Abstract 4154: Multi-parameter molecular characterization of circulating tumor cells (CTC): Development of a CTC-endocrine therapy index (CTC-ETI)

Abstract Introduction. CTC can be reproducibly and reliably enumerated using a commercially-available, automated immunomagnetic system (CellSearch®; Veridex LLC). High levels of CTC predict rapid progression in patients with metastatic breast cancer (MBC). Only ∼ 50% of patients with estrogen receptor (ER) positive MBC benefit from endocrine therapy (ET). Patients with endocrine-refractory MBC are better palliated with chemotherapy. We have developed a multi-parameter assay using CellSearch® that may identify patients with ER positive MBC who are unlikely to benefit from ET and may be better served with chemotherapy. Methods. CellSearch® has four fluorescence channels. Three of these are used to distinguish CTC from WBC (DAPI, anti-cytokeratin, anti-CD45). The 4th “empty” channel was used to measure ER, Bcl-2, HER2, and Ki67 expression with antigen-specific fluorescent-labeled antibodies. These four markers were chosen because of their associations with sensitivity (ER, Bcl-2) or resistance (HER2, Ki-67) to ET. Cultured human breast cancer cells (MCF-7: ER +, BCL-2 +, HER2 -, Ki67 +; MDA-MB-231: ER -, Bcl-2 -, HER2 -, Ki67 +; BT-474: ER +, Bcl-2 +, HER2 +, Ki67 +) were spiked into 7.5 ml human whole blood from normal donors and separated and characterized using the CXC CellSearch® kit. Results. Each cell line stained appropriately for the respective markers, with appropriate negative controls, although staining was heterogeneous, even within a single cell line. Using these preliminary data, we have developed a CTC-ETI in which scores are assigned to the individual categories consisting of cell counts coupled with the relative percent and degree of cell positivity of each marker. We predict that lower scores (low or no CTC, or CTC with high % and intensity of ER and Bcl-2; low HER2 and Ki-67) will be associated with favorable response to ET. Conclusions. CellSearch® can be used to measure the expression of 4 clinically useful and proven breast cancer biomarkers. A clinical trial is underway at U. Michigan to permit calculation of CTC-ETI in patients with MBC, which will lead to a prospective trial to determine if high CTC-ETI predicts resistance and rapid progression on ET. Supported by Veridex, LLC, Fashion Footwear Charitable Foundation of New York/QVC Presents Shoes on Sale ™ (DFH), Associazione Sandro Pitigliani and by a studentship from FIRC (CP) Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4154. doi:10.1158/1538-7445.AM2011-4154