Abstract OT3-18-02: A comparative study of two detection platforms of circulating tumour cells in patients with metastatic breast cancer
Authors: Peeters Dieter , Buys Andy , Ledegen Hannah , Moehlig Kathlyn , Oeyen Steffi , Rondas Dieter , De Beukelaer Alexia , Van Laere Steven , Vervoort Liesbet , Vermeulen Peter , Ung Christopher , Kockx Mark , Dirix Luc 
Published: March 2020

Abstract
Background: The enumeration of circulating tumour cells (CTCs) using the FDA-cleared CellSearch system has repeatedly been proven to bear prognostic significance in patients with localized and metastatic breast cancer (MBC) (Bidard et al. Lancet Oncol 2014; Janni et al. CCR 2016). In addition, CTC count has been suggested to be a valuable alternative for physician-based decision making in choosing between hormone therapy and chemotherapy as frontline treatment for patients with estrogen receptor-positive, HER2-negative MBC (Bidard et al. SABCS 2018). Challenges for the implementation of CTCs as a biomarker or a source of liquid biopsy in clinical practice include that most isolation methods only detect a limited number of CTCs in a blood sample in a subset of patients, even in those with clinically proven metastatic disease, and the limited availability of comparative data on technical variability between different CTC detection assays.
Methods: In this study, we compare CTC detection rates in paired 7.5 ml blood samples from patients with MBC starting a new line of treatment using two commercially available CTC detection assays. All patients are recruited at GZA Hospitals, campus Sint-Augustinus, Antwerp, Belgium. The first CTC detection system is the CellSearch system, currently the only FDA-cleared system for the enumeration of CTCs in patients with MBC. This system employs an immunomagnetic CTC enrichment based on the expression of Epithelial Cell Adhesion Molecule (EPCAM) followed by an immunofluorescent CTC detection based on the expression of cytokeratins (CK) in EPCAM+ enriched cells. With this system, only EPCAM/CK double positive cells can be qualified as CTCs. The second system is the Rarecytes system, an automated scanner for immunofluorescently stained cell smears of the entire buffy coat of blood samples. With this system, CTCs will be enriched and detected in a single-step measurement using a cocktail of anti-EPCAM and anti-CK fluorescently labeled antibodies, thereby allowing to detect also single-marker positive CTCs. Based on CTC detection prevalence data in patients with MBC that are available for the CellSearch system and a prespecified hypothesis that with both detection methods a discordant result (relative to a cut-off of &gt;= or &lt;5 CTCs/7.5 ml blood) will be measured in 25% of patients, we aim to include 100 patients with MBC in this benchmarking study in order to be able to detect at least a 15% difference in CTC detection rate in favor of one of both techniques with 80% power at a significance level of 0.05. Concordance/discordance of CTC results between both detection methods will be analyzed both as a dichotomized variable relative to different cut-off values using the McNemar test and Cohen’s kappa test and as a continuous variable using the intraclass correlation coefficient.
Expected results and conclusions: Upon submission of the abstract, 30 patients with MBC have been included in this trial after an accrual period of 4 months. Full results are expected mid 2020. Detailed comparison of CTC detection rates between both techniques will not only render analytical data on the performance of the Rarecytes system compared to the CellSearch system - the current gold standard in the field - but might also shed light on the frequency of EPCAM/CK single-positive CTCs in patients with MBC.
Conflicts of interest: This study is partially funded by a grant from Rarecyte, Inc.
Contact details for collaboration: Dieter Peeters (HistoGeneX NV, Antwerp, Belgium): dieter.peeters@histogenex.com; Andy Buys (Translational Cancer Research Unit, Antwerp, Belgium): andy.buys@gza.be.
Citation Format: Dieter Peeters, Andy Buys, Hannah Ledegen, Kathlyn Moehlig, Steffi Oeyen, Dieter Rondas, Alexia De Beukelaer, Steven Van Laere, Liesbet Vervoort, Peter Vermeulen, Christopher Ung, Mark Kockx, Luc Dirix. A comparative study of two detection platforms of circulating tumour cells in patients with metastatic breast cancer [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr OT3-18-02.