Variation of circulating tumor cell levels during treatment of metastatic breast cancer: prognostic and therapeutic implications.

This study aimed to evaluate the prognostic significance of circulating tumor cells (CTCs) detection in advanced breast cancer patients. We tested 80 patients for CTC levels before starting a new treatment and after 4, 8 weeks, at the first clinical evaluation and every 2 months thereafter. CTCs were detected using the CellSearch System. Forty-nine patients had >or=5 CTCs at baseline. At the multivariate analysis, baseline number of CTCs was significantly associated with progression-free survival [hazard ratio (HR) 2.5; 95% confidence interval (CI) 1.2-5.4]. The risk of progression for patients with CTCs >or=5 at last available blood draw was five times the risk of patients with 0-4 CTCs at the same time point (HR 5.3; 95% CI 2.8-10.4). Patients with rising or persistent >or=5 CTCs at last available blood draw showed a statistically significant higher risk of progression with respect to patients with <5 CTCs at both blood draws (HR 6.4; 95% CI 2.8-14.6). CTCs basal value is a predictive indicator of prognosis and changes in CTC levels during therapy may indicate a clinical response. Testing CTC levels during targeted treatments might substitute other measurement parameters for response evaluation.