Pembrolizumab, a PD-L1 checkpoint inhibitor, has been approved for several cancer types, including non-small cell lung cancer (NSCLC) and head and neck squamous cell cancer (HNSCC). However, all past acquired indication of pembrolizumab was based on the location of the tumor, not based on a specific biomarker. Recently, based on five single-arm multi-cohort trials recruiting 149 patients comprised total 15 cancer types which mainly enrolled colorectal, endometrial and other gastrointestinal cancers, the US FDA has now approved pembrolizumab for the treatment in patients with microsatellite instability (MSI)-high or mismatch repair (MMR)-deficient solid cancers. The objective response rate was 39.6%. 48 patients achieved partial responses and 11 patients achieved complete responses. Furthermore, 78% of the responders experienced response duration for 6 months or greater. Pembrolizumab hence shows prominence as a new treatment option for patients with MSI-high and MMR-deficient cancers.