Expression of CEA, CA19-9, CA125, and EpCAM in pseudomyxoma peritonei

Pseudomyxoma peritonei is a fatal clinical syndrome with mucinous tumor cells disseminated into peritoneal cavity and secreting abundant mucinous ascites. The serum tumor markers CEA, CA19-9, and CA125 are used to monitor pseudomyxoma peritonei remission, but their expression at tissue level has not been well characterized. Herein, we analyzed expression of these proteins and the adenocarcinoma marker EpCAM in 92 appendix-derived pseudomyxoma peritonei tumors by immunohistochemistry. All tumors were found to ubiquitously express CEA and EpCAM. In the majority of the tumors (94.6%), CEA showed polarized immunostaining, but in 5 aggressive high-grade tumors containing numerous signet ring cells, a nonpolarized staining was detected. We found preoperative CEA serum values to correlate with peritoneal cancer index. However, the serum values of the advanced cases with nonpolarized staining pattern were normal, and the patients died within 5 years after diagnosis. Thus, serum CEA measurements did not reflect aggressiveness of these tumors. CA19-9 showed strong immunopositivity in most of the tumors (91.3%), and mutated enzyme FUT3 was demonstrated from the cases showing negative or weak staining. CA125 was infrequently expressed by tumor cells (focal staining in 6.5% of the cases), but in most of the cases (79.3%), adjacent nonneoplastic mesothelial cells showed immunopositivity. As a conclusion, CEA and EpCAM are invariably expressed by pseudomyxoma peritonei tumor cells and could be exploited to targeted therapies against this malignancy.