Current role of liquid biopsy in metastatic breast cancer and future perspectives

The possibility of tumor dissemination via the blood systemhas been known for many years. Circulating tumor cells (CTCs) and circulating tumor DNA (ctDNA) are detectable in the peripheral blood of patients with early as well as metastatic breast cancer. The prognostic relevance of these biomarkers has already been described. Repeated blood sampling along the course of disease enables CTCs and ctDNA to be monitored in terms of a regular "liquid biopsy". Combined with an additional molecular analysis, this might be helpful in gaining information about tumor characteristics, tumor heterogeneity, and possible therapy resistance based on these factors, without the necessity of an invasive core biopsy. The assessment of molecular attributesmay be indispensable for obtaining an optimized and personalized therapy aimed at extended survival and/or improved quality of life. This review summarizes current knowledge and describes possible future perspectives for the treatment of metastasized breast cancer.