PDCD1 and metastatic melanoma: Immune checkpoint inhibitors (ICIs) targeting the programmed cell death protein-1 (PD-1)/programmed cell death ligand-1 (PD-L1) axis or cytotoxic T-lymphocyte–associated protein 4 (CTLA-4) receptor, either as monotherapy or as combined treatment, have shown response rates of approximately 40%–60% in patients with metastatic melanoma, with progression-free and overall survival (1–8).