CD274 and head and neck squamous cell carcinoma: Moreover, inhibition of this pathway has proved to be clinically relevant since blocking antibodies against PD-1 or PD-L1 have demonstrated encouraging clinical activity in patients with metastatic melanoma, renal cell carcinoma (RCC), non-small cell lung cancer (NSCLC), and head and neck cancer (HNSCC), where PD-L1 tumor expression enriched for clinical responders (Brahmer et al., 2012; Topalian et al., 2012; Ferris et al., 2016).