PDCD1 and melanoma: Fortunately, melanoma is one of the most immunogenic tumors and therefore has the greatest potential for response to immunotherapy (10), so that it has been the most important tumor driving the development of solid tumor immunotherapy, especially immune checkpoint inhibitors (ICIs) targeting such as programmed cell death protein 1 (PD-1), PD-1 ligand (PD-L1), and cytotoxic T lymphocyte antigen 4 (CTLA4) (11).