Immune checkpoint inhibitors (ICIs) are a class of immunotherapy drugs that have revolutionized cancer treatment by targeting membrane protein programmed cell death protein 1 (PD-1), programmed cell death protein ligand 1 (PD-L1), and cytotoxic T-lymphocyte associated protein 4 (CTLA-4) and blocking the inhibitory signal on the T cells, thus reactivating both innate and adaptive immune systems against cancer cells.1 The gene discussed is CTLA4; the disease is cancer.