The distinction between pleural mesothelioma (MS), reactive mesothelium (RM), and adenocarcinoma (AC) in serous effusions continues as a diagnostic problem in pathology. Immunohistochemistry can help, especially in surgical samples, but the optimum panel of antibodies has yet to be reported. The application of these antibodies to serous effusions has displayed variable results. The aim of this study was to evaluate the usefulness of eight monoclonal antibodies in the differential diagnosis of MS, RM, and AC in serous effusions.
A total of 44 cytologic specimens of serous effusions (26 pleural, 15 peritoneal, and 3 pericardial) from 30 ACs, 3 MSs, and 11 RMs, previously stained with Papanicolaou stain, were selected retrospectively from our files and stained with HBME-1, thrombomodulin, calretinin, MOC-31, Ber-EP4, E-cadherin, CEA, and CD-15. The immunoreactions were evaluated independently by two pathologists. A stepwise logistic regression analysis was applied to the data to select an appropriate panel of antibodies.
Statistical significance was found with HBME-1, thrombomodulin, MOC-31, Ber-EP4, and CD-15, when comparing both AC versus MS, and AC versus any type of mesothelial proliferation (MS or RM). Using HBME-1, 80% of ACs were negative whereas all three MSs reacted strongly with P = 0.003. A P = 0.02 was reached with thrombomodulin with 76.5% of ACs showing no immunoreactivity. Ber-EP4 and MOC-31 displayed good results with a P < 0.001 and 0.01, respectively. CD-15 reached a P = 0.034. No differences were found using the other antibodies. Ten ACs, all 3 MSs, and 10 RMs were double immunostained with HBME-1 and/or MOC-31 and Ber-EP4 successfully.
Immunohistochemical studies performed on Papanicolaou stained cytologic smears proved to be useful in the differentiation between metastatic AC and mesothelial proliferation. HBME-1, thrombomodulin, MOC-31, Ber-EP4, and CD-15 were the most useful. In selected cases, it appeared that double immunostaining aided the differential diagnosis. Cancer (Cancer Cytopathol)