Abstract
Breast cancer is the most frequent neoplastic disease in populations of developed countries. It will affect 1 of every 6 or 7 women during their lifetime. The disease eventually evolves to a metastatic stage, and currently appears to be not curable at that stage. Thus, understanding mechanisms that result in the establishment of tumor at sites distant from the primary location is of the utmost importance. Equally important is the definition of a metastatic state, especially in regard to the detection of micrometastases. Finally, the presence of circulating tumor cells in the peripheral blood of patients who undergo progenitor mobilization, collection and reinfusion may be of clinical significance in the setting of high-dose chemotherapy for breast cancer.