n cases of pleural mesothelioma, asbestos exposure occurs via inhalation of asbestos fibers. Once these fibers have entered the lungs, they work their way to the pleural membrane, and the body experiences great difficulty in expelling the fibers. Over a long period of time - typically two decades or more - asbestos fibers cause changes in these pleural cells, which may cause scarring of the lungs and, eventually, the formation of tumors.
When pleural cells become cancerous, they are no longer regulated by the mechanisms that control division of normal healthy cells. They begin to divide continuously, and this causes thickening of pleural membranes. As a result, lung capacity is reduced, and fluid begins to build up between pleural layers.
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