Imfinzi Plus Chemotherapy Raises 3-Year Survival to 69% in Gastric Cancer

Imfinzi (durvalumab) plus chemotherapy before and after surgery helped patients with gastric or gastroesophageal junction (GEJ) cancer live longer than chemotherapy alone, according to final results from the phase 3 MATTERHORN trial published in The Lancet.

At three years, 69% of patients who received Imfinzi plus chemotherapy were alive compared with 62% of patients who received chemotherapy alone. Overall, Imfinzi reduced the risk of death by 22%.

The findings involved patients with gastric or GEJ adenocarcinoma that could be removed with surgery. The Food and Drug Administration (FDA) approved Imfinzi for this use in November 2025 based on earlier results from MATTERHORN.

How did Imfinzi affect survival in the MATTERHORN trial?

Among 948 patients in the trial, 160 of 474 patients treated with Imfinzi died during follow-up compared with 192 of 474 patients who received chemotherapy alone.

At two years, 76% of patients treated with Imfinzi were alive compared with 70% of patients who received chemotherapy alone. At three years, survival rates were 69% and 62%, respectively.

Median overall survival, the point when half of the patients in a group have died, had not been reached in either group. This means more than half of the patients in both groups were still alive when researchers analyzed the results.

The researchers stated that Imfinzi plus chemotherapy represents a new treatment option for patients with resectable gastric or GEJ adenocarcinoma.

Which patients with gastric cancer benefited from Imfinzi?

The survival benefit with Imfinzi appeared across most of the patient groups researchers analyzed.

This included patients regardless of their levels of PD-L1, a protein that can help doctors predict whether some cancers may respond to immunotherapy. Patients whose tumors had PD-L1 levels of at least 1% and those with levels below 1% both had a 21% lower risk of death with Imfinzi.

Patients whose cancer had spread to nearby lymph nodes before treatment had a 27% lower risk of death with Imfinzi. Researchers did not see a difference between treatments among patients without lymph node involvement.

However, MATTERHORN was not designed to determine whether Imfinzi works better in one of these groups than another. The difference between the groups could have occurred by chance.

Did Imfinzi help eliminate more cancer before surgery?

Researchers examined tissue removed during surgery to determine how much cancer remained after treatment.

A pathological complete response, which means no viable cancer cells remained in the removed tumor or lymph nodes, occurred in 24% of patients treated with Imfinzi compared with 9% of patients who received chemotherapy alone.

A major pathological response, which means only isolated cancer cells or very small clusters remained, occurred in 33% of patients in the Imfinzi group compared with 18% of patients in the chemotherapy-alone group.

Patients treated with Imfinzi were also more likely to have no cancer found in their lymph nodes after surgery, at 58% compared with 45%.

Event-free survival, the amount of time patients lived without their cancer growing, returning or causing death, also favored Imfinzi among patients who had some degree of pathological response.

The analysis of patients who had a complete response included only 11 events, so researchers cautioned that those results should be interpreted carefully.

What treatment did patients receive in the MATTERHORN trial?

MATTERHORN included 948 patients treated at 147 medical centers across 20 countries. Patients had stage 2 to stage 4a gastric or GEJ adenocarcinoma that could be removed with surgery and had not previously received cancer treatment.

Half of the patients received Imfinzi and half received a placebo. Both groups also received FLOT chemotherapy, a four-drug combination of fluorouracil, leucovorin, oxaliplatin and docetaxel.

Patients received two cycles of FLOT before surgery and two cycles after surgery, along with either Imfinzi or placebo. They then received 10 additional cycles of Imfinzi or placebo without chemotherapy.

Imfinzi did not appear to interfere with surgery. Doctors were able to completely remove the tumor in 92% of patients who underwent surgery in both treatment groups.

What side effects occurred with Imfinzi plus chemotherapy?

Rates of side effects were similar between the two groups. Grade 3 or 4 side effects occurred in 72% of patients treated with Imfinzi and chemotherapy and 71% of patients treated with chemotherapy alone.

Serious side effects occurred in 48% and 44% of patients, respectively. Side effects caused 30% of patients in the Imfinzi group and 23% of patients in the chemotherapy-alone group to stop at least part of their treatment.

Imfinzi works by helping the immune system attack cancer, but this can also cause the immune system to attack healthy tissues. These immune-related side effects occurred in 23% of patients treated with Imfinzi compared with 7% of patients who received chemotherapy alone.

The most common side effects among patients treated with Imfinzi included diarrhea, nausea, low levels of infection-fighting white blood cells and hair loss.

The researchers noted several limitations. Some analyses only included patients who underwent surgery, who may have had a better prognosis than the overall trial population. Black patients were also underrepresented, and the study did not include patients from several countries with high rates of gastric and GEJ cancer, including China.

Researchers plan to continue following patients to evaluate five-year survival and study biomarkers that could help identify which patients are most likely to benefit from treatment.

Reference

1. Janjigian YY, et al. “Perioperative durvalumab plus FLOT for resectable gastric and gastro-oesophageal junction adenocarcinoma.” The Lancet. Published September 9, 2026.

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