Polypoid uterine leiomyosarcomas in a sheep.

Leiomyosarcoma was diagnosed in the uterus surgically removed from a 3-year-old pet Suffolk ewe with a history of bleeding from the vulva, spontaneous lactation, and nursing behavior. The uterus contained multiple well-circumscribed, soft, intraluminal polypoid masses of variable sizes (0.5-4 cm). The masses were red, with white, smooth, and glistening cut surfaces. Histologically they comprised variably dense sheets of moderately pleomorphic, plump spindle cells embedded in richly vascularized stroma. The mitotic index was usually low (0-1/high-power field), but in some polyps there were up to 10 mitoses/high-power field. Neoplastic cells stained positive for alpha smooth muscle actin (alpha-SMA) by immunohistochemistry. Ultrastructural features of neoplastic cells included the presence of basal lamina, scant microfilaments, contracted nuclei with blunt ends, and flat intercellular junctions. Uterine leiomyosarcoma was diagnosed based on cellular morphology and atypia and positive immunohistochemistry for alpha-SMA.