PDCD1 and cancer: Over the past decade, immune checkpoint-based immunotherapy (IPC), which uses drugs targeting inhibitory T-cell receptors, such as programed cell death 1 (PD-1) and its ligand (PD-L1), as well as cytotoxic T-lymphocyte-associated antigen 4, has revolutionized therapies for several cancers, including melanoma, non-small cell lung cancer, and renal cell carcinoma.