Estrogen receptor beta is not increasingly expressed in leiomyoma nodules which show no progressive enlargement in premenopausal women.

BACKGROUND AND PURPOSE: Studies on the expression of estrogen receptors (ERs) in uterine leiomyomata have yielded conflicting results. A controlled study focusing on leiomyomal nodules with same clinical presentations and hormonal milieu was conducted to investigate the role of ER beta (ERbeta) on leiomyomal growth. METHODS: Thirty pairs of leiomyomal and myometrial tissues were included in the study. The specimens were obtained from 30 premenopausal women (40-45 years old) with parity 2, and were sampled during the proliferative menstrual phase. All of the leiomyomal nodules were unifocal, medium sized (4-5 cm), intramurally located, and without progressive enlargement for 6 months. The expressions of ERbeta mRNA and protein in leiomyomata and their adjacent myometria were analyzed by reverse transcriptase-polymerase chain reaction and immunohistochemistry using ERbeta-specific antibody, respectively. ER alpha (ERalpha) was simultaneously studied using similar methods. The results were digitally quantified and compared with each other. RESULTS: All paired tissues (30/30, 100%) showed a higher ERalpha expression level (paired t test, p < 0.05). In most leiomyomal nodules (27/30, 90%), both ERbeta and ERalpha exhibited no differences in mRNA levels compared to their adjacent myometria (p > 0.05), but the ratio of ERbeta/ERalpha (expression index) was lower (p < 0.05) in leiomyomal tissue. Although the immunoreactivity scores for ERbeta were similar in paired tissues, more ERbeta-positive cells were detected in myometrial specimens than in their leiomyoma counterparts (mean of 62% vs 56%). Furthermore, the distribution pattern of ERbeta in leiomyoma (nuclear and cytoplasmic) was different from that in the corresponding myometrium (nuclear). The lower ERbeta/ERalpha expression index in stationary leiomyoma suggests that the relative abundance of ERbeta and ERalpha, rather than their individual amounts, determines the existence and development of leiomyoma. CONCLUSIONS: This study demonstrated that in premenopausal women, ERbeta is not increasingly expressed in the leiomyomal nodules which show no progressive enlargement. The distinctive ERbeta-to-ERalpha ratio rather than their individual amounts, is associated with the stationary status of the leiomyomal nodule.