An unusual case of an osteosarcoma arising in a leiomyoma of the uterus.

Leiomyoma is the most common uterine neoplasm. It has several histological variants such as atypical, cellular, myxoid, and epithelioid. Leiomyoma with heterologous elements is a rare variant of leiomyoma, which may contain heterologous elements such as fat, skeletal muscle, and chondroid and osseous tissues. The heterologous sarcomatous differentiation is also rarely seen. We report on a 53-year-old woman who was admitted with abnormal vaginal bleeding and symptoms related to an abdominal mass. She had a huge uterine leiomyoma that contained osteosarcomatous differentiation in several foci. Although malignant progression for leiomyoma is exceedingly rare, when it occurs it may result not only in a leiomyosarcoma but also in a heterologous sarcomatous differention. We have reported histopathological, immunohistochemical, and clinical features of this rare case and reviewed the published studies.