Abstract PO5-04-05: Clinical validation of the concordance performance of ERBB2 status by single-cells genomics ERBB2 (HER2) amplification Assay in Circulating Tumor Cells (CTCs) from patients with matched HER2 status from metastatic tissue biopsies

Abstract Background Liquid biopsies are a non-invasive diagnostic approach for detecting CTCs that may provide clinically actionable information for treatment decisions for metastatic breast cancer (MBC) patients when a conventional biopsy is infeasible. Blood-based liquid biopsy has the potential advantage that it allows broad sampling of metastatic tumor clones because it is capable of and likely to obtain cellular and genomic contributions from more than one metastatic site. Here we report the concordance performance of HER2 positivity by single-cell CTC genomics ERBB2 (HER2) amplification in patients with matched HER2 status from metastatic tissue biopsies. Methods A prospective Clinical Experience Program for CTC ERBB2 (HER2) Assay across 25 different United States-based cancer centers, was used to recruit 128 MBC patients with documented standard-of-care metastatic tissue biopsies performed within the last 5 years (Days from tissue biopsy to liquid biopsy, Median: 19.5; interquartile range: 40.75) CTCs from blood collection at each respective clinical site were isolated from plasma, nucleated cells were plated, interquartile range: 22) to the blood draw for the CTC ERBB2 (HER2) amplification assay. This showed dramatically improved concordance performance with a Sensitivity of 100%, and a Specificity of 75%. Conclusions Blood and tissue are two biologically distinct sample types where variations in HER2 and other biomarker results might be expected due to analytic, temporal and clinical differences. These data indicate that determination of HER2 status by single cell genomic ERBB2 (HER2) amplification assay can aid in the clinical assessment of ERBB2 status in patients with metastatic breast cancer (MBC) for whom tissue biopsy for HER2 status is not available, or infeasible. Additionally, these results provide evidence of the contribution of site differences (bone) of metastatic biopsies and also tumor evolution to discordance between the CTC ERBB2 (HER2) Assay and tumor biopsy. Citation Format: Giuseppe Di Caro, Ernest Lam, Megan Slade, Shuguang Huang, Rick Wenstrup, Lee Schwartzberg. Clinical validation of the concordance performance of ERBB2 status by single-cells genomics ERBB2 (HER2) amplification Assay in Circulating Tumor Cells (CTCs) from patients with matched HER2 status from metastatic tissue biopsies abstract. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO5-04-05.