Arcus Biosciences Inc. saw its stock fall about 4% on Monday after informing investors that the Phase 3 STAR-121 study would be discontinued following a futility recommendation from an Independent Data Monitoring Committee (IDMC).
The company disclosed the development in a filing with the Securities and Exchange Commission, saying the IDMC reached its recommendation after reviewing results from a pre-planned futility analysis. STAR-121 compared a regimen of domvanalimab, an anti-TIGIT antibody, combined with zimberelimab, an anti-PD-1 antibody, plus chemotherapy against pembrolizumab plus chemotherapy, as a first-line treatment for patients with metastatic non-small cell lung cancer.
Arcus said regular safety reviews conducted by the IDMC did not identify any new safety signals, but noted that safety was not evaluated as part of the futility analysis itself.
The study also included an exploratory assessment of zimberelimab plus chemotherapy. According to the filing, the zimberelimab combination was consistent with pembrolizumab plus chemotherapy with respect to overall survival in that exploratory comparison.
In addition to halting STAR-121, Arcus will discontinue the Phase 2 EDGE-Lung study. The filing indicates Gilead Sciences, which collaborated with Arcus on STAR-121, is in the process of communicating with study investigators to determine the next steps for patients currently enrolled in the affected trials.
Separately, Arcus disclosed that Gilead will allow its option rights under the companies' 2020 collaboration agreement to lapse on July 14, 2026, after electing not to make the option continuation payment. As a result, Gilead will not retain option rights to certain early-stage programs in Arcus’s pipeline, specifically the CCR6, CD89 and CD40L programs.
The filing clarifies that Gilead will continue to hold existing time-limited options to a select set of programs, including AB801, AB598, AB102 and a TNF small molecule inhibitor. Arcus also stated it retains full rights to casdatifan and that development program, except where rights are already licensed to Taiho in Japan and certain other Asian territories - excluding China.
Context and next steps
The company did not attach further clinical detail to the filing beyond the IDMC recommendation and the procedural notes on safety review and exploratory endpoints. Gilead and Arcus are working with investigators to determine care pathways and other actions for participants affected by the study terminations.
The filings make clear that the collaboration agreement's structure will change if Gilead does not make the scheduled payment that would have preserved broader option rights in Arcus's early-stage programs. The precise operational and strategic consequences for those programs were not elaborated in the notice.
Summary
The IDMC recommended stopping the Phase 3 STAR-121 trial for futility, Arcus will discontinue STAR-121 and the Phase 2 EDGE-Lung study, Gilead is notifying investigators about next steps for enrolled patients, and Gilead will allow certain option rights under the 2020 collaboration to end if it does not make the continuation payment.