X0306 4 2022-01-31 0 0001290149 Sierra Oncology, Inc. SRRA 0001793762 Richardson Joshua C/O SIERRA ONCOLOGY, INC. 2150 - 885 WEST GEORGIA STREET VANCOUVER A1 V6C 3E8 BRITISH COLUMBIA, CANADA 1 0 1 0 Common Stock 2022-02-02 4 P 0 175000 27.00 A 175000 I See footnote Common Stock 1964771 I See footnote The securities are held directly by Longitude Prime Fund, L.P. ("LPF"). Longitude Prime Partners, LLC ("LPP"), the general partner of LPF, may be deemed to have voting and investment power with respect to the shares held by LPF. Patrick G. Enright, Juliet Tammenoms Bakker and the Reporting Person, a member of the Issuer's board of directors, are each members of LPF and may be deemed to share voting, investment and dispositive power over such securities. Mr. Enright and Ms. Tammenoms Bakker are the managing members of LPP. Each of Mr. Enright, Ms. Tammenoms Bakker and the Reporting Person disclaim beneficial ownership of such shares except to the extent of their respective pecuniary interests therein, and the inclusion of such securities in this report shall not be deemed an admission of beneficial ownership of the reported securities for purposes of Section 16 or for any other purpose. The securities are held directly by Longitude Venture Partners III, L.P. ("LVP III"). Longitude Capital Partners III, LLC ("LCP III") is the general partner of LVP III and may be deemed to have voting, investment and dispositive power with respect to such securities. Patrick G. Enright, Juliet Tammenoms Bakker and the Reporting Person, a member of the Issuer's board of directors, are each members of LCP III and may be deemed to share voting, investment and dispositive power over such securities. Mr. Enright and Ms. Tammenoms Bakker are the managing members of LCP III. Each of LCP III, Mr. Enright, Ms. Tammenoms Bakker and the Reporting Person disclaim beneficial ownership over such securities except to the extent of their respective pecuniary interest therein, and the inclusion of such securities in this report shall not be deemed an admission of beneficial ownership of the reported securities for purposes of Section 16 or for any other purpose. /s/ Joshua Richardson 2022-02-02