[gdpawel]

Two points here: prognostication and drug selection.

The number of cells discovered in the CTC technique has turned out to be a good prognosticator of how well treatments are working. This is where the technique works well and I am very interested in CTCs, because monitoring CTCs could be utilized for confirmation after the patients is administered either empiric or assay-directed most beneficial therapeutic agents. But CTCs really aren't useful with respect to drug selection.

CTCs are of great promise for molecular profiling, where the endpoints (point of termination) are gene expression, examining a single process (pathway) within the cell or a relatively small number of processes (pathways), to test for "theoretical" candidates for targeted therapy.

But not for functional profiling, where the endpoints are expression of cell death, both tumor cell death and tumor associated endothelial (capillary) cell death, and examines not only for the presence of the molecular profile but also for their functionality, for their interaction with other genes, proteins and processes occuring within the cell, and for their response to anti-cancer drugs.

The core understanding is the cell, composed of hundreds of complex molecules that regulate the pathways necessary for vital cellular functions. If a targeted drug could perturb any of these pathways, it is important to examine the effects of drug combinations within the context of the cell. Both genomics and proeomics can identify potential therapeutic targets, but these targets require the determination of cellular endpoints.

Cell culture work is in three dimensional (3D) tumor cell clusters. Three dimensional clusters of cells do not circulate. It is useful in analyzing circulating endothelial cells (the tumor associated blood vessel cells).

Another problem with CTCs is in isolating (even by size) and analyzing single cancer cells. The supposition is that common cancers can be detected and cured through analysis at a genetic level of a small number of cells or even a single wayward cell.

Again, CTCs are free-floating cancer cells that can remain in isolation from a tumor for over twenty years. What is the relationship of such long-lasting cells to the tumor cells that needed to be attacked through tested substances?

And in regards to some molecular tests utilizing living cells, generally of individual cancer cells in suspension, sometimes derived from tumors and sometimes derived from CTCs, this was tried with the old human clonogenic assay, which had been discredited long ago.

One testing approach to find CTCs actually can miscount non tumor epithelial cells as tumor cells. And also highly invasive cells may not be detected if you are looking for epithelial antigens because the CTC also goes through a phase called 'epithelial to mesenchymal transition' - you will miss locating that tumor cell if you are targeting the antigen.

The key is to look for the tumor cell and not something else that 'hangs with the tumor cell.'"