Primary prostatic leiomyosarcoma with pulmonary metastases in a dog.

A 6-year-old, intact male Jack Russell terrier was diagnosed with a mass in the caudal abdomen, and ultrasound revealed a large prostatic mass. A total-body computed tomography scan was performed for staging, and lung nodules were detected. Histological examination showed a proliferation of spindle cells arranged in interlacing fascicles. Immunohistochemical staining revealed cells were cytokeratin negative and immunoreactive for vimentin and alpha-smooth muscle actin; cells stained with desmin and S-100 were negative. A diagnosis of primary prostatic leiomyosarcoma with pulmonary metastases was made. This is one of the rare cases of primary prostatic mesenchymal tumor in the canine species.