PDCD1 and melanoma: The introduction of immunotherapy, especially immune checkpoint inhibitors (ICIs), which boost the antitumor activity of T cells and rescue immune surveillance by blocking programmed cell death protein 1 (PD-1), programmed cell death 1 ligand 1 (PD-L1), and cytotoxic T lymphocyte associated antigen 4 (CTLA-4), has elicited tremendous excitement owing to its success in various types of cancers, including melanoma (1), hepatocellular carcinoma (2), and lung cancer (3).