Merck announced that the Food and Drug Administration (FDA) has approved Keytruda (pembrolizumab) for the treatment of patients with recurrent locally advanced or metastatic gastric or gastroesophageal junction (GEJ) adenocarcinoma whose tumors express PD-L1 (combined positive score [CPS] ≥1) as determined by an FDA-approved test, with disease progression on or after ≥2 prior lines of therapy including fluoropyrimidine- and platinum-containing chemotherapy, and if appropriate, HER2/neu-targeted therapy. 

This accelerated approval is based on tumor response rate and durability of response data from KEYNOTE-059 (n=259); continued approval may be based on verification and description of clinical benefit in confirmatory trials. In the multicenter, non-randomized, open-label, multi-cohort trial, patients must have previously received a fluopyrimidine and platinum doublet; HER2/neu-positive patients must have previously received an approved HER2/neu-targeted therapy. Study patients without disease progression were treated for 24 months. Objective response rate (ORR) was the major efficacy outcome measure, according to the RECIST 1.1. 

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Of the total patients, 55% had tumors expressing PD-L1 with a CPS ≥1 and microsatellite stable (MSS) tumor status or undetermined microsatellite instability (MSI) or mismatch repair (MMR) status. The ORR among these patients was 13.3% (95% CI: 8.2, 20.0) with a complete response seen in 1.4% and partial response in 11.9%. Of the 19 responders, duration of response ranged from 2.8 + to 19.4+ months; 11 of these patients had responses lasting ≥6 months and 5 patients had responses lasting ≥12 months. 

Keytruda, an anti-programmed death receptor-1 (PD-1) agent, is already indicated to treat urothelial and head and neck carcinomas; colorectal cancer, classical Hodgkin lymphoma, melanoma, and non-small cell lung cancer. 

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