Comparison of fluorescence in situ hybridization and immunohistochemistry for the evaluation of HER-2/neu in breast cancer.

PURPOSE: To compare fluorescence in situ hybridization (FISH) and immunohistochemistry (IHC) in the determination of HER-2/neu status of breast cancers. MATERIALS AND METHODS: FISH and IHC for HER-2/neu were performed on formalin-fixed paraffin sections of 100 consecutive invasive breast cancers. FISH was performed at Beth Israel Deaconess Medical Center, Boston, MA, using the Oncor/Ventana INFORM kit (Ventana Medical Systems, Tucson, AZ; formerly sold by Oncor, Inc, Gaithersburg, MD) in a laboratory certified as proficient in this procedure. IHC was performed at PhenoPath Laboratories, Seattle, WA, using a polyclonal antibody to the HER-2/neu protein. FISH and IHC were analyzed in a blinded fashion, and the results were then compared. Procedure and interpretation times and reagent costs for FISH and IHC were also compared. RESULTS: HER-2/neu was amplified by FISH in 26% of cases, and 23% were HER-2/neu-positive by IHC. FISH and IHC were both assessable in 90 cases. Concordance between FISH and IHC results was seen in 82 of these cases (91%, P <.001). The FISH procedure required more technologist time and more interpretation time per case for the pathologist than IHC. Reagent costs were substantially higher for FISH than for IHC. CONCLUSION: There is a high level of correlation between FISH and IHC in the evaluation of HER-2/neu status of breast cancers using formalin-fixed paraffin-embedded specimens. Although the choice of which assay to use should be left for individual laboratories to make based on technical and economic considerations, our results may make it difficult to justify the routine use of FISH for determination of HER-2/neu status in breast cancer.