Unusual histopathological features of a uterine leiomyosarcoma in a dog.

Background: Uterine leiomyosarcoma is a malignant neoplasm arising from leiomyocytes in the uterus. Case description: 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. Findings/treatment and outcome: 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. Conclusion: This report describes the histopathologic features and clinical outcome of an unusual variant of uterine leiomyosarcoma in a dog.