Sierra Oncology Announces Closing of Upsized Public Offering of $135.0 Million of Securities

Sierra Oncology, Inc. (Nasdaq: SRRA), a late-stage biopharmaceutical company dedicated to delivering targeted therapies for rare cancers, today announced the closing of its previously announced underwritten public offering of 4,074,075 shares of its common stock at a price to the public of $27.00 per share and, in lieu of shares of common stock, to a certain investor, pre-funded warrants to purchase up to 925,925 shares of common stock at a price to the public of $26.999 per pre-funded warrant, which represents the per share public offering price for the common stock less the $0.001 per share exercise price for each pre-funded warrant. The gross proceeds to Sierra Oncology from the offering were approximately $135.0 million, before deducting underwriting discounts and commissions and other offering expenses. Net proceeds to Sierra Oncology from the offering were approximately $126.6 million after deducting underwriting discounts and commissions and other offering expenses. Sierra Oncology intends to use the net proceeds of the offering to prepare for potential commercialization of momelotinib, clinical development of its other product candidates, research, clinical and process development and manufacturing of its product candidates, working capital, and capital expenditures and other general corporate purposes.

Jefferies and Cantor are acting as the joint book-running managers and representatives of the underwriters for the offering. LifeSci Capital, Oppenheimer & Co. and H.C. Wainwright & Co. are acting as lead managers for the offering.

A shelf registration statement on Form S-3 relating to the securities offered in the public offering described above was filed with the Securities and Exchange Commission (SEC) on November 5, 2021 and declared effective by the SEC on November 12, 2021. A final prospectus supplement and accompanying prospectus relating to the offering have been filed with the SEC and are available on the SEC's website at www.sec.gov. Copies of the final prospectus supplement and accompanying prospectus may also be obtained by contacting Jefferies LLC, Attention: Equity Syndicate Prospectus Department, 520 Madison Avenue, 2nd Floor, New York, NY 10022, by telephone at (877) 821-7388, or by email at [email protected]; or Cantor Fitzgerald & Co., Attention: Capital Markets, 499 Park Avenue, New York, New York 10022, or by e-mail at [email protected].

This press release shall not constitute an offer to sell or the solicitation of an offer to buy the securities being offered, nor shall there be any sale of the securities being offered in any state or other jurisdiction in which such offer, solicitation or sale would be unlawful prior to the registration or qualification under the securities laws of any such state or other jurisdiction.

About Sierra Oncology

Sierra Oncology is a late-stage biopharmaceutical company on a quest to deliver targeted therapies that treat rare forms of cancer. We harness our deep scientific expertise to identify compounds that target the root cause of disease to advance targeted therapies with assets on the leading edge of cancer biology. Our team takes an evidence-based approach to understand the limitations of current treatments and explore new ways to change the cancer treatment paradigm. Together we are transforming promise into patient impact.