingency is accrued in the financial statements if it is probable that a liability has been incurred and the amount of the loss can be reasonably estimated. The Company is not subject to any current pending legal matters or claims and no contingency losses were accrued at either December 31, 2021 or 2020.

Collaboration Agreements

Collaboration Agreements	12 Months Ended
	Dec. 31, 2021
Collaboration Agreements [Abstract]
Collaboration Agreements	7. Collaboration Agreements Collaboration and License Agreement with Hanmi In December 2019, the Company entered into a Collaboration and License Agreement with Hanmi (“Hanmi Agreement”), pursuant to which the Company granted Hanmi an exclusive license to develop, manufacture and commercialize FLX475 and related compounds and products with respect to human cancers in the Republic of Korea, the Republic of China (Taiwan) and the People’s Republic of China, including the special administrative regions of Macau and Hong Kong (the “Hanmi Territory”), and certain sublicense In consideration of such rights, under the Hanmi Agreement, the Company was entitled to $10.0 million, which consisted of an upfront payment of $4.0 million and a development milestone payment of $6.0 million that were received in December 2019 and April 2020, respectively. Additionally, the Company is eligible to receive contingent payments of up to $108.0 million upon the achievement of specified milestones, as well as double-digit royalties on future net sales of FLX475 in the Hanmi Territory. The Company identified the following promised goods and services at the inception of the Hanmi Agreement, including (1) the responsibility to complete certain Phase 2 clinical trials; and (5) the supply of FLX475 for use in Hanmi’s Phase 2 clinical trials for which Hanmi will reimburse the Company for the supply of FLX475. The Company determined that the identified performance obligations, except for the supply of FLX475, are not distinct and should be combined into one distinct performance obligation. The Company considered factors such as the novelty of the drug candidate and that the promised goods and services are highly interdependent and are expected to significantly modify one another. The Company determined that the transaction price as of December 31, 2019 was $10.0 million, which consisted of the upfront fee of $4.0 million and an unconstrained development milestone payment of $6.0 million. In December 2020, Hanmi requested the Company to supply FLX475, and as a result, the Company increased the transaction price by $0.4 million. Other future development milestones were constrained as their achievement was highly dependent on factors outside the Company’s control. The Company expects that the revenue from sales milestone and royalty payments will be recognized when the sales occur or the milestone is achieved. The Company will re-evaluate the transaction price at each reporting period. The Company recognizes revenue for the performance obligation by applying the cost-based input method over the estimated service period. The Company determined that this method most faithfully depicts the transfer of its performance obligations to Hanmi as it reflects the progress made towards providing Hanmi with the necessary know-how to continue developing FLX475 in the Hanmi Territory. For the years ended December 31, 2021 and 2020, $3.8 million and $5.0 million of revenue was recognized pursuant to the Hanmi Agreement, respectively. As of December 31, 2021, deferred revenue related to the Hanmi Agreement was $1.5 million and is expected to be recognized over the over the remaining period of the Company’s Phase 1/2 clinical trial of FLX475. Clinical Trial Collaboration and Supply Agreement with Merck In November 2018, the Company entered into a clinical trial collaboration and supply agreement with an affiliate of Merck (known as MSD outside the United States and Canada) under which the Company will conduct a clinical trial evaluating FLX475 in combination with pembrolizumab (KEYTRUDA ®

Common Stock

Common Stock	12 Months Ended
	Dec. 31, 2021
Equity [Abstract]
Common Stock	8. Common Stock The holders of the Company’s common stock have one vote for each share of common stock held by them. Holders of shares of the Company’s common stock are entitled to dividends when, as and if declared by the board of directors. No dividends had been declared as of December 31, 2021 or December 31, 2020. The Company had reserved the following shares of common stock, on an as-converted basis, for future issuance as follows: Year Ended December 31, 2021 2020 Options issued and outstanding under the 2019 Equity Incentive Plan and 2015 Stock Plan 2,024,681 1,481,100 Restricted stock units issued and outstanding under the 2019 Equity Incentive Plan 40,500 56,500 Options available for future grants 2,688,372 2,415,710 Shares reserved under the 2019 Employee Stock Purchase Plan 316,923 153,011 Total 5,070,476 4,106,321

Stock-Based Compensation

Stock-Based Compensation	12 Months Ended
	Dec. 31, 2021
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-Based Compensation	9. Stock-Based Compensation Stock Option Plan In 2015, the Company adopted the FLX Bio, Inc. 2015 Stock Plan (the “2015 Plan”). In connection with the consummation of the IPO in November 2019, the Company’s board of directors adopted the Company’s 2019 Equity Incentive Plan (the “2019 Plan” and collectively with the 2015 Plan, the “Option Plans”). Upon the effectiveness of the 2019 Plan, the Company’s 2015 Plan terminated and no further grants may be made thereunder. However, the 2015 Plan will continue to govern the terms and conditions of the outstanding awards previously granted thereunder. As of December 31, 2021, the Company had 2,688,372 shares of common stock available for grant under the Option Plans. In addition, the number of shares reserved for issuance under the Company’s 2019 Plan will automatically increase on January 1 of each year beginning January 1, 2020 by a number equal to (i) 4% of the shares of common stock outstanding on the last business day of the prior fiscal year or (ii) the number of shares determined by the Company’s board of directors. The Company’s Option Plans provided for the granting of incentive and non-statutory stock options and restricted shares of common stock options to eligible employees, officers, directors, advisors and consultants. Terms of the stock option agreements, including vesting requirements, are determined by the board of directors, subject to the provisions of the Options Plans. Options granted generally vest over four years and expire no later than ten years from the date of grant. As a private company, the estimated fair value of the Company’s underlying common stock was determined by the board of directors. Following the Company’s IPO in November 2019 the fair value of the Company’s common stock is based on the closing price of its common stock on the date of grant. Employee Stock Purchase Plan In October 2019, the Company adopted the 2019 Employee Stock Purchase Plan (the “2019 ESPP”). The Company reserved 240,336 shares of common stock pursuant to purchase rights to be granted to the Company’s employees. The 2019 ESPP provides that the number of shares reserved and available for issuance will automatically increase on January 1 of each calendar year, beginning January 1, 2020, by the lesser of (1) 1.0% of the total number of shares of common stock outstanding on December 31 of the preceding calendar year, (2) 240,336 shares or (3) a number determined by the board of directors that is less than (1) and (2). As of January 1, 2021, an additional 240,336 shares of common stock were authorized for issuance pursuant to the annual automatic increase to the authorized shares under the 2019 ESPP. Under the 2019 ESPP, eligible employees are granted rights to purchase shares of common stock, which can be funded through payroll deductions that cannot exceed 15% of each employee’s compensation. The 2019 ESPP generally provides for a 24-month offering period, which includes four six-month Stock Options Stock option activity under the Options Plan is set forth below for the year ended December 31, 2021: Number of Shares Outstanding Weighted Average Exercise Price Per Share Weighted Average Remaining Contractual Term (Years) Aggregate Intrinsic Value (in thousands) Balances at December 31, 2020 1,481,100 $ 16.13 8.36 $ 11,123 Stock options granted 794,095 21.62 Stock options exercised (120,178 ) 9.88 Stock options forfeited (130,336 ) 21.30 Balances at December 31, 2021 2,024,681 $ 18.33 8.04 $ 38,417 Vested and expected to vest at December 31, 2021 2,024,681 $ 18.33 8.04 $ 38,417 Exercisable at December 31, 2021 1,028,650 $ 14.75 7.41 $ 23,142 The aggregate intrinsic values of options outstanding, exercisable, vested and expected to vest were calculated as the difference between the exercise price of the options and the estimated fair value of the Company’s common stock, as determined by the board of directors, as of December 31, 2021. The options granted in the years ended December 31, 2021 and 2020 had a weighted average per share grant-date fair value of $15.04 and $24.57, respectively, and a total grant date fair value of $11.9 million and $8.7 million. The aggregate intrinsic value of stock options exercised in the years ended December 31, 2021 and 2020 was $2.4 million and $2.4 million, respectively. The aggregate fair value of options that vested in the years ended December 31, 2021 and 2020 was $6.8 million and $5.4 million, respectively. Restricted Stock Units Restricted Stock Units (“RSU”) activity under the 2019 Plan is set forth below for the year ended December 31, 2021: Number of Shares Outstanding Weighted Average Grant Price Fair Value Per Share RSUs outstanding at December 31, 2020 56,500 44.66 RSUs awarded — — RSUs released (14,125 ) 44.66 RSUs forfeited (1,875 ) 44.66 RSUs outstanding at December 31, 2021 40,500 44.66 Employee stock option valuation Prior to the Company’s IPO, the grant date fair value of the shares of common stock underlying stock options was determined by the Company’s board of directors with the assistance of management and an independent third-party valuation specialist. The grant date fair value of common stock was determined using valuation methodologies by considering a number of objective and subjective factors including important developments in the Company’s operations, valuations performed by independent third parties, sales of convertible preferred stock, actual operating results and financial performance, the conditions in the biotechnology industry and the economy in general, the stock price performance and volatility of comparable public companies and the lack of liquidity of the Company’s common stock, among other factors. In determining the fair value of the options granted, the Company uses the Black-Scholes option-pricing model and assumptions discussed below. Each of these inputs is subjective and generally requires significant judgment to determine. Expected term The expected term represents the period that the Company’s options granted are expected to be outstanding and is determined using the simplified method (based on the mid-point between the vesting date and the end of the contractual term). The Company has very limited historical information to develop reasonable expectations about future exercise patterns and post-vesting employment termination behavior for its stock option grants. Expected volatility Since the Company recently became a public company and has only a limited trading history for its common stock, the expected volatility was estimated based on the average historical volatility for comparable publicly traded biopharmaceutical companies and our historical volatility over a period, where available, equal to the expected term of the stock option grants. The comparable companies were chosen based on their similar size, life cycle stage or area of specialty. Risk-free interest rate The risk-free interest rate is based on the U.S. Treasury zero coupon issues in effect at the time of grant for periods corresponding with the expected term of the options. Expected dividend The Company has never paid dividends on its common stock and has no plans to pay dividends on its common stock. Therefore, the Company used an expected dividend yield of zero. The assumptions used to value employee and non-employee stock option awards granted under the Option Plans during the years ended December 31, 2021 and 2020, using the Black-Scholes option pricing model, were as follows: Year Ended December 31, 2021 2020 Expected term (in years) 3.93 - 6.05 5.19 - 6.07 Volatility 81.0% - 86.9% 84.0% - 87.0% Risk-free interest rate 0.55% - 1.26% 0.28% - 1.43% Dividend yield — — Employee stock purchase plan The fair value of the rights granted to employees under the 2019 ESPP was estimated using a Black-Scholes option-pricing model with the following valuation assumptions: Year Ended December 31, 2021 2020 Expected term (in years) 0.25 - 2.00 0.25 - 2.00 Volatility 71.3% - 92.9% 84.0% Risk-free interest rate 0.05% - 1.55% 0.11% - 1.57% Dividend yield — — Early exercise of stock options The terms of the 2015 Plan permitted option holders to exercise stock options before they are vested, subject to certain limitations. Such unvested shares were subject to repurchase by the Company at the original exercise price in the event the option holder’s service to the Company was terminated either voluntarily or involuntarily. As a result of early exercises under the 2015 Plan, approximately 0 and 3,000 shares were subject to repurchase as of December 31, 2021 and 2020, respectively. The Company treats cash received from the exercise of unvested options as a refundable deposit and classifies such amounts as a liability in its balance sheet. As of December 31, 2021 and 2020, the Company included cash received for the early exercise of unvested options of $0 and $6,000, respectively, in other current liabilities. Amounts included in liabilities were transferred into common stock and additional paid-in capital as the shares vested, which was generally over a period of 48 months. Stock-based compensation expense Total stock-based compensation expense recognized for stock options and RSUs granted to both employees and non-employees and for the employee stock purchase plan was as follows (in thousands): Year Ended December 31, 2021 2020 Research and development $ 5,310 $ 4,637 General and administrative 4,642 4,049 Total stock-based compensation expense $ 9,952 $ 8,686 As of December 31, 2021, unrecognized stock-based compensation cost related to outstanding unvested stock options and RSUs that are expected to vest was $15.7 million. This unrecognized stock-based compensation cost is expected to be recognized over 2.6

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2021
Income Tax Disclosure [Abstract]
Income Taxes	10. Income Taxes The following table presents domestic and foreign components of income (loss) before income taxes for the periods presented (in thousands): December 31, 2021 2020 United States $ (66,464 ) $ (49,961 ) Foreign (2,740 ) (1,941 ) $ (69,204 ) $ (51,902 ) The components of the provision for income taxes related to Korean withholding taxes on the near-term milestone payment the Company received pursuant to the Hanmi Agreement are as follows (in thousands): December 31, 2021 2020 Current Foreign — $ 990 Total provision for income taxes $ — $ 990 A reconciliation of the statutory U.S. federal rate and effective rate is as follows: December 31, 2021 2020 Federal tax 21.00 % 21.00 % Stock-based compensation (0.76 ) (0.55 ) Research and development tax credit 2.39 2.83 Foreign losses not benefited (2.14 ) — Withholding taxes, net of federal benefit — (1.51 ) Change in valuation allowance (20.86 ) (23.99 ) Other 0.37 0.31 Income tax expense — % (1.91 %) The Company has incurred net operating losses for all periods since inception. The Company has not reflected any benefit of such net operating loss carryforwards in the accompanying financial statements. The Company has established a full valuation allowance against its deferred tax assets due to the uncertainty surrounding the realization of such assets. The components of the Company’s deferred tax assets and liabilities are as follows (in thousands): December 31, 2021 2020 Deferred tax assets: Net operating loss carryforwards $ 49,791 $ 38,665 Federal and state research and development tax credits 7,756 6,103 Accrued liabilities and reserves 1,644 1,089 Stock-based compensation 2,331 1,273 Gross deferred tax assets 61,522 47,130 Valuation allowance (61,488 ) (47,060 ) Deferred tax liabilities: Depreciation and amortization (34 ) (70 ) Gross deferred tax liabilities (34 ) (70 ) Net deferred taxes $ — $ — Realization of deferred tax assets is dependent upon future taxable income, if any. The Company has established a valuation allowance to offset deferred tax assets as of December 31, 2021 and 2020, due to the uncertainty of realizing future tax benefits from its net operating loss carryforwards and other deferred tax assets. The valuation allowance increased by approximately $14.4 million and $12.5 million during the years ended December 31, 2021 and 2020, respectively. The increase in the valuation allowance is mainly related to the increase in net operating loss carryforwards incurred during the respective taxable years. As of December 31, 202 1 and 20 20 , the Company had federal net operating loss carryforwards of approximately $ 233.1 million and $ million , respectively. The federal net operating loss carryforwards generated during and after fiscal 2018 are carried forward indefinitely, while all others , along with the federal tax credit carryforwards, expire in years beginning in 2035 . As of December 31, 202 1 and 20 20 , the Company had state net operating loss carryforwards of approximately $ 12.1 million, which begin to expire in 2035 and are available to offset future taxable income. As of December 31, 202 1 and 20 20 , the Company had federal research and development tax credit carryforwards of approximately $ 6.1 million and $ 4.8 million , respectively . As of December 31, 202 1 and 20 20 , t he Company had state research and development tax credit carryforwards of approximately $ 5.5 million and $ 4.3 million , respectively . Moreover, as of December 31, 202 1 , the Company recorded federal and state reserves of approximately $ 1.5 million and $ 1.4 million , respectively, as uncertain tax positions. If not utilized, the federal credit carryforwards will begin expiring in 2035. The state credits carry forward indefinitely. In March 2020, the Coronavirus Aid, Relief, and Economic Security Act (“CARES Act”) was enacted in response to the COVID-19 pandemic. The tax relief measures under the CARES Act for businesses include a five-year net operating loss carryback, suspension of annual deduction limitation of 80% of taxable income from net operating losses generated in a tax year beginning after December 31, 2017, changes in the deductibility of interest, acceleration of alternative minimum tax credit refunds, payroll tax relief, and a technical correction to allow accelerated deductions for qualified improvement property. The CARES Act did not have a material effect on the realizability of deferred income tax assets or tax expense in 2021. The Company claimed employee retention tax credits in the amount of $0.4 million for the year ended December 31, 2020. Federal and state laws impose substantial restrictions on the utilization of net operating loss and tax credit carryforwards in the event of an ownership change for tax purposes, as defined in Section 382 of the Internal Revenue Code. As a result of such ownership changes, the Company’s ability to realize the potential future benefit of tax losses and tax credits that existed at the time of the ownership change may be significantly reduced. The Company’s deferred tax asset and related valuation allowance would be reduced as a result. The Company has not yet performed a Section 382 study to determine the amount of reduction, if any. The annual limitation may result in the expiration of net operating losses and credits before utilization. Under the new enacted law, the carryforward period of net operating losses generated from 2018 forward is indefinite; however, the carryforward period for net operating losses generated prior to 2018 remains the same. Therefore, the annual limitation may still result in the expiration of certain net operating losses and tax credit carryforwards before their utilization. On February 9, 2022, California Senate Bill 113 “SB 113” was signed into law. SB 113 lifted the limitation for California NOL and Credit utilization disallowed by California Assembly Bill 85. Given the Company’s expected loss position in the current year, the new legislations will not impact the current year provision. The Company will continue to monitor possible California net operating loss and credit limitation in future periods.. Tax benefits from uncertain tax positions are recognized when it is more likely than not that the position will be sustained upon examination, including resolutions of any related appeals or litigation processes, based on the technical merits. The amount recognized is measured as the largest amount of tax benefit that is greater than 50 percent likely of being realized upon effective settlement. A reconciliation of the beginning and ending amounts of unrecognized tax benefits for the years ended December 31, 2021 and 2020 resulting primarily from research and development tax credits claimed for both US and foreign operations on the Company’s annual tax returns were as follows (in thousands): December 31, 2021 2020 Balance at beginning of year $ 2,291 $ 1,747 Additions on tax positions related to prior years 807 — Additions on tax positions related to current year 1,336 544 Balance at end of year $ 4,434 $ 2,291 The Company does not expect that its uncertain tax positions will materially change in the next 12 months. The reversal of uncertain tax benefits would not impact the Company’s effective tax rate as the Company continues to maintain a full valuation allowance against its deferred tax assets. In accordance with ASC 740, the Company would classify interest and penalties related to uncertain tax positions in income tax expense, if applicable. There was no interest expense or penalties related to unrecognized tax benefits through December 31, 2021. The Company files income tax returns with varying statutes of limitations in the United States, various states and foreign jurisdictions. The Company is not currently under examination by income tax authorities in federal, state or other jurisdictions. All tax returns remain open for examination by federal and state authorities. The tax years from inception in 2015 forward remain open to examination due to the carryover of unused net operating losses and tax credits.

Net Loss Per Share

Net Loss Per Share	12 Months Ended
	Dec. 31, 2021
Earnings Per Share [Abstract]
Net Loss Per Share	11. Net Loss Per Share The following table sets forth the computation of the basic and diluted net loss per share of the years ended December 31, 2021 and 2020 (in thousands, except share and per share data): Year Ended December 31 2021 2020 Numerator: Net loss $ (69,204 ) $ (52,892 ) Denominator: Weighted average common shares outstanding 27,390,326 24,164,828 Less: weighted-average unvested early exercised common shares subject to repurchase — (30,523 ) Weighted-average shares used to compute net loss per share, basic and diluted 27,390,326 24,134,305 Net loss per share, basic and diluted $ (2.53 ) $ (2.19 ) Potentially dilutive securities that were not included in the diluted per share calculations because they would be anti-dilutive were as follows: Outstanding as of December 31, 2021 2020 Stock options issued and outstanding under the 2019 Equity Incentive Plan and 2015 Stock Plan 2,024,681 1,481,100 Estimated shares issuable under the 2019 ESPP 6,592 15,990 RSUs subject to future vesting 40,500 56,500 Total 2,071,773 1,553,590

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2021
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles (“U.S. GAAP”) and include the consolidated accounts of the Company and its wholly-owned subsidiary, RAPT Therapeutics Australia Pty Ltd., which was established in 2018. All intercompany balances and transactions have been eliminated in consolidation.
Use of Estimates	Use of Estimates The preparation of the consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. On an ongoing basis, management evaluates its critical accounting policies or estimates related to revenue recognition, clinical trial accruals, fair value of assets and liabilities and stock-based compensation. The Company bases its estimates on historical experience and market-specific or other relevant assumptions that it believes are reasonable under the circumstances. The amounts of assets and liabilities reported in the Company’s balance sheets and the amounts of expenses and revenue reported for each of the periods presented are affected by estimates and assumptions. Actual results could differ from such estimates or assumptions.
Concentration of Credit Risk and Other Risks and Uncertainties	Concentration of Credit Risk and Other Risks and Uncertainties The Company is subject to a number of risks similar to other biopharmaceutical companies in the early stage, including, but not limited to, the need to obtain adequate additional funding, possible failure of preclinical testing or clinical trials, the need to obtain marketing approval for its product candidates, competitors developing new technological innovations, the need to successfully commercialize and gain market acceptance of the Company’s products and protection of proprietary technology. If the Company does not successfully obtain regulatory approval, commercialize or partner any of its product candidates, it will be unable to generate revenue from product sales or achieve profitability. Financial instruments that potentially subject the Company to a concentration of credit risk consist of cash and cash equivalents and marketable securities. Substantially all the Company’s cash is held by two financial institutions. Such deposits may, at times, exceed federally insured limits. The Company invests its cash equivalents in highly rated money market funds and short-term marketable securities comprising commercial paper, corporate bonds and U.S. government agency securities.
Segments	Segments The Company operates as a single operating segment. The Company’s chief operating decision maker, its President and Chief Executive Officer, manages the Company’s operations on a consolidated basis for the purposes of allocating resources, making operating decisions and evaluating financial performance.
Fair Value of Financial Instruments	Fair Value of Financial Instruments The carrying amount of the Company’s financial instruments, including certain prepaid and accrued expenses, approximates fair value due to their short-term maturities.
Cash Equivalents	Cash Equivalents The Company considers all highly liquid investments with original maturities of 90 days or less from the date of purchase to be cash equivalents.
Marketable Securities	Marketable Securities Marketable securities primarily consist of commercial paper, corporate bonds and U.S. government agency securities
Property and Equipment	Property and Equipment Property and equipment consist of computer equipment, laboratory equipment, leasehold improvements and furniture and fixtures, and is recorded at cost, less accumulated depreciation and amortization. Depreciation and amortization are calculated using the straight-line method over the estimated useful lives of the respective assets, generally three to five years. Leasehold improvements are amortized over the shorter of the lease term or the estimated useful life of the improvements. Depreciation and amortization begin at the time the asset is placed in service. Maintenance and repairs are charged to expense as incurred. Upon sale or retirement of assets, the cost and related accumulated depreciation and amortization are removed from the balance sheet and the resulting gain or loss is reflected in the results of operations.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets The Company evaluates its long-lived assets for impairment annually or more frequently whenever events or changes in circumstances indicate that the carrying value of these assets may not be recoverable. Recoverability of these assets is measured by comparing the carrying amount of each asset to the future undiscounted cash flows the asset is expected to generate over its remaining life. If the asset is considered to be impaired, the amount of any impairment is measured as the difference between the carrying value and the fair value of the impaired asset. For the years ended December 31, 2021 and 2020, the Company did not record any impairment losses on long-lived assets.
Leases	Leases The Company leases office space and laboratory facilities under non-cancelable operating lease agreements and recognizes related rent expense on a straight-line basis over the term of the lease. Funding of leasehold improvements by the Company’s landlord is accounted for as a tenant improvement allowance and recorded as current and non-current deferred rent liabilities and amortized on a straight-line basis as a reduction of rent expense over the term of the lease.
Revenue	Revenue License and collaborative agreements consist of license, milestone and royalty payments generated through agreements with strategic partners for the development and commercialization of certain product candidates. The terms of an agreement may include a non-refundable upfront fee, payments based upon achievement of milestones and royalties on net product sales. If a portion of the nonrefundable upfront fee or other payments received is allocated to continuing performance obligations under the terms of an agreement, such portion is recorded as deferred revenue and recognized as revenue when (or as) the underlying performance obligation is satisfied. The Company recognizes revenue when it transfers promised goods or services to customers or counterparties in an amount that reflects the consideration to which the Company expects to be entitled in exchange for those goods or services. In determining the appropriate amount of revenue to be recognized, the Company performs the following steps: (i) identification of the promised goods or services in the agreement; (ii) determination of whether the promised goods or services are performance obligations, including whether they are distinct in the context of the agreement; (iii) measurement of the transaction price, including any constraint on variable consideration; (iv) allocation of the transaction price to performance obligations based on estimated selling prices; and (v) recognition of revenue when (or as) the Company satisfies each performance obligation. Licenses : If a license to the Company’s intellectual property is determined to be distinct from the other performance obligations identified in an agreement, the Company will recognize revenue from the nonrefundable, upfront fee allocated to the license when the license is transferred to the licensee and the licensee is able to use and benefit from the license. If a license is bundled with other performance obligations, the Company utilizes judgment to assess the nature of the combined performance obligations to determine whether the combined performance obligations are satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition. Milestone payments : If an agreement includes event-based or milestone payments, the Company evaluates whether the events or milestones are considered likely to be achieved and estimates the amount to be included in the transaction price using the most likely amount method. If it is unlikely that a significant revenue reversal of cumulative revenue recognized would occur, the value of the associated event-based or milestone payments is included in the transaction price. Event-based or milestone payments that are not within the control of the Company are not included in the transaction price until they become likely to be achieved. Royalties : If an agreement includes sales-based royalties and the license is deemed to be the predominant item to which the royalties relate, the Company will recognize revenue at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied (or partially satisfied).
Research and Development Costs	Research and Development Costs Research and development costs are expensed as incurred. Research and development costs consist primarily of salaries and benefits of research and development personnel, costs related to research activities, preclinical studies, clinical trials, drug manufacturing and allocated overhead and facility-related expenses. The Company accounts for non-refundable advance payments for goods or services that will be used in future research and development activities as expenses when the goods have been received or when the service has been performed rather than when the payment is made. Clinical trial costs are a component of research and development expenses. The Company expenses costs for its clinical trial activities performed by third parties, including clinical research organizations (“CROs”) and other service providers, as they are incurred, based upon estimates of the work completed over the life of the individual study in accordance with associated agreements. The Company uses information it receives from internal personnel and outside service providers to estimate the clinical trial costs incurred.
Share-Based Compensation	Stock-Based Compensation The Company measures employee and director stock-based compensation expense for all stock-based awards based on their grant date fair value using the Black-Scholes option-pricing model. For stock-based awards with service conditions only, stock-based compensation expense is recognized over the requisite service period using the straight-line method. Forfeitures are recognized as they occur. Stock-based compensation expense for nonemployee stock-based awards is measured at fair value using the Black-Scholes option-pricing model. The Company recognizes stock-based compensation expense for the estimated fair value of the vested portion of nonemployee awards in its consolidated statements of operations and comprehensive loss. Stock-based compensation expense related to stock-based awards to nonemployees is subject to re-measurement over the service period, which approximates the vesting period. Stock-based compensation expense related to restricted stock awards is determined using the estimated fair value of the Company’s common stock on the date of grant for the period prior to the IPO. The fair value of restricted stock awards granted after the IPO is determined based on the stock price on the date of grant. The estimated fair value is amortized as compensation expense over the service period of the award.
Foreign Currency Transactions	Foreign Currency Transactions The functional currency of RAPT Therapeutics Australia Pty Ltd., the Company’s wholly-owned subsidiary, is the Australian dollar. Accordingly, all monetary assets and liabilities of the subsidiary are translated into U.S. dollars at the current period-end exchange rates and non-monetary assets are translated using historical exchange rates. Income and expense elements are remeasured to U.S. dollars using the average exchange rates in effect during the period. Remeasurement gains and losses are recorded as other income (expense), net. The Company is subject to foreign currency risk with respect to its clinical contracts denominated in currencies other than the U.S. dollar. Payments on contracts denominated in foreign currencies are made at the spot rate on the day of payment. The cumulative adjustment resulting from the translation of financial statements to the reporting currency is recorded in other comprehensive income (loss).
Income Taxes	Income Taxes Income taxes are accounted for under the asset and liability method. Deferred tax assets and liabilities are recognized for the future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases and operating loss and tax credit carryforwards. Deferred tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the years in which those temporary differences are expected to be recovered or settled. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in income in the period such tax rate changes are enacted. The Company recognizes the effect of income tax positions only if those positions are more likely than not to be sustained. Recognized income tax positions are measured at the largest amount that is greater than 50% likely to be realized. Changes in recognition or measurement are reflected in the period in which the change in judgment occurs. Valuation allowances are established when necessary to reduce deferred tax assets to amounts more likely than not to be realized. Interest and penalties related to unrecognized tax benefits are recognized as a component of income tax expense.
Comprehensive Loss	Comprehensive Loss Comprehensive loss includes net loss and certain changes in stockholders’ deficit that are excluded from net loss, primarily unrealized gains and losses from marketable securities and foreign currency translation adjustments.
Net Loss Per Share	Net Loss Per Share Basic net loss per share is computed by dividing the net loss by the weighted average number of common shares outstanding during the period, without consideration of potential dilutive securities. Diluted net loss per common share is computed by dividing the net loss by the sum of the weighted average number of common shares outstanding during the period plus the number of potential dilutive securities outstanding during the period calculated in accordance with the treasury stock method. Diluted net loss per share is the same as basic net loss per share since the effect of potentially dilutive securities is anti-dilutive.
Recent Accounting Pronouncements	Recent Accounting Pronouncements From time to time, new accounting pronouncements are issued by the Financial Accounting Standards Board (“FASB”) or other standard setting bodies and adopted by the Company as of the specified effective date. Under the Jumpstart Our Business Startups Act of 2012, as amended (the “JOBS Act”), the Company meets the definition of an emerging growth company and has elected the extended transition period for complying with new or revised accounting standards pursuant to Section 107(b) of the JOBS Act.
Recent Accounting Pronouncements Not Yet Adopted	Recent Accounting Pronouncements Not Yet Adopted In February 2016, the FASB issued ASU No. 2016-02, Leases The adoption of the new standard will have a material impact on the Company’s consolidated balance sheet as of January 1, 2022, as we will recognize the right-of-use assets and liabilities for our operating leases. We expect to record lease liabilities of approximately $8 - $9 million based on the present value of the remaining minimum rental payments using discount rates as of the effective date. We also expect to record corresponding right-of-use assets of approximately $6 - 7 million, based on the operating lease liabilities adjusted for unamortized deferred rent and lease incentives. The Company, however, does not expect a material impact to its consolidated statements of operations and consolidated statements of cash flow. In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments – Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments Codification Improvements to Topic 326, Financial Instruments—Credit Losses, Topic 815, Derivatives and Hedging, and Topic 825, Financial Instruments Financial Instruments—Credit Losses, Topic 326 Financial Instruments—Credit Losses (Topic 326), Derivatives and Hedging (Topic 815), and Leases (Topic 842): Effective Dates Codification Improvements to Topic 326, Financial Instruments—Credit Losses .

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2021
Fair Value Disclosures [Abstract]
Schedule of Cash Equivalents and Marketable Securities Classified as Available-for-Sale Securities Measured at Fair Value on Recurring Basis	Cash equivalents and marketable securities, all of which are classified as available-for-sale securities and measured at fair value on a recurring basis, consisted of the following (in thousands): As of December 31, 2021 Fair Value Hierarchy Level Amortized Cost Unrealized Gains Unrealized Losses Fair Value Financial assets: Money market funds— classified as cash equivalents Level 1 $ 22,658 $ — $ — $ 22,658 Corporate debt Level 2 52,704 — (139 ) 52,565 Asset-backed securities Level 2 23,882 — (21 ) 23,861 Commercial paper Level 2 59,532 — — 59,532 U.S. government agency securities Level 2 29,744 — (75 ) 29,669 Total $ 188,520 $ — $ (235 ) $ 188,285 As of December 31, 2020 Fair Value Hierarchy Level Amortized Cost Unrealized Gains Unrealized Losses Fair Value Financial assets: Money market funds— classified as cash equivalents Level 1 $ 21,333 $ — $ — $ 21,333 Corporate debt Level 2 32,164 48 — 32,212 Asset-backed securities Level 2 12,367 2 (1 ) 12,368 Commercial paper Level 2 28,962 — — 28,962 U.S. government agency securities Level 2 13,047 3 — 13,050 Total $ 107,873 $ 53 $ (1 ) $ 107,925
Schedule of Remaining Contractual Maturities of Marketable Securities	The following table presents the remaining contractual maturities of the Company’s marketable securities as of December 31, 2021 (in thousands): December 31, 2021 Due in less than one year $ 132,804 Due in more than one year 55,481 Total $ 188,285

Property and Equipment (Tables)

Property and Equipment (Tables)	12 Months Ended
	Dec. 31, 2021
Property Plant And Equipment [Abstract]
Schedule of Property and Equipment	Property and equipment consisted of the following (in thousands): December 31, 2021 2020 Laboratory equipment $ 6,291 $ 5,966 Leasehold improvements 3,295 3,294 Computer equipment 482 447 Furniture and fixtures 357 357 Total property and equipment 10,425 10,064 Less accumulated depreciation and amortization (7,684 ) (7,082 ) Property and equipment, net $ 2,741 $ 2,982

Accrued Expenses (Tables)

Accrued Expenses (Tables)	12 Months Ended
	Dec. 31, 2021
Payables And Accruals [Abstract]
Schedule of Accrued Expenses	Accrued expenses consisted of the following (in thousands): December 31, 2021 2020 Accrued research and development expenses $ 2,205 $ 1,576 Accrued compensation 3,652 2,967 Accrued professional and consulting services 415 129 Other 54 263 Total accrued expenses $ 6,326 $ 4,935

Commitments (Tables)

Commitments (Tables)	12 Months Ended
	Dec. 31, 2021
Commitments And Contingencies Disclosure [Abstract]
Schedule of Future Minimum Non-Cancelable Lease Payments	As of December 31, 2021, future minimum non-cancelable lease payments, are as follows (in thousands): Year ending December 31: 2022 $ 2,037 2023 2,109 2024 2,183 2025 2,259 2026 2,137 Thereafter — Total minimum lease payments $ 10,725

Common Stock (Tables)

Common Stock (Tables)	12 Months Ended
	Dec. 31, 2021
Equity [Abstract]
Summary of Reserved Shares of Common Stock on Converted Basis for Future Issuance	The Company had reserved the following shares of common stock, on an as-converted basis, for future issuance as follows: Year Ended December 31, 2021 2020 Options issued and outstanding under the 2019 Equity Incentive Plan and 2015 Stock Plan 2,024,681 1,481,100 Restricted stock units issued and outstanding under the 2019 Equity Incentive Plan 40,500 56,500 Options available for future grants 2,688,372 2,415,710 Shares reserved under the 2019 Employee Stock Purchase Plan 316,923 153,011 Total 5,070,476 4,106,321

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2021
Summary of Option Plans	Stock Options Stock option activity under the Options Plan is set forth below for the year ended December 31, 2021: Number of Shares Outstanding Weighted Average Exercise Price Per Share Weighted Average Remaining Contractual Term (Years) Aggregate Intrinsic Value (in thousands) Balances at December 31, 2020 1,481,100 $ 16.13 8.36 $ 11,123 Stock options granted 794,095 21.62 Stock options exercised (120,178 ) 9.88 Stock options forfeited (130,336 ) 21.30 Balances at December 31, 2021 2,024,681 $ 18.33 8.04 $ 38,417 Vested and expected to vest at December 31, 2021 2,024,681 $ 18.33 8.04 $ 38,417 Exercisable at December 31, 2021 1,028,650 $ 14.75 7.41 $ 23,142
Summary of RSU Activity	Restricted Stock Units (“RSU”) activity under the 2019 Plan is set forth below for the year ended December 31, 2021: Number of Shares Outstanding Weighted Average Grant Price Fair Value Per Share RSUs outstanding at December 31, 2020 56,500 44.66 RSUs awarded — — RSUs released (14,125 ) 44.66 RSUs forfeited (1,875 ) 44.66 RSUs outstanding at December 31, 2021 40,500 44.66
Summary of Assumptions Used to Value Under Stock Option Plans	The fair value of the rights granted to employees under the 2019 ESPP was estimated using a Black-Scholes option-pricing model with the following valuation assumptions: Year Ended December 31, 2021 2020 Expected term (in years) 0.25 - 2.00 0.25 - 2.00 Volatility 71.3% - 92.9% 84.0% Risk-free interest rate 0.05% - 1.55% 0.11% - 1.57% Dividend yield — —
Summary of Stock-based Compensation Expense	Total stock-based compensation expense recognized for stock options and RSUs granted to both employees and non-employees and for the employee stock purchase plan was as follows (in thousands): Year Ended December 31, 2021 2020 Research and development $ 5,310 $ 4,637 General and administrative 4,642 4,049 Total stock-based compensation expense $ 9,952 $ 8,686
Employee and Non-employees
Summary of Assumptions Used to Value Under Stock Option Plans	The assumptions used to value employee and non-employee stock option awards granted under the Option Plans during the years ended December 31, 2021 and 2020, using the Black-Scholes option pricing model, were as follows: Year Ended December 31, 2021 2020 Expected term (in years) 3.93 - 6.05 5.19 - 6.07 Volatility 81.0% - 86.9% 84.0% - 87.0% Risk-free interest rate 0.55% - 1.26% 0.28% - 1.43% Dividend yield — —

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2021
Income Tax Disclosure [Abstract]
Schedule of Domestic and Foreign Components of Income (Loss) before Income Taxes	The following table presents domestic and foreign components of income (loss) before income taxes for the periods presented (in thousands): December 31, 2021 2020 United States $ (66,464 ) $ (49,961 ) Foreign (2,740 ) (1,941 ) $ (69,204 ) $ (51,902 )
Schedule of Components of Provision for Income Taxes	The components of the provision for income taxes related to Korean withholding taxes on the near-term milestone payment the Company received pursuant to the Hanmi Agreement are as follows (in thousands): December 31, 2021 2020 Current Foreign — $ 990 Total provision for income taxes $ — $ 990
Schedule of Effective Income Tax Rate Reconciliation	A reconciliation of the statutory U.S. federal rate and effective rate is as follows: December 31, 2021 2020 Federal tax 21.00 % 21.00 % Stock-based compensation (0.76 ) (0.55 ) Research and development tax credit 2.39 2.83 Foreign losses not benefited (2.14 ) — Withholding taxes, net of federal benefit — (1.51 ) Change in valuation allowance (20.86 ) (23.99 ) Other 0.37 0.31 Income tax expense — % (1.91 %)
Schedule of Components of Deferred Tax Assets and Liabilities	The components of the Company’s deferred tax assets and liabilities are as follows (in thousands): December 31, 2021 2020 Deferred tax assets: Net operating loss carryforwards $ 49,791 $ 38,665 Federal and state research and development tax credits 7,756 6,103 Accrued liabilities and reserves 1,644 1,089 Stock-based compensation 2,331 1,273 Gross deferred tax assets 61,522 47,130 Valuation allowance (61,488 ) (47,060 ) Deferred tax liabilities: Depreciation and amortization (34 ) (70 ) Gross deferred tax liabilities (34 ) (70 ) Net deferred taxes $ — $ —
Schedule of Reconciliation of Unrecognized Tax Benefits	A reconciliation of the beginning and ending amounts of unrecognized tax benefits for the years ended December 31, 2021 and 2020 resulting primarily from research and development tax credits claimed for both US and foreign operations on the Company’s annual tax returns were as follows (in thousands): December 31, 2021 2020 Balance at beginning of year $ 2,291 $ 1,747 Additions on tax positions related to prior years 807 — Additions on tax positions related to current year 1,336 544 Balance at end of year $ 4,434 $ 2,291

Net Loss Per Share (Tables)

Net Loss Per Share (Tables)	12 Months Ended
	Dec. 31, 2021
Earnings Per Share [Abstract]
Computation of Basic and Diluted Net Loss per Share	The following table sets forth the computation of the basic and diluted net loss per share of the years ended December 31, 2021 and 2020 (in thousands, except share and per share data): Year Ended December 31 2021 2020 Numerator: Net loss $ (69,204 ) $ (52,892 ) Denominator: Weighted average common shares outstanding 27,390,326 24,164,828 Less: weighted-average unvested early exercised common shares subject to repurchase — (30,523 ) Weighted-average shares used to compute net loss per share, basic and diluted 27,390,326 24,134,305 Net loss per share, basic and diluted $ (2.53 ) $ (2.19 )
Potentially Dilutive Securities not Included in Diluted per Share Calculations	Potentially dilutive securities that were not included in the diluted per share calculations because they would be anti-dilutive were as follows: Outstanding as of December 31, 2021 2020 Stock options issued and outstanding under the 2019 Equity Incentive Plan and 2015 Stock Plan 2,024,681 1,481,100 Estimated shares issuable under the 2019 ESPP 6,592 15,990 RSUs subject to future vesting 40,500 56,500 Total 2,071,773 1,553,590

Organization - Additional Infor

Organization - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended		12 Months Ended
	Jun. 30, 2021	Feb. 29, 2020	Dec. 31, 2021	Dec. 31, 2020	Nov. 30, 2020
Class Of Stock [Line Items]
Total shares reserved			5,070,476	4,106,321
Net loss			$ 69,204	$ 52,892
Cash used in operations			61,026	40,491
Cash and cash equivalents and marketable securities			189,700
Working capital			183,400
2021 Public Offering | Sales Agreement
Class Of Stock [Line Items]
Shares issued during period	4,356,060
Shares issued, price per share	$ 33
Net proceeds received after deducting underwriting discounts and other offering related costs	$ 134,800
Follow-on Offering
Class Of Stock [Line Items]
Shares issued during period		2,500,000
Shares issued, price per share		$ 30
Net proceeds received after deducting underwriting discounts and other offering related costs		$ 69,800
Underwriters | 2021 Public Offering | Sales Agreement
Class Of Stock [Line Items]
Shares issued during period	568,181
At The Market
Class Of Stock [Line Items]
Net proceeds received after deducting underwriting discounts and other offering related costs			$ 4,690	$ 0
At The Market | Sales Agreement
Class Of Stock [Line Items]
Shares issued during period			214,971	188,700
Net proceeds received after deducting underwriting discounts and other offering related costs			$ 4,700	$ 3,800
At The Market | Sales Agreement | Maximum
Class Of Stock [Line Items]
Securities that may be offered and sold					$ 350,000
Common stock that may be offered and sold, value					$ 100,000
Total shares reserved			90,900,000		1,000,000

Summary of Significant Accoun_3

Summary of Significant Accounting Policies - Additional Information (Details)	12 Months Ended
	Dec. 31, 2021USD ($)Institution	Dec. 31, 2020USD ($)
Significant Accounting Policies [Line Items]
Number of financial institutions | Institution	2
Impairment losses on long-lived assets	$ 0	$ 0
Minimum [Member]
Significant Accounting Policies [Line Items]
Property, plant and equipment, useful life	3 years
Lease liability	$ 8,000,000
Lease, right-of-use asset	$ 6,000,000
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration]	us-gaap:OtherAssets
Maximum
Significant Accounting Policies [Line Items]
Property, plant and equipment, useful life	5 years
Lease liability	$ 9,000,000
Lease, right-of-use asset	$ 7,000,000
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration]	us-gaap:OtherAssets

Fair Value Measurements - Sched

Fair Value Measurements - Schedule of Cash Equivalents and Marketable Securities Classified as Available-for-Sale Securities Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 188,520	$ 107,873
Unrealized Gains		53
Unrealized Losses	(235)	(1)
Fair Value	188,285	107,925
Level 1 | Money Market Funds | Cash Equivalents
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	22,658	21,333
Fair Value	22,658	21,333
Level 2 | Corporate Debt
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	52,704	32,164
Unrealized Gains		48
Unrealized Losses	(139)
Fair Value	52,565	32,212
Level 2 | Asset-backed Securities
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	23,882	12,367
Unrealized Gains		2
Unrealized Losses	(21)	(1)
Fair Value	23,861	12,368
Level 2 | Commercial Paper
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	59,532	28,962
Fair Value	59,532	28,962
Level 2 | U.S. Government Agency Securities
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	29,744	13,047
Unrealized Gains		3
Unrealized Losses	(75)
Fair Value	$ 29,669	$ 13,050

Fair Value Measurements - Sch_2

Fair Value Measurements - Schedule of Remaining Contractual Maturities of Marketable Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Investments Debt And Equity Securities [Abstract]
Due in less than one year	$ 132,804
Due in more than one year	55,481
Total	$ 188,285	$ 107,925

Property and Equipment - Schedu

Property and Equipment - Schedule of Property and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Property Plant And Equipment [Line Items]
Total property and equipment	$ 10,425	$ 10,064
Less accumulated depreciation and amortization	(7,684)	(7,082)
Property and equipment, net	2,741	2,982
Laboratory Equipment
Property Plant And Equipment [Line Items]
Total property and equipment	6,291	5,966
Leasehold Improvements
Property Plant And Equipment [Line Items]
Total property and equipment	3,295	3,294
Computer Equipment
Property Plant And Equipment [Line Items]
Total property and equipment	482	447
Furniture and Fixtures
Property Plant And Equipment [Line Items]
Total property and equipment	$ 357	$ 357

Property and Equipment - Additi

Property and Equipment - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Property Plant And Equipment [Abstract]
Depreciation and amortization expenses	$ 996	$ 1,123

Accrued Expenses - Schedule of

Accrued Expenses - Schedule of Accrued Expenses (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Payables And Accruals [Abstract]
Accrued research and development expenses	$ 2,205	$ 1,576
Accrued compensation	3,652	2,967
Accrued professional and consulting services	415	129
Other	54	263
Total accrued expenses	$ 6,326	$ 4,935

Commitments - Additional Inform

Commitments - Additional Information (Details)	1 Months Ended			12 Months Ended
	Feb. 28, 2019ft²	Apr. 30, 2018ft²	May 31, 2015ft²	Dec. 31, 2021USD ($)	Dec. 31, 2020USD ($)
Lessee Lease Description [Line Items]
Lease expiration period			2022-05
Additional laboratory and office facilities under lease	6,378	6,378
Increased of leased premises		36,754
Lessee operating lease extended lease term		2026-11
Lease existence of option to extend			true
Lessee operating lease option to extend			5 years
Lease termination term	2020-07
Operating lease rent expense | $				$ 2,300,000	$ 2,100,000
Contingency losses, accrued | $				$ 0	$ 0
South San Francisco and California
Lessee Lease Description [Line Items]
Laboratory and office facilities under lease			30,376

Commitments - Schedule of Futur

Commitments - Schedule of Future Minimum Non-Cancelable Lease Payments (Details) $ in Thousands	Dec. 31, 2021USD ($)
Operating Lease Liabilities Payments Due [Abstract]
2022	$ 2,037
2023	2,109
2024	2,183
2025	2,259
2026	2,137
Total minimum lease payments	$ 10,725

Collaboration Agreements - Addi

Collaboration Agreements - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Apr. 30, 2020	Dec. 31, 2019
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue recognized	$ 3,813,000	$ 5,042,000
Collaboration and License Agreement | Hanmi Pharmaceutical Co., LTD
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront and near-term milestone payment				$ 10,000,000
Upfront fee				4,000,000
Development milestone payment			$ 6,000,000
Unconstrained development milestone payment		400,000		6,000,000
Revenue recognized	3,800,000	$ 5,000,000
Deferred revenue	$ 1,500,000
Collaboration and License Agreement | Hanmi Pharmaceutical Co., LTD | Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Contingent payments upon achievement of specified milestones				$ 108,000,000

Common Stock - Additional Infor

Common Stock - Additional Information (Details)	12 Months Ended
	Dec. 31, 2021USD ($)vote	Dec. 31, 2020USD ($)
Equity [Abstract]
Number of votes for each share of common stock	The holders of the Company’s common stock have one vote for each share of common stock held by them
Number of votes per share | vote	1
Dividends declared | $	$ 0	$ 0

Common Stock - Summary of Reser

Common Stock - Summary of Reserved Shares of Common Stock on Converted Basis for Future Issuance (Detail) - shares	Dec. 31, 2021	Dec. 31, 2020
Class Of Stock [Line Items]
Total shares reserved	5,070,476	4,106,321
Options Available for Future Grants
Class Of Stock [Line Items]
Total shares reserved	2,688,372	2,415,710
2019 Equity Incentive Plan and 2015 Stock Plan | Options Issued and Outstanding
Class Of Stock [Line Items]
Total shares reserved	2,024,681	1,481,100
2019 Equity Incentive Plan | Restricted Stock Units Issued and Outstanding
Class Of Stock [Line Items]
Total shares reserved	40,500	56,500
2019 Employee Stock Purchase Plan
Class Of Stock [Line Items]
Total shares reserved	316,923	153,011

Stock-Based Compensation - Addi

Stock-Based Compensation - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	12 Months Ended
	Oct. 31, 2019	Dec. 31, 2021	Dec. 31, 2020	Jan. 01, 2021
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense		$ 9,952	$ 8,686
Weighted-average grant-date fair value per share		$ 15.04	$ 24.57
Stock options grant date fair value		$ 11,900	$ 8,700
Number of stock options, exercises intrinsic value		2,400	2,400
Stock option vested aggregate fair value		6,800	5,400
Expected dividend yield		0
Unrecognized stock-based compensation cost related to outstanding unvested stock options and RSUs that are expected to vest		$ 15,700
Unrecognized stock-based compensation cost, expected period to be recognized		2 years 7 months 6 days
2019 ESPP
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Percentage of increase in shares reserved for issuance on common stock outstanding	1.00%
Total shares reserved	240,336			240,336
Increase in shares at the beginning of each calendar year	240,336
Maximum employee subscription rate on salary	15.00%
Offering period	24 months
Purchase period	6 months
Purchase price of common stock as percentage of fair market value	85.00%
Stock-based compensation expense		$ 2,500	$ 2,700
Share-based compensation, employee purchased shares		76,424	87,325
Share-based compensation, shares at weighted average exercise price		$ 10.80	$ 10.27
Option Plans
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock available for grant		2,688,372
Option Plans | Employees, Officers, Directors, Advisors, and Consultants
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Award vesting period		4 years
Option Plans | Maximum | Employees, Officers, Directors, Advisors, and Consultants
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options granted, expiration period		10 years
2019 Stock Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Percentage of increase in shares reserved for issuance on common stock outstanding		4.00%
2015 Stock Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Award vesting period		48 months
Shares not vested and subject to repurchase		0	3,000
Cash received from early exercise of unvested options		$ 0	$ 6,000

Stock-Based Compensation - Summ

Stock-Based Compensation - Summary of Option Plans (Details) - Option Plans - Share-based Payment Arrangement, Option - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Shares Outstanding, Beginning Balance	1,481,100
Number of Shares Outstanding, Stock options granted	794,095
Number of Shares Outstanding, Stock options exercised	(120,178)
Number of Shares Outstanding, Stock options forfeited	(130,336)
Number of Shares Outstanding, Ending Balance	2,024,681	1,481,100
Number of Shares Outstanding, Vested and expected to vest	2,024,681
Number of Shares Outstanding, Exercisable	1,028,650
Weighted Average Exercise Price Per Share, Beginning Balance	$ 16.13
Weighted Average Exercise Price Per Share, Stock options granted	21.62
Weighted Average Exercise Price Per Share, Stock options exercised	9.88
Weighted Average Exercise Price Per Share, Stock options forfeited	21.30
Weighted Average Exercise Price Per Share, Ending Balance	18.33	$ 16.13
Weighted Average Exercise Price Per Share, Vested and expected to vest	18.33
Weighted Average Exercise Price Per Share, Exercisable	$ 14.75
Weighted Average Remaining Contractual Term (Years), Balance	8 years 14 days	8 years 4 months 9 days
Weighted Average Remaining Contractual Term (Years), Vested and expected to vest	8 years 14 days
Weighted Average Remaining Contractual Term (Years), Exercisable	7 years 4 months 28 days
Aggregate Intrinsic Value	$ 38,417	$ 11,123
Aggregate Intrinsic Value, Vested and expected to vest	38,417
Aggregate Intrinsic Value, Exercisable	$ 23,142

Stock-Based Compensation - Su_2

Stock-Based Compensation - Summary of RSU Activity (Details) - 2019 Plan - Restricted Stock Unit ("RSU")	12 Months Ended
	Dec. 31, 2021$ / sharesshares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Shares Outstanding, Beginning Balance | shares	56,500
Number of Shares Outstanding, RSUs released | shares	(14,125)
Number of Shares Outstanding, RSUs forfeited | shares	(1,875)
Number of Shares Outstanding, Ending Balance | shares	40,500
Weighted Average Grant Date Fair Value Per Share, Beginning Balance | $ / shares	$ 44.66
Weighted Average Grant Date Fair Value Per Share, RSUs released | $ / shares	44.66
Weighted Average Grant Date Fair Value Per Share, RSUs forfeited | $ / shares	44.66
Weighted Average Grant Date Fair Value Per Share, Ending Balance | $ / shares	$ 44.66

Stock-Based Compensation - Su_3

Stock-Based Compensation - Summary of Assumptions Used to Value Under Stock Option Plans (Details) - Employee and Non-employees - Share-based Payment Arrangement, Option	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
2019 ESPP
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Volatility, minimum	71.30%
Volatility, maximum	92.90%
Risk-free interest rate, minimum	0.05%	0.11%
Risk-free interest rate, maximum	1.55%	1.57%
Volatility		84.00%
Option Plans
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Volatility, minimum	81.00%	84.00%
Volatility, maximum	86.90%	87.00%
Risk-free interest rate, minimum	0.55%	0.28%
Risk-free interest rate, maximum	1.26%	1.43%
Minimum | 2019 ESPP
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (in years)	3 months	3 months
Minimum | Option Plans
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (in years)	3 years 11 months 4 days	5 years 2 months 8 days
Maximum | 2019 ESPP
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (in years)	2 years	2 years
Maximum | Option Plans
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (in years)	6 years 18 days	6 years 25 days

Stock-Based Compensation - Su_4

Stock-Based Compensation - Summary of Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 9,952	$ 8,686
Research and Development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	5,310	4,637
General and Administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 4,642	$ 4,049

Income Taxes - Schedule of Dome

Income Taxes - Schedule of Domestic and Foreign Components of Income (Loss) before Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Income Tax Disclosure [Abstract]
United States	$ (66,464)	$ (49,961)
Foreign	(2,740)	(1,941)
Net loss before taxes	$ (69,204)	$ (51,902)

Income Taxes - Schedule of Comp

Income Taxes - Schedule of Components of Provision for Income Taxes (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2020USD ($)
Income Tax Disclosure [Abstract]
Foreign	$ 990
Total provision for income taxes	$ 990

Income Taxes - Schedule of Effe

Income Taxes - Schedule of Effective Income Tax Rate Reconciliation (Details)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Federal tax	21.00%	21.00%
Stock-based compensation	(0.76%)	(0.55%)
Research and development tax credit	2.39%	2.83%
Foreign losses not benefited	(2.14%)
Withholding taxes, net of federal benefit		(1.51%)
Change in valuation allowance	(20.86%)	(23.99%)
Other	0.37%	0.31%
Income tax expense		(1.91%)

Income Taxes - Schedule of Co_2

Income Taxes - Schedule of Components of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Deferred tax assets:
Net operating loss carryforwards	$ 49,791	$ 38,665
Federal and state research and development tax credits	7,756	6,103
Accrued liabilities and reserves	1,644	1,089
Stock-based compensation	2,331	1,273
Gross deferred tax assets	61,522	47,130
Valuation allowance	(61,488)	(47,060)
Deferred tax liabilities:
Depreciation and amortization	(34)	(70)
Gross deferred tax liabilities	(34)	(70)
Net deferred taxes	$ 0	$ 0

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Income Tax Disclosure [Line Items]
Increase in valuation allowance	$ 14,400,000	$ 12,500,000
Interest expense or penalties related to unrecognized tax benefits	0
CARES Act
Income Tax Disclosure [Line Items]
Employee retention tax credits amount		400,000
Federal
Income Tax Disclosure [Line Items]
Operating loss carryforwards	$ 233,100,000	177,200,000
Operating loss carryforwards expiration beginning year	2035
Uncertain tax positions reserves	$ 1,500,000
Uncertain tax positions	1,400,000
Federal | Research and Development
Income Tax Disclosure [Line Items]
Tax credit carryforwards amount	6,100,000	4,800,000
State
Income Tax Disclosure [Line Items]
Operating loss carryforwards	$ 12,100,000	12,100,000
Operating loss carryforwards expiration beginning year	2035
Uncertain tax positions reserves	$ 1,500,000
Uncertain tax positions	1,400,000
State | Research and Development
Income Tax Disclosure [Line Items]
Tax credit carryforwards amount	$ 5,500,000	$ 4,300,000

Income Taxes - Schedule of Reco

Income Taxes - Schedule of Reconciliation of Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Balance at beginning of year	$ 2,291	$ 1,747
Additions on tax positions related to prior years	807
Additions on tax positions related to current year	1,336	544
Balance at end of year	$ 4,434	$ 2,291

Net Loss Per Share - Computatio

Net Loss Per Share - Computation of Basic and Diluted Net Loss per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Numerator:
Net loss	$ (69,204)	$ (52,892)
Denominator:
Weighted average common shares outstanding	27,390,326	24,164,828
Weighted-average shares used to compute net loss per share, basic and diluted	27,390,326	24,134,305
Net loss per share, basic and diluted	$ (2.53)	$ (2.19)
Early Exercised Stock
Denominator:
Less: weighted-average unvested common stock subject to repurchase		(30,523)

Net Loss Per Share - Potentiall

Net Loss Per Share - Potentially Dilutive Securities not Included in Diluted per Share Calculations (Details) - shares	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities	2,071,773	1,553,590
Stock Options Issued And Outstanding Equity Incentive Plan And Under 2019 Equity Incentive Plan And 2015 Stock Plan
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities	2,024,681	1,481,100
Estimated Shares Issuable Under Employee Stock Purchase Plan
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities	6,592	15,990
RSUs Subject to Future Vesting
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities	40,500	56,500