Fig. 3.

Non-keratinizing SCC of the sinonasal tract with inverted growth characterized by lobules of tumor cells with smooth and rounded borders (a). Despite some morphologic similarities to inverted Schneiderian papilloma, a synchronous or metachronous benign papilloma could not be histologically documented. Unlike the cases of Schneiderian papilloma with or without evidence of carcinomatous transformation, this carcinoma was positive for high-risk HPV (b) (high-risk HPV RNA in situ hybridization)