Abstract P3-01-04: DETECT V – Expression analysis of human epidermal growth factor receptor 2 and estrogen receptor on circulating tumor cells of metastatic breast cancer patients
Authors: Fehm T , Meier-Stiegen F , Riethdorf S , Rack B , Taran F-A , Pantel K , Müller V , Janni W , Huober J 
Published: May 2019

Abstract
Introduction: The prognostic relevance of Circulating Tumor Cells (CTCs) in patients with metastatic breast cancer (MBC) has been shown in multiple clinical trials. Beside their quantification it is of particular interest to analyze the predictive value of these cells and investigate if therapeutic decisions can be based on the phenotype of CTCs. The DETECT study concept evaluates this possible implication of CTCs. The DETECT V study compares endocrine therapy vs. chemotherapy, both combined with Trastuzumab and Pertuzumab in MBC patients with a HER2-positive (Human Epidermal Growth Factor Receptor 2), hormone receptor-positive tumor. Translational projects to identify potential predictive markers are associated to the study program. The expression of predictive markers HER2 and estrogen receptor (ER) on CTCs is analyzed to establish and validate an “Endocrine Responsiveness Score” (ERS). The ERS is aiming to estimate the potential benefit of endocrine therapy.
Methods: Quantification and characterization of CTCs was performed using Cell Search® CXC Kit. The staining protocol was validated using cell lines with known expression of ER and HER2. CTCs were quantified at randomization, after six weeks and at the end of treatment in two samples. Staining intensities of both markers were specified.
Results: Staining was successfully established. ER staining intensity was specified as negative or positive; HER2 staining intensity as negative, weak, moderate or strong. Detection and characterization of CTCs was analyzed for the first 30 patients. At time of randomization 17 of 26 samples were CTC positive with ≥1 CTC in one sample (HER2 and ER), 6/25 in both samples. After six weeks 8 of 26 patients contained ≥1 CTC in one sample and 5 of 26 in both samples. 11 of 15 CTC positive patients at time of randomization were CTC negative in the subsequent sample after six weeks. The cumulative frequency of ER- and HER2-positivity regarding CTCs detected in all samples was analyzed. 13% of all CTCs detected were ER positive (14/115). The percentage of HER2 3+ CTCs decreased from 27% at time of randomization (25/92) to 0% after six weeks (0/87). Analyzing the distribution of the expression of ER and HER2 in all CTCs of one sample, 10 of 19 samples containing ≥2 CTC showed heterogenic intensity of HER2-specific immunofluorescence. 8 of 14 samples containing ≥2 CTC showed heterogenic intensity of ER-specific immunofluorescence, respectively.
Conclusion: The implementation of “Endocrine Responsiveness Score” ERS aims to predict the potential benefit of endocrine therapy in patients with a HER2-positive, hormone receptor-positive tumor. Descriptive analysis of first patient samples has shown to detect heterogenic expression of HER2 and ER in CTCs of patients participating in the DETECT V study.
Citation Format: Fehm T, Meier-Stiegen F, Riethdorf S, Rack B, Taran F-A, Pantel K, Müller V, Janni W, Huober J. DETECT V – Expression analysis of human epidermal growth factor receptor 2 and estrogen receptor on circulating tumor cells of metastatic breast cancer patients [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P3-01-04.