Immunohistochemistry in the diagnosis of malignant mesothelioma.

The histological diagnosis of malignant mesothelioma of the pleura, especially the distinction from peripheral adenocarcinoma of the lung, may be difficult. The immunohistochemical reports previously published on this subject show diverging results mainly because a variety of antibodies and staining techniques have been used by the different authors. To obtain comparable and reproducible results standard techniques and commercialized antibodies should be applied in routine pathology. In order to investigate the value of immunohistochemistry for the separation of the two entities formalin fixed and paraffin embedded blocks of 47 mesotheliomas and 22 adenocarcinomas were investigated with the PAP technique and commercially available antibodies to carcino-embryonic antigen (CEA), keratin, vimentin, epithelial membrane antigen (EMA), pregnancy specific antigen (SP1), S-100 protein and monoclonal antibody lu-5 (mAB lu-5). CEA positivity was found in all 22 adenocarcinomas examined, but only 2/47 (4%) of all mesotheliomas showed a positive result. SP1 was positive in 13/22 (59%) of the adenocarcinomas, whereas only 3/47 (6%) mesotheliomas were positive for this marker. No significant difference in the rate of positive cases in the adenocarcinoma and mesothelioma group could be found with the other above mentioned antigens. The results of our study indicate that especially CEA, but also SP1 are valuable markers in the diagnosis of malignant mesothelioma.