CD274 and head and neck squamous cell carcinoma: Furthermore in 62 patients with R/M HNSCC treated with anti-PD-L1 durvalumab on a phase I/II study, ORR was 18% in patients with high PD-L1 expression (tumor cell ≥25%, Ventana PD-L1 (SP263) assay) compared to 8% in patients with tumor cell PD-L1–low/negative expression (tumor cell < 25%) [54, 55].