Effect of Tamoxifen and Raloxifene on the Proliferative Activity of the Breast Epithelium in Premenopausal Women

OBJECTIVES: To compare the effects of tamoxifen and raloxifene on the proliferative activity of normal breast tissue in premenopausal women as measured by Ki-67/MIB-1 expression. STUDY DESIGN: A total of 48 women with benign breast nodules and a recommendation for surgical removal of the lesion took part in this study. They were randomized to use tamoxifen or raloxifene for 22 days, after which they were submitted to surgery. During the surgical procedure, a 1-cm fragment of normal breast tissue was removed to study Ki-67 expression. RESULTS: The mean percentage ratios between immunolabeled and non-labeled cells were 2.02 ± 1.09 and 3.13 ± 3.23 for the tamoxifen and raloxifene groups, respectively. There was no statistically significant difference between the tamoxifen (n = 16) and raloxifene (n = 14) groups in relation to the immunohistochemical analysis of Ki-67 (P = 0.205). CONCLUSION: The results of this study showed no difference between tamoxifen and raloxifene with respect to the potential of these drugs to reduce the proliferative activity of the normal breast epithelium in premenopausal women.