the histological appearance of one of the cases, a poorly differentiated squamous cell carcinoma stained with Haematoxylin & Eosin. a: The field shows the border between normal epithelium and poorly differentiated squamous cell carcinoma. b: the equivalent field in an adjacent section showing immunohistochemical staining for p16, a surrogate marker for HPV. c: a higher power view of an adjacent section demonstrating the presence of high-risk HPV by in-situ hybridisation. The viral DNA is stained blue.