The 3 major histological types of mesothelioma are sarcomatous, epithelial, and mixed. Pleural mesothelioma usually begins as discrete plaques and nodules that coalesce to produce a sheetlike neoplasm. Tumor growth usually begins at the lower part of the chest. The tumor may invade the diaphragm and encase the surface of the lung and interlobar fissures.
The tumor may also grow along drainage and thoracotomy tracts. As the disease progresses, it often extends into the pulmonary parenchyma, chest wall, and mediastinum. Pleural mesothelioma may extend into the esophagus, ribs, vertebra, brachial plexus, and superior vena cava.
Asbestos, amphibole asbestos, asbestos-crocidolite, and amosite asbestos in particular, is the principal carcinogen implicated in the pathogenesis. Exposure to chrysotile asbestos is associated with a lower incidence of mesothelioma. The industries associated with asbestos exposure include mining, ship building involving the use of asbestos, asbestos cement manufacture, ceramics, paper milling, auto parts (asbestos brake lining), railroad repair, and insulation. In Turkey, the use of the fibrous substance erionite (similar to amphibole asbestos) in building construction has led to an epidemic of pulmonary mesothelioma. Environmental exposure to asbestos in areas polluted by the substance may increase the incidence of mesothelioma.
Most malignant mesotheliomas have complex karyotypes, with extensive aneuploidy and rearrangement of many chromosomes. A loss of a single copy on chromosome 22 is the most common abnormality.
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