PDCD1 and cancer: Immune checkpoint inhibitors (ICIs), targeting the programmed cell death 1 (PD-1), programmed cell death ligand 1 (PD-L1), and cytotoxic T-lymphocyte antigen 4 (CTLA-4) pathway, have been a major breakthrough in the treatment of many cancer types.[1] Nivolumab is a human immunoglobulin G4 PD-1 ICI antibody, which selectively blocks the PD-1 receptor on the surface of cytotoxic T cells to prevent downregulation of the immune response elicited by PD-L1 in malignant tumor cells.