These drugs are increasingly used to treat various cancers including melanoma, kidney adenocarcinoma, lung carcinomas, and hematological malignancies.1 They commonly target programmed death 1 (PD‐1) or cytotoxic T‐lymphocyte antigen‐4 (CTLA‐4) and, more rarely, PD‐ligand 1 (PD‐L1). The gene discussed is CTLA4; the disease is melanoma.