Uterine leiomyosarcoma and pyometra in a 7-year-old dog

Canine malignant uterine tumours are extremely rare. A 7-year-old intact female mongrel dog was presented with a two-day history of reduced appetite, abdominal distention and general dullness. Abdominal palpation revealed the presence of a large mass. Radiography showed a large mass occupying the left mid-abdominal area and loops of mild opacity occupying the right mid-abdominal area. Ultrasonography revealed a large heterogeneous mass with an anechoic area and some hyperechoic foci, indicative of calcification, in the mid-abdominal area. Anechoic areas were also found in the mid- and caudal abdominal area, and were presumed to be the fluid-filled uterus. On laparotomy, a 10.5 x 14.5cm, firm mass was found in the uterine body, while the uterine horns were filled with a thick red-brownish exudate; ovariohysterectomy was subsequently performed.Histologic examination of the mass showed a malignant mesenchymal tumour with cells arranged in large interlacing bundles or streams with little stroma, as well as severe endometritis. Immunohistochemistry was performed employing a streptavi-din-biotin-peroxidase protocol. The tumour cells were immuno-histochemically positive to desmin and alpha-smooth muscle action, indicating their smooth muscle origin and establishing the diagnosis of intermediate grade uterine leiomyosarcoma associated with pyometra. The use of immunohistochemistry allowed the differentiation between tumours of smooth muscle origin and other tumour types, particularly fibrosarcoma and poorly differentiated tumours. To the best of our knowledge, this is one of the few cases of uterine leiomyosarcoma described in the dog.