Rapid HER2 cytologic fluorescence in situ hybridization for breast cancer using noncontact alternating current electric field mixing

BACKGROUND: Human epidermal growth factor receptor 2‐in situ hybridization (HER2‐ISH) is widely approved for diagnostic, prognostic biomarker testing of formalin‐fixed paraffin‐embedded tissue blocks. However, cytologic ISH analysis has a potential advantage in tumor samples such as pleural effusion and ascites that are difficult to obtain the histological specimens. Our aim was to evaluate the clinical reliability of a novel rapid cytologic HER2 fluorescence ISH protocol (rapid‐CytoFISH). MATERIALS AND METHODS: Using a new device, we applied a high‐voltage/frequency, noncontact alternating current electric field to tissue imprints and needle rinses, which mixed the probe within microdroplets as the voltage was switched on and off (AC mixing). Cytologic samples (n = 143) were collected from patients with immunohistochemically identified HER2 breast cancers. The specimens were then tested using standard dual‐color ISH using formalin‐fixed paraffin‐embedded tissue (FFPE‐tissue DISH) for HER2‐targeted therapies, CytoFISH, and rapid‐CytoFISH (completed within 4 h). RESULTS: All 143 collected cytologic specimens (50 imprinted cytology specimens from resected tumors and 93 liquid‐based cytology specimens from needle rinses) were suitable for FISH analysis. The HER2/chromosome enumeration probe (CEP) 17 ratios did not significantly differ between FFPE‐tissue DISH and either CytoFISH protocol. Based on HER2 scoring criteria, we found 95.1% agreement between FFPE‐tissue DISH and CytoFISH (Cohen's kappa coefficient = 0.771 and 95% confidence interval (CI): 0.614–0.927). CONCLUSION: CytoFISH could potentially serve as a clinical tool for prompt determination of HER2 status in breast cancer cytology. Rapid‐CytoFISH with AC mixing will enable cancer diagnoses and HER2 status to be determined on the same day a patient comes to a clinic or hospital.