Previously, the human high mobility group protein member HMGA2 mRNA was reported to be expressed in peripheral blood of patients with breast cancer, but not in healthy individuals. Expression of HMGA2 in blood was suggested to be an independent indicator of poor prognosis in metastatic breast cancer. These very promising findings propose HMGA2 as a potential marker for the detection of circulating tumor cells in peripheral blood. Therefore, we analyzed peripheral blood specimens from healthy controls and patients with breast tumors for HMGA2 expression using TaqMan real-time RT-PCR to test if HMGA2 is a suitable marker for the early detection of breast cancer and monitoring therapy response in peripheral blood. Furthermore, we examined the possible involvement of HMGA2 expression in invasion investigated by an in vitro invasion assay using established breast cell lines. HMGA2 expression was detected in peripheral blood of breast cancer patients as well as of healthy individuals. No significant association of HMGA2 expression with any clinical or histopathological data was apparent. However, there was a significant correlation of HMGA2 expression in invasive and non invasive breast cell lines (p=0.0056). Although, HMGA2 obviously contributes to invasion it is not a specific marker for the detection of circulating tumor cells in peripheral blood.