Distinguishing between peritoneal epithelioid
mesotheliomas and papillary serous
carcinomas involving the peritoneum can be difficult on routine histological preparations, but this differential diagnosis can be facilitated by the use of immunohistochemistry. Recent investigations have indicated that PAX8, PAX2,
claudin-4, and h-
caldesmon are immunohistochemical markers that can assist in distinguishing between these two
malignancies; however, much of the information published on the value of these markers is either insufficient or contradictory. The purpose of this study is to resolve some of the existing controversies and to fully determine the practical value of these markers for assisting in the differential diagnosis between peritoneal
mesotheliomas and serous
carcinomas. In order to do so, a total of 40 peritoneal epithelioid
mesotheliomas and 45 serous
carcinomas (15 primary, 30 metastatic to the peritoneum) were investigated. PAX8 and PAX2 nuclear positivity was demonstrated in 42 (93%) and 25 (56%) of the serous
carcinomas, respectively, whereas none of the
mesotheliomas expressed either marker. Forty-four (98%) of the serous
carcinomas exhibited
claudin-4 reactivity along the cell membrane, whereas none of the
mesotheliomas were positive for this marker. All of the serous
carcinomas and
mesotheliomas were negative for h-
caldesmon. Based on these results, it is concluded that PAX8 and
claudin-4 have a higher sensitivity and specificity for assisting in discriminating between peritoneal epithelioid
mesotheliomas and serous
carcinomas when compared with all of the other positive
carcinoma markers that are, at present, recommended to be included in the immunohistochemical panels used in this differential diagnosis. Even though it is highly specific, PAX2 has little practical value in the diagnosis of peritoneal epithelioid
mesotheliomas as its sensitivity is low. The h-
caldesmon is not useful.