CD274 and head and neck squamous cell carcinoma: Considering the concordance of protein-mRNA expression and that over half of the HNSCCs showed a mutually exclusive B7-H4/PD-L1 pattern in the TMA IHC analysis, HNSCC cases with B7-H4+/PD-L1– may correspond with mRNA expression and express mutually exclusive patterns at the mRNA level.