HER-2 analysis in tissue microarrays of archival human breast cancer - Comparison of immunohistochemistry and fluorescence in situ hybridization

HER-2 gene alterations have been shown to have prognostic and predictive value for the treatment of breast cancer with therapeutic agents. As a result, the accurate evaluation of HER-2 status is crucial. HER-2 status is assessed at the protein level by immunohistochemistry and at the DNA level by fluorescence in situ hybridization (FISH). Although the best approach is to combine immunohistochemistry and FISH assays, doing so is not practical or cost-effective for routine histopathologic laboratories. The recent development of tissue microarray technology has allowed large-scale studies using formalin-fixed, paraffin-embedded material. We used this technique to assess HER-2 status in a cohort of 54 invasive breast cancer cases by immunohistochemistry and FISH assays to determine whether the results obtained were representative of the protein and gene expression patterns of the original whole tissue section. Concordance for HER-2 immunohistochemistry between the tissue microarray and full sections was 93%. Concordance for HER-2 FISH between the tissue microarray and full sections was 91%. Concordance between HER-2 FISH and HER-2 immunohistochemistry on the tissue microarray was 98%. We conclude that tissue microarrays provide highly comparable results in the assessment of HER-2 protein levels and allow large-scale analysis of the HER-2 gene by FISH.