Nevertheless, the US FDA approved the PD-1 inhibitors, including pembrolizumab and nivolumab, as the first-line treatment for patients with unresectable or metastatic MSI-H or dMMR colorectal cancer in 2020 [23] and 2019 [24], respectively (Table 1), for the treatment of tumors containing MSI-H or in cases of mCRC. This evidence concerns the gene PDCD1 and colorectal cancer.