PDCD1 and metastatic melanoma: Systemic therapy options for metastatic melanoma have expanded recently with the development of immune checkpoint inhibitors (monoclonal antibodies targeted against cytotoxic T-lymphocyte associated protein 4 (CTLA4) and programmed cell death 1 (PD-1), which has transformed the outlook and prognosis for patients, with long-term survival now a realistic goal in the majority 8.