The recent success of immunotherapy in clinic, especially with immune checkpoint inhibitors (ICIs) that impede the engagement of programmed cell death 1 (PD-1) or cytotoxic T lymphocyte-associated protein 4 (CTLA-4) with their respective ligand or receptor to boost anti-cancer immunity, has paved a way for these agents to become a part of standard treatment in many cancer types. This evidence concerns the gene CTLA4 and cancer.