Ultrastructural effects of estrogen replacement on postmenopausal endometrium.

Endometrial adenocarcinoma occurs almost exclusively in postmenopausal women, and excessive or unopposed estrogen stimulation is suspect as a causative factor in its pathogenesis. Furthermore, the incidence of endometrial adenocarcinoma has increased in women undergoing estrogen replacement therapy. In the present study, the cellular response of premenopausal and postmenopausal endometrium to estrogenic stimulation was compared with endometrial adenocarcinoma by the electron microscope. Tissues were obtained at hysterectomy, endometrial biopsy, or endometrial curettage and were processed routinely for light and electron microscopy. Ultrastructurally the endometrium from postmenopausal patients undergoing estrogen replacement therapy was similar to normal cyclic endometrium in the late proliferative phase. At least three features of the estrogen-treated postmenopausal tissue resembled those observed in adenocarcinoma of the endometrium: accumulation of lipid droplets, irregular nuclei, and perinuclear whorls of microfibrils.