Is oestrogen receptor-β a predictor of endocrine therapy responsiveness in human breast cancer?

Abstract

The role of oestrogen receptor (ER)β in human breast cancer remains unclear. However, it is now apparent that when considering ERβ in human breast cancer it is important to recognise two ERβ expressing groups, one in which ERβ is co-expressed with ERα and the other where ERβ is expressed alone. Emerging data support different functions between ERβ when it is expressed alone and when it is co-expressed with ERα. With regard to the latter group (ERα+/ERβ+), there are now 9 out of 10 retrospective clinical outcome studies published, that support the hypothesis that increased expression of ERβ is associated with increased likelihood of response to endocrine therapy. The data strongly support undertaking prospective studies to determine if the addition of ERβ to ERα is clinically beneficial and whether to include both ERβ and ERα when establishing clinically relevant cut-offs for defining ER status. © 2006 Society for Endocrinology.