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 immunohis tochemistry (IHC) in the determination of HER-2/neu status of breast cancer s. Materials and Methods: FISH and IHC for HER-2/neu were performed on formali n-fixed paraffin sections of 100 consecutive invasive breast cancers. FISH was performed at Beth Israel Deaconess Medical Center, Boston, MA, using th e Oncar/Ventana INFORM kit (Ventana Medical Systems, Tucson, AZ; formerly s old by Oncor, Inc, Gaithersburg, MD) in a laboratory certified as proficien t in this procedure. IHC was performed at Pheno-Path Laboratories, Seattle, WA, using a polyclonal antibody to the HER-2/neo protein. FISH and IHC wer e analyzed in a blinded fashion, and the results were then compared. Proced ure and interpretation times and reagent costs for FISH and IHC were also c ompared. 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. Conco rdance between FISH and IHC results was seen in 82 of these cases (91%, P < .001). The FISH procedure required more technologist rime and more interpr etation time per case for the pathologist than IHC. Reagent costs were subs tantially higher for FISH than for IHC. Conclusion: There is a high level of correlation between FISH and IHC in th e evaluation of HER-2/neo status of breast cancers using formalin-fixed par affin-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 u se of FISH for determination of HER-2/neo status in breast cancer. (C) 1999 by American Society of Clinical Oncology.