Preexisting Somatic Mutations of Estrogen Receptor Alpha (<i>ESR1</i>) in Early-Stage Primary Breast Cancer

Abstract

These population-based results indicate that <i>ESR1</i> mutations at diagnosis of primary breast cancer occur in about 1% of women and identify for the first time in the adjuvant setting that such preexisting mutations are associated to eventual resistance to standard hormone therapy. If replicated, tumor <i>ESR1</i> screening should be considered in ER-positive primary breast cancer, and for patients with mutated disease, ER degraders such as fulvestrant or other therapeutic options may be considered as more appropriate.