Advantages and limitations of CTCs vs. cfDNA
| Advantages | Limitations | |
| CTC | Allows in depth assessment of viable metastatic tumor cells, DNA, RNA, and protein; may reflect mechanisms of resistance; may reflect treatment efficacy; allows functionally analysis (in vitro/in vivo testing) | Few and fragile; requires sophisticated isolation techniques; EMT may cause false negative results; tumor heterogeneity within CTCs; unclear which CTCs cause metastases |
| Cell free cfDNA | May reflect mechanisms of resistance; may reflect treatment efficacy; sensitive biomarker; available from other sources: urine, plasma, ascitic fluid | Present in inflammatory states and aging (not cancer specific); contamination with DNA from lysed cells; unclear if clinically relevant given being released from dying tumor cells; predetermined somatic alterations need to be identified; does not permit single cell analysis |