Abstract 3758: Evaluation of breast cancer-derived extracellular vesicles as diagnostic indicator for HER2 status

Abstract HER2-low is a new distinct type of breast cancer that is characterized by low levels of the HER2 protein. As treatment paradigms for HER2-low breast cancer are rapidly evolving with the approval of antibody-drug conjugates, identification of HER2-low breast cancer with more sensitive and reproducible HER2 assays is needed. We aimed to investigate the utility of liquid biopsy in isolating tumor-derived extracellular vesicles (TDEs) for diagnosis of HER2 status. We adopted an affinity-based approach to isolate TDEs and performed CNV analysis of the ERBB2/neu genes using the tumor DNA present in TDEs (etDNA). HER2 status of etDNA had been determined by droplet digital PCR using HER2/EIF2C ratio, a highly accurate method to quantify DNA copy number. In our study, we utilized a variety of breast cancer cell lines categorized as HER2-low (MDA-MB-231, MCF7, ZR-75-1) and HER2-high (MDA-MB-453, BT-474, SK-BR-3) to confirm HER2 expression in extracellular vesicles (EVs) by flow cytometry. This analysis successfully demonstrated that EVs effectively reflect the HER2 status of the tumor cells, evidenced by a strong Pearson correlation coefficient (r=0. 987, p0. 001). Further clinical validation was conducted with plasma samples from 22 breast cancer patients. In the clinical study, we observed a significant correlation between the CNV of tumor DNA present in TDEs and the HER2 status of primary tumors (p0. 01). Additionally, the Receiver Operating Characteristic (ROC) analysis yielded an impressive area under the curve (AUC) value of 0. 838 (p0. 01), demonstrating a high level of accuracy in differentiating between high and low HER2 groups, with a sensitivity of 55. 6% and a specificity of 100%. In summary, we show potential diagnostic tools for real-time, less invasive determination of HER2 status in primary tumors, providing continuous monitoring methods for HER2 status. Although further validation in larger cohorts and prospective studies is needed, our study indicates that TDE analysis could contribute to the assays for identification of the HER2 status in breast cancer patients. Citation Format: Sol Moon, Min Woo Kim, Young Kim, Suji Lee, Hyojung Lee, Joon Ye Kim, Seung Il Kim, Jee Ye Kim. Evaluation of breast cancer-derived extracellular vesicles as diagnostic indicator for HER2 status abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 3758.