Expression of estrogen receptors alpha and beta in two uterine mesenchymal tumors after prolonged tamoxifen therapy. Report of two cases.

INTRODUCTION: Tamoxifen therapy is associated with an increased risk of endometrial carcinoma, and possibly uterine sarcomas. Little is known about hormone receptor expression in mesenchymal tumors of the uterus after tamoxifen therapy. CASES: The cases of two patients with uterine mesenchymal tumors after prolonged tamoxifen therapy due to breast cancer are presented. The expression of estrogen receptors alpha (ERalpha) and beta (ERbeta) and progesterone receptors (PR) was studied immunohistochemically in both cases. Both tumors were negative for ERalpha and positive for ERbeta. In the first case the tumor was negative for PR, while in the second only 20% of nuclei were PR-positive.
CONCLUSIONS: Consistent with previous studies, uterine mesenchymal tumors after tamoxifen therapy do not express ERalpha. The results of the present report provide for the first time evidence that tamoxifen might exert a stimulatory effect on the uterus, at least during tumor progression, through ERbeta but not through ERalpha.