Arcus Biosciences And Gilead Halt STAR-221 Trial After Failing To Meet Efficacy Targets In Gastric Cancer

Biopharmaceutical companies Arcus Biosciences, Inc. (RCUS) and Gilead Sciences, Inc. (GILD) have jointly announced the termination of their Phase 3 STAR-221 trial, marking a setback in the development of combination immunotherapies for advanced gastrointestinal malignancies. The Independent Data Monitoring Committee recommended halting the study due to futility following a pre-planned interim analysis focused on overall survival outcomes.

The trial had been investigating whether combining domvanalimab (an anti-TIGIT antibody) with zimberelimab (an anti-PD-1 antibody) alongside chemotherapy could outperform the standard nivolumab-plus-chemotherapy regimen as first-line treatment for advanced gastric and esophageal cancers. The interim data revealed that the experimental combination failed to demonstrate superior overall survival compared to the control arm. Tolerability and adverse event profiles were consistent between both treatment approaches, indicating that safety considerations were not the limiting factor.

Despite this clinical setback, both companies are redirecting resources toward alternative programs. Arcus is accelerating development of casdatifan, described as a potentially best-in-class HIF-2a inhibitor demonstrating meaningful monotherapy activity. The company anticipates multiple clinical readouts for this candidate throughout 2026. Notably, Taiho Pharmaceutical Co., Ltd. secured rights to casdatifan development in Japan and select Asian territories under an agreement finalized in October 2025, while Arcus retains global rights outside these regions.

The company is also prioritizing early-stage pipeline expansion targeting inflammatory and autoimmune diseases, with a lead MRGPRX2-targeting small molecule anticipated to enter clinical trials in 2026. With approximately $1 billion in cash reserves and investments, Arcus projects sufficient funding to sustain operations through at least the second half of 2028, providing runway for its restructured development strategy.