Table 1.

Methods utilized for analyzing CTCs and ctDNA

Methods		Mechanisms	Applications	Available products or markers
CTC isolation	Positive selection	Selection of epithelial adhesion molecule (EpCAM) positive cells [64,65]	Magnetic beads, columns, cartridges, magnetic nanoparticles (MNPs) [66,67], nanoclusters [68], immunomagnetic nanospheres (IMNs) [69,70], iron oxide magnetic particles [71], lipid microbubbles [72], and microchips [64]	CellSearch® system [73]
	Negative selection	Selection of CD45 negative cells [74,75]
	Physical isolation	Selection by the density [76], size [77,78], and deformability [79,80] by centrifugation [81], microporous filters [82], microfluidic technology [83], and adhesion-based methods [84]	The microfluid platform [85].
CTC analysis	Nucleic acid analysis		PCR, qRT-PCR, sequencing, array-comparative genomic hybridization [86]	KRAS, PIK3CA,and APC [86]
	Cell count	To count cell numbers and those that express certain markers.	Cytology, immunocytochemistry, flow cytometry
ctDNA analysis		To measure levels of ctDNA, and analyze sequences.	Real time PCR [88], droplet digital PCR (ddPCR) [89]; whole genome sequencing (WGS) [90], whole exome sequencing(WES) [91] and targeted region sequencing(TRS) [90,91]	Loss of heterozygosity, gene amplification, cancer-related viral sequences, hypermethylation in promoters, single-nucleotide mutations