Odontogenic myxoma in an 8-year-old Labrador Retriever dog

Odontogenic myxoma (OM) was diagnosed in an 8-year-old Labrador Retriever dog with an ulcerohemorrhagic mass located on the caudal area of the right maxillary gingiva. The neoplasm was characterized by a low mitotic index and moderate numbers of spindle, stellate, and round cells that were sparsely distributed in an alcian blue reactive myxomatous matrix. Individual neoplastic cells were characterized by small amounts of faintly eosinophilic staining cytoplasm, prominent nucleoli, and stippled amphophilic staining chromatin that was immunoreactive for vimentin but negative for cytokeratin and actin. To the authors' knowledge, this is the first reported case of canine OM from North America, and it shares histomorphologic and histochemical features with 3 other cases reported in dogs elsewhere. Whereas, a literature review suggests untreated canine OM is insidious and locally aggressive, the prognosis in the present dog remains unknown. These findings support previous recommendations for inclusion of canine OM on the World Health Organization list of odontogenic tumors.