Detection of circulating tumour cells in colorectal cancer: Emerging techniques and clinical implications

Table 1 Techniques for circulating tumour cell isolation, markers, and their limitations

No.	Name	Property	Markers	Limitations	Ref.
1	CellSearch	Isolation by anti-EpCAM antibody coated immunomagnetic beads	EpCAM, CKs, CD45, DAPI	Only suitable for cancer of epithelial origin but not for that undergoing the EMT	[48]
				Cells are not viable after detection
2	AdnaTest	Separation by way of anti-EpCAM and anti-MUC1 antibody coated immunomagnetic beads	EpCAM, MUC1, mucin-1, HER2	Possible false-positive finding due to expression of a selection marker being present in other cells other than CTCs	[49]
				Cells are not viable after detection
3	MACS	Immunomagnetic CTC enrichment by antibodies against cell surface markers	CK19, EpCAM, Her-2, MUC-1 CK7, CK8, CK18, CK19	Lengthy processing time and low sensitivity	[50]
4	MagSweeper (Illumina Inc)	Immunomagnetic isolation of CTC by antibodies against EpCAM and cellsurface markers	EpCAM, CD45, DAPI	Less sensitive during the early stages of tumour development	[51]
		Captured cells are viable with intact RNA
5	CTC Chip	Utilizes bifurcating traps to capture CTCs, release via flow reversal	EpCAM, CKs, CD45, DAPI	Identification of CTCs is lower than other methods	[52]
6	GEM chip	Geometrically enhanced mixing chip structure that allows enhanced capture of CTC on antibody coated surfaces	EpCAM, DAPI, CD45, cytokeratin	Low sensitivity	[53]
7	Onco Quick (Greiner BioOne, Frickenhausen, Germany)	Separation of erythrocytes and some leukocytes from CTC. High sensitivity, Quantification	CCNE2, DKFZp762E1312, EMP2	No morphology confirmation; not really capture CTCs	[54]
8	ISET (Rarecells Diagnostics)	Rapid processing; non-antigen dependent; Filter based approach	CKs, EGFR, VE-cadherin, Ki67	Size-dependent, manual processing	[55]
9	EPISPOT	Removes leukocytes via CD45 depletion	CD45, CK19, mucin-1, cathepsin-D	Problem arises when antigen levels are lower or binding efficiency is reduced	[56]
		Can detect viable CTCs
10	Ficoll + RT-PCR	Separation of CTC based on size dependent enrichment. High Sensitivity	CK-19, HER2, h-MAM, CEA, maspin, GABA A, B726P	No morphology confirmation	[57]
11	Cyttel Method	Negative immune-magnetic selection of WBC (CD45 antibody)-High detection rate	CD45	-	[58]
12	MetaCell	Size-based enrichment and separation for viable CTCs	CK-18, -19, -20, CK-7, EPCAM, MUC1, HER2, EGFR	Lengthy processing time	[59]

MACS: Magnetic-activated Cell Sorting; CTC: Circulating tumour cell; RT-PCR: Real-time polymerase chain reaction.