Estrogen receptor β in breast cancer

Estrogen receptor (ER) has been found to be a significant predictor of survival and response to hormonal therapy in women with breast cancer.
Recently, a second type of ER has been discovered. The “old” one is now called estrogen receptor alpha (ERα) and the newly discovered one is called estrogen receptor beta (ERβ). While much is known about ERα, the role of ERβ is still undefined. ER belongs to the steroid/thyroid nuclear receptor family. Both ER subtypes contain six functional domains, designated as A – F. There is a high homology at the C and E regions (96% and 58%, respectively) and reduced homology between the other parts of the molecule. The genes for both receptors are located on different chromosomes, ER on chromosome 6, while ERβ on chromosome 14. The tissue distribution and physiological functions of ERβ and ERα are different.
The exact role of ERβ in breast cancer remains unclear. Recent studies have demonstrated that ERβ could be a marker of good prognosis.
Complex machinery of ER transactivation of target genes by estrogen through both receptor subtypes (α and β), variant isoforms and coregulatory proteins show that the final effect depends on all these factors.