People who worked for an extended period of time in an environment where asbestos dust was regularly released are at greatest risk for pleural mesothelioma. The body's natural defense mechanisms successfully clear many asbestos fibers, but when asbestos exposure is heavy, these defense systems are overwhelmed. Mucus within the airways traps asbestos fibers and other toxins that are inhaled. These trapped foreign particles are either swallowed or coughed up.
These fibers travel to the lungs and become imbedded in the lung lining, outside of the lungs and inside the ribs. These long, pointed fibers can reach the pleural lining of the chest wall and lung. Once the fibers have penetrated the pleura they injure the mesothelial cells. When these jagged particles settle in the pleura, they cause inflammation. The inflammation, in turn, can lead to dangerous cancerous tumors. In some cases, those who've inhaled asbestos fibers will first develop the less-severe asbestosis, followed by mesothelioma several years later.
Upon diagnosis, patients usually exhibit multiple tumor masses affecting both the visceral (further from the lung) and parietal surfaces (closer to the lung) of the pleura. The parietal surface is more often affected than the visceral surface, and the right lung, due to its larger size, often suffers more damage than the smaller left lung. In addition, more asbestos tends to settle in the lower lungs than the upper lungs.
These tumors often grow quickly in size and can cover the entire lung cavity, making it very difficult to breathe and causing excruciating pain. Also, in the advanced stages of pleural mesothelioma, the cancer may spread to other nearby organs, including the heart, abdomen, and lymph nodes.
The tissue changes leading to mesothelioma occur slowly. The symptoms of mesothelioma generally do not appear for 20 to 30 years after the initial asbestos exposure. A latency period of up to 50 years has been known.
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