HER۲ Testing in Invasive Breast Cancer: A Comparison Between Immunohistochemistry and Fluorescence In Situ Hybridization Assays

Background: HER۲ status testing in breast cancer is crucial for the detection of eligible patients for trastuzumab therapy. In this study, the relative copy number of HER۲ 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. Material and Methods: HER۲ status of ۳۱ invasive breast cancer samples was compared using IHC and FISH techniques. The ratio of HER۲/CEP۱۷ was used to determine the amplification of the HER۲ gene. If the ratio of HER۲/CEP۱۷ is greater than ۲.۲, HER۲ gene amplification has occurred in the cancer cells. Then, a comparative analysis is performed to estimate the concordance rate between FISH and IHC results. Results: The gene amplification of HER۲ was observed in ۲۶% of cases by FISH. The IHC and FISH results showed ۱۰۰%, ۳۶.۳۶%, and ۸۵.۷۱% concordance rates for cases with IHC scores of ۳+, ۲+, and ۰/+۱, respectively. The overall concordance between the two methods was ۸۰%. Based on statistical analysis, HER۲ status showed a considerable correlation with tumor grade (P= ۰.۰۲). No correlation was observed between HER۲ gene status and the size and type of tumor, characteristics of lymph node, and patients’ age. Conclusion: The data suggested that IHC results are reliable for HER۲ status testing in cases with IHC scores ۰/+۱ and ۳+. However, in patients with an IHC score of +۲, it is necessary to perform a complimentary test to evaluate HER۲ status to avoid haphazard treatment with trastuzumab in negative cases and identifying positive cases for suitable treatment.

Keywords:

Breast cancer , FISH , IHC , HER۲