Circulating tumour cell (CTC) detection: a direct comparison between the CellSearch system, the AdnaTest, CK19/MAM RT-PCR and unmethylated/methylated free DNA in patients with metastatic breast cancer.

Abstract

Abstract Abstract #5025 Introduction: The detection, enumeration and isolation of CTC has considerable potential to influence the clinical management of patients with breast cancer. There is however a substantial variability in the rates of positive samples using existing detection techniques. This study was designed to compare the sensitivities and specificities of three techniques for detecting CTC in blood of patients with metastatic breast cancer (MBC). Furthermore, correlations between CTC and circulating total and tumor-related methylated DNA were investigated.
 Material and Methods: The presence of CTC in blood samples of 80 patients with MBC and 20 healthy controls was assessed by two commercial systems: i) the CellSearch System (Veridex LLC, Warren, NJ), in which epithelial cells are immunomagnetically separated and fluorescently labeled, and nucleated (DAPI+) cells with the EpCAM+, cytokeratin (CK) 8/18/19+, and CD45- phenotype are counted as CTC and ii) the AdnaTest and a real-time qRT-PCR assay for the detection of CK-19 and mammaglobin (MAM) transcripts. Plasma total DNA levels were measured by a qPCR method. Sera were analyzed by methylation-specific qPCR for three methylated markers: APC, RASSF1A and ESR1. The results obtained with AdnaTest are being analyzed and will be presented at the meeting.
 Results: Numbers of CTC identified by the CellSearch test were significantly higher in blood samples of patients with MBC than in healthy controls: the median number of CTC detected in 7.5 ml of blood was 1 (range 0-2617) in patients with MBC and 0 (range 0-1) in controls (P<0.001). Using ≥2 cells as a threshold for positivity, which corresponds to 100% specificity in the control population, 34% of samples from patients with MBC were positive with the CellSearch test. Using a cut-off to ensure 100% specificity in the control population, 31% of patients were positive for CK-19, 49% for MAM and 61% for CK-19 and/or MAM by qRT-PCR. When the CellSearch test and the qRT-PCR for CK-19 and MAM were compared, the concordance was 57%. Positive samples with the CellSearch test, but not with the qRT-PCR assay, also showed significantly higher levels of circulating total DNA and were more likely to be positive for one of the methylated DNA markers in serum.
 Conclusion : We observed a substantial variation in the detection rates of CTC in blood from breast cancer patients using different techniques. A higher rate of positive samples was observed using a combined qRT-PCR approach for CK-19 and MAM, which suggests that this is currently the most sensitive technique for detecting CTC. Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 5025.