Background: HER2 targeted therapies, such as HER2 monoclonal antibodies, HER2 tyrosine kinase inhibitors, and HER2 antibody drug conjugates, are approved for the treatment of HER2-positive breast, gastric and colorectal cancers. However, inter- and intra-tumoral heterogeneity in HER2 status presented a significant challenge in identifying patients that may benefit from HER2-targeted therapies. Detection of ERBB2 amplification in Circulating Tumor Cells (CTCs) may circumvent tissue heterogeneity issues and effectively predict the response of patients to anti-HER2 agents as a non-invasive alternative approach. Methods: A twenty-four patient pilot study was designed to compare HER2 status of traditional needle biopsies to high sensitivity CTC based liquid biopsies. HER2 status was determined using immunohistochemistry (IHC) and Fluorescence in Situ Hybridization (FISH) for tissue samples and FISH analysis for CTCs. Currently 21 patient samples have been compared in this study. Results: CTCs with HER2 amplified signals were found in patients with stages 2, 3, or 4 breast cancers. Based on the biopsies of the primary tumor or metastatic disease, 6 patients (29%) had HER2-overexpressing as defined by either HER2 IHC 3+ or HER2 FISH amplified. Analysis of CTCs showed 100% concordance (HER2 amplification detected in CTCs) in these patients with HER2-overexpressing breast cancer. Furthermore, an additional 4 (19%) patients had HER2 amplification by CTC analysis but not on needle biopsy. Conclusions: Our finding demonstrates that LiquidScan can be used as a rapid analysis tool to evaluate HER2 amplification in CTCs. This approach can potentially help identify additional cohort of patients (HER2 non-amplified tumor / HER2 amplified CTCs) who may benefit from the new generation of HER2 targeted therapies. Studies are ongoing to include an expanded cohort of patients with early stage disease, as well as HER2-low disease, in order to evaluating dynamics of ERBB2 gene amplification, expression, and pathway activation while on active systemic therapy.