Study of Pembrolizumab in Subjects With Advanced Gastric or Gastroesophageal Junction Adenocarcinoma Who Progressed After First-Line Therapy With Platinum and Fluoropyrimidine: Integration of Molecular Subtypes Through Integrative Genomic Analysis

This is a single-arm, single-center, open-label trial of pembrolizumab (MK-3475) in subjects with advanced gastric or gastroesophageal junction (GEJ) adenocarcinoma who have progressed after failure of any combination chemotherapy containing a platinum and a fluoropyrimidine agent. Approximately 60 subjects will be enrollment to evaluate the efficacy and safety of pembrolizumab. Enrollment will begin with all subjects without regard for PD-L1 expression status. An evaluable specimen for PD-L1 status must be available and confirmed prior to enrollment. All study subjects will be evaluated every 6 weeks (+/- 7 days) following the date of IP drug adminstration for the first six months and every 12 weeks (+/- 7 days) thereafter until progression of disease is documented with radiologic imaging (computed tomography or magnetic resonance imaging). In the expansion cohort (cohort B), it was expanded on the original cohort based on response analysis and will be opened separately. Of the 5 MSI-high patients who were enrolled on to original cohort, all 5 MSI high GC patients (100% response rate) demonstrated dramatic response rate. Based on this finding, in order to proven Pembrolizumab's efficacy to specific MSI-H GC population, we would like enroll 20 more patients in cohort B. Based on our screening protocol, the prevalence of MSI-high in GC is about 15 %. Only MSI-high GC patients will be included. All the eligibility will be the same.