Design: Global randomised, double-blind, placebo-controlled phase 3 trial across 147 centres in 20 countries
Population: 948 adults with untreated resectable stage II-IVa gastric or gastro-oesophageal junction adenocarcinoma, median age 62 years
Primary outcome: Overall survival in the intention-to-treat population (key secondary endpoint; event-free survival was the primary)
Effect: Hazard ratio 0.78 (95% CI 0.63-0.96; p=0.021 against a threshold of p<0.0499); possibly treatment-related deaths 6/475 with durvalumab vs 2/469 with placebo

MATTERHORN randomised 948 adults with resectable stage II-IVa gastric or gastro-oesophageal junction adenocarcinoma across 147 centres in 20 countries to perioperative durvalumab plus FLOT chemotherapy or placebo plus FLOT, double-blind. Event-free survival and pathological complete response had already favoured durvalumab; this report gives the overall survival result, which is the endpoint that settles the question.

Overall survival improved, with a hazard ratio of 0.78 (95% CI 0.63-0.96, p=0.021 against a prespecified threshold of 0.0499). Deaths from adverse events possibly related to treatment occurred in 6 of 475 in the durvalumab group and 2 of 469 on placebo. The authors call it a new standard treatment option, and on a positive overall survival readout in a trial of this size that is a fair description rather than a promotional one.

For clinicians outside oncology the consequence is about sequence. Resectable gastric cancer is now a disease where the systemic decision is made before the operation, not after it — so a patient found to have one at endoscopy needs a multidisciplinary discussion that includes medical oncology before a surgical date is set. Where durvalumab is not available or not affordable, perioperative FLOT remains the comparator arm and remains appropriate; the trial does not make chemotherapy alone wrong.

Refer newly diagnosed resectable gastric or junctional adenocarcinoma for multidisciplinary discussion before surgery is booked
Note that the regimen is perioperative: two neoadjuvant and two adjuvant cycles with FLOT, then ten further cycles of durvalumab alone
Treatment-related deaths were uncommon but higher with durvalumab — 1% versus under 1%
Where the drug is unavailable, perioperative FLOT is still the established standard
Access and cost in India will determine uptake; the trial included Asian centres but availability is a separate question

Why it matters

It moves the systemic treatment decision in resectable gastric cancer to before the operation, where the surgeon alone no longer owns it.

The statistics, in plain English

A hazard ratio of 0.78 means roughly a 22% lower rate of death over the follow-up period, and the confidence interval running from 0.63 to 0.96 stays entirely below 1.0 — so the direction is established, though the upper end is close enough to 1.0 that the true benefit could be small. Overall survival was a key secondary endpoint rather than the primary one, which is why the prespecified significance threshold was set below the usual 0.05; it was met.