Mesothelin is overexpressed in the vast majority of ductal adenocarcinomas of the pancreas: identification of a new pancreatic cancer marker by serial analysis of gene expression (SAGE).

Effective new markers of pancreatic carcinoma are urgently needed. In a previous analysis of gene expression in pancreatic adenocarcinoma using serial analysis of gene expression (SAGE), we found that the tag for the mesothelin mRNA transcript was present in seven of eight SAGE libraries derived from pancreatic carcinomas but not in the two SAGE libraries derived from normal pancreatic duct epithelial cells. In this study, we evaluate the potential utility of mesothelin as a tumor marker for pancreatic adenocarcinoma. Mesothelin mRNA expression was evaluated in pancreatic adenocarcinomas using reverse-transcription PCR (RT-PCR) and in situ hybridization, whereas mesothelin protein expression was evaluated by immunohistochemistry. Using an online SAGE database (http://www.ncbi.nlm.gov/SAGE), we found the tag for mesothelin to be consistently present in the mesothelioma, ovarian cancer, and pancreatic cancer libraries but not in normal pancreas libraries. Mesothelin mRNA expression was confirmed by in situ hybridization in 4 of 4 resected primary pancreatic adenocarcinomas and by RT-PCR in 18 of 20 pancreatic cancer cell lines, whereas mesothelin protein expression was confirmed by immunohistochemistry in all 60 resected primary pancreatic adenocarcinomas studied. The adjacent normal pancreas in these 60 cases did not label, or at most only rare benign pancreatic ducts showed weak labeling for mesothelin. Mesothelin is a new marker for pancreatic adenocarcinoma identified by gene expression analysis. Mesothelin overexpression in pancreatic adenocarcinoma has potential diagnostic, imaging, and therapeutic implications.