Gilead Provides Update on Phase 3 STAR-221 Study

Foster City, Calif., December 12, 2025 - Gilead Sciences and Arcus Biosciences today announced the discontinuation of the Phase 3 STAR-221 study evaluating the anti-TIGIT antibody domvanalimab plus anti-PD-1 antibody zimberelimab and chemotherapy versus nivolumab plus chemotherapy as first-line treatment for HER2-negative advanced gastric and esophageal cancers. The decision is based on the recommendation from the Independent Data Monitoring Committee (IDMC) following their review of data from a pre-specified interim analysis of overall survival (OS).

In the pre-specified interim analysis, the combination of domvanalimab plus zimberelimab and chemotherapy did not improve OS relative to nivolumab plus chemotherapy, the standard of care, and there was low likelihood of achieving a positive survival benefit with further follow-up. The safety profile for the combination of domvanalimab plus zimberelimab and chemotherapy was consistent with the control arm, nivolumab plus chemotherapy, and there were no new safety findings.

The companies are informing regulators and communicating with investigators for the STAR-221 and the Phase 2 EDGE-Gastric studies to determine appropriate next steps for patients. The companies are conducting a detailed analysis to understand these results, which will be published in the future.

"These results offer valuable insights into the complexity of treating advanced gastroesophageal cancers," said Dietmar Berger, MD, PhD, Chief Medical Officer at Gilead Sciences. "We will collaborate closely to understand the full scope of the data and engage key stakeholders in determining the appropriate next steps. We are deeply grateful to the patients, families, and healthcare professionals who participated in the STAR-221 study and contributed to this important work."

Currently, there are no changes to other ongoing domvanalimab studies beyond the upper gastrointestinal (GI) program. Arcus and Gilead will share further guidance as it becomes available.

Domvanalimab and zimberelimab are investigational molecules, and neither Gilead nor Arcus has received approval from any regulatory authority for any use globally, and their safety and efficacy have not been established.

About Gilead Sciences

Gilead Sciences, Inc. is a biopharmaceutical company that has pursued and achieved breakthroughs in medicine for more than three decades, with the goal of creating a healthier world for all people. The company is committed to advancing innovative medicines to prevent and treat life-threatening diseases, including HIV, viral hepatitis, COVID-19, cancer, and inflammation. Gilead operates in more than 35 countries worldwide, with headquarters in Foster City, Calif.

Forward-Looking Statements

This press release includes forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995 that are subject to risks, uncertainties and other factors, including Gilead's ability to initiate, progress or complete clinical trials within currently anticipated timelines or at all, and the possibility of unfavorable results from ongoing or additional clinical trials, including those involving domvanalimab and zimberelimab (such as STAR-221 and EDGE-Gastric); uncertainties relating to regulatory applications and related filing and approval timelines, including potential applications for programs and/or indications currently under evaluation, and the risk that any such approvals, if granted, may be subject to significant limitations on use or subject to withdrawal or other adverse actions by the applicable regulatory authority; the possibility that Gilead may make a strategic decision to discontinue development of domvanalimab and zimberelimab for indications that are currently under evaluation and, as a result, these programs may never be successfully commercialized for such indications; the risk that Gilead may not realize the potential benefits of its collaboration with Arcus or its other investments in oncology; difficulties or unanticipated expenses in connection with the collaboration and the potential effects on Gilead's revenues and earnings; and any assumptions underlying any of the foregoing. These and other risks, uncertainties and other factors are described in detail in Gilead's Quarterly Report on Form 10-Q for the quarter ended September 30, 2025, as filed with the U.S. Securities and Exchange Commission. These risks, uncertainties and other factors could cause actual results to differ materially from those referred to in the forward-looking statements. All statements other than statements of historical fact are statements that could be deemed forward-looking statements. The reader is cautioned that any such forward-looking statements are not guarantees of future performance and involve risks and uncertainties, and is cautioned not to place undue reliance on these forward-looking statements. All forward-looking statements are based on information currently available to Gilead, and Gilead assumes no obligation and disclaims any intent to update any such forward-looking statements.

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