Abstract
A 12-year-old thoroughbred mare with four days history of anorexia and high fever was submitted to the Equine Hospital. She failed to conceive in the following the breeding season in spring. In rectal palpation, mass could be palpable surrounding ovary. Because of the poor prognosis, full necropsy for mare was decided. The mass is located between right large and small colon, cranial to ovary using ultrasonography. Grossly, the mass was about $5{\times}3.5{\times}4cm$ in size, and the cut surface of mass showed brownish yellow in color with red-to orange granular areas Histopathologically, neoplastic cells were mixed with well differentiated spindle shape cells arranged in interlacing, interwoven pattern and poorly differentiated spindle cells. Neoplastic cells had abundant pink cytoplasm and bland and cigar-shaped nuclei with low mitotic figures. Many arteriole-like blood vessels with thick muscular wall were present throughout the mass. Masson's trichrome staining revealed muscle origin tumors in this case. Immunohistochemically, the neoplastic spindle cells showed positive reactions for smooth muscle actin and desmin. In our best knowledge, this is the first report of uterine angioleiomyoma in mare in Korea.