Determination of HER-2/neu gene Status by Chromogenic in Situ Hybridisation Assay on Borderline (2+) Immunohistochemistry Cases in Patients with Invasive Breast Carcinoma: An Experimental Study on Preserved Tissue

Abstract

HER-2 (also known as HER-2/neu) is a member of the epidermal growth factor (EGF) receptor family. The amplification of oncogene HER-2 is presented in 20 to 30% of breast cancers and results in an increase of the protein expression. HER-2 over expression has also been shown to correlate with poor prognosis. It is associated with poorly differentiated high grade tumors with lymph node involvement, greater risk of recurrence and relative resistance to some types of chemotherapy. The receptor is however a target for treatment with anti HER-2 antibody trastuzumab (Herceptin). Immunohistochemistry analysis for HER 2 scoring is subjective, requires trained personnel and expertise. One of the main concerns with IHC is that there is evidence of significant inter-observer variation in the assessment of staining, which can lead to misclassification of HER2 status. Chromogenic in situ hybridization (CISH) testing is sensitive and specific in detecting HER-2/neu gene amplification.  Direct evaluation of gene amplification using CISH assay is a reliable method for routine diagnostic evaluation of HER2/neu status in breast cancer patients, especially in specimens showing 2+ IHC score. This observational experimental study was carried out in the Department of Pathology, Bangabandhu Sheikh Mujib Medical University, Dhaka, during the period of July 2014 to June 2015, The aim of this study was to assess HER-2 expression accurately in equivocal immunohistochemistry (2+) invasive breast cancer cases by Chromogenic in situ hybridization (CISH) and to associate the findings of CISH assay with  the histologic prognostic and predictive factors (eg: tumor size, regional lymph node metastases, tumor grade and type. A total of 20 archival paraffin tissue blocks and IHC slides with IHC score 2+ for HER-2 were included in this study. All the slides were reviewed. CISH assay was done on section from archival paraffin block.CISH assay showed amplification of the HER-2 neu gene in 30% of cases. Majority (60%) was nonamplified. In two cases the results were unsatisfactory for interpretation. The differences were not statistically significant (p>0.05) among three groups (amplified, nonamplified and unsatisfactory) regarding the baseline characteristics (age and sex) with CISH. All the results of CISH assay in association with tumor size, tumor grade and lymphnode metastasis were not statistically significant. HER-2 / neu status is the one of the most important prognostic and predictive factor. It is a target for treatment with anti HER-2 antibody trastuzumab (Herceptin). Detection of HER-2/ neu status by IHC may sometimes be difficult and inaccurate, specially in IHC score 2+ cases. Based on the findings of the study, CISH can be considered a useful, simple and reproducible method for detecting HER-2/ neu gene amplification in cases with borderline (2+) immunohistochemistry score , and patients may be benefited from Trastuzumab therapy.