PDCD1 and cancer: Immune checkpoint inhibitors (ICI) have transformed cancer treatment, leading to significantly improved clinical outcomes across a range of malignancies by blocking immune checkpoint pathways, such as programmed cell death protein-1 (PD-1), its ligand PD-L1, and cytotoxic T-lymphocyte-associated protein 4 (CTLA-4), enabling cytotoxic T cells to recognize and attack cancer cells more effectively [1].