RAHWAY, N.J.--( BUSINESS WIRE )--Merck (NYSE: MRK), known as MSD outside of the United States and Canada, today announced that the Phase 3 KEYNOTE-811 trial investigating KEYTRUDA, Merck's anti-PD-1 therapy, in combination with trastuzumab and chemotherapy met one of its dual primary endpoints of progression-free survival (PFS) for the first-line treatment of human epidermal growth factor receptor 2 (HER2)-positive advanced gastric or gastroesophageal junction (GEJ) adenocarcinoma. At a pre-specified interim analysis conducted by an independent Data Monitoring Committee, KEYTRUDA in combination with trastuzumab and chemotherapy demonstrated a statistically significant improvement in PFS compared to placebo in combination with trastuzumab and chemotherapy in the intention-to-treat (ITT) study population.