Immune checkpoint inhibitors (ICIs) are complementary therapies of cancers and are considered to be the most innovative and promising drugs in cancer treatment, including programmed death 1(PD-1), programmed cell death-Ligand 1(PD-L1), and cytotoxic T lymphocyte-associated antigen 4 (CTLA-4) monoclonal antibodies against these suppressor receptors expressed by tumor cells, T cells, and other immune cells. This evidence concerns the gene PDCD1 and cancer.