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Since pulmonary adenocarcinomas, malignant mesotheliomas (MM), and sometimes benign mesothelial proliferations show a great histomorphological resemblance to each other, an immunohistochemical panel is usually necessary for differential diagnosis. D2-40 is an available monoclonal antibody, which is already in use as a lymphatic endothelial marker. It has also been suggested to be useful in identifying the mesothelial differentiation. The aim of this study is to compare D2-40 immunostaining in MM, pulmonary adenocarcinoma, and benign mesothelial proliferations. In this retrospective study, D2-40 immunostaining was investigated in 37 cases of MM, 36 cases of pulmonary adenocarcinoma, and 31 cases of benign mesothelial proliferation. The diagnosis of MM had previously been confirmed by a panel including calretinin, CK5/6, and CEA. Predominantly membranous immunoreactivity was observed in 51% of MMs and in 55% of benign mesothelial proliferations. All the 36 pulmonary adenocarcinomas were negative. These results were statistically significant (p<0.001). We believe that D2-40 may be helpful in the differential diagnosis of MM from pleural involvement of pulmonary adenocarcinoma.

Primary lung adenocarcinomas and metastatic adenocarcinomas may show a great morphologic resemblance to malignant mesothelioma. There are numerous immunohistochemical markers being used, but none of them were proved to be effective enough to reach a certain diagnosis. The current study was performed to evaluate the utility of thyroid transcription factor-1 (TTF-1) and surfactant protein-B (SP-B) expression in the differential diagnosis between lung adenocarcinomas and pleural mesotheliomas. In this retrospective study, TTF-1 and SP-B were applied to 30 cases with adenocarcinoma and 15 cases with pleural mesothelioma, immunohistochemically, using an avidin-biotin detection system. Twenty percent of adenocarcinomas and 13.3% of pleural mesothelioma stained positive for SP-B. TTF-1 stained 24 of the 30 adenocarcinomas (80%) and none of the 15 mesotheliomas (0%). TTF-1 positivity in adenocarcinomas was found to be statistically significant, while SP-B had no important practical value either used alone or in combination with TTF-1. There was no statistically significant correlation between the differentiation level of adenocarcinomas and TTF-1 staining pattern. In conclusion, we believe that TTF-1 may be helpful in distinguishing lung adenocarcinoma from pleural mesothelioma.