Expression of steroid receptors, Ki-67, and epidermal growth factor receptor in tamoxifen-treated endometrium

Endometrial specimens of 34 (25 premenopausal and 9 postmenopausal) breast cancer patients receiving tamoxifen were immunohistochemically examined using estrogen receptor (ER), progesterone receptor (PR), Ki-67, and epidermal growth factor receptor (EGFR) antibodies. Proliferative (n = 6), secretory (n = 9), and postmenopausal (n = 6) endometria served as controls. The ER and PR expressions of the glandular cells in tamoxifen-treated patients did not differ from those of the glandular cells in the control women regardless of menopausal status. The Ki-67 index of glandular cells in tamoxifen-induced amenorrheic women was found to be lower than that of the proliferative glandular cells in the control women (p < 0.03), whereas the Ki-67 index of glandular cells in the tamoxifen-treated postmenopausal patients was higher than that of the glandular cells in the control women (p < 0.02). No EGFR overexpression was found in the glandular cells of the tamoxifen-treated premenopausal patients, but expression of EGFR was high in glandular cells of the tamoxifen-treated postmenopausal patients associated with a high Ki-67 index. In competition with ovarian estrogen secretion, tamoxifen may have an antiestrogenic effect on the endometrium, but tamoxifen probably has an estrogenic effect in the absence of ovarian estrogen secretion. This estrogenic effect of tamoxifen may be associated with an EGFR autocrine system.