False-positive diagnosis in fine-needle aspiration of an atypical Warthin's tumor: histochemical differential stains for cytodiagnosis.

Cytologic smears of a Warthin's tumor (WT) typically consist of sheets of oncocytic (oxyphilic) cells and scattered lymphocytes. Reparative foci within this neoplasm can occur, which may give rise to exfoliated, malignant-appearing, squamous-like cells. A false-positive diagnosis of squamous carcinoma can occur when these atypical cells dominate the cytologic aspirate. Histochemical and immunoperoxidase stains may aid in diagnosing an atypical WT when the usual cytologic features are absent.