CD274 and head and neck squamous cell carcinoma: Based on the radiosensitivity analysis and the expression level of PD-L1 of locally advanced HNSCC patients, the overall patients were stratified into four groups, as follows: RR and PD-L1-high group, RR and PD-L1-low group, RS and PD-L1-high group, and RS and PD-L1-low group.