Ossifying Oronasal Carcinoma in a Horse

Abstract

Oral and nasal carcinomas are common in domestic animals, but osseous neoformation in epithelial tumors is rare. This is the first case of an ossifying carcinoma described in horse. This report describes a case of oronasal ossifying carcinoma in a 5-year-old Quarter Horse stallion that developed swelling on the right side of the face. Grossly, there was a neoplastic mass that occupied the entire right nasal cavity and extended into the oral cavity. Histologically, there was neoplastic proliferation of epithelial cells, which were arranged in cords and nests supported by an abundant fibrovascular stroma with osteoid deposition and osseous differentiation in the stroma with abundant osteoclast-like cells. Immunohistochemistry demonstrated immunopositivity for cytokeratin in epithelial cells and immunopositivity for vimentin in stromal cells including the osteoclast-like cells. Immunohistochemical findings favored a diagnosis of ossifying oronasal carcinoma.