Potential Use of Extracellular Vesicles for the HER2 Status Assessment in Breast Cancer Patients

Human epithelial growth factor receptor 2 (HER2)-targeted therapies are effective in patients with HER2-positive breast cancer. Recent advances have shown that HER2-targeted therapies can also be of benefit when treating tumors expressing low levels of HER2, highlighting the importance of identifying the HER2-low subgroup. This clinical trend has opened new therapeutic avenues for patients who were previously ineligible for HER2-targeted therapies. Thus, the development of new diagnostic methods for real-time HER2 profiling is crucial for accurately tailoring the treatment for these patients. We hypothesized that tumor-derived extracellular vesicles (TEVs) could reflect the HER2 profiles of primary tumors and potentially serve as diagnostic tools for HER2 status. This approach was validated using six breast cancer cell lines, which confirmed that the TEVs accurately reflected the HER2 profiles of the tumor cells. TEVs were isolated using an immunoaffinity method, and copy number variation (CNV) in the ERBB2/EIF2C ratio was assessed using droplet digital PCR of DNA from these vesicles. Clinical validation using plasma samples from 33 breast cancer patients further reinforced the diagnostic potential of our method. Pearson's correlation coefficient analysis of the flow cytometry results demonstrated that TEVs reflected HER2 expression in primary cells. To distinguish between HER2-negative and HER2-low patients, the area under the curve (AUC) of the ROC curve in our method was 0.796, with a sensitivity of 53.8% and a specificity of 100%. These findings suggest the clinical utility of extracellular vesicles derived from plasma and emphasize the need for further research to distinguish HER2-negative from HER2-low patients.