PDCD1 and melanoma: ICI for immunotherapy is mainly based on cytotoxic T lymphocyte antigen 4 (CTLA-4) (ipilimumab) or programmed cell death protein 1 (PD-1)/programmed cell death ligand 1 (PD-L1) (pembrolizumab) inhibition and yields excellent performance against various malignancies, such as melanoma, lung cancer, and urothelial carcinoma (8–10).