Table 2.

The Summary of different Circulating Tumor Cell isolation methods currently used in research.

Isolation method	Mode of action	Advantages	Disadvantages	Examples
FDA approved (clinical trials)	EpCAM positive based selection	Has become the “gold standard” for validation of CTCs with an epithelial phenotype. High reproducibility. High specificity. FDA-approved method.	CTCs can undergo EMT which may result in reduced expression of epithelial markers, leading to loss of effective capturing of cells with mesenchymal characteristics following EMT.	Cellsearch (Menarini Silicon Biosystems, Italy)
Positive Immunoselection	EpCAM positive based selection	Ability to process larger volumes of blood for the capture of higher numbers of CTCs.	As above	GILUPI CellCollector (GILUPI Nanomedizin) (55) Ephesia CTC-chip (56)
Negative Immunoselection	Depletion of Leukocytes by CD45 Antibodies	Has the ability to avoid false-negative results or loss of CTCs due to phenotypic heterogeneity.	CTCs are often contaminated with remaining blood cells resulting in low purity.	RosetteSep (StemCell Technologies, Canada) (57) EPISPOT (Epithelial Immunospot Assay; France) (58)
Size-Based Filtration	Cells are separated using filtration to remove smaller cells in the blood (e.g., White blood cells)	Simple process.	Will exclude small sized CTCs, filter clogging and limited blood processing/filter are potential problems.	Screen Cell (France) MetaCell (Ostrava, Czech Republic) Isolation by Size of Epithelial Tumor cells (ISET) (Rarecells Diagnostics, Paris, France) (59) Microdevice- Cote's group (60) Parsortix (61) Microcavity array System (MCA) (62)
Density-based Filtration	Cells are separated based on different densities after centrifugation.	Cells separated into distinct layers	CTC size and density not uniform CTCs may get lost in plasma or by formation of CTC aggregates Poor sensitivity	Ficoll Lymphoprep (Stem Cell Technologies, Vancouver, Canada) (63) OncoQuick (VWR, Radnor, PA) Accucyte (64)
Microfluidics	Cells are separated based on their biological or physical properties	Higher sensitivity, purity, lower cost, reduced sample size, short processing time, compatibility with downstream assays	Small CTCs of comparable size to WBCs would typically be missed Cell morphology may be altered due to high shear stress during microfiltration	Isoflux (Fluxion Biosciences) (65) CTC iChip (Nagrath) (66, 67) ClearCell FX/Spiral Microfluidics (ClearbridgeBiomedics, Singapore) (54) Herringbone Chip (Nagrath) (31)
Immunomagnetic	Enriches target cells and eliminates cells that are not bound to magnetic particles	Isolate cells easily accessible	Nonspecific contamination can be from adsorption of background cells to the capturing device	MagSweeper (Jeffrey Lab, Stanford, CA) (68) AdnaTest (Qiagen, Hannover, Germany) (69) Magnetic Activated Cell Sorting System (Miltenyi Biotec, Germany) (70, 71) MagSifter (72)
Electrophoresis	Cells are separated based on their electrical signature using an electric field	Single-cell-level precision High accuracy and precision	Process can be slow resulting in low sample throughput	DEPArray (Silicon Biosystems)
Enrichment free platforms	Cells are detected through imaging platforms with no need for enrichment due to advancements in fluorescence imaging	Multiple analysis parameters can be used to identify and characterize specific populations of interest High specificity and sensitivity. No need for enrichment.	Potential for high speed imaging to reduce resolution thereby worsening accuracy.	HD-CTC (EPIC Sciences, California) (44, 73, 74) FastCell (SRI Biosciences) (75) CytoTrack (Denmark) (76, 77)