Immune checkpoint inhibitors (ICIs), such as monoclonal antibodies (mAbs) against programed cell death 1 (PD-1), programmed cell death-ligand 1 (PD-L1) and cytotoxic T-lymphocyte antigen 4 (CTLA-4), have led to advances in cancer therapy, and ICI therapy has improved survival in patients with advanced-stage cancers. This evidence concerns the gene CTLA4 and cancer.