Pembrolizumab for the treatment of gastric cancer.

INTRODUCTION: Gastric cancer is one of a few gastrointestinal malignancies in which immunotherapy has shown meaningful activity. Pembrolizumab is the first and only immune checkpoint inhibitor to be FDA-approved in gastric cancer. Areas Covered: This review summarizes the current and emerging clinical evidence for immune checkpoint inhibitors in advanced and metastatic gastric cancer, with a focus on pembrolizumab. Expert Commentary: Pembrolizumab has shown impressive activity in the third-line treatment of locally advanced and metastatic gastric cancer. It is currently being studied as upfront therapy in combination with chemotherapy. The emerging understanding of the molecular alterations and tumor immune microenvironment as predictors of immunotherapy response in gastric cancer are discussed. The impact of gastric mucosal dysbiosis on gastric carcinogenesis and the modulation of immunotherapy response by the gut microbiome are also reviewed.