Figure 1.
Schematic representation of epithelial to mesenchymal transition (EMT), by which adherent epithelial cells are thought to acquire migratory cell fates, combined with the activation of proteases which compromise the integrity of the basement membrane (BM) and the extracellular matix (ECM), leading to intravasation of tumor cells into the bloodstream. The rare tumor cells that are present in the bloodstream, admixed with billions of normal blood cells, are defined as circulating tumor cells (CTC). A subset of CTCs are thought to extravasate at distal sites such as the lung, liver, bone and brain to establish metastatic lesions. Isolation, enumeration, and genetic and biomarker analysis of CTCs will provide insight into the biology of these putative metastatic precursors.