RNA Profiles of Circulating Tumor Cells and Extracellular Vesicles for Therapy Stratification of Metastatic Breast Cancer Patients

Liquid biopsies are discussed to provide surrogate markers for therapy stratification and monitoring. We compared messenger RNA (mRNA) profiles of circulating tumor cells (CTCs) and extracellular vesicles (EVs) in patients with metastatic breast cancer (MBC) to estimate their utility in therapy management. Blood was collected from 35 hormone receptor-positive/HER2-negative patients with MBC at the time of disease progression and at 2 consecutive staging time points. CTCs were isolated from 5 mL of blood by positive immunomagnetic selection, and EVs from 4 mL of plasma by a membrane affinity-based procedure. mRNA was reverse transcribed, preamplified, and analyzed for 18 genes by multimarker quantitative polymerase chain reaction (qPCR) assays. RNA profiles were normalized to healthy donor controls (n = 20), and results were correlated with therapy outcome. There were great differences in mRNA profiles of EVs and CTCs, with only 5% (21/403) of positive signals identical in both fractions. Transcripts involved in the PI3K signaling pathway were frequently overexpressed in CTCs, and , , and signals appeared more often in EVs. Of all patients, 40% and 34% showed and signals, respectively, in CTCs, which was significantly associated with disease progression ( = 0.007). Whereas signals in CTCs significantly correlated with response ( = 0.046), signals in EVs indicated therapy failure ( = 0.011). The presence of signals in EVs seemed to be a marker for the indication of unsuccessful treatment of bone metastasis. These results emphasize the potential of CTCs and EVs for therapy monitoring and the need for critical evaluation of the implementation of any liquid biopsy in clinical practice.