EpCAM+ and EpCAM- circulating tumor cells in metastatic lung cancer

Proceedings: AACR 106th Annual Meeting 2015; April 18-22, 2015; Philadelphia, PA Purpose: The presence of Circulating Tumor Cells (CTC) in metastatic carcinomas detected by CellSearch is associated with poor outcome. CellSearch uses an enrichment step based on the EpCAM antibody and enumerates CTC using antibodies targeting specific cytokeratins. Here we investigate the presence and role of CTC not detected by CellSearch in lung cancer patients. Methods: Blood discarded by CellSearch after EpCAM based enrichment was collected and enriched for CTC by filtration through microsieves and enumerated after fluorescent labeling. Additional anti-cytokeratin antibodies were added to the CellSearch test to increase the cytokeratin coverage. This approach was validated using different cell lines spiked into blood and tested on blood samples of 28 metastatic lung cancer patients. Results: The majority of spiked EpCAM+ cells could be detected with CellSearch whereas few cells were detected with low or no EpCAM expression (EpCAM-). Recovery of cells on microsieves depended strongly on cell size. One or more CTC were detected in 39% of the patient samples, this increased to 75% when adding the CTC detected in the discarded blood and to 82% with the use of additional cytokeratin antibodies. Presence of CTC was significantly associated with poor Overall Survival (OS) when detected by CellSearch without (p = 0.004) and with additional cytokeratins (p = 0.007), but not with EpCAM-CTC in the blood discarded by CellSearch (p = 0.271) or all CTC detected (p = 0.354) Conclusions: Expanding the cytokeratin coverage and including EpCAM-CTC, double the number of patients with CTC and the number of CTC detected with CellSearch. In contrast with EpCAM+ CTC, the presence of EpCAM-CTC in this group of patients was not associated with poor OS. The metastatic lung cancer patients included in this study were very diverse with respect to cancer type, line of therapy and quite small in numbers to make any definitive conclusions. Still, this pilot study warrants a larger study to confirm the findings. In addition an in-depth characterization of the EpCAM+ and EpCAM-CTC is needed to confirm that the EpCAM-, panCK+ CTC are indeed tumor cells and unravel the genetic difference with the EpCAM+, panCK+ CTC. Citation Format: Sanne de Wit, Guus van Dalum, Aufried T.M. Lenferink, Arjan G.J. Tibbe, Jeroen T.N. Hiltermann, Harry J.M. Groen, Cees van Rijn, Leon W.M.M. Terstappen. EpCAM+ and EpCAM- circulating tumor cells in metastatic lung cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 377. doi:10.1158/1538-7445.AM2015-377