Comparison of two density gradient centrifugation systems for the enrichment of disseminated tumor cells in blood

Background: The detection of disseminated tumor cells in peripheral blood is limited by the presence of very few tumor cells within a large number of blood cells. Therefore, tumor cell detection calls for enrichment systems with effective depletion of blood cells and high tumor cell recovery. Methods: We compared the new density gradient centrifugation method OncoQuick with the standard method of Ficoll. The enriched cell fractions were quantified. Tumor cell spiking experiments examined the recovery of tumor cells as detected by immunocytochemistry and cytokeratin-20 reverse transcriptase-polymerase chain reaction (RT-PCR). Clinical application of OncoQuick was evaluated in 37 peripheral blood samples of patients with gastrointestinal carcinomas. Results: The depletion of mononuclear cells (MNCs) in the enriched cell fraction after OncoQuick centrifugation was 632-fold, with an average cell number of 9.5 × 10⁴, compared with Ficoll, with a depletion factor of 3.8 and a mean number of 1.6 × 10⁷ MNCs. The mean tumor cell recovery rates were 87% for OncoQuick and 84% for Ficoll. The increased depletion of MNCs with OncoQuick centrifugation further simplified immunocytochemical evaluation by reducing the number of cytospins and increasing the tumor cell density. Due to the reduced number of co-enriched MNCs by OncoQuick, the blood volume, which could be analyzed in one RT-PCR reaction, was increased up to 30 ml. Examination of peripheral blood samples from 37 patients with gastrointestinal tumors showed a cytokeratin-20 detection rate of 30% and a significant correlation with the presence of distant metastases (P < 0.02). Conclusions: OncoQuick significantly reduced the coenriched number of MNCs, with a high tumor cell recovery rate. Processing blood from tumor patients with OncoQuick increased the chance of detecting circulating tumor cells.