Chromogenic In Situ Hybridization Analysis to Determinate HER-2/neu Status in Breast Carcinoma

Purpose: The determination of HER-2/neu gene amplification has become necessary for the selection of breast cancer patients to undergo anti-HER-2/neu therapy, using a humanized monoclonal antibody. Chromogenic in situ hybridization (CISH) detection of the HER-2/neu gene, a newly developed method, utilizes a robust and unique-sequence DNA probe labeled with digoxygenin, which is sequentially incubated with antidigoxygenin fluorescein, antifluorescein peroxidase and diaminobenzidine. The aim of this study was to establish a CISH assay for the detection of HER-2/neu amplification. The results were compared with those of the immunohistochemistry (IHC) methods, most frequently used for detecting HER-2/neu alteration. Methods: CISH was performed in 4 groups of infiltrating breast carcinomas. Each group was comprised of 20 cases in which the HER-2/neu stati had previously been scored on a four value scale: 0, 1+, 2+ and 3+ by IHC. The results of CISH and IHC were compared for each tumor group. The HER-2/neu gene amplification detected by CISH was thpically visualized as large DAB-stained clusters or by many dots in the nucleus. Results: The concordance between the CISH and IHC was 95% (=0.901). Three IHC-positive cases (score 2+) showed no gene amplification and one IHC-negative case (score 1+) showed gene amplification by CISH. Conclusion: The current study showed excellent agreement between the CISH and IHC methods. CISH is an accurate, practical and economical approach for determining the HER-2/neu stati in breast carcinomas. It is also a useful methodology for confirming the IHC results in paraffin-embedded tumor samples, so offers a promising alternative to IHC in a routine diagnostic setting.