Her2 amplification: correlation of chromogenic in situ hybridization with immunohistochemistry and fluorescence in situ hybridization.

Detecting Her2 gene amplification has become routine in predicting therapeutic responsiveness in patients with breast carcinoma. Fluorescence in situ hybridization (FISH) is a common technique for detecting Her2 amplification, yet dark field fluorescence microscopy remains problematic for many pathologists. Thus, a technique such as chromogenic in situ hybridization (CISH), in which the more familiar light microscopy can be used, is appealing. Paraffin-embedded sections from 61 breast carcinomas were tested for Her2 amplification by immunohistochemistry (IHC) and CISH. FISH was used to confirm CISH results. Excellent correlation was found between IHC and CISH except in cases considered negative (1+ on the DAKO scale) by IHC. CISH detected low-level Her2 amplification in 4 of 9 of these cases. Amplification was subsequently confirmed by FISH in all but 1 case. When compared with FISH, CISH was more sensitive than IHC for detecting low levels of Her2 gene amplification. Moreover, excellent concordance was found between FISH and CISH, supporting the conclusion that the CISH assay for Her2 gene amplification provides an accurate, effective, and practical alternative to FISH.