Comparison of Real-Time PCR and Immunohistochemistry for HER-2/neu gene amplification assay in breast cancer tissue

Abstract

Background: HER-2/neu is one of the major molecular prognostic markers in breast cancer and due to treatment decision guidelines, the amplification of this gene is very important in breast cancer patients treatment. The most commonly used method for detecting HER-2/neu gene amplification is immunohistochemistry (IHC). Unquantifiable results, lack of reproducibility and long procedure time are among the drawbacks of this method which have persuaded researchers to seek alternative modern molecular based techniques such as Real-Time PCR. The aim of our study was the comparison of HER-2 gene amplification assessed by RealTime PCR and IHC method. Materials and Methods: After DNA extraction, 41 formalin-fixed paraffin-embedded (FFPE) breast carcinoma with known IHC results, had been assessed using Real-Time PCR and gene copy number of HER-2 were measured and compared with the results of IHC. Fluorescent in situ hybridization (FISH) for equivocal IHC and unreliable results were performed. The Fisher's Exact Test and Phi Cramer's V Coefficient were used for statistical analysis. Results: According to the results, 39% of samples tested by Real-Time PCR have HER-2/neu gene amplification and 36% of samples was positive by IHC. The correlation of two methods in positive and negative samples were 85% and 87% respectively. Overrall correlation between two methods was 71%. Also, IHC2+ results have been assessed by FISH technique and all of them were negative, which was in concordance with the results of the Real-Time PCR. Conclusion: About 71% concordance had been observed between two methods. In the case of IHC2+ results, FISH was performed and proved the Real-Time PCR results. Real-Time PCR could precisely measure the amount of tissue HER2 amplification and also were in agreement with IHC results. Since Real-Time PCR has high precision, also is cheaper and more accessible than other methods, we suggest it to be used to assess this indicator.