MALIGNANT MESOTHELIOMA - IMMUNOHISTOCHEMISTRY AND DNA-PLOIDY ANALYSISAS METHODS TO DIFFERENTIATE MESOTHELIOMA FROM BENIGN REACTIVE MESOTHELIAL CELL-PROLIFERATION AND ADENOCARCINOMA IN PLEURAL AND PERITONEAL EFFUSIONS

Objective.-To determine whether malignant mesotheliomas can be differe ntiated from adenocarcinomas and benign reactive mesothelial cells in pleural and peritoneal fluids using immunohistochemical analysis in co njunction with DNA ploidy analysis. Design.-Sixteen cases of malignant mesothelioma, including epithelial, sarcomatous, and biphasic types, were collected. DNA analysis using flow cytometry and/or image analysi s was performed on paraffin-embedded tissue from 15 of the mesotheliom a cases, as well as on cytospin cell preparations from samples of pleu ral and peritoneal fluids from cases with either cytologically proven adenocarcinoma (seven cases) or benign reactive mesothelial cells (sev en cases). Immunohistochemical studies were done in 15 mesotheliomas, 5 adenocarcinomas, and 4 benign reactive mesothelial cell effusions. R esults.-All malignant mesotheliomas tested (100%) stained positively f or prekeratin, whereas stains for carcinoembryonic antigen, B72.3, Leu -M1, and Ber-EP4 were negative. Stains vimentin, epithelial membrane a ntigen, and CA125 were positive in 75%, 75%, and 25% of cases tested, respectively. Benign reactive mesothelial cell cases stained similarly . Adenocarcinomas were more likely to react positively with B72.3, Ber -EP4, and carcinoembryonic antigen, and negatively with vimentin. DNA analysis showed that all benign cases were diploid, while all adenocar cinomas were nondiploid. Fifty-three percent of the malignant mesothel iomas were nondiploid. Sensitivity for detection of nondiploidy was gr eater for image analysis than for flow cytometry (100% vs 75%). Conclu sions.-B72.3, Ber-EP4, carcinoembryonic antigen, and vimentin are usef ul immunohistochemical markers in differentiating malignant mesothelio mas from adenocarcinomas, whereas immunohistochemistry does not reliab ly distinguish malignant from benign hyperplastic mesothelial cells. T he addition of DNA ploidy studies is useful for differentiating the la tter two groups.