Primary ovarian leiomyosarcoma in a dog

Ovarian leiomyosarcoma has not been reported previously in dogs. Here, we describe a case of ovarian leiomyosarcoma in an approximately 7-year-old Bichon Frise dog. The affected ovary had an irregular surface due to newly formed tissue and had been replaced by a white mass measuring 2.5 × 1.8 cm, with minimal normal ovarian structure remaining. Histologically, the ovary had been largely replaced by tumour cells, which were spindle-shaped and proliferated in a solid pattern with high cellular density. Cell borders were indistinct, and the tumour cells contained small to medium amounts of eosinophilic cytoplasm. The nuclei were cigar-shaped with blunt ends. Ten mitotic figures were observed in 10 high-power fields at ×400 magnification. Multifocal haemorrhages and foci of necrosis were present also. Immunolabelling was positive for smooth muscle actin, desmin and vimentin in the tumour cells. Based on these findings, we report for the first time a case of leiomyosarcoma arising from the ovary in a dog.