Mesothelioma (or, more precisely, malignant mesothelioma) is a rare form of cancer that develops from transformed cells originating in the mesothelium, the protective lining that covers many of the internal organs of the body. It is usually caused by exposure to asbestos. The most common anatomical site for the development of mesothelioma is the pleura (the outer lining of the lungs and internal chest wall), but it can also arise in the peritoneum (the lining of the abdominal cavity), and the pericardium (the sac that surrounds the heart), or the tunica vaginalis (a sac that surrounds the testis).
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