Detection of HER-2/neu (c-erbB-2) overexpression and amplification in breast carcinomas with ambiguous immunohistochemical results. A further contribution to defining the role of fluorescent in situ hybridization.

BACKGROUND The assessment of HER-2/neu status is a prerequisite in the clinical management of patients with breast cancer in order to obtain prognostic and predictive information, including Herceptin sensitivity. Immunohistochemistry (IHC) and fluorescent in situ hybridization (FISH) are the techniques recommended to detect HER-2/neu alterations and considerable attention is currently being focused on the standardization of these techniques. Intrinsic limitations of IHC, such as antigen preservation and antibody specificity, may make it difficult to score the membrane staining thereby resulting in inconclusive results. PATIENTS AND METHODS In this study, 65 invasive breast carcinomas, with doubtful IHC results using the monoclonal antibody CB11, were reanalyzed with two recently licensed assays, the Hercep Test (IHC) and the Path Vision (FISH). RESULTS IHC with Hercep Test detected HER-2 protein overexpression in 72% of cases, including nine (14%) strongly positive (3+), 13 (20%) medium positive (2+) and 25 (38%) weakly positive (1+) specimens. FISH testing, with interpretable results in 48 cases, showed a moderate HER-2 gene amplification in only 22% of carcinomas with 2+ or 3+ overexpression. CONCLUSION These data indicated an excessive sensitivity of the Hercep Test and suggested that, in the case of indeterminate results after standard IHC, the FISH technique is the best approach to establish HER-2 status.