PDCD1 and cancer: Immune checkpoint inhibitors targeting programmed cell death 1 (PD-1), programmed cell death 1 ligand 1 (PD-L1), and cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) have revolutionized cancer treatment by eliciting durable objective responses in multiple cancer types, often leading to improved overall survival [22, 23].