Oral leiomyosarcoma in a woodchuck (Marmota monax).

We report the case of a 4-year-old female woodchuck (Marmota monax) which presented with a white, firm and discrete mass in the hard palate. The mass extended into the oral cavity but it was well separated from the surrounding tissues. Histology of the tumor showed a malignant mesenchymal tumor with pleomorphic spindle cells varying in degrees of differentiation and density. The neoplastic cells had moderate amounts of granular or fibrillar eosinophilic cytoplasm with indistinct cell margins. Nuclei were oval to elongated and frequently blunt-ended with vesicular chromatin. Immunohistochemical study showed that the neoplastic cells expressed vimentin and alpha-smooth muscle actin but did not express desmin, pan-cytokeratin, and S-100. Therefore, histology and immunohistochemistry revealed that the tumor was oral leiomyosarcoma. Oral cavity is an extremely rare site for leiomyosarcoma and the present case is the first report of spontaneous oral leiomyosarcoma in animals.