Clinical studies with the specific ‘pure’ antioestrogen ICI 182780

Evaluation of monoclonal antibody MIB-1 in the mammary epithelium adjacent to fibroadenomas in premenopausal women treated with tamoxifen

The purpose of this study was to study the monoclonal antibody MIB-1 in the normal breast epithelium adjacent to a fibroadenoma in women in the luteal phase of the menstrual cycle who were treated with tamoxifen at doses of 10 and 20 mg for 22 days. The proliferative activity of the mammary epithelium adjacent to the fibroadenoma was studied by immunohistochemistry on the basis of the monoclonal antibody MIB-1 (Immunotech, catalog No. 0505, lot 001). The study was randomized and double blind and was conducted on 44 women with fibroadenomas divided into three groups: A (n=16, placebo), B (n=15, tamoxifen, 10 mg), and C (n=13, tamoxifen, 20 mg). Tamoxifen was administered for 22 days starting on the 2nd day of the menstrual cycle, and a biopsy was taken on the 23rd day. Serum estradiol, progesterone, sex hormone binding globulin, follicle-stimulating hormone, luteinizing hormone, and prolactin were measured before treatment (21st and 24th day of the previous menstrual cycle) and on the day of the biopsy. The mean percentage of stained nuclei per 1,000 cells was 9.2 in group A, 4.5 in group B, and 3.2 in group C. The Fisher's test revealed that tamoxifen significantly reduced MIB-1 at doses of 10 and 20 mg compared with the placebo group (p < 0.0001), with no significant differences between doses in terms of proliferative activity (p=0.21). Groups B and C presented a significant increase in progesterone (p=0.038), estradiol (p < 0.001), and sex hormone binding globulin (p=0.001) levels. Elevation of serum follicle-stimulating hormone concentration (p=0.0045) and a fall in prolactin levels (p=0.0055) were observed. We conclude that tamoxifen significantly reduced the proliferative activity of the mammary epithelium at the doses of 10 and 20 mg/day.