Sierra Oncology Presents Long-term Overall Survival and Sustained Efficacy Outcomes Data for Momelotinib at ASH Annual Meeting

December 5, 2020April 15, 2021 vanessa

–Momelotinib demonstrates robust overall survival in both JAKi-naïve and patients previously treated with ruxolitinib–

VANCOUVER, BC,Dec. 5, 2020/CNW/ – Sierra Oncology, Inc. (SRRA), a late-stage biopharmaceutical company on a quest to deliver targeted therapies that treat rare forms of cancer, today reported updated overall survival (OS) data for momelotinib in both JAKi-naïve and patients previously treated with ruxolitinib. The data were presented in an oral presentation at the 2020 American Society of Hematology Annual Meeting by Srdan Verstovsek, MD, PhD, Chief, Section for Myeloproliferative Neoplasms, Department of Leukemia, Division of Cancer Medicine, TheUniversity of TexasMD Anderson Cancer Center.”Momelotinib’s unique mechanism of action—targeting JAK1, JAK2 and ACVR1—is translating to durability of activity and survival data consistent with its clinical and biologic profile,” said Dr. Verstovsek. “Notably, momelotinib showed improved rates in transfusion independence and the duration thereof as well as overall survival, and that benefit was present regardless of whether or not the patient was previously treated with a JAK inhibitor.””As the SIMPLIFY data sets continue to mature, we are seeing increasingly exciting outcomes in terms of overall survival, as well as myelofibrosis disease hallmarks, including splenic response and transfusion independence,” saidBarbara Klencke, MD, Chief Development Officer at Sierra Oncology. “We believe these data presented at the ASH annual meeting, in combination with previously reported safety data, tell a truly innovative story for how momelotinib can fulfill an unmet need for intermediate and high-risk myelofibrosis patients who are not ideal candidates for currently approved therapies. We look forward to continuing enrollment in the Phase 3 MOMENTUM study to further highlight where momelotinib may be a preferred treatment option for patients and their physicians.”

Robust Overall Survival and Sustained Efficacy Outcomes During Long Term Exposure to Momelotinib in JAK Inhibitor Naïve and Previously JAK Inhibitor Treated Intermediate/High Risk Myelofibrosis Patients (Abstract #54)

The SIMPLIFY-1 (S1) and SIMPLIFY-2 (S2) Phase 3 studies evaluated momelotinib (MMB) against ruxolitinib (S1) or best available therapy (S2) for a 24-week randomization treatment phase, followed by an opportunity for extended momelotinib treatment for all patients. Results based on a total 588 patients presented by Dr. Verstovsek include:

Robust OS was observed in both JAKi-naïve and previously ruxolitinib-treated patients
- In S1, the median OS has not been reached in the MMB arm and 53.1 months in the control arm (HR=0.99, p=0.97)
- In S2, the median OS was 34.3 months in originally MMB-randomized patients and 37.5 months in the BAT/RUXàMMB arm (HR=0.96, p=0.86), representing the best reported OS in this previously RUX-treated setting
Sustained transfusion independence was observed with extended MMB treatment
- In S1, TI response at Week 24 was 67% in the MMB arm and 49% in the control arm (p<0.001). 40% of MMB-treated patients achieved a splenic response at any time during S1
  - The median duration of TI has not been reached after >3 years of follow up
- In S2, TI response at Week 24 was 43% in the MMB arm and 21% in the control arm (p=0.001)
Compound safety was favorable for MMB with limited hematological toxicity and lack of cumulative toxicity

Patients were randomized 1:1 (S1) and 2:1 (S2) to receive MMB (200 mg QD) versus RUX (20 mg BID) or BAT (88.5% RUX/RUX+) for 24 weeks followed by extended momelotinib treatment. Both trials had primary endpoints of Splenic Response Rate and secondary endpoints of Total Symptom Score and Transfusion Independence Rate.

About Momelotinib

Momelotinib is a selective and orally bioavailable JAK1, JAK2 and ACVR1 inhibitor currently under investigation for the treatment of myelofibrosis. Myelofibrosis results from dysregulated JAK-STAT signaling and is characterized by constitutional symptoms, splenomegaly (enlarged spleen) and progressive anemia.Momelotinib is currently under investigation in the MOMENTUM clinical trial, a global, randomized, double-blind Phase 3 study for symptomatic and anemic myelofibrosis patients. Top-line data are anticipated in H1 2022. The U.S. Food & Drug Administration has granted Fast Track designation for momelotinib.

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.For more information, visitwww.SierraOncology.com.

Cautionary Note on Forward-Looking Statements

This press release contains forward-looking statements within the meaning of the “safe harbor” provisions of the Private Securities Litigation Reform Act of 1995, including, but not limited to, statements regarding Sierra Oncology’s expectations from current data, anticipated clinical development activities, expected timing and success of enrollment of MOMENTUM and potential benefits of momelotinib. All statements other than statements of historical fact are statements that could be deemed forward-looking statements. These statements are based on management’s current expectations and beliefs and are subject to a number of risks, uncertainties and assumptions that could cause actual results to differ materially from those described in the forward-looking statements. Such forward-looking statements are subject to risks and uncertainties, including, among others, the risk that Sierra Oncology’s cash resources may be insufficient to fund its current operating plans and it may be unable to raise additional capital when needed, the risk that disruptions and impacts of COVID-19 will be significant and lengthy, Sierra Oncology may be unable to successfully develop and commercialize momelotinib, momelotinib may not demonstrate safety and efficacy or otherwise produce positive results, Sierra Oncology may experience delays in the clinical development of momelotinib, Sierra Oncology may be unable to acquire additional assets to build a pipeline of additional product candidates, Sierra Oncology’s third-party manufacturers may cause its supply of materials to become limited or interrupted or fail to be of satisfactory quantity or quality, Sierra Oncology may be unable to obtain and enforce intellectual property protection for its technologies and momelotinib and the other factors described under the heading “Risk Factors” set forth in Sierra Oncology’s filings with the Securities and Exchange Commission from time to time. Sierra Oncology undertakes no obligation to update the forward-looking statements contained herein or to reflect events or circumstances occurring after the date hereof, other than as may be required by applicable law.

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