Is D2-40 a useful marker for distinguishing malignant mesothelioma from pulmonary adenocarcinoma and benign mesothelial proliferations?

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.