CDKN2A and head and neck squamous cell carcinoma: Our aim was to assess the ability of simultaneous immunohistochemical staining (IHC) for p16 and p53 to accurately subclassify head and neck squamous cell carcinomas (HNSCC) as HPV-associated (HPV-A) versus HPV-independent (HPV-I) and compare p53 IHC staining patterns to TP53 mutation status, p16 IHC positivity and HPV status.