Table 1.

Comparison of various “liquid biopsy” tests in non-small cell lung cancer

Type of “liquid biopsy”	Source	Methods of isolation	FDA-approved assays	Sensitivity of available assays	Specificity of available assays
Circulating tumor cells (CTCs)	Shed from primary tumors	Epithelial cell adhesion molecule (EpCAM)-independent or EpCAM-dependent assays	None yet approved	23–90% (detection rates)	N/A
Cell-free nucleic acid (cfNA)	Passive release from apoptosis/necrosis or active secretion; from both tumor and healthy cells	Many extraction kits with further enrichment using digital droplet PCR (ddPCR) or next generation sequencing (NGS)	cobas EGFR Mutation Test v2‡ (assesses for EGFR sensitizing mutations)	15–100%	89–100%
Extracellular vesicles (EVs)	Membranous lipid structures secreted by both tumor and healthy cells	Differential ultra-centrifugation (gold standard); assays not needing special equipment to isolate EVs based on their physical properties are also available	None yet approved	N/A (technology still being developed)	N/A (technology still being developed)
Urine cfNA	cfNA that is either filtered by the kidney or from cells that came into direct contact with urine	Extraction kits with further enrichment through ddPCR or NGS as in plasma cfNA	None yet approved	81–100% (Concordance rates)	N/A

^†Myriad Genetics

^‡Roche