Tumours of the urinary bladder represent less than 0.5% of all primary neoplasms in canine patients. Of these tumours, most are of epithelial origin (80%) and most are malignant. Leiomyosarcoma and leiomyoma are the most common mesenchymal tumors of the bladder in cats and dogs, accounting for up to 12% of all primary bladder tumors. Leiomyosarcomas are locally aggressive and infrequently metastasize to regional lymph nodes, liver, pancreas, kidneys, intestines, omentum, diaphragm, heart, and lungs.
The aim of this study is to show the importance of immunohistochemistry for a diagnosis of leiomyosarcoma of the urinary bladder in a young dog.
A bitch, 1.5-year-old Lhasa Apso, presented with hematuria. In the ultrasonography exam a mass was visualized in the bladder with 1.2 cm of diameter and the guided cytology was diagnostic of high-grade sarcoma. Afterward the animal was routed to surgery and the mass was sent to histopathology and immunohistochemistry.
Microscopic analysis showed highly cellular, consisting of interlacing fascicles of spindle cells with marked nuclear atypia, coagulative tumor necrosis and highly mitotic activity. Diagnosis was malignant mesenchymal tumor high-grade. We found a positive immunohistochemistry stain for alpha actin and vimentin antibodies, negative stain for cytokeratin and factor VIII proteins. Ki67 stain showed a high number of positive cells.
Immunohistochemistry is important to the diagnosis of undifferentiated mesenchymal tumors, and in this case we defined the diagnosis of leiomyosarcoma.