The effects of tamoxifen on proliferation and steroid receptor expression in postmenopausal enclometriurn

Aim: To study the effects of tamoxifen on the proliferation index and oestrogen receptor (ER) and progesterone receptor (PR) expression in postmenopausal endometrium.Methods: A total of 125 endometrial specimens of postmenopausal women, comprising benign endometria from tamoxifen users (n=35) and non-users (n=24), and endometrial cancer from tamoxifen users (n=15) and non-users (n=51), were immunohistochemically examined using MIB-1, anti-ER, and anti-PR antibodies in endometrial epithelium and stroma.Results: In benign endometrium the mean MIB-1 index in the epithelium was higher in tamoxifen users than in non-users (mean, 13% (SD, 13%) v mean, 2% (SD, 2%); pConclusion: The proliferation index (as measured by MIB-1) in benign endometrial epithelium is higher in tamoxifen users than in non-users, and this might play a role in the reported higher incidence of endometrial cancer in postmenopausal tamoxifen users. The increased expression of PR in stroma from tamoxifen users with both benign and malignant endometrium demonstrates an additional oestrogenic effect of tamoxifen on the endometrial stroma.