Uterine epithelioid leiomyosarcoma in a pig-tailed macaque

During ultrasonographic examination following spontaneous abortion, an approximately 6-cm diameter mass of mixed echogenicity is detected in the uterine wall of a mature pig-tailed macaque (Macaca nemestrina). Grossly, the mass is associated with the uterine fundus, multilobulate and tan with red-black mottled foci on cut surface. Microscopically, the invasive mass is composed of poorly differentiated round cells arranged in sheets and bundles supported by a fine fibrous stroma. On immunohistochemical evaluation, neoplastic cells contain vimentin, desmin, muscle actin, and smooth muscle alpha-actin antigens and do not react with antibodies to low and high molecular-weight cytokeratins. Cell morphology and immunohistochemical results indicate a diagnosis of epithelioid leiomyosarcoma (clear cell variant).