Checkpoint inhibitors include cytotoxic T-lymphocyte-associated antigen (CTLA)-4 inhibitors (ipilimumab, tremelimumab) and programmed cell death protein 1 pathway/programmed cell death protein 1 ligand inhibitors (PD1/PD-L1) (pembrolizumab, nivolumab, durvalumab, atezolizumab), are more frequently used in clinical trials for the treatment of several cancers [123]. This evidence concerns the gene PDCD1 and cancer.