Sierra Oncology, Inc. announced two abstracts have been accepted into the program for the Annual Meeting of the American Society of Clinical Oncology (ASCO) being held June 3-7, 2022, in Chicago and online. An abstract presenting the full data from the pivotal phase 3 MOMENTUM study in myelofibrosis patients who are symptomatic and anemic has been selected for an oral presentation on June 7. An additional subset analysis from the trial evaluating safety and efficacy for patients with low platelet counts has been selected for poster presentation. Abstract: 7002: MOMENTUM: Phase 3 Randomized Study of Momelotinib (MMB) versus Danazol (DAN) in Symptomatic and Anemic Myelofibrosis (MF) Patients Previously Treated with a JAK Inhibitor: The primary and all key secondary results, as well as safety data, from the MOMENTUM pivotal Phase 3 trial of momelotinib will be presented in an oral presentation by Ruben Mesa, MD, co-Principal Investigator of the study.

Key data to be presented include: Primary Endpoint of Total Symptom Score (TSS) of >50%: 25% in the MMB arm vs. 9% in the control arm (p=0.0095); Secondary Endpoint of Transfusion Independence (TI): 31% in the MMB arm vs. 20% in the control arm (one-sided p=0.0064; non-inferiority); Secondary Endpoint of Splenic Response Rate (SRR) >35%: 23% in the MMB arm vs.

3% in the control arm (p=0.0006); SRR of >25% was 40% in the MMB arm and 6% in the control arm. A trend toward improved overall survival is demonstrated in the MMB arm based on data up to Week 24 (p=0.0719) and overall (p=0.3510); The rate of Grade 3 or worse adverse events in the randomized treatment period was 54% in the MMB arm and 65% in the control arm. Serious treatment emergent adverse events were 35% in the MMB arm and 40% in the control arm.

The most frequent non-hematologic adverse events were diarrhea, nausea, asthenia, pruritis and increased blood creatinine; Mean baseline characteristics for all patients were TSS of 27, Hemoglobin (Hgb) of 8 g/dL and platelet count of 145 x 109/L. Abstract 7061: Thrombocytopenic Myelofibrosis (MF) Patients Previously Treated with a JAK Inhibitor in a Phase 3 Randomized Study of Momelotinib (MMB) versus Danazol (DAN) [MOMENTUM]: Abstract 7061 will highlight an analysis of MOMENTUM patients with baseline platelet counts as low as 25 x 109/L on study endpoints, including Week 24 TSS reduction of >50% from baseline, transfusion independence rates, and SRR of >35% from baseline. Results to be presented include: Of the 195 patients enrolled in the MOMENTUM study, 124, 100 and 31 patients had baseline platelet counts of less than 150, 100, and 50 x 109/L, respectively.; In patients with baseline platelets <100 x 109/L (MMB: n=66; DAN: n=34): TSS responder proportion was 29% in the MMB arm and 15% in the control arm; TI response proportion was 27% in the MMB arm and 21% in the control arm; SRR was 20% in the MMB arm and 6% in the control arm; In patients with baseline platelets <50 x 109/L (MMB: n=18; DAN: n=13): TSS responder proportion was 22% in the MMB arm and 8% in the control arm; TI response proportion was 17% in the MMB arm and 15% in the control arm; SRR was 22% in the MMB arm and 0% in the control arm; The broader thrombocytopenic subgroup with baseline platelets <150 x 109/L demonstrated similar efficacy and safety as described in the published abstract; In patients with baseline platelets below 50 x 109/L, mean platelet levels remained stable over time in both the MMB and control arms; Overall Survival directionally favored the MMB arm, consistent with the survival results in the intent-to-treat population; The proportion of patients who experience Grade 3 or higher treatment-emergent adverse events were comparable between the study arms; Mean baseline characteristics for patients with baseline platelets <100 x 109/L included TSS of 28 and 25 and Hgb of 8.1 and 7.8 g/dL for the MMB and control arms, respectively. In thrombocytopenic, symptomatic and anemic patients with myelofibrosis, including those with platelets as low as 25 x 109/L, momelotinib was administered safely and demonstrated improvements in symptom responses, transfusion independence rates and spleen responses as compared to danazol.

Consistent with the overall intent-to-treat MOMENTUM population, platelets levels remained stable over time, survival favored momelotinib versus danazol, and the safety profile was generally maintained in thrombocytopenic myelofibrosis patients receiving momelotinib.