Le DT, Kim TW, Cutsem EV, et al. - In this phase II open-label study (KEYNOTE-164) that involved 128 centers globally of 124 patients aged ≥ 18 years who had metastatic microsatellite instability–high/mismatch repair–deficient (MSI-H/dMMR) colorectal cancer (CRC) treated with ≥ 2 former lines of standard therapy, including fluoropyrimidine, oxaliplatin, and irinotecan with or without anti–vascular endothelial growth factor/epidermal growth factor receptor monoclonal antibody (cohort A, n = 61) or ≥ 1 previous line of therapy (cohort B, n = 63), experts assessed the antitumor activity of pembrolizumab in formerly treated, metastatic, MSI-H/dMMR CRC. Treatment-related grade 3-4 adverse events were seen in ten patients in cohort A and eight in cohort B, with the most prevalent occurring in ≥ 2 patients being pancreatitis, fatigue, increased alanine aminotransferase, and elevated lipase in cohort A. Results imply that in individuals with MSI-H/dMMR CRC, pembrolizumab was discovered to be efficient with an easy safety profile.