CD274 and head and neck squamous cell carcinoma: Previous clinical trials consistently showed that PD-L1 expression is an important biomarker for predicting anti-PD-1/PD-L1 treatment in various cancer types including HNSCC [21, 22]; thus, PD-L1 assessment should be performed in recent biopsy samples in order to precisely determine whether anti-PD-1/PD-L1 inhibitors should be used.