Immune checkpoint inhibitors, such as those targeting programmed cell death protein 1 (PD-1)/programmed cell death-ligand 1 (PD-L1) and cytotoxic T-lymphocyte-associated protein 4 (CTLA-4), have demonstrated remarkable clinical efficacy in cancers such as melanoma, non-small cell lung cancer (NSCLC), and renal cell carcinoma. This evidence concerns the gene PDCD1 and cancer.