PDCD1 and neoplasm: In recent years, research on factors related to tumor immunity, including programmed cell death 1 (PD-1), programmed cell death ligand 1 (PD-L1), and cytotoxic T lymphocyte–associated protein 4 (CTLA-4) has advanced worldwide to encompass aspects ranging from basic research to clinical indications in head-neck SCC [8–11].