(A) Basaloid squamous carcinoma. A base of tongue tumor, predominantly nonkeratinizing, composed of tumor nests with peripheral palisading and central, small tumor cells without much cytoplasm. (B) A p16 immunostain demonstrating uniform and diffuse staining of both nuclei and cytoplasm that characterizes a positive reaction. Less than 70% positivity is regarded as negative. A positive stain for p16 is interpreted as a surrogate for the presence of high-risk human papillomavirus (HPV).
