EFFECTS OF TAMOXIFEN ON THE BREAST IN THE LUTEAL-PHASE OF THE MENSTRUAL-CYCLE

Objectives: The effect of tamoxifen on cyclic mastalgia and on chemopr ophylaxis against breast cancer is little known, mainly due to the dif ficulties in studying the normal human gland. We proposed to evaluate the mitotic index and the nuclear volume of the lobule of women medica ted with tamoxifen only during the luteal phase of the menstrual cycle in order to observe the effect of tamoxifen on the normal human mamma ry gland. Methods: Twenty-four premenopausal women with fibroadenoma d iagnosed via biopsy were studied. The phase of the cycle was determine d by the date of menstruation and serum progesterone level in the lute al phase (greater than or equal to 3 ng/ml). The patients admitted to the study and were given written informed consent to participate in th e investigation, which was previously approved of by the hospital Ethi cs Committee. Patients were divided at random into two groups: Group I consisted of 12 untreated women (control) and Group II consisted of 1 2 patients treated with 20 mg/day tamoxifen for 10 consecutive days be ginning on the 13th day of the menstrual cycle. In both groups, the pa tients were submitted to biopsies of the nodule and of a 1-cm(3) fragm ent of adjacent mammary parenchyma between the 23rd and 26th day of th e cycle. The mitotic index (number of mitoses/1000 nuclei counted) and mean nuclear volume (mean of 10 nuclear volumes for each case) were m easured. Results: No mitosis was observed in Group II. There was a red uction in the mean nuclear volume in Group II (Mann-Whitney test). Con clusions: Tamoxifen, when administered only during the luteal phase of the menstrual cycle, significantly reduces the nuclear volume and mit otic activity of the epithelium. This data demonstrates an antagonisti c action of tamoxifen on estrogen even when administered for short per iods of time. (C) 1998 International Federation of Gynecology and Obst etrics.