Circulating tumor cells in metastatic breast cancer: Are they a strong and independent predictor of poor progression-free and overall survival?

1090 Background: Circulating tumor cells (CTCs) are detected in 30–60% of patients with metastatic breast cancer (MBC). The aim of this prospective multi-center study was to evaluate the impact of CTCs on progression free survival (PFS) and overall survival (OS) in a large cohort of 486 patients with progressive metastatic disease. Methods: CTC levels were determined for 486 patients at nine German University Breast Cancer Centers between 12/2007 and 06/2011. Samples of 7.5 ml blood were taken before initiation of a new line of therapy and CTCs were enumerated using the CellSearch System (Veridex LLC, Raritan, NJ, USA). CTC status (≥ 5 CTCs vs. < 5 CTCs per 7.5 ml blood) was assessed as a prognostic factor for PFS and OS using univariate (log-rank test) and multivariate (Cox regression model) statistical methods. Results: CTCs were detected in 205/486 (42%) patients. The median CTC count was 2 (range 0–6380) per 7.5 ml blood. The presence of ≥ 5 CTCs/7.5 ml blood did not correlate with any of the established clinicopathological factors except estrogen receptor status (p = 0.038). PFS and OS were both significantly shorter in patients with ≥ 5 CTCs/7.5 ml than in those with < 5 CTCs/7.5 ml blood. PFS was 5.0 [95% CI 4.1–5.8] months vs.7.6 [95% CI 5.9–9.3] months, p < 0.001; and OS was 15.0 [95% CI 13.5–16.5] months vs. 18.3 [95% CI 17.4–19.2] months, p < 0.001. In the multivariate analysis considering all clinicopathological factors and the CTC status, independent predictors of reduced OS and PFS were site of metastasis (visceral vs. bone), number of metastatic sites (multiple sites vs. one site), and CTC status. Conclusions: The presence of ≥ 5 CTCs/7.5 ml blood is a strong and independent predictor of poor PFS and OS in patients with MBC.