PDCD1 and melanoma: Checkpoint inhibitors, such as pembrolizumab, nivolumab, and ipilimumab, have revolutionized the treatment of malignancies, including non-small cell lung cancer (NSCLC) and melanoma, by targeting the programmed cell death protein 1 (PD-1) and cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) pathways (15-17).