Discordance Between Her-2/Neu Expression Assessed Using Immunohistochemistry (Ihc) And Fluorescence In Situ Hybridization (Fish): Is It Important To Detect?

Purpose: Assessment of HER-2 has become of great importance following the advent of HER-2 antibody treatment. Use of trastuzumab therapy depends on the assessment of HER-2 via standard immunohistochemistry (IHC) assays for protein overexpression or via fluorescence in situ hybridization (FISH) for gene amplification. The aim of this study was to determine the rate of discordance between FISH and IHC in our hospital. The rate of discordance varies from hospital to hospital, and due to certain staff, technical, and biological reasons, IHC and FISH may not be concordant in every patient. It is important to determine the rate of discordance between these 2 methods and attempt to lower it. In addition to the rate of discordance, we also investigated the reasons for the discordance and what affect it has on the progression of the disease and treatment.Material and Methods: A total of 79 patients with breast cancer were assessed for HER-2 protein expression via IHC and HER-2 gene amplification via FISH.Results: Among these 79 patients, 47 (59.5%) were FISH (-) and 32 (40.5%) were FISH (+), whereas FISH was negative in 8 (10.4%) patients that were HER-2 (3+) and FISH was positive in 9 (11.4%) patients that were HER-2 (1+). The discordance rate was 21.5%.Conclusion: The clinical implication of this discordance rate and it's affect on the choice of appropriate therapy are of critical importance. As such, it would be beneficial for each hospital to determine its own discordance rate.