Estrogen and progesterone receptor expression of decidual endometrium in a postmenopausal woman treated with tamoxifen and megestrol acetate.

To the best of our knowledge, this is the first report of in vivo endometrial estrogen and progesterone receptor induction as a result of tamoxifen exposure in a postmenopausal breast cancer patient. The following observations, that the postmenopausal endometrium is sensitive to tamoxifen, that this agent can act as an estrogen-like substance, and that it may cause proliferation of the endometrium in the absence of progestin, may explain the endometrial decidual changes described herein as a protective mechanism against possible neoplastic endometrial changes.