CD274 and head and neck squamous cell carcinoma: The phase Ib trial published in 2016, KEYNOTE-012 (NCT01848834), was the first study investigating PD-1 blockade therapy in 104 recurrent/metastasis (R/M) HNSCC patients expressing PD-L1 (38% were HPV-positive and 62% were HPV-negative) (70).