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 treatment of breast cancer, deserves more investigation for the determination of its efficacy as a prophylactic agent against breast cancer in high risk women. Thus, the action of tamoxifen on the human mammary gland was studied by measuring the number of lysosomes in normal mammary epithelium during the administration of tamoxifen. Methods: Tamoxifen was administered only during the luteal phase of the menstrual cycle to avoid interference with corpus luteum formation. A fragment of breast 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 tamoxifen and 17 were used as controls. Lysosome counts were performed under the light microscope on slides submitted to the acid phosphatase cytochemical technique and the data were analyzed statistically by the Mann-Whitney test. Results: The fragments from the group treated with tamoxifen showed a significant decrease in lysosome numbers. Conclusions. Tamoxifen administered after ovulation significantly decreases the number of lysosomes in the cells of normal mammary epithelium, demonstrating the antiestrogenic effect of the drug on this target tissue. (C) 1997 International Federation of Gynecology and Obstetrics.