EVALUATION OF A NOVEL FLOW CYTOMETRY-BASED SYSTEM FOR THE DETECTION OF CIRCULATING TUMOR CELLS

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Abstract

Background

The presence and number of circulating tumor cells (CTCs) in the blood of solid tumor patients is predictive of clinical outcome. The CellSearch system is the only FDA-approved CTCs enumeration system; however, sensitivity issues due to EpCAM-based enrichment and limited capability for subsequent molecular analysis need to be addressed for the use of CTCs in the clinical setting. We have developed a flow cytometry-based CTCs detection system which allows enumeration and characterization of CTCs for multiple molecular analyses. Here we report the results of preclinical and clinical study with this novel flow cytometry-based CTCs detection system.

Materials and methods

Cancer cells were spiked into 4 ml of peripheral blood from healthy donors. Samples were negatively enriched using anti-CD45-coated magnetic beads to remove white blood cells followed by fixation and labeling with Alexa Fluor 700-CD45, PE-EpCAM and/or FITC-cytokeratin (CK) antibodies. The number of cancer cells in the enriched sample was counted using a novel FISHMAN-R flow cytometry system. CTCs enumeration and a head-to-head comparison with CellSearch system were carried out in a blinded manner at two different sites: Shizuoka cancer center (SCC) and National cancer center Tokyo (NCC) in parallel.

Results

Various numbers of EpCAM-positive gastric cancer cell line KATO-III were spiked into 4 ml. This study was carried out at two different sites. Recovery rate ranged from 89.0% to 120.0% at SCC and from 88.0% to 130.0% at NCC, respectively, suggesting the robustness of our detection system. In the following head-to-head comparison study with CellSearch system in a blinded manner, the average recovery rate was 90.3% at SCC, 87.6% at NCC and 62.0% by CellSearch system, respectively. EpCAM-negative lung cancer cell line PC-14 cells were also spiked into 4 ml of peripheral blood and enumerated by our system and CellSearch system. Markedly higher recovery rate was observed with our system (90.0%–102.0%) than with CellSearch system (0%), suggesting superior sensitivity of our system in capturing EpCAM-negative tumor cells. Clinical trial is now ongoing to assess the validity of this system.

Conclusions

These data imply the potential of our detection system for clinical application.

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