Unusual Immunophenotype of a Soft Tissue Sarcoma in a European Polecat (Mustela putorius)

: The most commonly reported tumors in ferrets are carcinomas, followed by round cell tumors. Soft tissue sarcomas are reported and characterized much less frequently. Because domesticated ferrets (Mustela putorius furo) are direct descendants of European polecats (Mustela putorius), the types and prevalence of tumors are expected to be similar in the two species. Presented here is a case report of unusual immunohistochemical staining characteristics of an abdominal wall leiomyosarcoma in a close relative of domestic ferrets, the European polecat. Sections of tissue were preserved in 10% buffered formalin, embedded in paraffin, and sectioned at 5 mm. Routine staining with hematoxylin and eosin and several immunohistochemical tests were performed to identify the tumor tissue of origin. Although the tumor did not stain with antibody to desmin, further staining for smooth muscle actin was consistent with a smooth muscle origin. To the authors' knowledge, this report is the first description of a leiomyosarcoma in the European polecat. This report emphasizes the importance of using additional secondary markers to accurately diagnose anaplastic tumors.