Estrogen receptors in breast carcinogenesis and endocrine therapy

Excessive exposure to estrogen has long been associated with an increased risk for developing breast cancer and anti-estrogen therapy is the gold standard of care in the treatment of estrogen receptor (ER) cc-positive breast cancers. However, there are several mysteries concerning both anti-estrogen, tamoxifen, and estrogen. The most important of these are: (1) some ER alpha-positive breast cancers do not respond to tamoxifen; (2) some ER alpha-negative breast cancers do respond to tamoxifen; (3) initial or acquired resistance to tamoxifen occurs with recurrent tumors; (4) estrogen can cause marked tumor regression in long-term tamoxifen-resistant ERa-positive breast cancer. These mysteries indicate that we do not know enough about estrogen signaling to understand the effects of targeting these receptors in cancer. The discovery of ER beta, the second estrogen receptor, has added another level of complexity to estrogen signaling. This review summarizes recent publications and makes an updated portrait of ER alpha and ER beta in breast carcinogenesis and endocrine cancer therapy. (C) 2014 Elsevier Ireland Ltd. All rights reserved.