Gene expression profiling of circulating tumor cells from breast cancer patients

Abstract

10769 Background: Levels of circulating tumor cells (CTC) have prognostic and predictive significance in metastatic breast cancer. However, since CTCs are extremely rare, little is known about the actual phenotype of these cells. In order to characterize these cells, we performed cDNA microarray analyses of CTC isolated from peripheral blood (PB) of breast cancer patients. Methods: CTCs were directly isolated via immunomagnetic enrichment (IE) followed by fluorescence activated cell sorting (FACS). Total RNA was then subjected to two rounds of linear amplification and hybridized to cDNA microarrays (∼40,000 cDNAs). Validation studies used spiked BT474 cells. Clinical studies used PB (10–20 ml) from patients with metastatic breast cancer. Results: Rare spiked tumor cells (e.g., 320 cells in 10 mL PB) were efficiently recovered by IE/FACS (50% yield). Expression profiles of recovered cells, both by TaqMan of a 37 gene panel as well as by global gene expression analysis, matched that of BT474 cells in culture. In contrast, these profiles were clearly distinct from that of normal PB, ruling out significant contamination from blood elements. In clinical studies, IE/FACS isolated small numbers of CTCs (10–1000 cells). Expression profiles of CTCs were compared to that of normal blood, primary breast tumors, and normal epithelial samples. Unsupervised hierarchical clustering revealed that CTC profiles were readily distinguished from that of normal blood and normal epithelium; and further analysis revealed that CTC cluster with a subset of primary breast tumors, particularly the basal-like phenotype. Candidate genes associated with the CTC phenotype were also identified. Conclusions: We have developed and validated a method to isolate rare CTCs and profile them via cDNA microarray analysis. In addition, our gene expression analyses of CTC further provide evidence to the malignant nature of these cells. Further expression profiling of CTC may yield insights into their phenotype, pathophysiology and potential as biomarkers. [Table: see text]