The effect of progestins on the mitotic activity of uterine fibromyomas.

Previous studies have shown increased mitotic activity in uterine fibromyomas in patients using exogenous hormones. This study has compared the mitotic activity of fibromyomas in three groups of patients. The first group was using a progestin-only preparation (usually depo-medroxyprogesterone acetate). The second group of age-matched controls had never used any exogenous hormone. The third group of patients was using a combined estrogen/progestin oral contraceptive. The results show that patients using a progestin-only preparation have a significantly higher mitotic activity in fibromyomas than patients from the other two groups; results from patients using a combined estrogen/progestin preparation were the same as the controls. The highest count was 39 mitoses/100 high power fields (HPF), but focal areas containing up to 8 mitoses/10 HPF could be found. In none of the fibromyomas examined did the count exceed 10 mitoses/10 HPF, and none showed significant pleomorphism that might have been confused with malignancy.