Peripheral ameloblastic carcinoma is an extremely rare odontogenic tumor derived from the remnants of dental lamina and/or mucosal epithelium of the oral mucosa. We present a case of secondary peripheral ameloblastic carcinoma of the mandibular gingiva. The patient was a 71-year-old man with gingival swelling and persistent bleeding. Exfoliative cytology revealed cohesive clusters composed of basaloid cells with nuclear atypia and various forms of keratinized cells of dysplastic squamous appearance. Some cell groups had a peripheral palisade. Histology of the biopsy and surgically removed specimens revealed characteristic features resembling squamous cell carcinoma, basal cell carcinoma, and benign follicles of ameloblastoma. These neoplastic structures, as well as proliferation and elongation of the mucosal epithelium, comprised an extensive network. The varied cytopathologic findings may be related to proliferation and transformation of basal cells of the mucosal epithelium toward ameloblastic carcinoma and variable squamous differentiation.
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