The Concordance between Immunohistochemical Staining and Silver In Situ Hybridization for HER2 Status in Breast Cancer Tissue Samples

Abstract: The human epidermal growth factor receptor-2 (HER2) protein has been associated with breast cancer progression and the HER2 status can be used to determine the type of treatment for each breast cancer patient. The purpose of this study was to examine the HER2 protein and gene statuses in breast cancer tissue samples using two methods and analyze the concordance between them. Ten paraffin-embedded, formaldehyde-fixed breast cancer tissue samples from the Biobank at the Department of Pathology and Cytology at Sundsvall Hospital were analyzed in this study. All samples were from women born between 1931 and 1976. The methods used were immunohistochemistry (IHC) to visualise the HER2 protein and silver in situ hybridization (SISH) to detect gene amplification. The IHC staining method is an indirect detection of the HER2 protein using antibodies. The SISH method used in this study is a Dual ISH which detects both the HER2 gene and the centromere region of Chromosome 17 on the same tissue slide. A HER2 gene/Chromosome 17 ratio was calculated according to the manufacturer’s instructions. This ratio was used to determine HER2 gene status. Out of ten samples, seven were positive with IHC and three were negative. The results from the SISH staining exposed a gene amplification in three of the IHC positive samples, while seven samples did not contain any amplified HER2 genes. The conclusion was that the concordance between IHC and SISH for HER2 was 60 percent.