Table 1. Techniques used to identify ctDNA and their advantages and limitations.

Techniques used to identify ctDNA	Description	Sensitivity	Advantages	Limitations	Ref.
ctDNA, circulating tumor DNA; WGS, whole genome sequencing; WES, whole-exome sequencing; PCR, polymerase chain reaction; ddPCR, droplet digital PCR; NGS, next-generation sequencing; CAPP-Seq, cancer personalized profiling by deep sequencing; TS, target-panel sequencing; SNV, single nucleotide variation.
WGS	Target whole genome	Moderate to low	Detects innovative mutations, has multiplex capabilities and high throughput diagnosis	Costly and requires bioinformatics analysis support	(22,23)
WES	Target whole genome	Moderate to low	Detects innovative mutations, has multiplex capabilities and high throughput diagnosis	Costly and requires bioinformatics analysis support	(22,23)
Digital PCR	Known and specific regions	Relatively high	Cheaper comparatively	Low throughput and does not detect innovative targets	(22,23)
ddPCR	Known and specific regions	High	Rapid and sensitive	Low throughput and does not detect innovative targets	(22,23)
Allele-specific PCR	Amplify rare mutant DNA sequences	Lower	Easy to use, budget friendly	detect only small number of genomic sequences in sample	(23)
NGS-amplicon	Deep sequencing of entire genome	High (some methods)	Less expensive than other NGS methods	Less extensive, cannot detect rearrangements without customizing assay	(23)
CAPP-Seq	Target only hybrid capture	High	Detects rearrangements and highly sensitive for SNV	Less extensive than WGS or WES	(23)
iDES enhanced CAPP-Seq	Target hybrid capture and integrated error suppression	High	Has flexibility and coverage, highly reliable to detect all aberrations in a single assay	Less extensive than WGS or WES	(23)
TS	Panel-size targeting	Relatively high	Detects innovative mutations, has multiplex capabilities and high throughput diagnosis	Costly and requires bioinformatics analysis support	(22,23)