Laboratory assessment of the status of Her-2/neu protein and oncogene in breast cancer specimens: comparison of immunohistochemistry assay with fluorescence in situ hybridisation assays

Aim-To evaluate the clinical usefulness of three commercially available ass ays for Her-2/neu oncogene and protein measurements. The Her-2/neu protein is overexpressed, mostly as a result of gene amplification, in 20-30% of hu man breast cancers, and has been shown to have prognostic and predictive va lue for treatment with chemotherapy or the new monoclonal antibody, Hercept in. Methods-An immunohistochemistry (IHC) assay using the Dako polyclonal antib ody A0485, which measures the Her-2/neu protein, was compared with two new Food and Drug Administration (FDA) approved fluorescence in situ hybridisat ion (FISH) assays-INFORM(TM) and PathVysion(TM), in a cohort of 52 formalin fixed, paraffin wax embedded breast tissues. These tissues were selected r andomly from 84 consecutive infiltrating breast cancer specimens, which wer e first stratified according to the Her-2/neu protein levels as measured by IHC. Results-The two FISH assays achieved a 98% concordance rate: 14 specimens ( 27%) showed Her-2/neu gene amplification and 37 specimens (71%) showed no H er-2/neu gene amplification. The PathVysion assay had certain advantages ov er the INFORM assay. In contrast, the IHC assay detected Her-2/neu overexpr ession in a high percentage of cases, including 13 high positive specimens (25%) and 13 medium positive specimens (25%). Although 10 of these 13 IHC h igh positive specimens showed gene amplification by FISH, nine of 13 MC med ium positive specimens showed no gene amplification. Statistical analyses s howed that the differences between IHC and FISH assays were primarily in th e specimens with medium positive IHC, but negative FISH results. Conclusions-Because of the increasing importance of the Her-2/neu oncogene and oncoprotein in the clinical management of patients with breast cancer, the accurate and consistent evaluation of Her-2/neu status is crucial. This study suggests that the best approach is to combine both IHC and FISH assa ys; that is, to use the IHC assay as a triage step, followed by the PathVys ion FISH assay to analyse the IHC medium and high positive cases.