DETECT V – expression of human epidermal growth factor receptor 2 and estrogen receptor on circulating tumor cells of metastatic breast cancer patients

Introduction:

Circulating Tumor Cells (CTCs) are a prognostic marker in patients with metastatic breast cancer (MBC). The possible implication of CTCs on predictive relevance is under investigation. The DETECT V study compares endocrine vs. chemotherapy, combined with trastuzumab and pertuzumab in MBC patients with a HER2-positive, hormonereceptor-positive tumor. Associated is a translational project which analyzes expression of predictive markers HER2 and estrogen receptor (ER) on CTCs to establish and validate an “Endocrine Responsiveness Score” (ERS) aiming to predict the potential benefit of endocrine therapy.

Methods:

Analysis of CTCs was performed using CellSearch CXC Kit. The staining protocol was validated using cell lines with known expression of both markers. Blood was drawn at randomization, after six weeks and at end of treatment. CTCs were enumerated; staining intensities of ER and HER2 were specified.

Results:

Staining was successfully established, staining intensities were classified. HER2 staining intensity was specified as negative, weak, moderate or strong; ER staining as negative or positive. Analyzing the first patients at time of randomization 80% (8/10) contained ≥1 CTC in one sample (HER2 and ER), 30% (3/10) in both samples. CTC positivity rate at the end of treatment was decreased to 50% (5/10) to contain ≥1 CTC in one sample, 10% in both samples. All categories of HER2 and ER staining were detected in patients' samples.

Conclusion:

The implementation of ERS aims to estimate the potential benefit of endocrine therapy. Analysis of first patient samples has shown to detect all categories of HER2 and ER staining in CTCs.