Immune checkpoint blockade (ICB) therapies, such as monoclonal antibodies against programmed death 1 (PD-1) or programmed death ligand 1 (PD-L1) and cytotoxic T-lymphocyte associated protein 4 (CTLA4), have achieved unprecedented efficacy in a wide range of malignancies through boosting the immune system to fight cancer. The gene discussed is CTLA4; the disease is cancer.