Abstract
PURPOSE: Circulating tumor cell (CTC)-based ERBB2 (HER2) assay is a laboratory test developed by Epic Sciences using single-cell genomics to detect ERBB2 (HER2) amplification in CTCs found in the peripheral blood of metastatic breast cancer (MBC) patients. PATIENTS AND METHODS: Peripheral blood was collected in Streck tubes and centrifugation was used to remove plasma and red blood cells. The remaining nucleated cells were deposited on glass slides, immunofluorescent-stained with proprietary antibodies, scanned by a high-definition digital scanner, and analyzed by a proprietary algorithm. In addition, single-cell genomics was performed on selected CTC. Analytical validation was performed using white blood cells from healthy donors and breast cancer cell lines with known levels of ERBB2 amplification. Clinical concordance was assessed on MBC patients whose blood was tested by the CTC ERBB2 (HER2) assay and those results are compared to results of matched metastatic tissue biopsy (immunohistochemistry [IHC] 3+ or IHC2+/in situ hybridization [ISH+]). RESULTS: Epic's ERBB2 (HER2) assay detected 2-fold ERBB2 amplification with 85% sensitivity and 94% specificity. In the clinical concordance study, among the 50% of the cases that had ERBB2 status results from CTCs found to be chromosomally-unstable, the CTC ERBB2 (HER2) assay showed sensitivity of 69% and specificity of 78% when compared to HER2 status by metastatic tissue biopsy. CONCLUSIONS: The CTC ERBB2 (HER2) assay can consistently detect ERBB2 status in MBC cell lines and in the population of patients with MBC with detectable chromosomally unstable CTCs for whom tissue biopsy is not available or is infeasible.