CD274 and head and neck squamous cell carcinoma: Evidence is building that PD-L1 expression on TCs is associated with improved survival in patients with HNSCC treated with IO agents and yet the role of PD-L1 in outcomes irrespective of treatment (i.e. prognosis) is still unclear, with conflicting reports of PD-L1 as both a negative and positive prognostic factor [17–23].