PDCD1 and cancer: Currently, immunotherapy together with immune checkpoint inhibitors (ICIs) such as cytotoxic T-lymphocyte-associated protein 4 (CTLA-4), programmed death-ligand 1 (PD-1), or programmed cell death 1 (PD-L1) inhibitor with specific monoclonal antibodies has been effective at treating advanced melanoma, lung cancer, renal cancer, and other types of cancers [3].