FLX475 Combined With Pembrolizumab in Patients With Advanced or Metastatic Gastric Cancer

Inclusion Criteria: * All patients must have histologically or cytologically confirmed, advanced, relapsed or metastatic gastric or gastroesophageal junction adenocarcinoma * Patient must have one of the following diagnoses to be eligible for enrollment into cohorts: * Cohort 1: Checkpoint inhibitor naïve Epstein-Barr Virus negative (EBV-) gastric cancer patient who has had a disease progression after at least 2 prior systemic treatments for advanced or metastatic gastric cancer * Cohort 2: Checkpoint inhibitor naïve Epstein-Barr virus positive (EBV+) gastric cancer patient (as determined by standard methods, e.g. EBER ISH or LMP-1 IHC) who had at least 1 prior systemic treatment for advanced or metastatic gastric cancer * Eastern Cooperative Oncology Group (ECOG) Performance Status 0-1 * Patient must have at least one measurable lesion at baseline by computed tomography(CT) or magnetic resonance imaging (MRI) * Tumor available for biopsy Exclusion Criteria: * Prior therapy with an anti-PD-1, anti-PD-L1, or anti-PD-L2 agent or an agent directed to another stimulatory or co-inhibitory T-cell receptor (e.g., CTLA-4, OX-40, CD137), any history of discontinuing from that treatment due to Grade 3 or higher immune-related adverse event (irAE) * Patient with MSI-H status * Active autoimmune disease or serious autoimmune disease within past 2 years requiring systemic therapy * History of idiopathic pulmonary fibrosis, organizing pneumonia, drug-induced pneumonitis, idiopathic…