Sierra Oncology (SRRA) 10-Q 2018 Q1 Quarterly report

EXHIBIT 32.2

CERTIFICATION PURSUANT TO

18 U.S.C. SECTION 1350

AS ADOPTED PURSUANT TO SECTION 906

OF THE SARBANES-OXLEY ACT OF 2002

I, Sukhi Jagpal, Chief Financial Officer of Sierra Oncology, Inc. (Company), do hereby certify, pursuant to 18 U.S.C. Section 1350, as adopted pursuant to Section 906 of the Sarbanes-Oxley Act of 2002, that to the best of my knowledge:

• the Quarterly Report on Form10-Q of the Company for the quarter ended March 31, 2018 (Report), as filed with the Securities and Exchange Commission, fully complies with the requirements of Section 13(a) or 15(d) of the Securities Exchange Act of 1934; and

• the information contained in the Report fairly presents, in all material respects, the financial condition and results of operations of the Company for the periods presented therein.

Date: May 10, 2018

/s/ Sukhi Jagpal

Sukhi Jagpal

Chief Financial Officer

(Principal Financial Officer)