Mitotically active leiomyomas of the uterus.

A series of 15 uterine smooth muscle tumors with histologic features of typical leiomyomas, except for the presence of mitotic activity exceeding 4 mitotic figures per 10 high-power fields (HPF), were studied. The patients' ages ranged from 25 to 50 years (median, 37 years). At least 60% of the tumors were submucosal. The maximum dimension of the tumors ranged from 1.3 to 8.0 cm (median, 3.8 cm). On gross examination, the tumors appeared to be generally unremarkable. By definition, none had cytologic atypia. Mitosis counts were performed in the most active areas by two methods. Counts ranged from 5 to 15 mitotic figures per 10 HPFs when the highest count in any single set of 10 HPFs was recorded (method A) and from 4.2 to 10.2 mitotic figures per 10 HPFs when the average count from 50 consecutive HPFs was determined (method B). Treatment included hysterectomy in eight patients, myomectomy followed by hysterectomy in one, and myomectomy only in six. All but one patient with evaluable endometria were in the secretory phase of the menstrual cycle. Follow-up periods ranged from 6 months to 10.5 years (mean, 2.5 years; median, 2.1 years). None developed local recurrences or metastases. The benign clinical behavior of such tumors warrants the designation of mitotically active leiomyoma rather than smooth muscle tumor of uncertain malignant potential or low-grade leiomyosarcoma.