PDCD1 and melanoma: Immune checkpoint inhibitors (ICIs) targeting programmed cell death protein 1 (PD-1) and cytotoxic T-lymphocyte–associated antigen 4 (CTLA-4) have become the standard care of advanced melanoma in the past 10 years and revolutionized the treatment of melanoma by significantly increasing the overall survival of melanoma patients [116,117,118,119,120].