Comparative analysis of HER-2/neu amplification, overexpression and polysomy 17 in patients with metastatic breast cancer

Abstract

Amplification or overexpression of HER-2/neu oncogene is associated with poor prognosis and has been correlated with the response to trastuzumab treatment. Chromosomal copy number changes of chromosome 17 occurs in breast cancers and effect the copy number of HER-2/neu gene and consequently IHC score relatively. The aim of this study was to investigate the contribution of chromosome 17 polysomy to positive HER-2/neu immunostaining independent of HER-2/neu amplification using dual-color FISH technique on the paraffin-embedded tissues of metastatic breast cancers. Paraffin-embedded speciment of 32 metastatic breast cancer cases were analysed using dual-color FISH probes specific to HER-2/neu gene and chromosome 17. Results showed significant association between the cases with IHC 2+ and polysomy 17 (p=0.011), and IHC 3+ and HER-2/neu amplification (p=0.023). In conclusion, increased HER-2/neu gene copy number in accordance with polysomy 17 might lead to a strong protein overexpression in the metastatic breast cancer. Therefore FISH technique may also be more sensitive interpretation tool in cases with polysomy 17.