HER-2/neu Oncogene Amplification by Chromogenic in situ Hybridization and Immunohistochemical Expression of Topoisomerase II-alpha in the Breast Cancer

ABSTRACT

BACKGROUND: Amplifications of the HER-2/neu oncogene and the Topoisomerase II-alpha gene are important determiners of the response to chemotherapy in the breast cancer. For detecting HER-2/neu amplification, fluorescent in situ hybridization and immunohistochemistry are currently regarded as standard methods. Chromogenic in situ hybridization (CISH) is investigated as a new modification of in situ hybridization. The purpose of this study is to compare the efficacy of CISH and immunohistochemistry (IHC) in detecting HER-2/neu oncogene amplification and to investigate the prognostic significance of the HER-2/neu oncogene and the Topoisomerase II-alpha gene in breast cancer. METHODS: Using CISH and IHC the amplifications and protein expressions of the HER-2/neu oncogene were studied on paraffin sections of 43 infiltrating duct carcinomas. The expression of the Topoisomerase II-alpha gene was studied immunohistochemically. RESULTS: Of the 43 infiltrating duct carcinomas, amplifications of the HER-2/neu oncogene by CISH were observed in 8 cases (18.6%), and the HER-2/neu protein was deemed overexpressed by IHC in 9 cases (20.9%). The amplifications of the HER-2/neu oncogene showed a statistically significant correlation with tumor size, histological grade, and the Topoisomerase II-alpha index. The Topoisomerase II-alpha index showed a statistically significant correlation with tumor size, lymph node status, stage, histologic grade, and estrogen receptor status. CONCLUSIONS: CISH is a useful alternative for determining HER-2/neu amplification, especially for confirming the immunohistochemical staining results. HER-2/neu amplification and the Topoisomerase II-alpha gene index may be prognostic factors of breast cancer.