PDCD1 and metastatic melanoma: Subsequently, other targeted agents have been approved for the treatment of patients with metastatic melanoma, including the MEK inhibitors, cobimetinib [10] and trametinib [11], the anti-cytotoxic T-lymphocyte antigen 4 (CTLA-4) inhibitor ipilimumab [12], and the anti-programmed cell death-1 (PD-1) agents nivolumab [13] and pembrolizumab [14].