The immunohistochemical characterization of sarcomatoid malignant mesothelioma of the pleura.

The immunohistochemical characteristics of epithelioid malignant mesothelioma are well described. However, immunohistochemical analyses of sarcomatoid mesothelioma, the less common type, are limited and its distinction from other tumors of the chest wall, lung and pleura is often problematic. We evaluated 24 patients with pleural sarcomatoid mesothelioma who had surgery (12 extrapleural pneumonectomies, 9 pleurectomies and 3 large biopsies) between 1989 and 2005. Clinicopathologic features and demographic data were recorded. We describe immunohistochemical results for 10 antibodies: AE1/AE3, CAM5.2 and MNF-116 keratins, calretinin, WT-1 protein, bcl-2, CD34, desmin, D2-40 and podoplanin. The patients were 23 men and one woman with a median age at diagnosis of 64.7 years (range 47 to 76). Tumor cells were positive for the keratin proteins AE1/AE3 in 18/24 cases, CAM 5.2 in 23/24 cases and MNF-116 in 21/21 cases. Calretinin was positive in 6/24 cases, WT-1 (nuclear) in 8/24 cases, bcl-2 in 0/24 cases, CD34 in 0/24 cases, desmin in 0/24 cases, D2-40 in 24/24 cases and podoplanin in 24/24 cases. This panel of antibodies may be helpful in establishing a pathologic diagnosis of sarcomatoid mesothelioma. In our study, D2-40 and podoplanin are highly sensitive immunohistochemical markers for sarcomatoid mesothelioma. Additional studies are required to define their role in the differential diagnosis of other spindle cell tumors.