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Document and Entity Information - shares	6 Months Ended
Document and Entity Information - shares	Jun. 30, 2020	Aug. 07, 2020
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q2
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	No
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		24,468,910
Entity Interactive Data Current	Yes
Title of 12(b) Security	Common Stock $0.0001 par value per share
Security Exchange Name	NASDAQ
Entity Incorporation, State or Country Code	DE
Document Quarterly Report	true
Document Transition Report	false

CONDENSED CONSOLIDATED BALANCE SHEETS (Unaudited) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 28,957	$ 77,383
Marketable securities	103,993
Prepaid expenses and other current assets	3,127	3,123
Total current assets	136,077	80,506
Property and equipment, net	3,210	3,707
Other assets	389	389
Total assets	139,676	84,602
Current liabilities:
Accounts payable	2,381	1,143
Accrued expenses	4,256	3,642
Deferred revenue, current	6,013	4,000
Other current liabilities	430	471
Total current liabilities	13,080	9,256
Deferred rent, net of current portion	2,210	2,225
Deferred revenue, non-current	1,775
Commitments
Stockholders' equity:
Preferred stock
Common stock	2	2
Additional paid-in capital	309,908	235,049
Accumulated other comprehensive income	177	20
Accumulated deficit	(187,476)	(161,950)
Total stockholders' equity	122,611	73,121
Total liabilities and stockholders' equity	$ 139,676	$ 84,602

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS (Unaudited) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Income Statement [Abstract]
Revenue	$ 1,277,000		$ 2,212,000
Operating expenses:
Research and development	10,986,000	$ 8,267,000	21,669,000	$ 16,137,000
General and administrative	2,802,000	2,692,000	6,091,000	4,366,000
Total operating expenses	13,788,000	10,959,000	27,760,000	20,503,000
Loss from operations	(12,511,000)	(10,959,000)	(25,548,000)	(20,503,000)
Other income, net	391,000	333,000	526,000	689,000
Net loss before taxes	(12,120,000)	(10,626,000)	(25,022,000)	(19,814,000)
Provision for income taxes	267,000	0	504,000	0
Net loss	(12,387,000)	(10,626,000)	(25,526,000)	(19,814,000)
Other comprehensive income (loss):
Foreign currency translation adjustment	(199,000)	2,000	5,000	2,000
Unrealized gain on marketable securities	369,000		152,000
Total comprehensive loss	$ (12,217,000)	$ (10,624,000)	$ (25,369,000)	$ (19,812,000)
Net loss per share, basic and diluted	$ (0.51)	$ (14.78)	$ (1.08)	$ (28.80)
Weighted average number of shares used in computing net loss per share, basic and diluted	24,336,102	719,026	23,743,058	687,870

CONDENSED CONSOLIDATED STATEMENT OF CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS' EQUITY (DEFICIT) (Unaudited) - USD ($) $ in Thousands	Total	Convertible Preferred Stock	Series C-2 Convertible Preferred Stock	Common Stock	Additional Paid-In Capital	Related Party Promissory Notes for the Purchase of Common Stock	Accumulated Deficit	Accumulated Other Comprehensive Income (Loss)
Beginning balance at Dec. 31, 2018		$ 161,111
Beginning balance, shares at Dec. 31, 2018		98,491,880
Beginning balance at Dec. 31, 2018	$ (97,113)			$ 1	$ 22,441	$ (598)	$ (118,953)	$ (4)
Beginning balance, shares at Dec. 31, 2018				878,413
Issuance of convertible preferred stock, net of issuance cost			$ 6,947
Issuance of convertible preferred stock, net of issuance cost, shares			3,039,908
Issuance of common stock upon exercise of stock options, net of repurchase	66				66
Issuance of common stock upon exercise of stock options, net of repurchase, shares				3,685
Repurchase of common stock from related party	109					109
Repurchase of common stock from related party, shares				(53,649)
Interest on promissory notes from related parties for purchase of common stock	(2)					(2)
Stock-based compensation	377				377
Net loss	(9,188)						(9,188)
Ending balance at Mar. 31, 2019		$ 168,058
Ending balance, shares at Mar. 31, 2019		101,531,788
Ending balance at Mar. 31, 2019	(105,751)			$ 1	22,884	(491)	(128,141)	(4)
Ending balance, shares at Mar. 31, 2019				828,449
Beginning balance at Dec. 31, 2018		$ 161,111
Beginning balance, shares at Dec. 31, 2018		98,491,880
Beginning balance at Dec. 31, 2018	(97,113)			$ 1	22,441	(598)	(118,953)	(4)
Beginning balance, shares at Dec. 31, 2018				878,413
Foreign currency translation adjustment	2
Net loss	(19,814)
Ending balance at Jun. 30, 2019	175,509
Ending balance, shares at Jun. 30, 2019		104,803,325
Ending balance at Jun. 30, 2019	(115,503)			$ 1	23,265		(138,767)	(2)
Ending balance, shares at Jun. 30, 2019				812,759
Beginning balance at Mar. 31, 2019		$ 168,058
Beginning balance, shares at Mar. 31, 2019		101,531,788
Beginning balance at Mar. 31, 2019	(105,751)			$ 1	22,884	(491)	(128,141)	(4)
Beginning balance, shares at Mar. 31, 2019				828,449
Issuance of convertible preferred stock, net of issuance cost	7,451
Issuance of convertible preferred stock, net of issuance cost, shares			3,271,537
Issuance of common stock upon exercise of stock options, net of repurchase	34				34
Issuance of common stock upon exercise of stock options, net of repurchase, shares				13,996
Repurchase of common stock from related party	65					65
Repurchase of common stock from related party, shares				29,686
Paydown of promissory notes from related parties for purchase of common stock	73					73
Forgiveness of promissory notes from related parties for purchase of common stock	353					$ 353
Stock-based compensation	347				347
Foreign currency translation adjustment	2							2
Net loss	(10,626)						(10,626)
Ending balance at Jun. 30, 2019	175,509
Ending balance, shares at Jun. 30, 2019		104,803,325
Ending balance at Jun. 30, 2019	(115,503)			$ 1	23,265		(138,767)	(2)
Ending balance, shares at Jun. 30, 2019				812,759
Beginning balance at Dec. 31, 2019	$ 73,121			$ 2	235,049		(161,950)	20
Beginning balance, shares at Dec. 31, 2019	21,833,037			21,833,037
Issuance of common stock, net of issuance costs	$ 69,842				69,842
Issuance of common stock, net of issuance costs, shares				2,500,000
Issuance of common stock upon exercise of stock options, net of repurchase	30				30
Issuance of common stock upon exercise of stock options, net of repurchase, shares				970
Stock-based compensation	2,088				2,088
Foreign currency translation adjustment	204							204
Unrealized gain (loss) on marketable securities	(217)							(217)
Net loss	(13,139)						(13,139)
Ending balance at Mar. 31, 2020	131,929			$ 2	307,009		(175,089)	7
Ending balance, shares at Mar. 31, 2020				24,334,007
Beginning balance at Dec. 31, 2019	$ 73,121			$ 2	235,049		(161,950)	20
Beginning balance, shares at Dec. 31, 2019	21,833,037			21,833,037
Foreign currency translation adjustment	$ 5
Unrealized gain (loss) on marketable securities	152
Net loss	(25,526)
Ending balance at Jun. 30, 2020	$ 122,611			$ 2	309,908		(187,476)	177
Ending balance, shares at Jun. 30, 2020	24,442,842			24,442,842
Beginning balance at Mar. 31, 2020	$ 131,929			$ 2	307,009		(175,089)	7
Beginning balance, shares at Mar. 31, 2020				24,334,007
Issuance of common stock upon exercise of stock options, net of repurchase	453				453
Issuance of common stock upon exercise of stock options, net of repurchase, shares				68,485
Stock-based compensation	2,035				2,035
Issuance of common stock under the employee stock purchase plan	411				411
Issuance of common stock under the employee stock purchase plan, shares				40,350
Foreign currency translation adjustment	(199)							(199)
Unrealized gain (loss) on marketable securities	369							369
Net loss	(12,387)						(12,387)
Ending balance at Jun. 30, 2020	$ 122,611			$ 2	$ 309,908		$ (187,476)	$ 177
Ending balance, shares at Jun. 30, 2020	24,442,842			24,442,842

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Operating activities
Net loss	$ (25,526)	$ (19,814)
Adjustments to reconcile net loss to net cash used in operating activities:
Amortization of premium on marketable securities	51	0
Depreciation and amortization	595	669
Stock-based compensation expense	4,123	724
Gain on foreign currency translation	5	2
Noncash interest income (loss), net	0	(2)
Changes in operating assets and liabilities:
Prepaid expenses and other long-term assets	(4)	(2,317)
Accounts payable and accrued liabilities	1,811	3,091
Deferred revenue	3,788	0
Deferred rent	(15)	0
Net cash used in operating activities	(15,172)	(17,647)
Investing activities
Purchase of marketable securities	(111,892)	0
Proceeds from maturities of marketable securities	8,000	0
Purchase of property and equipment	(98)	(787)
Net cash used in investing activities	(103,990)	(787)
Financing activities
Proceeds from public offering, net of issuance costs	69,842	0
Proceeds from the sale of convertible preferred stock, net of issuance costs	0	14,398
Proceeds from issuance of common stock under the employee stock purchase plan	411	0
Proceeds from issuance of common stock, net of repurchases	483	100
Net cash provided by financing activities	70,736	14,498
Net decrease in cash and cash equivalents	(48,426)	(3,936)
Cash and cash equivalents at beginning of period	77,383	63,798
Cash and cash equivalents at end of period	28,957	59,862
Supplemental disclosures of non-cash investing and financing information
Property and equipment purchases included in accounts payable	$ 0	$ 61

Organization

6 Months Ended

Jun. 30, 2020

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Organization

1. Organization

Description of the Business

RAPT Therapeutics, Inc. (“RAPT” or the “Company”) is a clinical-stage, immunology-based biopharmaceutical company focused on discovering, developing and commercializing oral small molecule therapies for patients with significant unmet needs in oncology and inflammatory diseases. Utilizing its proprietary drug discovery and development engine, the Company develops highly selective small molecules that are designed to modulate the critical immune responses underlying these diseases. In May 2019, the Company changed its name from FLX Bio, Inc. to RAPT Therapeutics, Inc.

The Company is located in South San Francisco, California.

Equity Financing

In February 2020, the Company completed an underwritten public offering (the “Follow‑on Offering”) of 2,500,000 shares of common stock at an offering price of $30.00 per share. The Company received approximately $69.8 million in net proceeds from the Follow-on Offering, after deducting underwriting discounts and other offering-related costs.

Summary of Significant Accounting Policies

6 Months Ended

Jun. 30, 2020

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

2. Summary of Significant Accounting Policies

Basis of Presentation

The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles (“U.S. GAAP”) for interim financial information and pursuant to Article 10 of Regulation S‑X of the Securities Act of 1933, as amended (the “Securities Act”). Accordingly, they do not include all of the information and notes required by U.S. GAAP for complete financial statements. These unaudited condensed consolidated financial statements include only normal and recurring adjustments that the Company believes are necessary to fairly state the Company’s financial position and the results of its operations and cash flows. Interim-period results are not necessarily indicative of results of operations or cash flows for a full year or any subsequent interim period. The condensed balance sheet at December 31, 2019 has been derived from the audited financial statements at that date but does not include all disclosures required by U.S. GAAP for complete financial statements. Because all of the disclosures required by U.S. GAAP for complete financial statements are not included herein, these unaudited condensed consolidated financial statements and the notes accompanying them should be read in conjunction with the Company’s audited consolidated financial statements included in its Annual Report on Form 10-K for the year ended December 31, 2019 filed on March 30, 2020 with the Securities and Exchange Commission.

The accompanying consolidated financial statements have been prepared in accordance with 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.

Revenue

License and collaborative agreement revenue consists 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 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).

Stock-Based Compensation

The Company measures stock-based compensation expense for all employee and non-employee stock-based awards based on their grant date fair value using the Black-Scholes option-pricing model. Subsequent to the adoption of ASU 2018-07, Stock Compensation (Topic 718): Improvements to Nonemployee Share-Based Payment Accounting, stock-based compensation expense for non-employee stock-based awards is also measured based on the grant date fair value with the estimated fair value expensed over the period for which the non-employee is required to provide service in exchange for the award. For stock-based awards with service conditions only, stock-based compensation expense is recognized over the requisite service period using the straight-line method. For awards with performance conditions, the Company evaluates the probability of achieving performance conditions at each reporting date. The Company recognizes stock-based compensation expense using an accelerated attribution method when it is deemed probable that the performance condition will be met. Forfeitures are recognized as they occur.

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 Company’s initial public offering (“IPO”) in November 2019. 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.

Stock-based compensation expense related to the Company’s employee stock purchase plan is recognized based on the fair value of each award estimated on the first day of the offering period using the Black‑Scholes option-pricing model and recorded as expense over the service period using the straight‑line method.

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 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 for all periods presented since the effect of including potential dilutive securities is anti-dilutive.

Marketable securities

Marketable securities primarily consist of commercial paper, corporate bonds and U.S. government agency securities. The Company has classified its marketable securities as available-for-sale and may sell these securities prior to their stated maturities. The Company views these marketable securities as available to support current operations and classifies marketable securities with maturities beyond 12 months as current assets. The Company’s marketable securities are carried at estimated fair value, which is derived from independent pricing sources based on quoted prices in active markets for similar securities. Unrealized gains and losses are reported as a component of accumulated other comprehensive loss, net of tax. The amortized cost of marketable securities is adjusted for amortization of premiums and accretion of discounts to maturity, which is included in interest income on the condensed consolidated statements of operations.

Recent Accounting Pronouncements

From time to time, new accounting pronouncements are issued by the Financial Accounting Standards Board (the “FASB”) or other standard setting bodies and adopted by the Company as of the specified effective date. Unless otherwise discussed, the impact of recently issued standards that are not yet effective will not have a material impact on our condensed consolidated financial statements upon adoption. 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.

Adopted Accounting Pronouncements

In June 2018, the FASB issued ASU No. 2018-07, Compensation—Stock Compensation (Topic 718): Improvements to Non-Employee Share-Based Payment Accounting as part of the FASB’s simplification initiative. ASU 2018‑07 expands the scope of Topic 718 and allows the application of the requirements of Topic 718 to certain non-employee awards to acquire goods and services from non‑employees. The Company adopted ASU 2018‑07 in the first quarter of 2020 using a modified retrospective method and there was an insignificant impact to the Company’s financial position and results of operations related to this adoption.

In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurements (Topic 820): Disclosure Framework—Changes to the Disclosure Requirements for Fair Value Measurement as part of the FASB’s disclosure framework project. ASU 2018-13 removes certain disclosure requirements, including the amount and reasons for transfers between Level 1 and Level 2 of the fair value hierarchy, the policy for timing of transfers between levels and the valuation process for Level 3 fair value measurements. This ASU also modifies existing disclosure requirements by clarifying that the measurement uncertainty disclosure is to communicate information about the uncertainty in measurement as of the reporting date, and adds disclosure requirements over Level 3 fair value measurements. The Company adopted ASU 2018-13 in the first quarter of 2020 and there was no impact to the Company’s financial position or results of operations related to this adoption.

In December 2019, the FASB issued ASU No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes, which simplifies the accounting for income taxes by removing certain exceptions to the general principles in Topic 740. ASU 2019-12 also improves the consistent application, and the simplification, of other areas of Topic 740 by clarifying and amending existing guidance. The Company adopted ASU 2019-12 in the fourth quarter of 2019 and there was no impact to the financial position or results of operations related to this adoption.

Recently Issued Accounting Pronouncement Not Yet Adopted

In February 2016, the FASB issued ASU No. 2016-02, Leases. ASU 2016-02 requires lessees to record most leases on their balance sheet while recognizing expense in a manner similar to the accounting under the original lease guidance (Topic 840). ASU 2016‑02 states that a lessee would recognize a lease liability for the obligation to make lease payments and a right-to-use asset for the right to use the underlying asset for the lease term. ASU 2016-02 is effective for the Company’s fiscal year beginning after December 15, 2021 and early adoption is permitted. The Company is currently assessing the timing of adoption of ASU 2016-02 and the impact that adoption will have on its consolidated financial statements and related disclosures.

In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments – Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments. ASU 2016-13 amended guidance on reporting credit losses for assets held at amortized cost basis and available-for-sale debt securities. For available-for-sale debt securities, credit losses will be presented as an allowance rather than as a write-down. In April 2019, the FASB issued ASU No. 2019-04, Codification Improvements to Topic 326, Financial Instruments—Credit Losses, Topic 815, Derivatives and Hedging, and Topic 825, Financial Instruments, to increase awareness of the amendments and to expedite improvements to Topic 326. In May 2019, the FASB issued ASU No. 2019-05, Financial Instruments—Credit Losses, Topic 326, providing companies with an option to irrevocably elect the fair value option for certain financial assets previously measured at amortized cost basis. These ASUs do not change the core principle of the guidance in ASU 2016-13; instead, these amendments are intended to clarify and improve operability of certain topics. In November 2019, the FASB issued ASU No. 2019-10, Financial Instruments—Credit Losses (Topic 326), Derivatives and Hedging (Topic 815), and Leases (Topic 842): Effective Dates and ASU No. 2019-11, Codification Improvements to Topic 326, Financial Instruments—Credit Losses, which defer the effective date of the new credit loss standard. ASU 2016-13 and its related amendments are effective for the Company’s fiscal year beginning after December 15, 2022 and early adoption is permitted. The Company is currently assessing the timing of adoption of ASU 2016-13 and the impact that adoption will have on its consolidated financial statements and related disclosures.

Fair Value Measurements

6 Months Ended

Jun. 30, 2020

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 such as cash and cash equivalents, accounts payable and accrued liabilities 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 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 using valuations obtained from third-party pricing services. The pricing services utilize industry standard valuation models, including both income and market-based approaches, for which all significant inputs are observable, either directly or indirectly, to estimate fair value. These inputs include reported trades of and broker/dealer quotes on the same or similar securities, issuer credit spreads, benchmark securities, prepayment/default projections based on historical data and other observable inputs.

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 June 30, 2020
	Fair Value Hierarchy Level	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
Financial assets:
Money market funds—classified as cash equivalents	Level 1	$	26,711	$	—	$	—		$	26,711
Corporate debt	Level 2		47,818		151		(1	)		47,968
Commercial paper	Level 2		23,438		—		—			23,438
U.S. government agency securities	Level 2		32,585		2		—			32,587
Total		$	130,552	$	153	$	(1	)	$	130,704

As of December 31, 2019, the financial assets subject to fair value measurement on a recurring basis consisted of money market funds with a fair value of $77.4 million.

As of June 30, 2020, the Company’s marketable securities had remaining contractual maturities of less than two years. 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 June 30, 2020 were temporary in nature.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Property and Equipment

6 Months Ended

Jun. 30, 2020

Property Plant And Equipment [Abstract]

Property and Equipment

4. Property and Equipment

Property and equipment consisted of the following (in thousands):

	June 30,			December 31,
	2020			2019
Laboratory equipment	$	5,763		$	5,752
Leasehold improvements		3,294			3,294
Computer equipment		362			326
Furniture and fixtures		394			394
Total property and equipment		9,813			9,766
Less accumulated depreciation and amortization		(6,603	)		(6,059	)
Property and equipment, net	$	3,210		$	3,707

Depreciation and amortization expense was $0.4 million for each of the three months ended June 30, 2020 and 2019, and $0.6 million and $0.7 million for the six months ended June 30, 2020 and 2019, respectively.

Accrued Expenses

6 Months Ended

Jun. 30, 2020

Payables And Accruals [Abstract]

Accrued Expenses

5. Accrued Expenses

Accrued expenses consisted of the following (in thousands):

	June 30,		December 31,
	2020		2019
Accrued clinical expenses	$	1,770	$	1,353
Accrued compensation		2,139		1,779
Accrued professional and consulting services		149		192
Accrued lab supplies		34		29
Other		164		289
Total accrued expenses	$	4,256	$	3,642

Collaboration Agreements

6 Months Ended

Jun. 30, 2020

Collaboration Agreements [Abstract]

Collaboration Agreements

6. Collaboration Agreements

Collaboration and License Agreement with Hanmi

In December 2019, the Company entered into a Collaboration and License Agreement with Hanmi (the “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 rights.

In consideration of the rights granted under the Hanmi Agreement, the Company was entitled to $10.0 million in an upfront payment of $4.0 million and a near-term milestone payment of $6.0 million. The milestone payment was received in April 2020. Additionally, the Company will be 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 determined that the transaction price as of June 30, 2020 was $10.0 million, consisting of the upfront fee of $4.0 million and the near-term milestone payment of $6.0 million, which was consistent with the transaction price as of December 31, 2019. 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 three and six months ended June 30, 2020, the Company recognized $1.3 million and $2.2 million, respectively, as revenue pursuant to the Hanmi Agreement. As of June 30, 2020 and December 31, 2019, deferred revenue related to the Hanmi Agreement was $7.8 million and $4.0 million, respectively. The deferred revenue is expected to be recognized over the remaining period of the Company’s Phase 1/2 clinical trial of FLX475.

Convertible Preferred Stock

6 Months Ended

Jun. 30, 2020

Temporary Equity Disclosure [Abstract]

Convertible Preferred Stock

7. Convertible Preferred Stock

Immediately prior to the closing of the Company’s IPO on November 4, 2019, all outstanding shares of convertible preferred stock converted into 17,467,184 shares of common stock.

Common Stock

6 Months Ended

Jun. 30, 2020

Equity [Abstract]

Common Stock

8. Common Stock

As of June 30, 2020 and December 31, 2019, 24,442,842 shares and 21,833,037 shares of common stock were outstanding, respectively, which includes shares subject to repurchase of 19,528 and 51,098, respectively, as a result of early exercise of stock options not yet vested. The holders of common stock have one vote for each share of common stock held by them. Holders of shares of common stock are entitled to dividends when, as and if declared by the board of directors. No dividends had been declared as of June 30, 2020.

As of June 30, 2020, the Company had reserved the following shares of common stock for future issuance:

Options issued and outstanding under the 2019 Equity Incentive Plan and 2015 Stock Plan		1,525,827
Restricted stock units issued and outstanding under the 2019 Equity Incentive Plan		56,500
Options available for future grants		1,592,506
Shares reserved under the 2019 Employee Stock Purchase Plan		199,986
Total		3,374,819

Stock-based Compensation

6 Months Ended

Jun. 30, 2020

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Stock-based Compensation

9. Stock-based Compensation

In 2019, the Company adopted the 2019 Equity Incentive Plan (the “2019 Plan”) for eligible employees, officers, directors, advisors and consultants, which provides for the grant of incentive and non-statutory stock options and restricted stock units (“RSUs”) of common stock. The Company’s 2015 Stock Plan (the “2015 Plan”) terminated in 2019 and no further grants may be made thereunder.

Stock option activity under the 2019 Plan is set forth below for the six months ended June 30, 2020:


							Weighted
							Average
				Number of			Exercise
	Shares			Shares			Price Per
	Available			Outstanding			Share
Balances at December 31, 2019		1,874,759			1,313,468		$	9.77
Stock options granted		(297,088	)		297,088			35.94
Stock options exercised		—			(69,894	)		6.00
Stock options forfeited		14,835			(14,835	)		13.31
Balances at June 30, 2020		1,592,506			1,525,827		$	15.00

RSU activity under the 2019 Plan is set forth below for the six months ended June 30, 2020:

			Weighted
			Average
	Number of		Grant Date
	Shares		Fair Value
	Outstanding		Per Share
Balances at December 31, 2019		—	$	—
RSUs granted		56,500		44.66
RSUs vested and settled		—		—
RSUs forfeited		—		—
Balances at June 30, 2020		56,500	$	44.66

Stock-based compensation expense

Total stock-based compensation expense recognized for options and RSUs granted to both employees and non-employees and for the employee stock purchase plan was as follows (in thousands):

	For the Three Months Ended				For the Six Months Ended
	June 30,				June 30,
	2020		2019		2020		2019
Research and development	$	1,243	$	197	$	2,325	$	399
General and administrative		792		150		1,798		325
Total stock-based compensation expense	$	2,035	$	347	$	4,123	$	724

As of June 30, 2020, unrecognized stock-based compensation expense related to outstanding unvested stock options and RSUs that are expected to vest was $13.8 million. This unrecognized stock-based compensation expense is expected to be recognized over 2.41 years.

2019 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).

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 purchase periods. At the end of each purchase period, eligible employees are permitted to purchase shares of common stock at 85% of the lower of fair market value at the beginning of the offering period or fair market value at the end of the purchase period. The 2019 ESPP is considered a compensatory plan and the Company recorded stock-based compensation expense of $0.8 million and $1.3 million for the three and six months ended June 30, 2020, respectively.

Income Taxes

6 Months Ended

Jun. 30, 2020

Income Tax Disclosure [Abstract]

Income Taxes

10. Income Taxes

The Company recorded a provision for income taxes of $0.3 million and $0.5 million for the three and six months ended June 30, 2020, respectively, related to Korean withholding taxes on the near-term milestone payment the Company received pursuant to the Hanmi Agreement. No provision had been recorded for the three and six months ended June 30, 2019. In addition, the Company’s deferred tax assets continue to be subject to a full valuation allowance.

On March 27, 2020, President Trump signed into U.S. federal law the CARES Act, which provides emergency assistance and health care for individuals, families and businesses affected by the COVID-19 pandemic. Based on the Company’s preliminary analysis, the relief provisions will not have a material impact on the Company’s condensed consolidated financial statements.

- Definition

The entire disclosure for income taxes. Disclosures may include net deferred tax liability or asset recognized in an enterprise's statement of financial position, net change during the year in the total valuation allowance, approximate tax effect of each type of temporary difference and carryforward that gives rise to a significant portion of deferred tax liabilities and deferred tax assets, utilization of a tax carryback, and tax uncertainties information.

+ References + Details

Net Loss Per Share

6 Months Ended

Jun. 30, 2020

Earnings Per Share [Abstract]

Net Loss Per Share

11. Net Loss Per Share

Net loss per share

The following table sets forth the computation of the basic and diluted net loss per share for the three and six months ended June 30, 2020 and 2019 (in thousands, except share and per share data):

	Three Months Ended June 30,						Six Months Ended June 30,
	2020			2019			2020			2019
Numerator:
Net loss	$	(12,387	)	$	(10,626	)	$	(25,526	)	$	(19,814	)
Denominator:
Weighted average common shares outstanding		24,376,891			794,840			23,788,944			789,777
Less: weighted-average unvested restricted common stock subject to repurchase		—			(45,451	)		—			(58,628	)
Less: weighted-average unvested common shares subject to repurchase		(40,789	)		(30,363	)		(45,886	)		(43,279	)
Weighted-average shares used to compute net loss per share, basic and diluted		24,336,102			719,026			23,743,058			687,870
Net loss per share, basic and diluted	$	(0.51	)	$	(14.78	)	$	(1.08	)	$	(28.80	)

Potential dilutive securities that were not included in the diluted per share calculations because they would be anti-dilutive were as follows:

	June 30,
	2020		2019
Convertible preferred stock		—		104,803,325
Common stock options issued and outstanding		1,525,827		1,049,976
Estimated shares issuable under the employee stock purchase plan		16,457		—
RSUs subject to future vesting		56,500		—
Total		1,598,784		105,853,301

Summary of Significant Accounting Policies (Policies)	6 Months Ended
Summary of Significant Accounting Policies (Policies)	Jun. 30, 2020
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles (“U.S. GAAP”) for interim financial information and pursuant to Article 10 of Regulation S‑X of the Securities Act of 1933, as amended (the “Securities Act”). Accordingly, they do not include all of the information and notes required by U.S. GAAP for complete financial statements. These unaudited condensed consolidated financial statements include only normal and recurring adjustments that the Company believes are necessary to fairly state the Company’s financial position and the results of its operations and cash flows. Interim-period results are not necessarily indicative of results of operations or cash flows for a full year or any subsequent interim period. The condensed balance sheet at December 31, 2019 has been derived from the audited financial statements at that date but does not include all disclosures required by U.S. GAAP for complete financial statements. Because all of the disclosures required by U.S. GAAP for complete financial statements are not included herein, these unaudited condensed consolidated financial statements and the notes accompanying them should be read in conjunction with the Company’s audited consolidated financial statements included in its Annual Report on Form 10-K for the year ended December 31, 2019 filed on March 30, 2020 with the Securities and Exchange Commission. The accompanying consolidated financial statements have been prepared in accordance with 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.
Revenue	Revenue License and collaborative agreement revenue consists 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 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).
Share-Based Compensation	Stock-Based Compensation The Company measures stock-based compensation expense for all employee and non-employee stock-based awards based on their grant date fair value using the Black-Scholes option-pricing model. Subsequent to the adoption of ASU 2018-07, Stock Compensation (Topic 718): Improvements to Nonemployee Share-Based Payment Accounting, stock-based compensation expense for non-employee stock-based awards is also measured based on the grant date fair value with the estimated fair value expensed over the period for which the non-employee is required to provide service in exchange for the award. For stock-based awards with service conditions only, stock-based compensation expense is recognized over the requisite service period using the straight-line method. For awards with performance conditions, the Company evaluates the probability of achieving performance conditions at each reporting date. The Company recognizes stock-based compensation expense using an accelerated attribution method when it is deemed probable that the performance condition will be met. Forfeitures are recognized as they occur. 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 Company’s initial public offering (“IPO”) in November 2019. 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. Stock-based compensation expense related to the Company’s employee stock purchase plan is recognized based on the fair value of each award estimated on the first day of the offering period using the Black‑Scholes option-pricing model and recorded as expense over the service period using the straight‑line method.
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 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 for all periods presented since the effect of including potential dilutive securities is anti-dilutive.
Marketable Securities	Marketable securities Marketable securities primarily consist of commercial paper, corporate bonds and U.S. government agency securities. The Company has classified its marketable securities as available-for-sale and may sell these securities prior to their stated maturities. The Company views these marketable securities as available to support current operations and classifies marketable securities with maturities beyond 12 months as current assets. The Company’s marketable securities are carried at estimated fair value, which is derived from independent pricing sources based on quoted prices in active markets for similar securities. Unrealized gains and losses are reported as a component of accumulated other comprehensive loss, net of tax. The amortized cost of marketable securities is adjusted for amortization of premiums and accretion of discounts to maturity, which is included in interest income on the condensed consolidated statements of operations.
Recent Accounting Pronouncements	Recent Accounting Pronouncements From time to time, new accounting pronouncements are issued by the Financial Accounting Standards Board (the “FASB”) or other standard setting bodies and adopted by the Company as of the specified effective date. Unless otherwise discussed, the impact of recently issued standards that are not yet effective will not have a material impact on our condensed consolidated financial statements upon adoption. 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.
Adopted Accounting Pronouncements	Adopted Accounting Pronouncements In June 2018, the FASB issued ASU No. 2018-07, Compensation—Stock Compensation (Topic 718): Improvements to Non-Employee Share-Based Payment Accounting as part of the FASB’s simplification initiative. ASU 2018‑07 expands the scope of Topic 718 and allows the application of the requirements of Topic 718 to certain non-employee awards to acquire goods and services from non‑employees. The Company adopted ASU 2018‑07 in the first quarter of 2020 using a modified retrospective method and there was an insignificant impact to the Company’s financial position and results of operations related to this adoption. In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurements (Topic 820): Disclosure Framework—Changes to the Disclosure Requirements for Fair Value Measurement as part of the FASB’s disclosure framework project. ASU 2018-13 removes certain disclosure requirements, including the amount and reasons for transfers between Level 1 and Level 2 of the fair value hierarchy, the policy for timing of transfers between levels and the valuation process for Level 3 fair value measurements. This ASU also modifies existing disclosure requirements by clarifying that the measurement uncertainty disclosure is to communicate information about the uncertainty in measurement as of the reporting date, and adds disclosure requirements over Level 3 fair value measurements. The Company adopted ASU 2018-13 in the first quarter of 2020 and there was no impact to the Company’s financial position or results of operations related to this adoption. In December 2019, the FASB issued ASU No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes, which simplifies the accounting for income taxes by removing certain exceptions to the general principles in Topic 740. ASU 2019-12 also improves the consistent application, and the simplification, of other areas of Topic 740 by clarifying and amending existing guidance. The Company adopted ASU 2019-12 in the fourth quarter of 2019 and there was no impact to the financial position or results of operations related to this adoption.
Recently Issued Accounting Pronouncements Not Yet Adopted	Recently Issued Accounting Pronouncement Not Yet Adopted In February 2016, the FASB issued ASU No. 2016-02, Leases. ASU 2016-02 requires lessees to record most leases on their balance sheet while recognizing expense in a manner similar to the accounting under the original lease guidance (Topic 840). ASU 2016‑02 states that a lessee would recognize a lease liability for the obligation to make lease payments and a right-to-use asset for the right to use the underlying asset for the lease term. ASU 2016-02 is effective for the Company’s fiscal year beginning after December 15, 2021 and early adoption is permitted. The Company is currently assessing the timing of adoption of ASU 2016-02 and the impact that adoption will have on its consolidated financial statements and related disclosures. In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments – Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments. ASU 2016-13 amended guidance on reporting credit losses for assets held at amortized cost basis and available-for-sale debt securities. For available-for-sale debt securities, credit losses will be presented as an allowance rather than as a write-down. In April 2019, the FASB issued ASU No. 2019-04, Codification Improvements to Topic 326, Financial Instruments—Credit Losses, Topic 815, Derivatives and Hedging, and Topic 825, Financial Instruments, to increase awareness of the amendments and to expedite improvements to Topic 326. In May 2019, the FASB issued ASU No. 2019-05, Financial Instruments—Credit Losses, Topic 326, providing companies with an option to irrevocably elect the fair value option for certain financial assets previously measured at amortized cost basis. These ASUs do not change the core principle of the guidance in ASU 2016-13; instead, these amendments are intended to clarify and improve operability of certain topics. In November 2019, the FASB issued ASU No. 2019-10, Financial Instruments—Credit Losses (Topic 326), Derivatives and Hedging (Topic 815), and Leases (Topic 842): Effective Dates and ASU No. 2019-11, Codification Improvements to Topic 326, Financial Instruments—Credit Losses, which defer the effective date of the new credit loss standard. ASU 2016-13 and its related amendments are effective for the Company’s fiscal year beginning after December 15, 2022 and early adoption is permitted. The Company is currently assessing the timing of adoption of ASU 2016-13 and the impact that adoption will have on its consolidated financial statements and related disclosures.

Fair Value Measurements (Tables)

6 Months Ended

Jun. 30, 2020

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 June 30, 2020
	Fair Value Hierarchy Level	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
Financial assets:
Money market funds—classified as cash equivalents	Level 1	$	26,711	$	—	$	—		$	26,711
Corporate debt	Level 2		47,818		151		(1	)		47,968
Commercial paper	Level 2		23,438		—		—			23,438
U.S. government agency securities	Level 2		32,585		2		—			32,587
Total		$	130,552	$	153	$	(1	)	$	130,704

Property and Equipment (Tables)

6 Months Ended

Jun. 30, 2020

Property Plant And Equipment [Abstract]

Schedule of Property and Equipment

Property and equipment consisted of the following (in thousands):

	June 30,			December 31,
	2020			2019
Laboratory equipment	$	5,763		$	5,752
Leasehold improvements		3,294			3,294
Computer equipment		362			326
Furniture and fixtures		394			394
Total property and equipment		9,813			9,766
Less accumulated depreciation and amortization		(6,603	)		(6,059	)
Property and equipment, net	$	3,210		$	3,707

Accrued Expenses (Tables)

6 Months Ended

Jun. 30, 2020

Payables And Accruals [Abstract]

Schedule of Accrued Expenses

Accrued expenses consisted of the following (in thousands):

	June 30,		December 31,
	2020		2019
Accrued clinical expenses	$	1,770	$	1,353
Accrued compensation		2,139		1,779
Accrued professional and consulting services		149		192
Accrued lab supplies		34		29
Other		164		289
Total accrued expenses	$	4,256	$	3,642

Common Stock (Tables)

6 Months Ended

Jun. 30, 2020

Equity [Abstract]

Summary of Reserved Shares of Common Stock for Future Issuance

As of June 30, 2020, the Company had reserved the following shares of common stock for future issuance:

Options issued and outstanding under the 2019 Equity Incentive Plan and 2015 Stock Plan		1,525,827
Restricted stock units issued and outstanding under the 2019 Equity Incentive Plan		56,500
Options available for future grants		1,592,506
Shares reserved under the 2019 Employee Stock Purchase Plan		199,986
Total		3,374,819

Stock-based Compensation (Tables)

6 Months Ended

Jun. 30, 2020

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of Stock Option Activity

Stock option activity under the 2019 Plan is set forth below for the six months ended June 30, 2020:


							Weighted
							Average
				Number of			Exercise
	Shares			Shares			Price Per
	Available			Outstanding			Share
Balances at December 31, 2019		1,874,759			1,313,468		$	9.77
Stock options granted		(297,088	)		297,088			35.94
Stock options exercised		—			(69,894	)		6.00
Stock options forfeited		14,835			(14,835	)		13.31
Balances at June 30, 2020		1,592,506			1,525,827		$	15.00

Summary of RSU Activity

RSU activity under the 2019 Plan is set forth below for the six months ended June 30, 2020:

			Weighted
			Average
	Number of		Grant Date
	Shares		Fair Value
	Outstanding		Per Share
Balances at December 31, 2019		—	$	—
RSUs granted		56,500		44.66
RSUs vested and settled		—		—
RSUs forfeited		—		—
Balances at June 30, 2020		56,500	$	44.66

Summary of Stock-based Compensation Expense

Total stock-based compensation expense recognized for options and RSUs granted to both employees and non-employees and for the employee stock purchase plan was as follows (in thousands):

	For the Three Months Ended				For the Six Months Ended
	June 30,				June 30,
	2020		2019		2020		2019
Research and development	$	1,243	$	197	$	2,325	$	399
General and administrative		792		150		1,798		325
Total stock-based compensation expense	$	2,035	$	347	$	4,123	$	724

Net Loss Per Share (Tables)

6 Months Ended

Jun. 30, 2020

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 for the three and six months ended June 30, 2020 and 2019 (in thousands, except share and per share data):

	Three Months Ended June 30,						Six Months Ended June 30,
	2020			2019			2020			2019
Numerator:
Net loss	$	(12,387	)	$	(10,626	)	$	(25,526	)	$	(19,814	)
Denominator:
Weighted average common shares outstanding		24,376,891			794,840			23,788,944			789,777
Less: weighted-average unvested restricted common stock subject to repurchase		—			(45,451	)		—			(58,628	)
Less: weighted-average unvested common shares subject to repurchase		(40,789	)		(30,363	)		(45,886	)		(43,279	)
Weighted-average shares used to compute net loss per share, basic and diluted		24,336,102			719,026			23,743,058			687,870
Net loss per share, basic and diluted	$	(0.51	)	$	(14.78	)	$	(1.08	)	$	(28.80	)

Potential Dilutive Securities not Included in Diluted per Share Calculations

Potential dilutive securities that were not included in the diluted per share calculations because they would be anti-dilutive were as follows:

	June 30,
	2020		2019
Convertible preferred stock		—		104,803,325
Common stock options issued and outstanding		1,525,827		1,049,976
Estimated shares issuable under the employee stock purchase plan		16,457		—
RSUs subject to future vesting		56,500		—
Total		1,598,784		105,853,301

Organization - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	6 Months Ended
	Feb. 29, 2020	Jun. 30, 2020	Jun. 30, 2019
Class Of Stock [Line Items]
Net proceeds received after deducting underwriting discounts and other offering related costs		$ 69,842	$ 0
Follow-on Offering
Class Of Stock [Line Items]
Shares issued during period	2,500,000
Shares issued, price per share	$ 30.00
Net proceeds received after deducting underwriting discounts and other offering related costs	$ 69,800

Fair Value Measurements - Schedule of Cash Equivalents and Marketable Securities Classified as Available-for-Sale Securities Measured at Fair Value on Recurring Basis (Details) $ in Thousands	Jun. 30, 2020 USD ($)
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 130,552
Unrealized Gains	153
Unrealized Losses	(1)
Fair Value	130,704
Level 1 \| Money Market Funds \| Cash Equivalents
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	26,711
Fair Value	26,711
Level 2 \| Corporate Debt
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	47,818
Unrealized Gains	151
Unrealized Losses	(1)
Fair Value	47,968
Level 2 \| Commercial Paper
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	23,438
Fair Value	23,438
Level 2 \| U.S. Government Agency Securities
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	32,585
Unrealized Gains	2
Fair Value	$ 32,587

Fair Value Measurements - Additional Information (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable securities remaining contractual term	2 years
Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Money market fund, fair value		$ 77.4

Property and Equipment - Schedule of Property and Equipment (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Property Plant And Equipment [Line Items]
Total property and equipment	$ 9,813	$ 9,766
Less accumulated depreciation and amortization	(6,603)	(6,059)
Property and equipment, net	3,210	3,707
Laboratory Equipment
Property Plant And Equipment [Line Items]
Total property and equipment	5,763	5,752
Leasehold Improvements
Property Plant And Equipment [Line Items]
Total property and equipment	3,294	3,294
Computer Equipment
Property Plant And Equipment [Line Items]
Total property and equipment	362	326
Furniture and Fixtures
Property Plant And Equipment [Line Items]
Total property and equipment	$ 394	$ 394

Property and Equipment - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Property Plant And Equipment [Abstract]
Depreciation and amortization expense	$ 400	$ 400	$ 595	$ 669

Accrued Expenses - Schedule of Accrued Expenses (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Payables And Accruals [Abstract]
Accrued clinical expenses	$ 1,770	$ 1,353
Accrued compensation	2,139	1,779
Accrued professional and consulting services	149	192
Accrued lab supplies	34	29
Other	164	289
Total accrued expenses	$ 4,256	$ 3,642

Collaboration Agreements - Additional Information (Details) - USD ($)	3 Months Ended	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2020	Apr. 30, 2020	Dec. 31, 2019
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue recognized	$ 1,277,000	$ 2,212,000
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	10,000,000		$ 10,000,000
Upfront fee receivable	4,000,000	4,000,000		4,000,000
Milestone payment	6,000,000	6,000,000	$ 6,000,000
Revenue recognized	1,300,000	2,200,000
Deferred revenue	$ 7,800,000	$ 7,800,000		4,000,000
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

Convertible Preferred Stock - Additional Information (Details)	Nov. 04, 2019 shares
Common Stock
Temporary Equity [Line Items]
Conversion of convertible preferred stock, common stock shares issued	17,467,184

Common Stock - Additional Information (Details)	6 Months Ended	12 Months Ended
Common Stock - Additional Information (Details)	Jun. 30, 2020 USD ($) vote shares	Dec. 31, 2019 shares
Equity [Abstract]
Common stock shares outstanding	24,442,842	21,833,037
Shares subject to repurchase as a result of early exercise of stock options not yet vested	19,528	51,098
Number of votes for each share of common stock	The holders of common stock have one vote for each share of common stock held by them
Number of votes per share \| vote	1
Dividends declared \| $	$ 0

Common Stock - Summary of Reserved Shares of Common Stock for Future Issuance (Details)	Jun. 30, 2020 shares
Class Of Stock [Line Items]
Total shares reserved	3,374,819
Options Available for Future Grants
Class Of Stock [Line Items]
Total shares reserved	1,592,506
2019 Equity Incentive Plan and 2015 Stock Plan \| Options Issued and Outstanding
Class Of Stock [Line Items]
Total shares reserved	1,525,827
2019 Equity Incentive Plan \| Restricted Stock Units Issued and Outstanding
Class Of Stock [Line Items]
Total shares reserved	56,500
2019 Employee Stock Purchase Plan
Class Of Stock [Line Items]
Total shares reserved	199,986

Stock-based Compensation - Summary of Stock Option Activity (Details) - 2019 Plan - Stock Option	6 Months Ended
	Jun. 30, 2020 $ / shares shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares Available, Beginning Balance	1,874,759
Shares Available, Stock options granted	(297,088)
Shares Available, Stock options forfeited	14,835
Shares Available, Ending Balance	1,592,506
Number of Shares Outstanding, Beginning Balance	1,313,468
Number of Shares Outstanding, Stock options granted	297,088
Number of Shares Outstanding, Stock options exercised	(69,894)
Number of Shares Outstanding, Stock options forfeited	(14,835)
Number of Shares Outstanding, Ending Balance	1,525,827
Weighted Average Exercise Price Per Share, Beginning Balance \| $ / shares	$ 9.77
Weighted Average Exercise Price Per Share, Stock options granted \| $ / shares	35.94
Weighted Average Exercise Price Per Share, Stock options exercised \| $ / shares	6.00
Weighted Average Exercise Price Per Share, Stock options forfeited \| $ / shares	13.31
Weighted Average Exercise Price Per Share, Ending Balance \| $ / shares	$ 15.00

Stock-based Compensation - Summary of RSU Activity (Details) - 2019 Plan - Restricted Stock Unit (“RSU”)	6 Months Ended
	Jun. 30, 2020 $ / shares shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Shares Outstanding, RSUs granted \| shares	56,500
Number of Shares Outstanding, Ending Balance \| shares	56,500
Weighted Average Grant Date Fair Value Per Share, RSUs granted \| $ / shares	$ 44.66
Weighted Average Grant Date Fair Value Per Share, Ending Balance \| $ / shares	$ 44.66

Stock-based Compensation - Summary of Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 2,035	$ 347	$ 4,123	$ 724
Research and Development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	1,243	197	2,325	399
General and Administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 792	$ 150	$ 1,798	$ 325

Stock-based Compensation - Additional Information (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		6 Months Ended
	Oct. 31, 2019	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense		$ 2,035	$ 347	$ 4,123	$ 724
2019 ESPP
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total shares reserved	240,336
Percentage of increase in shares reserved for issuance on common stock outstanding	1.00%
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		800		1,300
Outstanding Unvested Stock Options and RSUs
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized stock-based compensation expense		$ 13,800		$ 13,800
Unrecognized stock-based compensation expense, expected period to be recognized				2 years 4 months 28 days

Income Taxes - Additional Information (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Income Tax Disclosure [Abstract]
Provision for income taxes	$ 267,000	$ 0	$ 504,000	$ 0

- Definition

Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

+ References + Details

Net Loss Per Share - Computation of Basic and Diluted Net Loss per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019
Numerator:
Net loss	$ (12,387)	$ (13,139)	$ (10,626)	$ (9,188)	$ (25,526)	$ (19,814)
Denominator:
Weighted average common shares outstanding	24,376,891		794,840		23,788,944	789,777
Less: weighted-average unvested common stock subject to repurchase	(40,789)		(30,363)		(45,886)	(43,279)
Weighted-average shares used to compute net loss per share, basic and diluted	24,336,102		719,026		23,743,058	687,870
Net loss per share, basic and diluted	$ (0.51)		$ (14.78)		$ (1.08)	$ (28.80)
Restricted Stock
Denominator:
Less: weighted-average unvested common stock subject to repurchase			(45,451)			(58,628)

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References

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+ Details

Net Loss Per Share - Potential Dilutive Securities not Included in Diluted per Share Calculations (Details) - shares	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potential dilutive securities	1,598,784	105,853,301
Convertible Preferred Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potential dilutive securities		104,803,325
Common Stock Options Issued and Outstanding
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potential dilutive securities	1,525,827	1,049,976
Estimated Shares Issuable Under Employee Stock Purchase Plan
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potential dilutive securities	16,457
RSUs Subject to Future Vesting
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potential dilutive securities	56,500