36P Automated Quantitative Her2 Assessment in Circulating Tumor Cells: Discrepancies with Primary Tumor in Neoadjuvant and Metastatic Trials

Abstract

Background: Circulating tumor cells (CTC) can provide the basis for a real-time liquid biopsy and may guide the use of targeted therapies. Several attempts have been made to assess the Her-2 status of CTC detected in breast cancer patients, but already reported techniques are either observer-dependent and/or unfit for large scale screening of patients. We report here on unbiased quantification of Her-2 protein expression of CTC in 103 metastatic (M1) and 88 non-metastatic (M0) breast cancer patients included in three prospective studies (IC 2006-04, Beverly01, Beverly02). Methods: Digital images obtained by the CellSearch1 system were stored in which CTC were identified by an automated algorithm. Furthermore, this algorithm determined the Her-2 positivity threshold in each sample, using the fluorescence of leukocytes within each sample as internal control. Results: This automated Her-2 assessment method successfully distinguished Her-2 positive from Her-2 negative breast cancer cell lines. We report here for the first time that Her-2 expression of CTC varied greatly between but also within patients, suggesting a possible mechanism of treatment resistance. However, in M1 patients, a threshold of 75% of Her-2 positive CTC in patients with ≥5 CTC showed a relatively low discrepancy rate between the primary tumor and CTC Her-2 status. Applying this threshold, ∼2% of M1 patients with Her-2 negative primary tumors had Her-2 positive CTC status and ∼30% of M1 patients with Her-2 positive primary tumors had Her-2 negative CTC status. Interestingly, no Her-2 discrepancy was observed between CTC and primary tumors in M0 patients. Conclusions: Our results suggest that Her-2 status shift appears mostly at metastatic relapse, and consists generally in Her-2 low expression on CTC isolated from M1 patients with Her-2 positive primary tumors. These findings also demonstrate the feasibility of real-time quantitative and reproducible assessment of treatment targets on CTC, opening a path towards personalized treatment.