Lymphohistiocytoid mesothelioma - An often misdiagnosed variant of sarcomatoid malignant mesothelioma

Three cases of lymphohistiocytoid mesothelioma, a rare variant of pleural s arcomatoid malignant mesothelioma, are described Histologically, the neopla sms were characterized by a diffuse discohesive proliferation of atypical h istiocytoid cells intermixed with a marked lymphocytic and lesser plasmacyt ic infiltrate. One case initially was misdiagnosed as a ganglioneuroma, a s econd case tvas misinterpreted as malignant lymphoma, and a third case was sent in consultation with the differential diagnosis of inflammatory pseudo tumor vs mesothelioma. Immunohistochemical studies showed strong and genera lized expression of cytokeratins and vimentin by the neoplastic histiocytoi d cells in all 3 cases. Two cases were positive for calretinin, one of whic h also was positive for HBME-1, thrombomodulin, and LeuM1. None of the case s stained with the epithelial glycoprotein markers carcinoembryonic antigen , B72.3, and Ber-EP4, or the blood group antigen, BG-8. The immunophenotype of the lymphoplasmacytic infiltrate revealed predominantly reactive, matur e T cells, with fewer polytypic plasma cells, histiocytes, and B cells. In lymphohistiocytoid! mesothelioma, as in the usual examples of sarcomatoid m esothelioma, the demonstration of cytokeratin expression by the neoplastic cells is the most useful diagnostic finding that allows exclusion of other neoplasms with which this entity may be confused.