Antigenic phenotype of malignant mesotheliomas and pulmonary adenocarcinomas. An immunohistologic analysis demonstrating the value of Leu M1 antigen.

To evaluate the usefulness of an immunohistologic approach to the differential diagnosis of mesothelioma and pulmonary adenocarcinoma, the authors studied paraffin-embedded, fixed tissue sections from 50 primary adenocarcinomas of the lung and 28 mesotheliomas of the pleura by using a panel of monoclonal antikeratin, antihuman milk fat globule (HMFG-2), anti-Leu M1, and monoclonal anticarcinoembryonic antigen (CEA) antibody; we also used a conventional heterologous anti-CEA antiserum with and without prior absorption with spleen powder to remove antibodies to nonspecific cross-reacting antigen (NCA). Keratin was present in both mesotheliomas and adenocarcinomas and did not help in distinguishing between these two neoplasms. HMFG-2 was detected in 48 (96%), and Leu M1 was positive in 47 (94%) of the adenocarcinomas, but not in any of the mesotheliomas. By using conventional rabbit antiserum, the authors detected CEA in the majority of adenocarcinomas (96%), but also in two cases of mesothelioma. When the anti-CEA antiserum was absorbed with NCA, the number of positively reacting adenocarcinomas decreased considerably to 76%; however, after this treatment, none of the mesotheliomas gave positive reactions. The monoclonal anti-CEA antibody was reactive in 36 of the adenocarcinomas (72%), but in none of the mesotheliomas. Our results indicate that, in addition to HMFG-2 and CEA, the expression of Leu M1 antigen by most primary pulmonary adenocarcinoma (94%) and its absence in mesothelioma could be used as a valuable marker for primary adenocarcinoma of the lung that involves the pleura and permits its differentiation from mesothelioma.