EXPRESSION OF MYELOMONOCYTIC ANTIGENS IN MESOTHELIOMAS AND ADENOCARCINOMAS INVOLVING THE SEROSAL SURFACES

Because of the demonstrated effciacy of Leu-M1 as a discriminant between malignant epithelioid mesothelioma (MEM) and adenocarcinomas involving the serosal surface (ACSs), the authors assessed the reactivities of related 'myelomonocytic' antigens in this context. Paraffin sections from 41 MEMs and 43 ACSs (pulmonary, 'serous surface papillary', and metastatic mammary adenocarinomas) were evaluated for their expression of Leu-M1, LN1, LN2, and the Mac 387 antigen. Diagnoses were based in each case on the results of conventional histologic and electron microscopic examinations. Leu-M1 was detected only in minute foci of three peritoneal MEMs and was absent entirely in pleural mesotheliomas. Conversely, 38 of 43 ACSs expressed this marker. Three cases of peritoneal MEM and one pleural mesothelioma were multifocally LN2 positive, as were 39 of 43 ACSs. LN1 was the most frequently expressed antigen in MEM, being observed in 18 such tumors (10 pleural; 8 peritoneal); it was also detected in 37 of 43 ACSs. Mac 387 failed to label any of the neoplasms assessed in this series. These results demonstrate similar patterns of 'myelomonocytic' antigen expression by diverse ACS and a general absence of Leu-M1 and LN2 in MEM. LN1 and the Mac 387 antigen appear to have no additional value when compared with Leu-M1 and LN2 in the immunohistochemical evaluation of serosal neoplasms.