HER 2/neu expression and gene amplification in colon cancer

Abstract

HER 2/neu is an important oncogene in breast cancer, but the prevalence and significance of HER 2/neu gene amplification in colon cancer have been poorly documented. We have evaluated HER 2/neu gene amplification and protein overexpression in a series of colon cancers to assess the frequency, concordance and clinical significance of these events. HER 2/neu gene copy number was measured in 154 primary colon tumors, 15 liver metastases and matched normal tissues using a quantitative PCR/ligase detection reaction (LDR) technique developed and validated in our laboratory. HER 2/neu copy number was confirmed by fluorescent in situ hybridization (FISH) in all tumors found to have gene amplification. In an independent and blinded fashion, HER 2/neu expression was assessed in paraffin sections from 139 of the tumor specimens using the HercepTest kit. HER 2/neu gene amplification was observed in 4 (2.4%) of the 169 tumor specimens and in none of the normal tissues. There was no apparent association with stage of disease, tumor grade or patient survival. Among 139 cases evaluated by immunohistochemistry (IHC), HER 2/neu overexpression was seen in 5 cases (3.6%). There was extremely high concordance (kappa = 0.852) between gene amplification and protein overexpression. The low prevalence of HER 2/neu gene amplification and protein overexpression suggests that this oncogene plays an infrequent role in the development and progression of colon cancer. These data indicate that the primary mechanism of dysregulated HER 2/neu expression in colon cancer, as in breast cancer, is gene amplification.