A Multi-Method Analysis of c-erbB2/HER2 in FFPE Tissue: Correlation of a Novel and Rapid In Situ Hybridization Procedure, HER2 CISH and IHC.
Authors: Tacha D. , Alba Dominguez J. , Gutierrez Bernal J. , Henshall-Powell R. , Vargas J. , DeGolia C. , Kyshtoobayeva A. , Alba Losada J. 
Published: December 2010

Background: Overexpression of HER2/neu gene or protein is found in 20% to 30% of breast carcinomas and is predictive of response to treatment by trastuzumab. Methods such as FISH or CISH determine gene amplification status, however, amplified genes may or may not be all transcribed at equivalent levels. Recently, a new c-erbB-2 probe for rapid in situ hybridization (rapid ISH) has been designed. This probe consists of 2 fragments of single-stranded DNA with lengths of 672 and 1143 nucleotides that are targeted against mRNA sequences transcribed from the HER2/neu gene. The extended probe sequence confers increased specificity, sensitivity and speed of reaction with the target mRNA. In this study, the correlation of the Rapid ISH method to FDA approved IHC and CISH methods and a method employing a rabbit monoclonal antibody is assessed. Equivocal IHC cases (IHC 2+) will also be validated.Methods: Two TMA blocks (98 cases: 2 cores/case) of FFPE cases of invasive breast carcinomas were used. Blocks were previously scored by IHC. IHC was assessed by Dako HercepTest®, and a rabbit monoclonal antibody [EP1045Y]; and two ISH methods, a c-erbB-2 probe, and HER2 CISH. All cores were assessed for IHC 0, 1+, 2+ and 3+ staining and ISH was scored as positive, or negative, according to the FDA approved interpretation scheme. Rapid ISH is scored as negative or positive.Results: IHC scores 0 and 1+ were considered negative. IHC 2+ scores were considered negative or positive after confirmation by CISH, and 3+ scores were positive. ISH was scored negative or positive. In a 98 case study, there was a 94% (92/98) concordance between HER2 CISH and IHC, 92% (90/98) concordance between Rapid ISH and IHC; and HER2 CISH and Rapid ISH showed a 98% (96/98) concordance. In one case a 1+ IHC score by HercepTest was determined to be positive by CISH and Rapid ISH.Score01+2+3+HercepTest® (%)41.0%20.5%10.3%28.2%c-erbB-2/HER2 RbMab (%)39.8%15.3%11.2%33.7%c-erbB-2/HER2 RISH Probe + (%)1.0%1.0%1.0%38.8%HER2 CISH + (%)0.0%2.0%1.0%36.7%Table 1: Correlation of c-erbB-2/HER2 by IHC, Gene Amplification (CISH) and mRNA (Rapid ISH) on TMA. Total 98 cases (*except HercepTest® which had 39 cases).Conclusion: c-erbB2 protein was assessed by IHC using the HercepTest®, HER2 gene amplification was quantified using HER2 CISH and HER2 mRNA transcription was determined using a chromogenic single stranded DNA probe (Rapid ISH). A 95% correlation was achieved between the two IHC methods (HercepTest® and a rabbit monoclonal antibody). Concordance between HER2 CISH and Rapid ISH methods was 98%. The rabbit monoclonal antibody IHC method achieved a 94% correlation with HER2 CISH compared to 95% for HercepTest®. In conclusion, this study demonstrates the high concordance between Rapid ISH and the common methods (IHC, FISH/CISH) for assessment of c-erbB2 or HER2/neu status in breast cancer. Based upon these results, it may be proposed that Rapid ISH or HER2 CISH be used in the primary screening of HER2 status.

Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 6009.