Sec Form 3 Filing - Abingworth LLP @ Sierra Oncology, Inc. - 2021-11-05

FORM 3 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person Abingworth LLP 2. Issuer Name and Ticker or Trading Symbol Sierra Oncology, Inc. [ SRRA] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director X __ 10% Owner _____ Officer (give title below) _____ Other (specify below) (Last) (First) (Middle) PRINCES HOUSE 38 JERMYN STREET 3. Date of Earliest Transaction (MM/DD/YY) 11/05/2021 (Street) LONDON, X0SW1Y 6DN 4. If Amendment, Date Original Filed (MM/DD/YY) 6. Individual or Joint/Group Filing (Check Applicable Line) __ X __ Form filed by One Reporting Person _____ Form filed by More than One Reporting Person (City) (State) (Zip)

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned 1.Title of Security (Instr. 3) 2. Transaction Date (MM/DD/YY) 2A. Deemed Execution Date, if any (MM/DD/YY) 3. Transaction Code (Instr. 8) 4. Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5) 5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4) 6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 7. Nature of Indirect Beneficial Ownership (Instr. 4) Code V Amount (A) or (D) Price Common Stock, $0.001 par value 878,656 I See Footnote ( 1 )

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned ( e.g. , puts, calls, warrants, options, convertible securities) 1. Title of Derivative Security (Instr. 3) 2. Conversion or Exercise Price of Derivative Security 3. Transaction Date (MM/DD/YY) 3A. Deemed Execution Date, if any (MM/DD/YY) 4. Transaction Code (Instr. 8) 5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4, and 5) 6. Date Exercisable and Expiration Date (MM/DD/YY) 7. Title and Amount of Underlying Securities (Instr. 3 and 4) 8. Price of Derivative Security (Instr. 5) 9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4) 10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4) 11. Nature of Indirect Beneficial Ownership (Instr. 4) Code V (A) (D) Date Exercisable Expiration Date Title Amount or Number of Shares Series A Warrants $ 13.2 01/22/2020 01/22/2025 Common Stock 871,125 ( 2 ) I See footnote ( 1 ) Series B Warrants $ 13.2 01/22/2020 ( 3 ) Common Stock 287,471 ( 3 ) I See footnote ( 1 ) Stock Option (Right to Buy) $ 13.868 ( 6 ) 11/29/2029 Common Stock 1,500 I See footnotes ( 4 ) ( 5 ) Stock Option (Right to Buy) $ 13.98 ( 7 ) 06/09/2030 Common Stock 6,874 I See footnotes ( 4 ) ( 5 ) Stock Option (Right to Buy) $ 18.11 ( 8 ) 06/08/2031 Common Stock 6,000 I See footnotes ( 4 ) ( 5 )

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other Abingworth LLP PRINCES HOUSE 38 JERMYN STREET LONDON, X0SW1Y 6DN X Signatures /s/ John Heard 11/05/2021 Signature of Reporting Person Date

Explanation of Responses:

( 1 )The securities of Sierra Oncology, Inc. (the "Issuer") are held by Abingworth Bioventures VII, LP ("ABV VII"). Abingworth Bioventures VII GP LP ("Abingworth GP") serves as the general partner of ABV VII. Abingworth General Partner VII LLP, serves as the general partner of Abingworth GP. ABV VII (acting by its general partner Abingworth GP, acting by its general partner Abingworth General Partner VII LLP) has delegated to Abingworth LLP, all investment and dispositive power over the securities held by ABV VII. Abingworth LLP holds the reported securities indirectly through ABV VII. Abingworth LLP disclaims beneficial ownership of such securities, except to the extent of its pecuniary interest therein. This report shall not be deemed an admission that the reporting person, ABV VII, Dr. Sinclair or any other person is the beneficial owner of the securities reported herein for purposes of Section 16 of the Securities Exchange Act of 1934, as amended, or for any other purpose. ( 2 )Each Series A Warrant is currently exercisable for one share of Common Stock, provided that, at each holder's election, the holder will be prohibited, subject to certain exceptions, from exercising the Series A Warrant for shares of Common Stock if, as a result of such exercise, the holder, together with its affiliates and other attribution parties, would own more than 19.99% of the total number of shares of Common Stock then issued and outstanding, which percentage may be changed at the holder's election to a lower percentage at any time or to a higher percentage upon 61 days' notice to the Issuer. ( 3 )Each Series B Warrant is currently exercisable for 0.33 shares of Common Stock, provided that, at each holder's election, the holder will be prohibited, subject to certain exceptions, from exercising the Series B Warrant for shares of Common Stock if, as a result of such exercise, the holder, together with its affiliates and other attribution parties, would own more than 19.99% of the total number of shares of Common Stock then issued and outstanding, which percentage may be changed at the holder's election to a lower percentage at any time or to a higher percentage upon 61 days' notice to the Issuer. Each Series B warrant will expire on the 75th day anniversary of the Issuer's announcement of top-line data from its MOMENTUM Phase 3 clinical trial of momelotinib and may only be exercised by paying the exercise price in cash. ( 4 )This option was granted to Dr. Andrew Sinclair as director's compensation. Dr. Sinclair is a Partner of Abingworth LLP. Under an agreement between Dr. Sinclair and Abingworth LLP, Dr. Sinclair is deemed to hold the options and any shares of Common Stock issuable upon exercise of the options for the benefit of ABV VII, and must exercise the options solely upon the direction of Abingworth LLP. ( 5 )ABV VII may be deemed the indirect beneficial owner of the option, and Dr. Sinclair may be deemed the indirect beneficial owner of the option through his indirect interest in ABV VII. Abingworth LLP disclaims beneficial ownership of the option except to the extent, if any, of its pecuniary interest therein. This report shall not be deemed an admission that Abingworth LLP, ABV VII, Dr. Sinclair or any other person is the beneficial owner of the securities reported herein for purposes of Section 16 of the Securities Exchange Act of 1934, as amended, or for any other purpose. ( 6 )The option vested in equal monthly installments over a period of 12 months commencing on December 29, 2019, and is fully vested. ( 7 )The option vested as to 8.333% of the total shares monthly, commencing on July 9, 2020, and is fully vested. ( 8 )The option fully vests and becomes exercisable on June 8, 2022, subject to Dr. Sinclair's provision of services to the Issuer as of the vesting date.

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