Detection of Activating Estrogen Receptor Gene (<i>ESR1</i>) Mutations in Single Circulating Tumor Cells.

Abstract

<b>Purpose:</b> Early detection is essential for treatment plans before onset of metastatic disease. Our purpose was to demonstrate feasibility to detect and monitor estrogen receptor 1 (<i>ESR1</i>) gene mutations at the single circulating tumor cell (CTC) level in metastatic breast cancer (MBC).<b>Experimental Design:</b> We used a CTC molecular characterization approach to investigate heterogeneity of 14 hotspot mutations in <i>ESR1</i> and their correlation with endocrine resistance. Combining the CellSearch and DEPArray technologies allowed recovery of 71 single CTCs and 12 WBC from 3 ER-positive MBC patients. Forty CTCs and 12 WBC were subjected to whole genome amplification by MALBAC and Sanger sequencing.<b>Results:</b> Among 3 selected patients, 2 had an <i>ESR1</i> mutation (Y537). One showed two different <i>ESR1</i> variants in a single CTC and another showed loss of heterozygosity. All mutations were detected in matched cell-free DNA (cfDNA). Furthermore, one had 2 serial blood samples analyzed and showed changes in both cfDNA and CTCs with emergence of mutations in <i>ESR1</i> (Y537S and T570I), which has not been reported previously.<b>Conclusions:</b> CTCs are easily accessible biomarkers to monitor and better personalize management of patients with previously demonstrated ER-MBC who are progressing on endocrine therapy. We showed that single CTC analysis can yield important information on clonal heterogeneity and can be a source of discovery of novel and potential driver mutations. Finally, we also validate a workflow for liquid biopsy that will facilitate early detection of <i>ESR1</i> mutations, the emergence of endocrine resistance and the choice of further target therapy. <i>Clin Cancer Res; 23(20); 6086-93. ©2017 AACR</i>.