Circulating Tumor Cells: The Importance of Single Cell Analysis

Cancer cells that have shed from the primary tumor are able to invade into surrounding tissues, to intravasate into the bloodstream to become circulating tumor cells (CTCs), at least one part of that cells will be able to generate distant metastases. The discovery of CTCs has improved the study of cancer disease as it represents a non invasive biopsy that can be used as prognostic and prediction biomarkers. Tumour heterogeneity is a concept related to differences in tumor cells within the same tumor or between tumours in terms of genetic and phenotypic profiles, such as morphology, metabolic activity, proliferation rate, migration and metastatic abilities. Characterization of heterogeneity among CTCs at the single cell level may be useful to better understand the causes and progression of disease and for an accurate selection of molecular prognostic/prediction markers. In this chapter we aimed to describe methods for CTC enrichment and isolation as well as current methodologies for single cell analysis at different levels, including RNA, DNA, protein and epigenetic events. Finally we wanted to stress clinical and biological importance of single CTC analysis by reviewing some studies carried out in different cancer subtypes.