HER-2/neu status in breast carcinoma: overexpression versus amplification

Verdú M1, Colomer A2, Román R2, Erill N2, Moreno A1, Cordón-Cardo C1,2, Puig X1,2.

1HISTOPAT Laboratoris & 2BIOPAT. Grup Assistència. Barcelona (Spain).

HER-2/neu is a critical marker in assessing the molecular profile of breast cancer, as it represents a target for therapeutic intervention. HER-2/neu gene amplification has been reported to be associated with treatment response. Immunohistochemistry (IHC) to detect HER-2/neu protein overexpression was initially recommended as the technique of choice to assign patients to Herceptin clinical treatment. However, different studies have shown that IHC results are not always conclusive, since they can render false positive and negative results depending on the antibody used. It has also been reported that defining gene amplification by FISH provides more accurate information on response to treatment and to be a better criterion for patient treatment selection. We undertook this study to analyze the concordance between both approaches: protein overexpression vs. gene amplification.

We studied 204 formalin-fixed paraffin-embedded cases of breast carcinoma prospectively compiled. A hundred cases were processed, including fixation, in our laboratory under specific protocol conditions, whereas the remaining tumors were submitted by external laboratories and underwent heterogeneous conditions of processing and fixation. Sections were immunostained using both CB11 (Novocastra) and TAB250 (Zymed) monoclonal antibodies, following an overnight procedure that ended with avidin-biotin immunoperoxidase detection. Additionally, consecutive sections were analyzed by FISH, using probes directed against the HER-2/neu locus and the centromeric region of chromosome 17 (Vysis).

Based on the differences in sensitivity and specificity observed for CB11 and TAB250, we conclude that the IHC results obtained from the use of these antibodies are not equivalent. We found a decrease in the specificity of TAB250 in the cases submitted by external laboratories. This phenomenon, added to the fact that a significant percentage of external cases are not-evaluable by FISH, let to the conclusion that controlled processing and fixation conditions are required in order to minimize diagnostic errors. Strict criteria and good expertise of the laboratory personal are also crucial requirements for the interpretation of IHC results. Finally, the application of FISH as a support technique is essential to obtain the best predictive information.

Abstract exhibited at the:


12-15 February 2003. Barcelona-Spain.