Coexpression of EGFR and HER-2 in pancreatic ductal adenocarcinoma: a comparative study using immunohistochemistry correlated with gene amplification by fluorescencent in situ hybridization.

Pancreatic ductal adenocarcinoma (PDAC) is the major pancreatic tumor and carries an extremely poor prognosis. Coexpression of epidermal growth factor receptor (EGFR) and the HER-2 oncoprotein has been reported to be related to the invasion and an adverse clinical outcome of human pancreatic ductal adenocarcinomas. HER-2 amplification, as determined by fluorescent in situ hybridization (FISH) analysis, has been identified as a positive predictor of response to EGFR tyrosine kinase inhibitor treatment in some other cancers. The aim of this study was to investigate the coexpression rate and amplification status of HER-2 oncogene in EGFR positive pancreatic ductal adenocarcinoma (PDAC) by immunohistochemistry and FISH. Overexpression of EGFR (>or=2+) was seen in 65% (21/32) of the study cases. EGFR gene amplification was not detected in any of the 32 PDACs. Overexpression of HER-2 protein (>or=2+) was seen in 17% (5/28) of the study cases and in 24% (5/21) of EGFR positive cases. None of the EGFR negative tumors showed HER-2 overexpression or gene amplification. The HER-2 gene locus was amplified in 11% (3/28) of the study cases and in 14% (3/21) of EGFR positive PDACs. There was 60% concurrence between HER-2 gene amplification and HER-2 protein expression in this study. These results suggest that HER-2 is an important cooperating member of the EGFR signal pathway in a subset of PDAC.