CTLA4 and metastatic melanoma: Immunotherapeutic approaches, most notably immune checkpoint inhibitors epitomized by antibodies directed against T-lymphocyte regulators, cytotoxic T-lymphocyte-associated protein 4 (CTLA-4), and PD-1, have demonstrated efficacy in a variety of solid tumors, including metastatic melanoma and lung cancer, and have already received U.S. Food and Drug Administration approval.