[Circulating tumor cells: a new challenge for laboratory medicine].

Circulating tumor cells (CTCs) can be detected in the blood of patients with nearly all types of locally and metastatic adenocarcinomas. CTCs are epithelial cells whose release from a primitive tumor or a metastatic localization may be mediated by an epithelial-mesenchymal transition. Their pro-metastatic potential is still under debate because their phenotypes may be very heterogeneous, even within the same patient (expression of stem-cells markers, apoptotic status...). They often exhibit discrepancies with the primitive tumor, especially concerning the molecular basis of sensitivity/resistance to targeted therapies (expression of HER2 and hormone receptors, mutations responsible for resistance to tyrosine-kinase inhibitors). Many methods for CTCs analysis are commercially available but very few are evaluated and standardized enough for clinical applications. The CellSearch device is the only one which is validated by the FDA for managing metastatic breast, prostate and colo-rectal cancer. It was used in most of the studies having demonstrated the prognostic and predictive value of CTCs in many tumoral localizations. Other studies are wanted to assess the ability of CTCs to optimize the therapeutic choices, to monitor drug efficiency in real-time as well as to become a surrogate end-point for evaluation of new therapies. Beyond CTCs enumeration, their biological features will need to be investigated.