Detection of Circulating Tumor Cells from Lung Cancer Patients in the Era of Targeted Therapy : Promises, Drawbacks and Pitfalls

Interest in biomarkers in the field of thoracic oncology is focused on the search for new robust tests for diagnosis (in particular for screening), prognosis and theragnosis. These biomarkers can be detected in tissues and/or cells, but also in biological fluids, mainly the blood. In this context, there is growing interest in the detection of circulating tumor cells (CTCs) in the blood of lung cancer patients since CTC identification, enumeration and characterization may have a direct impact on diagnosis, prognosis and theragnosis in the daily clinical practice. Many direct and indirect methods have been developed to detect and characterize CTCs in lung cancer patients. However, these different approaches still hold limitations and many of them have demonstrated unequal sensitivity and specificity. Indeed, these methods hold advantages but also certain disadvantages. Therefore, despite the promises, it is currently difficult and premature to apply this methodology to the routine care of lung cancer patients. This situation is the consequence of the analysis of the methodological approaches for the detection and characterization of CTCs and of the results published to date. Finally, the advent of targeted cancer therapies in thoracic oncology has stimulated considerable interest in non-invasive detection of genomic alterations in tumors over time through the analysis of CTCs, an approach that may help clinicians to optimize therapeutic strategies for lung cancer patients. We describe here the main methods for CTC detection, the advantages and limitations of these different approaches and the potential usefulness and value of CTC characterization in the field of thoracic oncology.