Comparison of chromogenic in situ hybridisation with fluorescence in situ hybridisation and immunohistochemistry for the assessment of her-2/neu oncogene in archival material of breast carcinoma.

The successful treatment of breast cancer is dependent upon a number of complex factors. Her-2/neu gene amplification is known to be one of the most common genetic alterations associated with breast cancer and its accurate determination has become necessary for the selection of patients for trastuzumab therapy. The aim of this study was to prove the consistency of chromogenic in situ hybridisation (CISH) technique after analyzing the overexpression of the Her-2/neu proto-oncogene in 100 invasive breast carcinomas and by comparing CISH results with immunohistochemistry (IHC) and fluorescence in situ hybridisation (FISH). Moreover, it was done to evaluate the possible correlation of estrogen (ERs) and progesterone receptors (PRs), the proliferation marker Ki67 and the tumour suppressor gene p53 with HER-2/neu status of these breast carcinomas. Of the 100 breast carcinomas that were analysed, 22 cases showed HER-2/neu amplification, 66 cases showed no amplification, whereas 12 cases were non-interpretable in both assays (FISH and CISH). Consequently, the overall concordance between FISH and CISH was 100%. Additionally, it was observed that when HER-2/neu gene was overexpressed, there was an association with negative PRs and ERs status, negative p53 protein expression and high Ki67 labelling index. It is concluded that patients with tumours scoring 2+ with the CBE356 antibody (borderline immunohistochemistry-tested cases) would also benefit from CISH as it is shown to be highly accurate, practical and can be easily integrated into routine testing in any histopathology laboratory. Finally, CISH represents an important addition to the HER2 testing algorithm.