PDCD1 and neoplasm: It suppresses the cytotoxic immune response mediated by CD8+ tumor–infiltrating T lymphocytes by stimulating programmed cell death 1 protein (PD-1) receptors localized on lymphocyte surfaces.10 While the mechanism of action of PD-L1 and PD-1 complex is well known, the prognostic role of PD-L1 expression in patients with HNSCC remains largely uncertain.