Malignant transformation of exophytic Schneiderian papilloma of the nasal cavity.

Schneiderian papilloma (SP) is classified into three types: inverted, oncocytic, and exophytic. Malignant transformation occurs in 10% of SP; most are inverted and oncocytic types. Malignant transformation of polypoid exophytic SP is exceptional; only two cases have been reported in the English literature. A 58-year-old man consulted our hospital because of nasal obstruction. Nasal endoscopy and imaging modalities showed a polyp in the right nasal cavity. Biopsy findings showed compatibility with SP. However, since fludeoxyglucose positron emission tomography (FDG-PET) showed signals, polypectomy was performed. Grossly, the polyp was reddish white and measured 2 cm. Histologically, the polyp consisted of a non-invasive squamous cell carcinoma (SCC) component (70%), a mature squamous component (20%), and Schneiderian epithelium (10%). Vague koilocytosis was present in the SCC component. The three components were arranged in an exophytic papillary pattern. Immunohistochemically, the non-invasive SCC component was positive for cytokeratins (AE1/3, CAM5.2, CK5/6), p63, p53, and Ki67 (labeling 50%). The mature squamous component was positive for cytokeratins (AE1/3, CAM5.2 and CK5/6), p63, and Ki67 (labeling 6%). The Schneiderian component was positive for cytokeratins (AE1/3, CAM5.2, and CK5/6), p63, and Ki-67 (labeling 4%). The tumor was HPV negative in the three components. The polyp was diagnosed as exophytic Schneiderian carcinoma arising from exophytic SP. The patient is now free from tumor 4 years after the operation.