RNA-Based CTC Analysis Provides Prognostic Information in Metastatic Breast Cancer

In metastatic breast cancer (MBC) the molecular characterization of circulating tumor cells (CTCs) provides a unique tool to understand metastasis-biology and therapy-resistance. We evaluated the prognostic significance of gene expression in EpCAM⁽⁺⁾ CTCs in 46 MBC patients based on a long follow-up. We selected a panel consisting of stem cell markers (CD24, CD44, ALDH1), the mesenchymal marker TWIST1, receptors (ESR1, PGR, HER2, EGFR) and the epithelial marker CK-19. Singleplex RT-qPCR was used for TWIST1 and CK-19 and multiplex RT-qPCR for stem cell markers and receptors. A group of 19 healthy donors (HD) was used as control. Univariate (p = 0.001) and multivariate analysis (p = 0.002) revealed the prognostic value of combined gene expression of CK-19(+), CD44, ALDH1 and HER2 over-expression for overall survival (OS). The Kaplan-Meier estimates of OS were significantly different in patients positive for CK-19 (p = 0.028), CD44 (p = 0.002), ALDH1 (p = 0.007) and HER2-positive (p = 0.022). Our results indicate that combined gene expression analysis in EpCAM⁽⁺⁾ CTCs provides prognostic information in MBC.