PDCD1 and melanoma: ICIs, targeting programmed cell death protein 1 (PD-1), programmed cell death protein 1 ligand (PD-L1), or cytotoxic T-cell antigen 4 protein (CTLA-4), have proven to be effective for many patients with solid tumors, especially those with advanced-stage melanoma, renal cell carcinoma (RCC), and non–small cell lung cancer (NSCLC) (1–4).