Mesothelioma, a cancer affecting the lining of the thoracic and abdominal cavities known as the mesothelium, is a serious cancer that can attack the lungs, stomach, heart and other organs. Statistically, it tends to occur in men more than in women and has a high incidence in people who worked closely with asbestos-containing materials. Since mesothelioma is an environmental cancer, the risk factors for meso are very specific, as are the causes, discussed below.

There is typically a period of decades from the time of asbestos exposure to the time people develop mesothelioma. This latency period means that by the time malignant mesothelioma is diagnosed, it's already advanced and unlikely to go into remission. The life expectancy for mesothelioma victims varies from months to years, but as of this writing averages 12 to 18 months.

So what causes mesothelioma? The dominant theory is that the inhaling of the tiny fibers of asbestos causes mesothelioma by insulting the tissue of the mesothelium. 70 to 80 percent of the 2,000 to 3,000 people who are diagnosed with the cancer each year in the U.S. were exposed to asbestos in their work environment, in some cases many years ago. The exact mechanism that causes the cancer, of which the two most common types are pleural mesothelioma or peritoneal mesothelioma, is not known, and that's what researchers are trying to figure out.

Exposure to asbestos, and mineral fibers similar to asbestos, only account for the majority of cases of mesothelioma--not all cases. (See Asbestos and Mesothelioma: The Cancer Connection for more information). According to Malignant Mesothelioma (Springer, 2005), genetics and heredity may play a part, too, although the authors speculate that it's difficult to isolate the environmental from the genetic influence within families. For example, a man who worked with asbestos may have regularly carried home asbestos particles on his hair, skin and clothes that were then inhaled by other family members.

Whether it was exposure or hereditary factors or a combination is unclear. The data on mesothelioma remains sketchy, as it is a very uncommon, and formerly rare, type of cancer.

While the exact mechanism isn't known, researchers believe that inhaled asbestos fibers travel to the pleura and damage mesothelial cells. The result is either inflammation and scarred tissue or direct molecular DNA damage at the stage of cell division or replication--researchers aren't sure. Eventually, pleural mesothelioma cancer occurs as cancerous cells grow, multiplying abnormally where they would normally die off and be cleared by the immune system.

Peritoneal mesothelioma is hypothesized to be the result of swallowing asbestos fibers. As for tunica vaginalis testis mesothelioma, the type of mesothelioma that attacks the male internal organs, this may occur when asbestos fibers, which are quite small and jagged, migrate through the mesothelial tissue and the diaphragm and find a path to the testes.

It's thought that more than one cause of mesothilioma commonly comes into play. People's genes and heredity play a part, as does their health, environment, and way of living.

When asbestos doesn't seem implicated, some possible alternative causes of mesothelioma include:

Zeolites - Zeolite is a class of minerals similar to asbestos in chemical structure. Weathered and hardened volcanic ash present in soil and rock can harbor zeolite. Certain regions have a higher concentration of these tiny particles, as is the case of erionite, a form of zeolite concentrated in areas such as Cappadocia, Turkey, which is known for having a high incidence of mesothelioma attributed to zeolite exposure.

Radiation - Radiation is a suspected cause of mesothelioma, particularly in the case of lymphoma patients. Injections of Thorotrast, or thorium dioxide, were given before some people were exposed to radiation in x-rays for the radiation treatment of lymphoma. Later found to be a carcinogen, Thorotrast was discontinued.

Simian Virus 40 - The SV40 virus originated in rhesus monkeys and spread to humans. It was believed to have been spread in part by polio vaccines given worldwide in the 1950s and 1960s to millions of people--30 million people in the U.S. alone. The simian virus in combination with asbestos exposure may increase a person's risk of developing malignant mesothelioma. According to the American Cancer Society, the research is still out on this one, and is waiting for the people who were exposed to the SV 40 virus between 1955 and 1963 to age to the time when mesothelioma is typically diagnosed--between the ages of 50 and 70--and show a normal or increased risk of mesothelioma.

This article is in no way meant to substitute for medical advice. If you are concerned about mesothelioma or any other health condition, talk to your doctor.