Why Did Arcus Biosciences Stock Slump 10% Today?

Arcus will stop testing a domvanalimab-based drug combination in upper gastrointestinal cancers after independent reviewers found the treatment did not improve survival.

• The Phase 3 STAR-221 trial compared an anti-TIGIT and anti-PD-1 antibody duo plus chemotherapy to the established nivolumab-based regimen.
• Arcus Biosciences is now concentrating its development resources on its HIF-2a inhibitor, casdatifan.
• The company plans to call for multiple casdatifan data readouts and study initiations throughout 2026.

Arcus Biosciences, Inc. (RCUS), announced on Friday that it is stopping its Phase 3 STAR-221 trial after it failed to show meaningful progress.

The company will stop testing a domvanalimab-based drug combination in upper gastrointestinal cancers after independent reviewers found the treatment did not improve survival.

STAR-221 Study Discontinued

The Phase 3 STAR-221 trial, which compared an anti-TIGIT and anti-PD-1 antibody duo plus chemotherapy to the established nivolumab-based regimen, did not show a survival advantage at the planned interim review.

The decision marks a setback for the domvanalimab program, which was being developed alongside zimberelimab for advanced gastric and esophageal cancers.

Following the update, Arcus Biosciences’ stock traded 10% lower by mid-morning on Friday. On Stocktwits, retail sentiment around the stock changed to ‘extremely bearish’ from ‘bearish’ territory the previous day. Message volume changed to ‘high’ from ‘normal’ levels in the last 24 hours. 

Refocusing On Casdatifan

With the STAR-221 trial ending, Arcus is concentrating its development resources on its HIF-2a inhibitor, casdatifan, which has shown encouraging single-agent results in clear cell renal cell carcinoma (ccRCC) studies. 

Early data demonstrated meaningful improvements in key measures such as response rates and progression-free survival in over 120 patients, and plans call for multiple casdatifan data readouts and study initiations throughout 2026. 

“The results from STAR-221 are not what we had hoped for, and we have important work ahead to meet the needs of patients on our domvanalimab studies and also accelerate the casdatifan and I&I programs.”

-Terry Rosen, CEO, Arcus

RCUS stock has gained over 51% in 2025 and over 31% in the last 12 months. 

For updates and corrections, email newsroom[at]stocktwits[dot]com.<