CD274 and head and neck squamous cell carcinoma: The expression of PD-L1, the ligand of the PD-1 receptor, was studied, as the PD-1/PD-L1 axis is involved in cancer immune escape which can be targeted by IC inhibitors such as pembrolizumab and nivolumab, that are clinically used in recurrent or metastatic HNSCC patients [37, 38].