CD274 and head and neck squamous cell carcinoma: In this paper, we describe the development and validation of the VENTANA PD-L1 (SP263) Assay (PD-L1 [SP263]) (Ventana Medical Systems Inc., Tucson, AZ, USA), which has been designed for the detection of PD-L1 protein in formalin-fixed, paraffin-embedded (FFPE) NSCLC and HNSCC tumor samples.