The assay detected PD-L1 immunoreactivity with the anticipated staining patterns in a panel of normal tissue samples with known PD-L1 expression (e.g., placental trophoblasts and immune cells) and in tumor cells from NSCLC and HNSCC tissue samples with a range of PD-L1 staining intensities and frequencies representing the heterogeneity of tissue expression. This evidence concerns the gene CD274 and head and neck squamous cell carcinoma.