THE DIAGNOSTIC-VALUE OF THROMBOMODULIN IMMUNOLOCALIZATION IN SEROUS EFFUSIONS

Objective.-To test the value of an antithrombomodulin monoclonal antib ody as a diagnostic tool in detecting mesothelial cells and in differe ntiating mesothelioma from other malignant effusions. Design.-Thrombom odulin is a thrombin receptor that is distributed on surfaces where an anticoagulant activity is expected, including mesothelium. Antigen ex pression was studied by immunocytochemistry in 226 peritoneal and pleu ral exudates. Results.-The antigen was found in 33 of 33 mesotheliomas , 35 of 35 reactive effusions, 57 of 145 carcinomatous fluids, and in one case of angiosarcoma among seven metastatic nonepithelial tumors. Three distinct staining patterns were demonstrated: (1) thin cell memb ranes in benign mesothelial cells; (2) thick cell membranes in mesothe liomas; and (3) cytoplasm in carcinomas. All squamous cell carcinomas had demonstrable thrombomodulin, suggesting that antigen expression li kely correlates with squamous differentiation. Conclusions.-Thrombomod ulin is of diagnostic utility in distinguishing mesothelioma from aden ocarcinoma, provided the characteristic ''thick membrane'' pattern is present, but it should be used in panels with other markers of mesothe lial and/or epithelial differentiation.