HER2/neu expression and gene alterations in pancreatic ductal adenocarcinoma: a comparative immunohistochemistry and chromogenic in situ hybridization study based on tissue microarrays and computerized image analysis.

CONTEXT HER2/neu overexpression is observed in many cancers including pancreatic ductal adenocarcinoma. Although immunohistochemistry remains the basic method for evaluating HER2/neu protein expression, significant information regarding gene status cannot be assessed. DESIGN Using tissue microarray technology, fifty histologically confirmed pancreatic ductal adenocarcinomas were cored twice and re-embedded in one paraffin block. Immunohistochemistry (clone TAB 250) and chromogenic (HER2/neu amplification Spot Light kit) in situ hybridization protocols were performed. The immunostained slides were evaluated by conventional eye microscopy and digital image analysis. The chi square test and the kappa statistic were applied by running the SPSS package. MAIN OUTCOME MEASURES The levels of staining intensity were estimated by the performance of a semi automated image analysis system. RESULTS HER2/neu gene amplification was detected in 8/50 cases (16%). Chromosome 17 aneuploidy was detected in 19 cases (38%). Significant improvement in interobserver agreement (kappa=0.76 vs. 0.94) was achieved correlating the immunohistochemical results obtained by conventional eye and digital microscopy, especially in the cases of overexpression (2+, 3+). Finally, 29 (58%), 11 (22%), 6 (12%) and 4 (8%) cases were characterized as 0, 1+, 2+ and 3+, respectively. HER2/neu protein expression was significantly associated with grade (P=0.019), but not with stage (P=0.466). in addition, chromosome 17 and gene status were not correlated with stage and grade. CONCLUSION Our results indicate that a subset of pancreatic ductal adenocarcinomas is characterized by HER2/neu gene amplification. In contrast to breast cancer, protein overexpression does not predict this specific gene deregulation mechanism. This event may reflect the different biological role of the molecule in those two solid tumours, affecting the response to novel targeted agents, such as monoclonal anti-HER2/neu antibodies. Furthermore, evaluation of HER2/neu protein expression based on digital image analysis and not only on conventional eye microscopy improves the accuracy and reliability of immunohistochemical estimation, although that does not demonstrate clinical significance and prognostic value in pancreatic ductal adenocarcinoma.