Efficacy and Safety Study of Pembrolizumab (MK-3475) Versus Paclitaxel in Asian Participants With Advanced Gastric or Gastroesophageal Junction Adenocarcinoma Who Progressed After First-line Therapy With Platinum and Fluoropyrimidine (MK-3475-063/KEYNOTE-063)

The study will compare the efficacy and safety of treatment with pembrolizumab (MK-3475) versus paclitaxel in Asian, programmed death-ligand 1 (PD-L1) positive participants with advanced gastric or gastroesophageal junction (GEJ) adenocarcinoma who have progressed after failure of any combination chemotherapy containing a platinum and a fluoropyrimidine agent. The primary study hypotheses are that pembrolizumab prolongs Overall Survival (OS) compared to paclitaxel and that pembrolizumab prolongs Progression-free Survival (PFS) per Response Evaluation Criteria in Solid Tumors version 1.1 (RECIST 1.1) assessed by blinded central radiologists' review compared to paclitaxel.