CD274 and head and neck squamous cell carcinoma: Anti-PD-1 or anti-PD-L1 blockade is expected to hold promise as a treatment of patients with HNSCC based on the preliminary results of clinical trials using pembrolizumab or durvalumab (MEDI4736), which demonstrated that PD-L1 expression might be a predictive biomarker for the efficacy of anti-PD-1/PD-L1 blockade2, 6, 7.