Abstract 1626: Comparison of two flow cytometry detection methods of circulating tumor cells: Direct identification and EpCAM affinity based enrichment
Authors: Zhao Li , Jachimowicz Lauren , Lei Ming , Ye Peifang , Guenther Garret , LI Nancy 
Published: August 2019

Abstract
The dissemination of cancer and development of metastases is the cause of nearly all cancer deaths. Circulating tumor cells (CTC) are cells that detach from the primary solid tumor or metastases and circulates through the peripheral blood. Accumulating evidence shows the importance of CTC detection for cancer prognosis also referred to as a “liquid biopsy”, biomarker for metastatic cancer, as well as therapeutic response monitoring. However, detection of CTC in peripheral blood is made difficult because they are present at extremely low concentrations; in some patients as little as a few CTC per million blood cells. Flow cytometry a standard equipment available in many laboratories is capable of analyzing thousands of cells per second, allowing rare cell detection and has been demonstrated to be useful for CTC studies. CTC detection can be further aided by affinity based enrichment methods that eliminate other blood cells from the sample before analysis. In these experiments, we analyzed a colon cancer cell line (SW620) by 2 methods; either direct flow cytometry identification or following EpCAM affinity based enrichment. First, SW620 cells were spiked into blood cells and analyzed of the NovoCyte Quanteon and other comparison cytometers to determine the rare event detection sensitivity. The results show a good linear relationship between the number of cells detected and the predicted number added with a sensitivity of 0.00001% or 1 CTC per million cells. Colon cancer CTC and many other CTC have high expression of epithelial markers, such as epithelial cell surface marker, EpCAM. Affinity based enrichment methods utilize distinct antigens expressed either by CTCs but not blood cells such as EpCAM to separate CTC from blood cells and increase the detection capacity of CTC in the blood. In the next experiments, SW620 cells were spiked into blood samples to simulate CTC in cancer patients. CTC were then enriched by EpCAM affinity based magnetic bead enrichment. The recovery rate of the spiked tumor cells was then detected by flow cytometry to determine the accuracy and specificity of the enrichment process. The results show that a greater number of CTC present in the spiked blood sample increased the recovery rate of CTC through the enrichment process. A high precision syringe pump allowed the direct enumeration of CTC without the need of reference beads. These data demonstrate the high specificity and accuracy of CTC detection by flow cytometry by both direct identification and the use bead based enrichment methods.
Citation Format: Li Zhao, Lauren Jachimowicz, Ming Lei, Peifang Ye, Garret Guenther, Nancy LI. Comparison of two flow cytometry detection methods of circulating tumor cells: Direct identification and EpCAM affinity based enrichment [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1626.