Effect of leukapheresis on efficient CTC enrichment for comprehensive molecular characterization and clinical diagnostics

e21020 Background: Circulating tumor cells (CTCs) are promising biomarkers for diagnosis and systemic therapy. However, their infrequent detection rates limit currently their clinical use. Here we tested whether leukapheresis could be a suitable method to increase CTC yields and detection rates by increasing dramatically the analyzed blood volume. Methods: We screened 3x106 PBMNCs of 48 historical leukapheresis products harvested from 24 breast cancer patients in the setting of high-dose chemotherapy and from a non-cancer control group (n=10), respectively, with a standard immuno-assay using an anti-cytokeratin antibody (A45/BB3) to detect CTCs. Detected CTCs were isolated, their genomic DNA amplified, and the whole genome screened for chromosomal aberrations using comparative genomic hybridization (CGH) (n=48). To validate the CTC detection frequencies in leukapheresis products, we initiated a prospective pilot-study and performed leukapheresis in 13 cancer patients (breast and pancreatic cancer). 1 mL of the leukapheresis product (total volume: up to 150 ml) was analyzed using the CellSearch® system as well as 7.5 ml peripheral blood taken from the same patients. Results: 44/48 (91.7%) of leukapheresis samples contained CTCs with a median count of 3.0 in 3x106 PBMNC (range: 1-35 CTCs). None of the 10 analyzed healthy controls displayed CTCs. We successfully performed single cell CGH of 48 CTCs from 19 patients revealing aberrant CGH profiles in 56% with gains and losses typical for breast cancer. Interestingly, CTCs with high aberration numbers were associated with early metastatic relapse. The validation study using CellSearch® in 13 cancer patients demonstrated in leukapheresis products significantly higher CTC detection frequencies (13/13 vs. 5/13) and CTC numbers (median: 13, range: 1-51 vs. median 0, range: 0-7; p