CD274 and head and neck squamous cell carcinoma: The VENTANA PD-L1 (SP263) Assay met all of the predefined acceptance criteria (according to its proposed intended use as a clinical diagnostic test), showing analytical specificity, sensitivity, robustness and precision, and obtaining the required performance scores for day-to-day, site-to site and observer-to-observer repeatability and reproducibility, confirming its reliability for staining of FFPE NSCLC and HNSCC samples across different testing environments.