Analysis of ERBB2 and TOP2A gene status using fluorescence in situ hybridization versus immunohistochemistry in localized breast cancer.

The aim of our study was to assess the ERBB2 and TOP2A gene status in breast carcinoma tissue using fluorescence in situ hybridization (FISH) and to compare their amplification with immunohistochemistry assay (IHC) of the ERBB2, resp. topoisomerase IIalpha proteins. TOP2A status is important in tailored treatment as topoisomerase IIalpha is the molecular target for topoisomerase IIalpha inhibitors. This study was conducted to determine whether the methods are equivalent in their assessment of TOP2A status and to correlate the genetic findings with basic tumor and disease characteristics. Locus specific ERBB2, TOP2A genes and chromosome 17 centromeres (CEP17) probes were hybridized to 72 formalin-fixed paraffin-embedded (FFPE) tissue samples from patients with non-metastatic breast carcinoma (M0). The ERBB2, TOP2A and CEP17 signals were counted and gene numbers per nucleus or per CEP17 were calculated, respectively. Sections were also stained with commercial polyclonal antibody (HercepTestTM), anti-topoisomerase IIalpha monoclonal antibody (clone SWT3D1) and scored for the presence of membrane/nuclear staining. ERBB2 amplification was found in 20.3%, ERBB2 and TOP2A co-amplification was detected in 14.5% of cases. Deletion of the ERBB2/TOP2A gene was found in 1.4/2.8% of sections, respectively. Concordance of FISH and IHC techniques in the evaluation of ERBB2 and TOP2A status was found in 88.4% and 66.7%, respectively. The low concordance of FISH versus IHC in the evaluation of TOP2A status was mainly due to the presence of TOP2A amplified tumors in IHC negative or weakly positive specimens. Topoisomerase IIalpha expression was increased in bigger tumors, although direct correlation with tumor grading was not found. ERBB2 amplification was found in more aggressive breast cancers with grades 2 and 3, respectively. Interestingly, chromosome 17 polysomy was more frequently observed among older women (>55 years), suffering usually from less aggressive disease. Our results confirm the high concordance of the ERBB2 and TOP2A gene co-amplification in breast carcinoma. Differences between FISH and IHC in the case of ERBB2 gene status were found only in IHC 2+ sections as reported in the literature. However, our study points to the importance of FISH examination of TOP2A gene status in all tumors with ERBB2 amplification.