From the Academic Department of Biochemistry, Royal Marsden Hospital, London, United Kingdom
Author's disclosure of potential conflicts of interest is found at the end of this article.
Address reprint requests to Mitchell Dowsett, PhD, Academic Department of Biochemistry, Royal Marsden Hospital, Fulham Road, London, SW3 6JJ, UK; e-mail: mitch.dowsett{at}icr.ac.uk
Overview: Between 75% and 80% of breast cancer is estrogen receptor (ER)-positive and is treated with some form of endocrine therapy. It is clear that patients do not benefit from this therapy equally, and major efforts have been undertaken to identify biomarkers that predict the sensitivity to tamoxifen, and more recently, to aromatase inhibitors. Low levels of ER and human epidermal growth factor receptor 2 (HER2)-positive status seem to negatively affect response to tamoxifen; there is evidence for HER2 that this relative insensitivity may not extend to aromatase inhibitors in terms of early response, but data from adjuvant trials do not reveal differential benefit between tamoxifen and aromatase inhibitors on the basis of HER2 status. Progesterone receptor expression has strong prognostic significance in ER-positive disease but is not predictive of benefit from endocrine therapy.
