Mitotic activity in uterine leiomyomas during the menstrual cycle.

To investigate the role of the menstrual cycle in the growth of uterine leiomyomas, the mitotic count per 100 high-power fields and the relation of this to the patient's age (30 to 54 years) were examined in tissue sections of leiomyomas from 181 surgically removed myomatous uteri. The mean mitotic count in the secretory phase (12.7 per 100 high-power fields) was significantly higher than that of the proliferative phase (3.8 per 100 high-power fields) (p less than 0.01) or menses (8.3 per 100 high-power fields) (p less than 0.05). We found the highest mitotic count (54 per 100 high-power fields) in a leiomyoma at the early secretory phase. In the secretory phase, the younger age group exhibited a significantly higher mitotic count than the older group. Increased mitotic activity in leiomyomas under the hormonal milieu of the secretory phase of the menstrual cycle suggests that the growth of these tumors is affected by progesterone level. In addition, this study defined the range of mitotic counts occurring in the tissue sections of typical leiomyomas during the menstrual cycle.