Circulating tumor cells and circulating tumor DNA

Background Classic tissue biopsies or surgical resections are invasive procedures that capture only a single snapshot in the evolution of cancer. In contrast, a blood-based test or “liquid biopsy” has the potential to characterize the evolution of a solid tumor in real time by extracting molecular information from circulating tumor cells (CTCs), circulating tumor DNA (ctDNA), circulating miRNAs, or exosomes. Molecular characterization of CTCs and ctDNA holds considerable promise for the identification of therapeutic targets and resistance mechanisms and for real-time monitoring of the efficacy of systemic therapies. The major potential advantage of CTC and ctDNA analysis is that they are minimally invasive and can be serially repeated. Content This overview is focused on the diagnostic, prognostic, and predictive value of CTCs and ctDNA in cancer patients. It includes key studies in different cancers and incorporates the latest advances in genome-wide analysis of ctDNA. Focus includes (1) CTC isolation, enumeration, and detection systems; (2) clinical applications of CTC; (3) different forms of ctDNA; (4) ctDNA isolation and detection systems; (5) clinical applications of ctDNA; (6) quality control and standardization of liquid biopsy assays; (7) the potential of liquid biopsy in the clinical laboratory; and (8) the potential of the molecular characterization of CTCs and ctDNA analysis as a liquid biopsy for individualized therapy. With respect to the clinical laboratory, the development of targeted molecular assays as companion diagnostics, for disease monitoring, and even for early cancer detection are all potential possibilities at various stages of development.