Circulating cancer cells.

Circulating tumour cells (CTCs) can be detected in the blood of many patients with different types of early or advanced cancer using antibody-based assays or molecular methods. In many studies the detection and quantification of CTCs has been linked to unfavourable prognosis. CTC detection offers the opportunity for individualized risk assessment beyond that determined by TNM staging. However, discordant results have been reported when different methodologies for CTC detection were used. Therefore, well-standardized detection methods cross-validated between different laboratories are still needed. CTCs are a heterogeneous population of cells with biological characteristics often different from those of their respective primary tumour cells. Pilot studies have shown that phenotyping of CTCs could be used to predict response to targeted therapies. In the era of biological therapeutics, CTC characterization at different time points during the course of disease may provide useful predictive information for the selection of the most appropriate treatment. Therefore, in the future, CTC detection and characterization might become a valuable tool to refine prognosis and serve as a real-time tumour biopsy for individually tailored cancer therapy. Prospective randomized studies are warranted to evaluate the utility of assessing and monitoring CTCs and modifying accordingly treatment strategies in order to improve the clinical outcome of cancer patients.