Immune checkpoint inhibitors (ICPIs) such as ipilimumab, a CTLA-4 inhibitor, and nivolumab, a PD-1 inhibitor, are more widely used to treat various types of cancers, but they can also be associated with immune-related adverse reactions (irAEs) including enterocolitis, hepatitis, or skin rash. The gene discussed is CTLA4; the disease is cancer.