Initial success was achieved in the treatment of patients with unresectable or metastatic CRC with heavy gene mutation burdens (>12 per 106 bases) caused by mismatch-repair deficiency (dMMR) or a high level of microsatellite instability (MSI-H), which led to US Food and Drug Administration (FDA) approval of the single use of ICIs pembrolizumab and nivolumab (anti-programmed death 1 [PD-1] monoclonal antibody [mAb]) in 2017 and the combinatorial use of nivolumab and ipilimumab (anti-CTLA4 mAb) in 2018.3 This evidence concerns the gene PDCD1 and colorectal carcinoma.