ESTROGENIC ACTIVITY OF TAMOXIFEN ON NORMAL MAMMARY PARENCHYMA IN THE LUTEAL-PHASE OF THE MENSTRUAL-CYCLE

Objectives: Tamoxifen, an anti-estrogenic drug used in the adjuvant tr eatment of breast cancer, deserves more investigation for the determin ation of its efficacy as a prophylactic agent against breast cancer in high risk women. Thus, the action of tamoxifen on the human mammary g land was studied by measuring the number of lysosomes in normal mammar y epithelium during the administration of tamoxifen. Methods: Tamoxife n was administered only during the luteal phase of the menstrual cycle to avoid interference with corpus luteum formation. A fragment of bre ast tissue adjacent to a fibroadenoma was obtained during surgery from 35 premenopausal women aged 15 to 37 years who had been eumenorrheic for at least 6 months; 18 of these patients were treated with tamoxife n and 17 were used as controls. Lysosome counts were performed under t he light microscope on slides submitted to the acid phosphatase cytoch emical technique and the data were analyzed statistically by the Mann- Whitney test. Results: The fragments from the group treated with tamox ifen showed a significant decrease in lysosome numbers. Conclusions. T amoxifen administered after ovulation significantly decreases the numb er of lysosomes in the cells of normal mammary epithelium, demonstrati ng the antiestrogenic effect of the drug on this target tissue. (C) 19 97 International Federation of Gynecology and Obstetrics.