Pathology of malignant mesothelioma.

The diagnosis of malignant mesothelioma relies firstly on the identification of the mesothelial nature of the neoplastic cell and secondly on the demonstration of the invasive properties of the proliferation. The latter aspect cannot be achieved by studying cellular material yet, in the right clinical setting, it is often possible to make a presumptive diagnosis of malignant mesothelioma based on exudates. Differentiation between mesothelial hyperplasia and metastatic adenocarcinoma by cytological examination alone is unreliable, so further evidence can be gathered from techniques such as histopathology, histochemistry and electron microscopy. Immunohistochemistry aims to confirm the mesothelial nature of the neoplastic cells while ruling out metastatic lesions. At present there is no single reliable marker for neoplastic mesothelioma, although evidence has been presented on a large variety of gene products. In an attempt to differentiate between hyperplastic mesothelium and malignant mesothelioma, Dhaene has been able to show that over 90% of malignant mesotheliomas show telomerase activity and express telomerase subunits.