CD274 and head and neck squamous cell carcinoma: Antibodies targeting PD-1/PD-L1 interactions have been approved by the Food and Drug Administration (FDA) in seven types of malignancies, namely, melanoma, nonsmall cell lung carcinoma, renal cell carcinoma, urothelial carcinoma, colorectal carcinoma, head and neck squamous cell carcinoma and Hodgkin lymphoma [35].