Expression of mesothelin, fascin, and prostate stem cell antigen in primary ovarian mucinous tumors and their utility in differentiating primary ovarian mucinous tumors from metastatic pancreatic mucinous carcinomas in the ovary.

Metastatic pancreatic mucinous adenocarcinomas in the ovaries can be difficult to distinguish from primary ovarian mucinous neoplasms because the former can simulate the latter grossly and histologically and both tumor types share the same cytokeratin 7/cytokeratin 20 immunoprofile. We previously reported the utility of loss of Dpc4 expression in distinguishing metastatic pancreatic carcinomas from primary ovarian mucinous tumors. Recently several new pancreatic carcinoma markers have been identified, including mesothelin, fascin, and prostate stem cell antigen (PSCA). In this study we investigate the expression patterns of these markers in 35 primary ovarian mucinous tumors (28 atypical proliferative [borderline] tumors and 7 invasive carcinomas) and 11 metastatic pancreatic mucinous carcinomas in the ovary. Primary ovarian mucinous tumors expressed mesothelin (17%), fascin (26%), and PSCA (43%) less frequently than metastatic pancreatic adenocarcinomas (73%, 73%, and 82%, respectively). Expression of all three markers was seen only in metastatic pancreatic adenocarcinomas (45%), and coexpression of at least two markers was observed significantly more frequently in metastatic (82%) than primary ovarian mucinous tumors (17%). Our results indicate that an immunohistochemical panel including Dpc4, mesothelin, fascin, and PSCA is useful for evaluating difficult mucinous tumors in the ovary when the differential diagnosis includes metastatic pancreatic adenocarcinoma.