Mesothelioma is the cancer of the mesothelium – the thin lining of tissue that surrounds the lungs and heart. It is a rare but aggressive form of cancer that usually comes with a very poor prognosis. About 90% of all mesothelioma cases are caused by asbestos exposure. The other 10% are difficult to explain, but some form of asbestos exposure is usually suspected. The most common type of mesothelioma affects the mesothelium of the pleura - the body cavity that sits between the lungs and the ribcage. When pleural mesothelioma develops, this cavity fills with fluid and swells, putting painful and uncomfortable pressure on the lungs. The swelling pleura can also cause a dramatic decrease in lung capacity, making it difficult to breathe and perform day-to-day activities.
Mesothelioma, like any cancer, is a complicated disease. Cells in the mesothelium mutate from normal, non-dividing cells into cancerous ones that are dividing uncontrollably and without any order. For this to happen, several fundamental changes in the cells' DNA must first take place. The cells must be induced to start dividing, and all the checks and safeguards that they have in place to prevent them from becoming harmful must be bypassed.
Exactly how asbestos triggers mesothelioma is still not completely understood. Some research suggests that the fibers can directly cause DNA damage and mutate genes. If this is true, then asbestos can be considered a direct carcinogen. Other research suggests that it can indirectly cause cancer as well - since asbestos seems to illicit an immune response, it causes swelling and an increase in nutrients to feed the ongoing assault. This increase in nutrients can inadvertently make conditions perfect for growing cancerous cells and feeding the tumor as it grows.
Just how asbestos fibers get from the lungs to the pleura is not fully understood either. Most hypotheses agree that they are probably carried there by the white blood cells that are attempting to destroy them. Other possibilities include the fact that they might simply be small enough to wind their way between the thin layers of the lungs to the pleura.
In addition to a personal history of direct asbestos exposure, there are a few other things that may cause mesothelioma. Living with someone who works with asbestos can expose someone to the asbestos dust that they accidentally bring home with them. There have been cases of wives of asbestos mine workers contracting mesothelioma because they would handle the workers' contaminated clothing when cleaning the laundry.
Many scientists think that smoking can increase a person's chances of contracting mesothelioma. However, whether or not smoking can increase the risk of mesothelioma in people who are exposed to asbestos is still highly debated. Simian virus 40 (SV40) has also been suspected of causing cancer in patients who received the contaminated polio vaccination between 1955 and 1963. The radioactive substance thorium dioxide was also linked to mesothelioma. However, thorium dioxide has not been used since the 1950s, when it was discovered to cause a variety of cancers. All of these possible reasons need more research to be done before any conclusion about developing mesothelioma can be reached.