Table 2.

Schematic representation of the main CTC label-independent isolation techniques.

	CTC Isolation Technique	Method	Tumor Type	Clinical Objective	Major Advantages	Major Disadvantages	Ref.
Label-Independent Isolation	Filtration	Filter-based isolation and enrichment	Breast Melanoma Liver Lung Pancreatic	Diagnosis Prognosis Treatment	Very Fast High efficiency	Low purity Filter clogging	[31]
	Microfluidics (no antibodies)	Microscale separation of CTCs according to their dimensions and deformability	Ovarian	Diagnosis	High sensitivity High cell viability	Small sample vol.	[32]
	Density gradient separation	Centrifugal separation of CTCs from blood cells based on their varying densities	Breast Gastric Pancreatic NSCLC	Prognosis	Inexpensive Efficient process	Low purity Loss of cells	[33]
	Imaging	Utilization of a fiber optic array laser scanning system for visual identification of CTCs	Breast Prostate Liver	Diagnosis Prognosis Treatment	High resolution Enumeration of CTCs	Not very precise Difficult sample processing Loss of cells	[34]
Label-Independent Isolation	Dielectrophoresis	Detection of CTCs with application of non-uniform electric field	Breast	Prognosis	High recovery rate High efficiency High cell viability Detection accuracy	Limited volume Low purity Very elaborate procedure	[35]
	Inertial focusing	CTC separation using fluid inertia at high flow rates and inertial focusing	Breast Lung	Diagnosis Prognosis Treatment	High cell viability High precision Speed of processes	Deformation of cells	[36,37]

Abbreviations: NSCLC: non-small-cell lung cancer; CTC: circulating tumor cell.