Durable response to programmed death-1 (PD-1) blockade in a metastatic gastric cancer patient with mismatch repair deficiency and microsatellite instability

Mismatch repair deficiency (dMMR) or microsatellite instability (MSI) has been reported as a predictive biomarker for responses to programmed death-1 (PD-1) blockade in metastatic colorectal cancer. A high response rate to anti-PD-1 therapy was observed in other cancer types with MSI. We report a chemotherapy-refractory metastatic gastric cancer patient with dMMR and MSI who responded remarkably well to pembrolizumab, a PD-1 monoclonal antibody. The satisfactory objective response has lasted for more than 24 months as of this report.