HER2/neu Testing In 432 Consecutive Breast Cancer Cases using FISH and IHC - A Comparative Study.

INTRODUCTION: The development of trastuzumab, a HER-2/neu targeted monoclonal antibody resulted in significant improvements in clinical response and survival in HER-2/neu gene amplified group of patients. Thus, accurate assessment of HER-2/neu status becomes critical. Fluorescence In Situ Hybridization (FISH) and Immunohistochemistry (IHC) are the most commonly used methods for this purpose and specific recommendations exist with regard to the concordance to be observed between the two tests. AIM: Here, we report and evaluate the concordance rate between FISH and IHC for HER-2/neu status in breast cancer specimens. MATERIALS AND METHODS: Archival paraffin blocks of tumour tissue from 450 patients of breast cancer were analyzed for Her-2/neu status using FISH and IHC. RESULTS: There was a highly significant concordance between the results of FISH and IHC assays in HER-2/neu status assessment in invasive breast cancer cases. There were inverse associations between the expression of Oestrogen Receptors/Progesterone Receptors (ER/PR) and HER-2/neu amplification. CONCLUSION: Although, IHC gave significant concordant results with FISH in determining HER-2/neu status, its subjective grading system precludes its use as a gold standard. FISH should always be used to determine true gene amplification when the IHC results are equivocal.