Acquisition of HER2/neu over-expression on circulating tumor cells (CTCs) in patients (pts) with advanced breast cancer (ABC) during chemotherapy

11017 Background: CTCs can be detected and isolated from the peripheral blood of women with ABC. In addition to enumeration, an exciting area of research involves the phenotyping and expression profiling of CTCs. In this regard, assessing the presence of target antigens on CTCs could be considered as a real-time biopsy allowing the possibility to evaluate the change in tumour phenotype during the clinical course of the disease. HER2/neu status of tumor cells detected in metastatic sites may differ from the original primary tumor in about 5–20% of cases. Furthermore, there is evidence that nearly one third of pts whose primary tumors were HER2/neu negative might have amplified HER2/neu on CTCs. Methods: We collected 7.5 ml blood samples from each of 40 pts with ABC. CTCs were isolated with the CellSearch System® (Immunicon Co.) by means of immunomagnetic separation, using ferrofluid nanoparticles binding anti-epithelial cell adhesion molecules (EpCAM), and fluorescently stained with Epithelial Cell Kit®. C...