CD274 and head and neck squamous cell carcinoma: Category 1 evidence from KEYNOTE-048 showed both significantly improved OS for patients with R/M HNSCC with PD-L1 CPS ≥20 and ≥ 1 upon treatment with pembrolizumab monotherapy (200 mg Q3W) as well as for biomarker-unspecified R/M HNSCC patients upon treatment with pembrolizumab (200 mg Q3W) + chemotherapy (cisplatin 100 mg/m2 or carboplatin AUC 5 Q3W + 5-FU 1000 mg/m2/d for 4 d Q3W).