Leiomyosarcoma arising in a patient with prior mitotically active leiomyoma

Mitotically active leiomyomas exhibiting insignificant cytologic atypia (none to mild) with an increased mitotic count of 5-20 mitotic figures per 10 high power fields, and without coagulative tumor cell necrosis or atypical mitoses, tend to have a benign clinical course. We encountered a case of a mitotically active leiomyoma and malignant transformation after a total hysterectomy. The recurrent multiple abdominal masses were removed surgically; most of them were benign leiomyomas, but some were leiomyosarcomas. Although most mitotically active leiomyomas have a benign clinical course, these lesions can recur and have the potential for malignant transformation. Therefore, patients with mitotically active leiomyomas require close follow-up.