Abstract
Disseminated tumor cells (DTC) are routinely detected in bone marrow (BM) in 30-40 % of primary breast cancer patients. Positive BM status at the time of diagnosis as well as DTC persistence after therapy are strong independent prognostic factors. Since repeated BM aspirations are not well tolerated, detection of single tumor cells in peripheral blood (circulating tumor cells; CTC) have become of interest in recent years. CTC are found in 10-80 % breast cancer patients. Variability can be explained by stage of the disease and detection method. Emerging data have shown CTC to be of prognostic relevance for both, patients with primary and metastatic disease. The assessment of CTC in blood may become an important biomarker for prognostication and therapy monitoring. Determination of their molecular characteristics will enable specific targeting of minimal residual as well as metastatic disease. This review summarizes recent research and future perspectives.