PDCD1 and head and neck squamous cell carcinoma: The Keynote-048 trial also showed that the combination of anti-PD-1 (Pembrolizumab) and chemotherapy is effective against R/M HNSCC, and the efficacy depends on the combined positive score (CPS) of Programmed cell Death-1 Ligand-1 (PD-L1) expression by tumor and immune cells [104].