Chromogenic in situ hybridisation (CISH) should be an accepted method in the routine diagnostic evaluation of HER2 status in breast cancer.

Introduction HER2 protein over-expression or gene amplification is detected in approximately 20% breast tumours, is associated with an aggressive phenotype and is predictive of response to trastuzumab therapy. The use of chromogenic in situ hybridisation (CISH) for evaluating HER2 status routinely is recognised in much of Europe but has yet to achieve widespread acceptance in the UK. Methods CISH analysis for HER2 status was performed on 161 breast cancer cases. Results were compared to immunohistochemistry (IHC) and dual colour fluorescent in situ hybridisation (FISH) data. Results There was 100% concordance between CISH and FISH but only 93.8% concordance between CISH and IHC. Performing CISH ‘in-house’ was found to cost approximately 50% less than the FISH / IHC protocol at the reference laboratory. Conclusion It is concluded that CISH is as accurate as FISH for diagnostic purposes and is more cost-effective than the IHC / FISH regimen currently favoured in the UK. Background Recent data show that amplification of the HER-2 gene is the most reliable predictor of response to trastuzumab therapy [1, 2] indicating that a gene-based assay, rather than a protein over-expression assay, would be the most suitable type of analysis for HER2 status in breast tumour samples. With the recent change in the licensing of trastuzumab to include its use as an adjuvant therapy (NICE 2006) it is important that patients most likely to benefit from its use are accurately identified. This change in the use of trastuzumab has increased the workload of the histopathology laboratories significantly as well as creating an additional financial burden for hospital Trusts. We investigated the possibility of setting up HER2 analysis within our pathology department. CISH, like FISH, directly visualises the number of gene copies present in the nucleus, it is cheaper and it produces a permanent record of the slide that can be interpreted with a light microscope in the context of the tumour histopathology. CISH and FISH have been compared for their sensitivity and specificity in numerous previous reports from across Europe [3-7], but it is not widely used in the UK [1]. The current study was done as a validation study prior to setting up a HER2 testing service using CISH but it was felt that our experience may be of interest to other laboratories considering setting up their own HER2 testing service. Methods One hundred and sixty one breast cancer cases for which material was obtainable and that had IHC and/or FISH data available were chosen for the study. The samples had been analysed by the DAKO HercepTest IHC (DakoCytomation, Ely, Cambridgeshire, UK) and a small number of them (n=24) had required confirmation by PathVysion dual colour FISH (Abbott UK, Queensborough, Kent, UK) mostly because they were IHC 2+. The manufacturer’s protocols and scoring systems for both procedures were followed. The same cases were subsequently examined using a commercially available CISH assay (Zymed, Invitrogen, Paisley, UK) and the manufacturer’s protocol was followed. The resulting slides were examined independently by two pathologists using light microscopy. The areas of invasive tumour were identified and the HER2 status was scored using the group.bmj.com on October 1, 2017 Published by http://jcp.bmj.com/ Downloaded from