The Combined Assessment of CTC and ESR1 Status in Liquid Biopsy Samples Enhances the Clinical Value of Prediction in Metastatic Breast Cancer

Monitoring of metastatic breast cancer (mBC) is an important issue in the clinical management of patients. Liquid biopsy has become a non-invasive method for detecting and monitoring cancer in body fluids. The presence of circulating tumor cells (CTCs) and circulating tumor DNA (ctDNA) in peripheral blood indicates poor prognosis and may contribute to early detection of progression, but assessment of these levels is still not routine clinical management. The main objective of this study was to estimate the frequency and clinical value of the <i>ESR1</i> and <i>PIK3CA</i> mutations identified in circulating free DNA (cfDNA.) The second goal was to evaluate whether simultaneous evaluation of CTCs and mutation status in cfDNA increases the prognostic value of liquid biopsy. The results of the analysis of the CTC number and <i>ESR1</i> and <i>PIK3CA</i> mutations in blood collected from 179 patients with metastatic breast cancer show that <i>ESR1</i> mutations are more frequent in patients with advanced luminal breast cancer regardless of the type of the treatment. <i>ESR1</i> mutations appear primarily during progression, as no mutations were found in primary tumor samples. The main conclusion of the study is that combined assessment of CTCs and <i>ESR1</i> status in liquid biopsy may improve the prognostic value of liquid biopsy.