Hypophysitis is a well-recognized, potentially life-threatening immune-related adverse event (irAE) of immune checkpoint inhibitors, and it appears to be more frequent in patients receiving anti-cytotoxic T-lymphocyte antigen 4 (CTLA-4) monoclonal antibodies or combination therapy with anti-programmed cell-death (PD) protein 1 (PD-1)/anti-PD ligand 1 (PD-L1) plus anti-CTLA-4 immune-checkpoint inhibitors. This evidence concerns the gene CTLA4 and hypophysitis.