Plasma Circulating Tumor DNA Analyses in ER+ Metastatic Breast Cancer

The primary objective of this 110 patient correlative biomarker study is to evaluate whether changes in mutant ESR1 allele fraction in plasma circulating tumor DNA (ctDNA) are predictive of progression-free survival in metastatic ER+ breast cancer patients who are receiving 2nd, 3rd, or 4th line systemic endocrine therapy. A secondary goal of this study is to explore the prevalence and kinetics of hotspot and non-hotspot ctDNA ESR1 mutations in this patient population, prior to initiating a new line of endocrine therapy as well as upon clinical progression, to identify potential mechanisms of resistance. Although initially to be opened at UNC Chapel Hill, our goal is to expand enrollment to include Rex Cancer Center in Raleigh, North Carolina, and collaborating institutions through the Translational Breast Cancer Research Consortium.