Dual color chromogenic in situ hybridization for determination of HER2 status in breast cancer: a large comparative study to current state of the art fluorescence in situ hybridization

Here it is reported from a comparative study where HER2 gene status obtained by HER2 CISH pharmDx？ Kit was compared to HER2 gene status obtained by the FDA approved HER2 FISH pharmDx？ Kit and the PathVysion HER-2 DNA probe Kit. The study included 365 formalin fixed and paraffin-embedded invasive breast cancer tissue specimens collected consecutively at a US reference laboratory.The data obtained revealed an overall HER2 status concordance of approximately 98% for comparisons of HER2 CISH pharmDx？ Kit to both HER2 FISH pharmDx？ Kit and PathVysion HER-2 DNA Probe Kit.The concordance between results obtained using the recently FDA approved HER2 CISH pharmDx？ Kit with previously FDA approved FISH techniques for HER2 gene status determination indicate that the HER2 CISH pharmDx？ Kit is a reliable chromogenic alternative to fluorescence-based methods.HER2 (Human Epidermal Growth Factor Receptor 2) is an important marker for invasive breast cancer. The assessment of the HER2 expression level is routinely done by examining protein expression and/or gene expression levels in formalin-fixed and paraffin-embedded (FFPE) histological sections. Overexpression of HER2 protein and/or HER2 (Human Epidermal Growth Factor Receptor 2 Gene) amplification is observed in approximately 22% of human breast cancers [1] and has been shown to be a marker of poor prognosis [2] and to predict benefit from treatment with the antibody based drug Herceptin (Genentech, San Francisco, CA, USA) [3].Tissue based assessment of HER2 protein expression levels is commonly achieved using immunohistochemistry (IHC), whereas tissue based analysis of HER2 amplification is mostly done by in situ hybridization (ISH) techniques either fluorescence (FISH) [4] or chromogenic (CISH or SISH) [5]. In ISH the specific recognition of HER2 target sequences in the nuclei of tumor cells is done by fluorescence- or hapten-labeled sequence pairing probes. Implementation of CISH for determination of HER2 amplification in bre