Unusual histopathological features of a uterine leiomyosarcoma in a dog.

Uterine leiomyosarcoma is a malignant neoplasm arising from leiomyocytes in the uterus. A 12-year-old mixed-breed intact female dog was presented with vaginal bleeding for the past 2 weeks. Abdominal ultrasonography revealed a mixed echogenic mass in the uterus, and right lateral abdominal radiography showed a large mid-abdominal mass. Exploratory celiotomy was performed, revealing a solid mass in the entire uterine body and both uterine horns. Ovariohysterectomy was performed and the uterine mass sample was microscopically examined. The mass was composed of a dense proliferation of neoplastic cells that display two morphologic features; spindloid and epithelioid appearances. Additionally, chondroid-like matrix was noted. Both components were negative for cytokeratin AE1/AE3, and strongly positive for vimentin. The spindloid component was strongly positive for α-SMA, while the epithelioid-like component was moderately positive for alpha-smooth muscle actin. These findings are suggestive of a leiomyosarcoma. Although the recovery immediately following surgery was smooth and without complications, the dog's condition worsened over the following month, ultimately leading to euthanasia. This report describes the histopathologic features and clinical outcome of an unusual variant of uterine leiomyosarcoma in a dog.