Comparative methodological analysis of erbB‐2/HER‐2 gene dosage, chromosomal copy number and protein overexpression in breast carcinoma tissues for diagnostic use

AIMS: This study was performed to test the validity of different methods for determining the status of the erbB-2/HER-2 oncogene in breast cancer tissues for diagnostic use. METHODS AND RESULTS: Forty formalin-fixed, paraffin-embedded breast carcinomas were investigated by fluorescence in situ and comparative genomic hybridization (FISH, CGH) as well as by immunohistochemistry (IHC) using Dako-HercepTest and CB11 antibody (Ventana). Additionally, competitive-differential polymerase chain reaction (cdPCR) was performed on frozen samples to estimate gene dosage alterations of erbB-2/HER-2. Amplification was detected in 12-23% and protein overexpression in 16-68% of the cases, depending on the methodology and/or the reagent used. Perfect concordance (100%) was found between the results of cdPCR and CB11-IHC, and a 97% concordance between FISH and CB11-IHC. The concordance between Dako-HercepTest and CB11-IHC was 78%: seven of eight 2+ carcinomas with the Dako-HercepTest were classified as nonamplified using FISH. CONCLUSIONS: Our results indicate that high-level expression as well as normal erbB-2/HER-2 status of breast carcinomas can be detected reliably both by IHC and gene dosage assessment in paraffin material for diagnostic use. However, borderline results, especially those with 2 + immunopositivity, should be interpreted with caution and increased emphasis should be given to other clinical and prognostic information available.