AstraZeneca's Imfinzi Shows Promise in Early-Stage Stomach Cancer Treatment

AstraZeneca's immunotherapy drug Imfinzi has demonstrated significant potential in treating early-stage stomach cancer, according to results from a phase 3 clinical trial presented at the 2025 American Society of Clinical Oncology (ASCO) annual meeting. The study, known as the Matterhorn trial, marks a pivotal moment in the treatment of resectable gastric and gastroesophageal junction (GEJ) cancers.

Matterhorn Trial Results: A New Paradigm in Gastric Cancer Treatment

The Matterhorn trial, involving 948 patients with stage 2 to 4a resectable gastric and GEJ cancers, showed that adding Imfinzi to the standard chemotherapy regimen FLOT (5-fluorouracil, leucovorin, oxaliplatin, and docetaxel) both before and after surgery resulted in a 29% reduction in the risk of disease recurrence, progression, or death compared to FLOT alone.

After a median follow-up of 31.5 months, more than half of the patients receiving Imfinzi and FLOT were still alive without cancer recurrence, worsening, or death. In contrast, the median event-free survival time for those who received a placebo and FLOT was 32.8 months.

Dr. Pamela Kunz, director of the Center for Gastrointestinal Cancers at Smilow Cancer Hospital and Yale Cancer Center, hailed the trial as defining "a new paradigm for patients with early-stage and locally advanced gastric and gastroesophageal junction cancers," emphasizing the benefits of administering optimal treatments earlier in the disease course.

Imfinzi's Safety Profile and Potential Overall Survival Benefit

The addition of Imfinzi to the FLOT regimen did not compromise the chance of complete tumor resection, with 92% of patients in both arms achieving complete resections. Dr. Yelena Janjigian from Memorial Sloan Kettering Cancer Center, the study's lead author, described Imfinzi's toxicity profile as "relatively expected," with similar rates of grade 3 or 4 adverse events between the treatment arms.

Importantly, Imfinzi showed an early favorable trend toward a potential life extension benefit. Although not yet statistically significant, with only 34% of deaths accrued for the final overall survival analysis, Imfinzi led to a preliminary 22% reduction in the risk of death. This potential overall survival benefit began to emerge around 12 months and has been sustained thus far.

Regulatory Considerations and Future Outlook

While the FDA and its external advisors have recently scrutinized clinical trials using a perioperative design, AstraZeneca's oncology R&D head, Dr. Susan Galbraith, does not anticipate regulatory issues for Imfinzi's perioperative use in this context. She emphasized that FLOT is already a standard perioperative treatment for early stomach cancer, and Imfinzi is being added to that continuous use.

Dr. Galbraith noted that the statistically significant event-free survival showing and the "strong trend" toward overall survival constitute a "compelling benefit." As the pharmaceutical industry continues to explore innovative approaches to cancer treatment, the Matterhorn trial results represent a significant step forward in the management of early-stage gastric and GEJ cancers.