Patients with dMMR metastatic colorectal cancer have been shown to have significant clinical responses to immunotherapy with antiprogrammed cell death 1 (PD-1)/antiprogrammed cell death ligand 1 (PD-L1) treatment in phase II trials21, in stark contrast to those in the MSS colorectal cancer subgroup where there was no objective response to immunotherapy.32 This evidence concerns the gene PDCD1 and colorectal cancer.