Clinical significance of estrogen receptor β in breast cancer

To estimate the clinical significance of estrogen receptor (ER) β in breast cancer we reviewed some reports and compared them with our preliminary results. The structure of ERβ is similar to that of ERar. The DNA binding domain of ERβ is 96% conserved compared with ERα, and the ligand binding domain shows 58% conserved residues, suggesting that both receptors can bind estrogen responsive elements on target genes and that they may also bind similar ligand. The target tissues of ERβ such as testis, prostate, lung, brain, thymus, and ovary, are different from those of ERα, ovary, uterus, endometrium, and breast. Although the function of ERβ in breast cancer progression is not well understood, 30-50% of breast cancers may express ERβ mRNA signals. Additionally, ERβ may be a useful prognostic factor in patients with breast cancer, because tumors that co-expressed ERα and ERβ might be node positive and tend to be of higher grade. Further characterization of the function of ERβ and its isoforms in breast cancer is warranted.