PDCD1 and melanoma: Despite significant advances in melanoma treatment brought by targeted therapies such as BRAF inhibitors, MEK inhibitors, and immune checkpoint inhibitors (ICIs) including programmed cell death protein 1 (PD-1)/programmed death ligand 1 (PD-L1) and cytotoxic T-lymphocyte-associated protein 4 (CTLA-4), the 5-year survival rate remains around 60%4,5.