Evaluation of immunohistochemistry technique in detecting HER2 overexpression in invasive ductal breast carcinoma using fluorescence in-situ hybridization method

Abstract

Background: Breast cancer is the most common cancer among women. HER2 gene is a proto-oncogene that encodes the receptor of tyrosine kinase from epidermal growth factor receptor (EFGR) family. It is an important prognostic factor with a determinant role in treatment of breast cancer. There is no globally accepted method for determining the status of this gene and the method of choice is still a matter of debate. We aimed to evaluate the validity of immunohistochemistry (IHC) method in predicting HER2 status using fluorescence in-situ hybridization (FISH) method and also, to investigate some clinicopathological variables associated with HER2 amplification. Methods: In this cross-sectional study, 190 formalin-fixed and paraffin-embedded tissue specimens of invasive breast carcinoma with HER2 of ++ and +++ in IHC evaluation were enrolled. FISH method was performed on all these samples and the relationship of HER2 status and clinicopathological variables was evaluated. Findings: The studied population included 160 specimens of ++ and 30 specimens of +++ HER2 in IHC evaluation. The estrogen and progesterone receptors (ER and PR) were expressed in 64.2 and 74.2 of the specimens, respectively. HER2 amplification on FISH method was found in 27.5 and 83.3 of specimens of ++ and +++ HER2 in IHC evaluation, respectively. Tumors with HER2 amplification were more likely to be negative for estrogen (52.2 vs. 26.4, P < 0.001) and progesterone (39.1 vs. 18.2 , P = 0.013) receptors. Conclusion: This study showed that immunohistochemistry is not a good method for evaluating HER2 status and decision making about trastuzumab therapy even in patients with +++ HER2. © 2016, Isfahan University of Medical Sciences(IUMS). All rights reserved.