Evaluation of estrogen and progesterone receptors in non-neoplastic breast tissue of women of reproductive age exposed to tamoxifen and raloxifene: a randomized, double-blind study

The objective of the present study was to compare the effects of tamoxifen and raloxifene in non-neoplastic breast epithelium. A randomized, double-blind study was carried out in 57 ovulatory, premenopausal women of 18–40 years of age, who had been diagnosed with fibroadenoma of the breast. The patients were divided into three groups: Group A: placebo, n = 20; Group B: tamoxifen 20 mg/day, n = 21; and Group C: raloxifene 60 mg/day, n = 16. The study medication was given for 22 days starting on the first day of the menstrual cycle. On the 23rd day, the fibroadenoma was removed and a sample of non-neoplastic breast tissue was collected for immunohistochemical evaluation of estrogen and progesterone receptors. Comparison between the mean percentages of stained nuclei in the three groups was performed by analysis of variance and multiple comparisons, using Tukey’s method to compare pairwise means, with significance established at P < 0.05. Exposition to tamoxifen or raloxifene resulted in a significant and similar reduction in the mean percentage of stained nuclei for estrogen and progesterone receptors (P < 0.0001). Tamoxifen and raloxifene reduce progesterone and estrogen receptor alpha expression significantly and to a similar extent in the non-neoplastic breast tissue of women of reproductive age.