Diagnostic value of IHC and FISH methods for HER2 gene amplification detection in paraffin embedded blocks of breast cancer

Introduction: Breast cancer is the leading cause of malignancy related deaths in women worldwide. In 20%-30% of breast cancers, HER2 gene amplification or overexpression is observed. Determination of HER2 amplification is performed mainly by IHC technique to measure its protein expression on the cell surface and by FISH to check gene amplification. This study was aimed to compare the sensitivity and specificity of IHC in comparison to the FISH method for detection of HER2 gene amplification. Methods: In this study which was performed in 2020, 44 paraffin embedded breast carcinoma tissues belonging to women with breast cancer which have been already examined with IHC technique have been analyzed using FISH technique to determine HER2+ overexpression. Data were analyzed using GraphPad (Anova ver8) software. P<0.05 was considered statistically significant. Results: Comparison of IHC results with FISH represented 16% false positive and 9% false negative, therefore the sensitivity of IHC for identifying of HER2+ the meaning of true positive was equal to 66.6% and the specificity of IHC in determining true negatives was equal to 78.1%. The results showed that IHC has many errors. Conclusion: The confidence level of positive results and negative results was equal to 53.3% and 86.2%, respectively. Therefore, FISH method should be used as an alternative method in conjunction with IHC.