Table 2  Prognostic significance of circulating tumour cells in breast cancer: the most important trials.

Trial	Number of patients	Stage	Positivity rate n (%)	Assay	Correlation with prognosis
1 defined as ≥ 1 CTC per 7.5 ml 2 defined as ≥ 5 CTCs per 7.5 ml Acronyms: BCSS – breast cancer-specific survival; DDFS – distant disease-free survival; DFS – disease-free survival; LRRFS – loco-regional recurrence-free survival; OS – overall survival; pCR – pathological complete response
Janni et al. 19	3173	Stage I – III	641 (20%) 1	CellSearch	DFS, DDFS, BCSS, OS
Cristofanilli et al. 20	2436	Stage IV	1099 (45.1%) 2	CellSearch	OS
Bidard et al. 21	1574	Stage I – III before neoadjuvant chemotherapy	398 (25.2%) 1	CellSearch	OS, DDFS, LRRFS; pCR rate higher in case of CTC positivity (24.2% vs. 17.4%)