Malignant pleural mesothelioma in a woodchuck (Marmota monax)

A spontaneous pleural mesothelioma was observed in a 4-year-old female woodchuck (Marmota monax). At necropsy, multifocal, tan to white, firm discrete nodules, 2 to 40 mm in diameter, were scattered over the ventral parts of the lungs and their corresponding parts of the diaphragm and the thoracic wall. Histopathologically, the tumor cells were large, cuboidal-shaped and variable size, and were weakly positive with PAS and Alcian blue. Immunohistochemically, neoplastic cells were positive for both vimentin and cytokeratin, indicating mesothelial origin. This report represents, as far as we know, the first reported case of a spontaneous mesothelioma in woodchucks.