Table 1.

CTCs compared with tissue biopsy for biomarker assessment in metastatic breast cancer.

Tissue biopsy	CTC analysis: “Liquid biopsy”
Invasive, can infrequently cause significant morbidity	Minimally invasive
Monitoring treatment response/disease course with multiple biopsies generally not feasible	Monitoring treatment response/disease course with multiple samples relatively easily achieved
High likelihood of obtaining adequate tissue for analysis	CTCs can be hard to isolate or may be missed
Relatively cheap	Expensive
No specialised analytical equipment required	Specialised analytical equipment required
Can be performed at the vast majority of treatment centres	Can only be performed in certain laboratories equipped for CTC analysis
Interpretation of IHC (+/− FISH) assessment of tumor tissue standardised for ER, PgR, HER2	Further validation of best method for interpretation of HER2 or ER expression on CTCs needed
Clinical impact of treatment decisions based on tissue biopsy biomarker assessment uncertain	Clinical impact of treatment decisions based on CTC biomarker assessment uncertain