Table 2.

Advantages and drawbacks of different cfDNA assays.

Assay	Advantages	Drawbacks
Mutations	Cancer-specific Correlates well with treatment response Can detect (well-documented) clinically actionable mutations Can detect/identify therapy-resistant mutations	Subclonal mutations might not reflect tumor response accurately Mutational prevalence low for certain genes Prior knowledge on mutation-status needed for targeted approaches Need for germline analysis to exclude identification of non-cancer related mutations from clonal haematopoiesis
DNA Methylation	Disease-specific Correlates well with tumor response Robust alteration with high penetrance over course of disease Also measurable in early disease	Challenging on small amounts of cfDNA due to indirect detection
Copy number variations	Disease-specific Correlates well with tumor response Measurable in all patients of their respective cohorts	ctDNA fraction of 5–10 percent required for adequate detection
cfDNA concentration	Universally applicable to all patients Not limited to dedicated biomarkers/assays	Not disease-specific Limited correlation with tumor response Only applicable for monitoring