Mesothelioma as a risk indicator of asbestos exposure: the role of the pathologist.

Malignant mesothelioma is an uncommon tumour, which has become an important epidemiological marker for exposure to asbestos. This tumour is characterised by a wide range of microscopic features which may be classified in three histologic patterns: epithelial, mesenchimal and mixed or biphasic. Histochemical staining is often necessary to distinguish mesothelioma from carcinoma. As regards immunohistochemistry, only the use of a combination of antibodies significantly decreases the risk of false-negative results. Analytic electron microscopy techniques may also be useful, permitting the evaluation of the cumulative fiber burden in the target organ.