PDCD1 and cancer: Immune checkpoint inhibitors (ICIs), such as monoclonal antibodies targeting Programmed Cell Death Protein 1 (PD-1), Programmed Death-Ligand 1 (PD-L1) and Cytotoxic T-Lymphocyte-Associated Protein 4 (CTLA-4), have revolutionized cancer therapy by reactivating suppressed anti-tumor immune responses.