PDCD1 and head and neck squamous cell carcinoma: Nivolumab, a monoclonal antibody against programmed cell death 1 (PD-1) has been widely used as the standard treatment for R/M HNSCC, because, in the CheckMate 141 study, nivolumab significantly improved the overall survival (OS) of platinum-refractory R/M HNSCC compared to conventional therapy3.