en زیست شناسی مولکولی Molecular biology پژوهشي Research <div style="text-align: justify;"><strong>Background:</strong> <em>HER2</em> status testing in breast cancer is crucial for the detection of eligible patients for trastuzumab therapy. In this study, the relative copy number of <em>HER2</em> gene, in patients with breast cancer, was determined by fluorescence in situ hybridization (FISH) and the results were compared with those of immunohistochemistry (IHC) to obtain the concordance rate between these two methods.<br> <strong>Material and Methods:</strong> <em>HER2</em> status of 31 invasive breast cancer samples was compared using IHC and FISH techniques. The ratio of <em>HER2/CEP17</em> was used to determine the amplification of the <em>HER2</em> gene. If the ratio of <em>HER2/CEP17</em> is greater than 2.2, <em>HER2</em> gene amplification has occurred in the cancer cells. Then, a comparative analysis is performed to estimate the concordance rate between FISH and IHC results.<br> <strong>Results:</strong> The gene amplification of <em>HER2</em> was observed in 26% of cases by FISH. The IHC and FISH results showed 100%, 36.36%, and 85.71% concordance rates for cases with IHC scores of 3+, 2+, and 0/+1, respectively. The overall concordance between the two methods was 80%. Based on statistical analysis, <em>HER2</em> status showed a considerable correlation with tumor grade (P= 0.02). No correlation was observed between <em>HER2</em> gene status and the size and type of tumor, characteristics of lymph node, and patients&rsquo; age.<br> <strong>Conclusion:</strong> The data suggested that IHC results are reliable for HER2 status testing in cases with IHC scores 0/+1 and 3+. However, in patients with an IHC score of +2, it is necessary to perform a complimentary test to evaluate <em>HER2</em> status to avoid haphazard treatment with trastuzumab in negative cases and identifying positive cases for suitable treatment.</div> Breast cancer, FISH, IHC, HER2 139 146 http://rmm.mazums.ac.ir/browse.php?a_code=A-10-1133-1&slc_lang=en&sid=1 Maryam Moradi Chaleshtori moradi_984@yahoo.com 10031947532846009057 10031947532846009057 No Genetics Division, Biology Department, Faculty of Sciences, University of Isfahan, Isfahan, Iran Zohreh Hojati z.hojati@sci.ui.ac.ir 10031947532846009058 10031947532846009058 No Genetics Division, Department of Biology, Faculty of Sciences, University of Isfahan, Isfahan, Iran Ali Jazaeri ali.jazaeri@yahoo.com 10031947532846009059 10031947532846009059 No Cellular and Molecular Research Center, Basic Health Sciences Institute, Shahrekord University of Medical Sciences, Shahrekord, Iran Hossein Teimori hosseintimm@yahoo.com 10031947532846009060 10031947532846009060 Yes Cellular and Molecular Research Center, Basic Health Sciences Institute, Shahrekord University of Medical Sciences, Shahrekord, Iran