Table 1.

ctDNA markers and detection methods.

Marker	Detection Chemistry	Advantages	Disadvantages
Point mutations	PCR/digital PCR	High sensitivity, quick, inexpensive	Few targets per analysis, only pre-identified mutations can be analyzed
Point mutations	Deep sequencing	High-throughput, detection of previously unknown mutations, tumor mutation burden (TMB) assessment	Moderate sensitivity, expensive, time-consuming
Copy number variations/trans-locations	PCR/digital PCR	High sensitivity, quick, inexpensive	Custom-designed assays needed, only pre-identified aberrations
Copy number variations/trans-locations	Low-pass whole-genome sequencing, targeted sequencing	Many and unknown targets	Low sensitivity, expensive, time-consuming
Hyper-methylation	Methylation-specific PCR	High sensitivity, low cost	Few targets per analysis, only pre-identified targets
Hyper-methylation	Bisulfite-sequencing	High-throughput, many targets	Low sensitivity for single markers, expensive