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 ≥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 (Cl) 1.2-5.4]. The risk of progression for patients with CTCs ≥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% Cl 2.8-10.4). Patients with rising or persistent >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% Cl 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.