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

Background: This study aimed to evaluate the prognostic significance of circulating tumor cells (CTCs) detection in advanced breast cancer patients.
Patients and Methods: 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.
Results: 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).
Conclusion: 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.