Clinical implication of liquid biopsy in oncology

Abstract

Highly sensitive methods have been developed to obtain circulating tumor cells (CTCs) from the peripheral blood. CTC enumeration and characterization with certified systems provides reliable information on prognosis and may serve as liquid biopsy to identify therapeutic targets or mechanisms of resistance on metastatic cells. Metastatic cells might have unique characteristics that can differ from the bulk of cancer cells in the primary tumor currently used for stratification of patients to systemic therapy. Moreover, monitoring of CTCs before, during and after systemic therapy (e.g., chemotherapy, hormonal therapy, antibody therapy) might provide unique information for the future clinical management of the individual cancer patient and might serve as surrogate marker for response to therapy. In the context of recent success in antibody-mediated blockade of immune checkpoint control molecules, expression of the PD-L1 on CTCs might be of interest as potential predictive marker. Functional characterization using specialized in vitro and in vivo test systems has started, which might provide novel insights into the biology of CTCs and serve as models for drug testing.