Liquid Biopsy-A new diagnostic concept in oncology

The analysis of tumor cells circulating in the blood or of products of tumor cells circulating in other body fluids has gained increasing attention in recent years and is summarized under the term liquid biopsy (LB). LB includes the analysis of circulating tumor cells, cell-free circulating tumor-associated nucleic acids, extracellular vesicles, proteins, or other products that are released into the peripheral bloodstream by the primary or metastatic tumor. For a huge number of solid tumor entities, LB has already been successfully applied in preclinical and clinical studies for the detection, risk stratification, treatment monitoring and relapse detection. LB provides valuable real-time information on tumor cell development, therapeutic targets, and mechanisms of therapy resistance using a non-invasive peripheral blood test. In this article, the most important LB analytes and the current state of research are presented. In addition, the remaining obstacles and the diverse efforts to implement LB in clinical routine are critically discussed.