Circulating tumor cells, disease progression, and survival in metastatic breast cancer.

Metastatic breast cancer (MBC) is considered incurable; therefore, palliative treatment is the only option. The biologic heterogeneity of the disease is reflected in its somewhat unpredictable clinical behavior. The presence of circulating tumor cells (CTCs) in patients with MBC about to start a new line of treatment has been shown to predict progression-free and overall survival. This prognostic value is independent of the line of therapy (eg, first or second line). Moreover, a multivariate analysis has shown the prognostic value of CTCs to be superior to that of site of metastasis, type of therapy, and length of time to recurrence after definitive primary surgery. These data suggest that the presence of CTCs may be used to modify the staging system for advanced disease. Larger studies are needed to confirm these data and evaluate the use of CTC detection in monitoring treatment and furthering our understanding of breast cancer biology when combined with other diagnostic technologies.