PDCD1 and melanoma: Immune checkpoint inhibitors (ICIs) such as anti-programmed cell death 1 (anti-PD-1; pembrolizumab, nivolumab), anti-programmed cell death-ligand 1 (anti-PD-L1), and anti-cytotoxic T-lymphocyte-associated protein-4 (anti-CTLA-4) agents have reshaped the management of advanced melanoma by restoring antitumor immune activity.