Immunohistochemical Profile of Ameloblastic Carcinoma Arising from an Amyloid-Producing Odontogenic Tumour in a Miniature Dachshund

A 13-year-old female miniature dachshund was presented with a centrally-located sublingual mass in the rostral mandibular region. The focally ulcerated growth completely covered the left (305) and right (405) premolar teeth and partially covered the right canine teeth (404). A punch biopsy sample revealed neoplastic proliferation of odontogenic epithelium arranged in irregular cords with frequent comedo-like necrosis. Following the initial diagnosis of ameloblastic carcinoma, a bilateral rostral hemimandibulectomy was performed. Although the detailed examination of the resected mass was consistent with the initial diagnosis, it also contained birefringent congophilic, amelogenin-labelled amyloid deposits similar to an amyloid-producing odontogenic tumour (APOT) in 30–40% of the mass, in continuity with the ameloblastic carcinoma. All neoplastic cells had diffuse moderate expression of cytokeratin (CK) AE1/AE3 and CK5, diffuse mild expression of CK14 and multifocal moderate expression of CK19. Because the APOT-like growth in the mass was histologically benign, the tumour was diagnosed as an ameloblastic carcinoma arising from an APOT.