The Problem with using size and deformability as the criteria to isolate Circulating tumor cells (CTC)

• “The size range of different tumor cells is highly variable and does overlap with that of normal blood cells” [1]
• However, CTC may not be always .8 mm making the sensitivity of this assay questionable. [2]
• However, these methods suffer from low cell viability resulting from potential damage incurred as the cells pass through narrow filter pores, which renders the use of microfilters less compatible for live cell interrogations (e.g., cell suspensions were partially fixed before being passed through a membrane micro-filter72) [3]
• Due to the force (centrifugation or pumping) many of the cells are destroyed (viability decreased upto 70% of CTCs). Many CTCs will pass through the narrow passage due to EMT as they become more flexible and bendable. Many blood cells still remain that produce contamination and noise. Hence it is not considered to be the best method[4]
• isolation of circulating tumor cells (CTCs) by size exclusion can yield poor purity and low recovery rates, due to large variations in size of CTCs, which may overlap with leukocytes and render size-based filtration methods unreliable [5].
• Physical size separations could potentially undercount a small portion of CTCs  [6]
• Our observations support the relationship between tumor-initiating capacity and cell deformability, and demonstrate that tumor-initiating cells are less differentiated in terms of cell biomechanics (from normal cells). Thus deformability-based techniques may miss tumor initiating cells. [7]
• Metastatic cells are more deformable and pass through capillaries faster than non metastatic cells [8]

[1] Current Opinion in Genetics & Development 2010, 20:96–99

[2] British Medical Bulletin 2010; 1–16

[3] Lab Chip, 2012, 12, 1753

[4] www.rgccusa.com/index.php/download_file/view/38/1/

[5] Anal Chem. 2012 Sep 4;84(17):7400-7

[6] Lab Chip, 2012,12, 4388-4396
[7] PNAS November 13, 2012 vol. 109no. 46 18707-18712
[8] http://www.pnas.org/content/early/2013/04/19/1218806110