Table 1. Comparison of circulating tumor cells and circulating-tumor DNA platforms.

	Advantages	Disadvantages
Circulating tumor DNA	ctDNA is easier to isolate; long-term storage for subsequent analysis feasible; analysis with real-time PCR or digital PCR for known point mutations and very low allele fractions, or targeted deep sequencing	Limited pre-analytical/analytical assay validation with some platforms; short fragment DNA from necrotic or apoptotic cancer cells; limited possibilities for downstream analysis (DNA only)
Circulating tumor cells	Evaluation of intact cancer cells is invaluable for downstream analyses allowing interrogation of the DNA, RNA or at the protein level; some CTC live cell isolation platforms can allow ex-vivo expansion and creating in-vitro and patient-derived xenograft models to investigate drug susceptibility and allow deeper understanding the molecular profiles; single-cell analysis technologies allow for new insights into the genetic make-up of CTCs	Complex detection and enrichment steps required and often require sophisticated technologies; low CTC numbers in non-metastatic and low disease burden settings