IMMUNOHISTOCHEMICAL EVIDENCE SUPPORTING THE APPENDICEAL ORIGIN OF PSEUDOMYXOMA PERITONEI IN WOMEN

Women with pseudomyxoma peritonei (PMP), characterized by multifocal m ucinous implants (disseminated peritoneal adenomucinosis), often have synchronous appendiceal and ovarian mucinous tumors. There has been co nsiderable debate as to whether the ovarian tumors are secondary to th e appendiceal tumor or are independent primary ovarian tumors, the lat ter are usually classified as mucinous tumors of low malignant potenti al (MLMP). It has been reported that cytokeratins (CK) 7, 18, and 20, carcinoembryonic antigen (CEA), and human alveolar macrophage 56 (HAM- 56) are useful markers for distinguishing primary ovarian neoplasms fr om metastases of intestinal origin. Nearly all primary ovarian MLMP tu mors and mucinous carcinomas are positive for CK 7, 18, and 20, CEA, a nd HAM-56, whereas most colorectal adenocarcinomas are negative for bo th CK 7 and HAM-56 and positive for CK 20 and CEA. Thirteen appendicea l and 14 ovarian mucinous tumors from 14 cases of PMP and 11 primary o varian MLMP tumors were studied immunohistochemically for expression o f CK 7, 18, and 20, monoclonal and polyclonal CEA (mCEA and pCEA), and HAM-56. Of 14 cases of PMP, 10 (71.4%) had identical staining pattern s for all antibodies in both the appendiceal and ovarian tumors. For e ight of these, the pattern of immunoreactivity was characterized by ne gative reactions for CK 7 and HAM-56 and positive reactions for CK 18 and 20, mCEA, and pCEA. One additional case for which only the ovarian tumor could be stained had the same pattern. The remaining two cases were also positive for CK 18 and 20 and CEA, but in addition were posi tive for CK 7. Two cases were discordant only for CK 7 and one case wa s discordant for both CK 7 and HAM-56. All 11 MLMP tumors were positiv e for CK 7 and 18, and pCEA. Eight (72.7%) of 11 were positive for HAM -56, mCEA, and CK 20. There was a statistically significant difference in the frequency of immunoreactivity for CK 7 (p = 0.0005) and HAM-56 (p = 0.0002) between the ovarian mucinous tumors in PMP and the MLMP tumors, with the ovarian tumors in PMP tending to be negative for CK 7 and HAM-56, similar to the appendiceal adenomas. Most ovarian mucinou s tumors in PMP demonstrate a pattern of immunoreactivity with CK 7, 1 8, and 20, CEA, and HAM-56 that is identical to the associated appendi ceal adenoma and distinct from primary ovarian MLMP tumors, consistent with the interpretation that these ovarian tumors an secondary to the appendiceal tumor.