ESR1 Amplification is Rare in Breast Cancer and is Associated with High Grade and High Proliferation: A Multiplex Ligation-Dependent Probe Amplification Study

Abstract

Background: Expression of estrogen receptor alpha (ERα) is predictive for endocrine therapy response and an important prognostic factor in breast cancer. Overexpression of ERα can be caused by estrogen receptor 1 (ESR1) gene amplification and was originally reported to be a frequent event associated with a significantly longer survival for ER-positive women treated with adjuvant tamoxifen monotherapy, which was however questioned by subsequent studies.