PDCD1 and melanoma: The approval of immune checkpoint inhibitors (ICI), such as cytotoxic T-lymphocyte-associated antigen 4 (CTLA-4) inhibitors and programmed cell death protein 1 (PD-1) inhibitors, and targeted therapies like BRAF and MEK inhibitors in the last decades, have improved overall survival (OS), with long-lasting antitumoral effects documented in patients with stage IV melanoma [6–13].