Significant Overall Survival Benefit Demonstrated: Merck Announces Positive Phase 3 Results of Keytruda as First-Line Treatment for HER2-Negative Gastric Cancer

On February 16, MSD announced the detailed data of the Phase III KEYNOTE-859 study on Keytruda combined with chemotherapy for first-line treatment of HER2-negative advanced gastric cancer or gastroesophageal junction (GEJ) adenocarcinoma, and stated that it would submit the data to regulatory authorities to expand the indications for Keytruda.

KEYNOTE-859 is a randomized, double-blind, placebo-controlled Phase III clinical trial (n=1579) designed to evaluate the efficacy and safety of Keytruda in combination with PF (5-fluorouracil + cisplatin) or CAPOX (capecitabine + oxaliplatin) compared to placebo plus PF/CAPOX as first-line treatment for patients with HER2-negative locally advanced unresectable or metastatic gastric cancer or GEJ adenocarcinoma. The primary endpoint of the study is overall survival (OS), and secondary endpoints include progression-free survival (PFS), objective response rate (ORR), duration of response (DOR), etc.

In the overall population (regardless of PD-L1 expression status), after a median follow-up of 31.0 months (15.3-46.3 months), the OS of patients in the Keytruda group was significantly prolonged compared to the placebo group (12.9 vs 11.5 months), with a 22% reduction in the risk of death (HR=0.78; 95% CI, 0.70-0.87; P<0.0001).

For secondary endpoints, patients in the Keytruda group experienced significantly longer PFS (6.9 vs 5.6 months) and DOR (8.0 vs 5.7 months), with a 24% reduction in the risk of disease progression or death (HR=0.76; 95% CI, 0.67-0.85; P<0.0001); the ORR was also higher in the Keytruda group compared to the placebo group (51.3% vs 42.0%, P=0.00009).

In terms of safety, the proportion of patients experiencing grade 3-5 treatment-related adverse events (TRAEs) was 59.4% in the Keytruda group and 51.1% in the placebo group.

Previously, Keytruda was approved by the FDA in May 2021 for use in combination with trastuzumab, fluorouracil, and platinum-containing chemotherapy as a first-line treatment for patients with locally advanced unresectable or metastatic HER2-positive gastric cancer or GEJ adenocarcinoma.

"Eighty percent of patients with locally advanced unresectable or metastatic gastric or GEJ adenocarcinoma fall into the HER2-negative gastric cancer category," said Dr. Scot Ebbinghaus, Vice President of Clinical Research at Merck Sharp & Dohme (MSD) Research Laboratories. "Based on data from the KEYNOTE-859 study, we aim to expand the use of Keytruda and provide an option in combination with chemotherapy to help more patients with HER2-negative gastric cancer extend their lives. These results also reinforce our commitment to gastrointestinal cancer research as we continue to evaluate additional combination regimens for Keytruda in both earlier and later stages of the disease."

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