Differential analysis of HER2 expression in breast cancer by IHC and FISH

Objective To compare the differences and correlation between immunohistochemistry (IHC) and fluorescence in situ hybridization (FISH) of HER2 in invasive breast cancer. Methods A total of 604 breast cancer specimens from Nov. 2014 to Dec. 2016 in Renmin Hospital of Wuhan University were evaluated for HER2 status by both IHC and FISH to calculate the concordance between these two assays and analyze the causes of discordant cases. Results Except for cases with IHC uncertainty (2+) , overall concordance between IHC and FISH in detection of HER2 was 97.2% (412/424) . The concordance for positive and negative detection was 93.0% (146/157) and 99.6% (266/267) , respectively. The main reasons for the difference of HER2 expression in breast cancer detected by the two methods were the incorrect interpretation of IHC, the higher or lower concentration of antibody, and the change in guidelines. Conclusion HER2 IHC assay is subjective and sensitive to technical factors for determining the expression levels of HER2 protein in breast cancer so that it is not as stable as HER2 FISH assay. Key words: Breast cancer; HER2 gene; IHC; FISH