Recent years have seen substantial advances in our understanding of ER positive/ HER2 negative breast cancer, both in the genetics of this subtype of breast cancer and the biological processes the drive tumor growth and resistance to therapy. Diverse targetable mutations have been identified in studies of primary breast cancer, along with acquired mutations in the estrogen receptor (ESR1) found in 30% of advanced breast cancers that progress on aromatase inhibitors. The therapeutic significance of this genetic diversity is being explored in ongoing studies. Therapies that target mTOR and CDK4/6 have entered routine clinical practice, demonstrating substantial improvements in progression free survival for patients with advanced cancer. The ongoing challenge is to identify biomarkers of sensitivity, to assist in selecting patients who benefit, and identify mechanisms of resistance to therapy to identify the optimal schedule of therapies and identify novel therapeutic approaches for resistant disease.

Citation Format: Turner NC. ES7-2 Mechanisms of resistant to therapy in ER positive cancer [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr ES7-2.