CD274 and head and neck squamous cell carcinoma: The HAWK study, an international phase II trial evaluating the objective response rates of durvalumab in 111 immunotherapy-naïve patients with platinum refractory recurrent/metastatic HNSCC with ≥25% PD-L1 expression, revealed a response rate of 16.2% in HPV positive patients and 10.9% in HPV negative patients.