Expression of erbB-3 protein in colorectal adenocarcinoma: correlation with poor survival

The family of erbB receptors includes four transmembrane glycoproteins with tyrosine kinase activity. These receptors are widely expressed in normal tissues, but they also have been implicated in the development of several human adenocarcinomas. c-erbB-3/HER-3 has been detected to a greater or lesser extent in many tissues from the digestive, urinary, reproductive and respiratory tracts. The overexpression of c-erbB-3/HER-3 protein has also been shown in 53%-88% of colorectal adenocarcinomas. In this study we investigated the expression of the c-erbB-3/ HER-3 gene product in colorectal tumour samples, and compared the results obtained with several clinicopathological parameters, including the survival of patients.

Paraffin-embedded tissue sections were analysed immunohistochemically, using monoclonal antibody RTJ1 to human erbB-3 protein. Antibody RTJ1 specificity was confirmed by immunoprecipitation followed by Western blotting analysis. Amplification of the erbB-3 oncogene was tested by dot-blot hybridization.

Adenocarcinomas of the colon were positive for erbB-3 protein in 78% of samples examined. Dot-blot analysis showed no amplification of the erbB-3 gene in colon adenocarcinomas. Statistical analysis showed that patients with tumours that could not be stained for erbB-3 protein survived significantly longer (P<0.05) than patients with tumours staining positive for the erbB-3 protein. A Cox proportional-hazards model with stepwise variable selection identified age, sex and erbB-3 expression as important prognostic factors.

These findings demonstrate that erbB-3 protein expression could serve as a prognostic factor in colorectal malignancies.