Oestrogen receptor β in breast cancer: good, bad or still too early to tell?

Two oestrogen receptors (ERs), ER alpha and ER beta, have been identified. ER alpha is by far the better characterized and is an established predictive marker in breast cancer which influences decisions on whether or not to give adjuvant anti-oestrogens, such as tamoxifen. In contrast, the function of ER beta in breast pathobiology is unclear, partly because most studies have focused on its mRNA rather than the protein. In this review, the significance of ER beta in the human breast is reviewed with respect to recent literature and its possible implications are discussed.