The histologic distinction between peritoneal epithelioid
mesotheliomas and serous
carcinomas diffusely involving the peritoneum may be difficult, but it can be facilitated by the use of immunohistochemistry and electron microscopy. D2-40 and podoplanin are two recently recognized lymphatic endothelial markers that can be expressed in normal mesothelial cells and
mesotheliomas. The purpose of this study is to compare the value of these new mesothelial markers with those that are commonly used for discriminating between
mesotheliomas and serous
carcinomas, and also to determine the current role of electron microscopy in distinguishing between these
malignancies. A total of 40 peritoneal epithelioid
mesotheliomas and 45 serous
carcinomas of the ovary (15 primary, 30 metastatic to the peritoneum) were investigated for the expression of the following markers: D2-40, podoplanin,
calretinin,
keratin 5/6,
thrombomodulin, MOC-31, Ber-EP4,
B72.3 (TAG-72), BG-8 (Lewis(Y)), CA19-9, and leu-M1 (CD15). All 40 (100%) of the
mesotheliomas reacted for
calretinin, 93% for D2-40, 93% for podoplanin, 93% for
keratin 5/6, 73% for
thrombomodulin, 13% for Ber-EP4, 5% for MOC-31, 3% for BG-8, and none for
B72.3, CA19-9, or leu-M1. All 45 (100%) serous
carcinomas were positive for Ber-EP4, 98% for MOC-31, 73% for
B72.3, 73% for BG-8, 67% for CA19-9, 58% for leu-M1, 31% for
keratin 5/6, 31% for
calretinin, 13% for D2-40, 13% for podoplanin, and 4% for
thrombomodulin. After analyzing the results, it is concluded that Ber-EP4 and MOC-31 are the best negative
mesothelioma markers for differentiating between epithelioid
mesotheliomas and serous
carcinomas. The best discriminators among the positive markers for
mesotheliomas are D2-40, podoplanin, and
calretinin. From a practical point of view, Ber-EP4 and MOC-31, in combination with
calretinin, and/or D2-40 or podoplanin allow the differential diagnosis to be established between
mesothelioma and serous
carcinoma in nearly all instances. As a clear distinction could be made between these two
malignancies in all of the cases in which electron microscopy was performed, this technique can be very useful in establishing the correct diagnosis when the immunohistochemical results are equivocal or further support of a diagnosis of either
mesothelioma or serous
carcinoma is needed.