Results from an international phase 3 clinical trial found that treating stage II, III, and IVA resectable gastric cancer (GC) and gastroesophageal junction cancer (GEJC) with perioperative durvalumab and FLOT chemotherapy helped patients live longer without cancer progression, recurrence or disease-related complications compared to placebo and FLOT chemotherapy.

The MATTERHORN study, presented at ASCO 2025, tested if adding durvalumab to the FLOT chemotherapy regimen before and after surgery, with follow-up treatment with durvalumab only, improved outcomes for patients with stage II, III, or IVA untreated, resectable GC and GEJC.

The study included 948 patients with a median age of 62 years. The patients lived in Europe (53%), Asia (19%), South America (19%) and North America (9%).

There were 474 patients randomly assigned to receive perioperative treatment with durvalumab plus FLOT chemotherapy before and after surgery, followed by treatment with durvalumab alone. There were 474 patients randomly assigned to receive perioperative treatment with a placebo plus FLOT chemotherapy before and after surgery, followed by treatment with placebo alone.

Most patients had GC (68% in the durvalumab plus FLOT arm vs. 67% in the placebo plus FLOT arm). In the durvalumab plus FLOT arm, 69% of patients were male and the median age was 62 years.

Key Findings

• There was a statistically significant improvement in event-free survival (EFS) between the durvalumab with FLOT arm compared to the placebo with FLOT arm. EFS is the amount of time after treatment starts without cancer recurrence, progression or treatment-related complications. Patients in the durvalumab plus FLOT arm experienced a 29% better EFS than those in the placebo plus FLOT arm.
• The median EFS in the placebo plus FLOT arm was 32.8 months. In the durvalumab plus FLOT arm, the median EFS had not been reached at the time of this reporting. This means that more than half of the participants in the durvalumab plus FLOT arm had not experienced cancer recurrence, progression or complications related to treatment.
• At 12 months, the durvalumab plus FLOT arm achieved an EFS rate of 78.2%, compared to 74% in the placebo plus FLOT group. At 24 months, there was a larger difference. The durvalumab plus FLOT group achieved an EFS of 67.4% compared to 58.5% in the placebo plus FLOT arm.
• The median overall survival rate has not yet been reached for the durvalumab plus FLOT arm. The median overall survival rate for the placebo plus FLOT arm was 47.2 months.
• The two treatment arms had a similar rate of grade 3 and 4 adverse events. The most common side effects in the durvalumab plus FLOT arm were diarrhea, nausea, neutropenia (low levels of white blood cells called neutrophils), hair loss and decreased appetite. Taking durvalumab with FLOT also did not delay surgery or any additional treatments.

“Despite advances in treatment and biomarker development, cure rates for early-stage gastroesophageal cancer remain below 50%, with most recurrences occurring within two years of surgery. MATTERHORN is the first global, randomised phase 3 trial to show improved event-free survival with an immunotherapy-based regimen in resectable gastric and gastroesophageal junction cancers. The use of immunotherapy in earlier-stage cancers, as demonstrated in this perioperative approach with durvalumab, can reduce the risk of recurrence and improve cure rates,” said lead study author Yelena Y. Janjigian, MD, Memorial Sloan Kettering Cancer Center in New York, New York.

“The pace of therapeutic advances in upper gastrointestinal cancers has accelerated in recent years. Now, the MATTERHORN trial shows that perioperative treatment with FLOT plus durvalumab is better than FLOT alone in reducing the risk of recurrence. This trial defines a new paradigm for patients with early-stage and locally advanced gastric and gastroesophageal junction cancers and shows the benefits of giving our best treatments earlier,” Pamela Kunz MD, PhD, Director of the Center for Gastrointestinal Cancers at Smilow Cancer Hospital and Yale Cancer Center and an ASCO Expert in gastrointestinal cancers.

The researchers will continue to follow these patients and report on overall survival.

Source: ASCO