Urethral sarcomatoid urothelial carcinoma with heterologous elements in a dog.

Sarcomatoid carcinoma is a biphasic tumour characterized by the co-existence of epithelial and mesenchymal differentiation that may contain heterologous components. These tumours are rare in domestic animals and have only been reported in the kidney and prostate gland. In this report we describe a French Bulldog with a perianal swelling that resulted in dyschezia. Ultrasound confirmed the presence of a mass in the lower abdominal cavity and surgery identified and removed a tumour close to the urethra. The dog was euthanized 3 weeks later due to poor condition. Histopathological analysis of the tumour revealed a biphasic morphology of malignant epithelial and mesenchymal cells, within which lay foci of cartilage and bone. Regions of neoplastic cells were immunopositive for GATA3, confirming urothelial origin, or for SATB2, confirming the presence of osseous differentiation. Electron microscopy revealed an epithelial cell population and a predominant population of irregular, spindle-shaped fibroblast-like cells. Based on these findings, the diagnosis was urethral sarcomatoid urothelial carcinoma (UC) with heterologous elements of chondrosarcoma and osteosarcoma. This is the first report of sarcomatoid UC of the urethra in domestic animals and the neoplasm had strong parallels with sarcomatoid UC of the lower urinary tract in humans, further supporting the One Medicine approach.