AN UNCOMMON CASE OF CLEAR CELL ODONTOGENIC CARCINOMA (CCOC) IN A DOG: IMMUNOMORPHOLOGICAL CHARACTERIZATION AND LITERATURE REVIEW

In dogs and cats, the oral cavity cancers are classified as odontogenic tumors (neoplasia arising from tooth-forming tissues), non-odontogenic tumors, or non-neoplastic lesions (WHO, 2010). To understand the classification of odontogenic tumors, generally considered to be rare, it should be remembered that dental organ pre-ameloblasts and basal lamina induce development of mesenchymal cells into odontoblasts, which produce dentin and induce pre-ameloblasts to mature into secretory ameloblasts. These reciprocal sequential inductive interactions between dental epithelium and mesenchyme form the basis for classifying epithelial odontogenic tumours, which comprehend mesenchimal inductive (ameloblastic fibroma, dentinoma, ameloblastic odontoma, complex odontoma, and compound odontoma) and non inductive (ameloblastoma, adenomatoid ameloblastoma, and calcifying epithelial odontogenic tumour). A few clear cells may be present in odontogenic cysts, while odontogenic neoplasms composed predominantly of clear cells are quite rare. They include calcifying epithelial odontogenic tumours, ameloblastoma and odontogenic carcinoma (Iezzi et al., 2002). Our case, belonging to a 8 yrs old Irish Setter unspayed female, showing a ulcerated 5x4x3 cm maxillary gingival mass localized at level of 4° superior premolar (tooth 208), consisted histologically of islands and sheets of moderately PAS-positive clear cells, that were separated by fibrous septa. Corresponding lymph-node was moderately involved. Immunohistochemically, the tumor cells were positive for pan-cytokeratins, epithelial membrane antigen (EMA), but negative for S-100 protein, smooth muscle actin, desmin, human melanosome-specific antigen-5 (HMSA-5), CD3, CD45, and glial fibrillary acidic protein. On the basis of these observations, a diagnosis of clear cell odontogenic carcinoma (CCOC) was made. To date, only 74 well-documented cases (Kalsi et al., 2014) have been reported in human, but no case in veterinary medicine. Based on its morphologic, histochemical and immunophenotypic features, CCOC was distinguished from other primary and metastatic clear cell tumors of the oral and maxillofacial regions. 1. Iezzi G, Rubini C, Fioroni M, Piattelli A. Clear cell odontogenic carcinoma. Oral Oncol. 2002. Feb;38(2):209-13. 2. WHO Classification of Tumors of the digestive system. World Health Organization; International Agency for Research on Cancer. Lyon : IARC Press, 2010, 4th edition. ISBN 9789283224327 3. Kalsi AS, Williams SP, Shah KA, Fasanmade A. Clear cell odontogenic carcinoma: a rare neoplasm of the maxillary bone. J Oral Maxillofac Surg. 2014 May;72(5):935-8.