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Malignant mesothelioma

Mesothelioma is cancer that starts in the cells that line certain parts of the body, especially the chest, belly (abdomen), and heart.

The lining formed by these cells is called mesothelium. These cells protect organs by making a special fluid that allows the organs to move. For instance, this fluid makes it easier for the lungs to move during breathing.

Tumors of the mesothelium can be benign or they can be cancerous. A cancerous tumor of the mesothelium is called a malignant mesothelioma, but this is often shortened to just mesothelioma. The information that follows covers only those tumors that are cancer.

Main types of mesothelioma

There are 3 main types of mesotheliomas based on how the cells look under a microscope:

  • Epithelioid – This is the most common type. It tends to have a better outlook (prognosis) than the other types.
  • Sarcomatoid (fibrous) – About 1 or 2 out of 10 mesotheliomas are of this type.
  • Mixed (biphasic) – This type has features of the 2 types above. About 3 or 4 out of 10 mesotheliomas are the mixed type.

About 3 out of 4 mesotheliomas start in the chest cavity. These are called pleural mesotheliomas. Another 10 to 20 percent begin in the abdomen (belly). These are called peritoneal mesotheliomas. Those starting around the heart are very rare. This cancer can also start in the tissue around the testicles, but this is also very rare.

The American Cancer Society’s most recent estimates for mesothelioma in the United States are from 2008, when they predicted 2,000-3,000 new cases.

Mesothelioma is fairly rare. Most people who get mesothelioma are over 65 years old. Men are much more likely than women to get this disease.

But while it is rare, this is a serious disease that can be hard to treat. It is often advanced before symptoms appear, so the outlook is not as good as it is for cancers that are found earlier. The average survival time is about one year. For the most part, survival times are likely to be higher for people with mesotheliomas that can be operated on than for those with cancers that have spread.

What causes mesothelioma?

Researchers have found some factors that increase a person’s risk of mesothelioma.

  • Asbestos – The main risk factor for mesothelioma is contact with asbestos. In fact, most cases of mesothelioma have been linked to asbestos in the workplace. In the past, asbestos was used in insulation, and in other things like floor tiles, door gaskets, roofing, patching compounds, and more. Since asbestos is a natural mineral, it can also be found in dust and rocks in certain parts of the United States. Most asbestos use stopped after 1989, but it is still used in some products. When asbestos fibers are breathed in, some can travel to the ends of the small air passages and reach the lining of the lungs. There they can damage the cells lining the lungs, and with time lead to pleural mesothelioma. If swallowed, these fibers can also reach the lining of the abdominal cavity where they play a part in causing peritoneal mesothelioma. People who may be at risk for asbestos exposure include some miners, factory workers, makers of insulation, railroad workers, ship builders, gas mask makers, and construction workers. Studies have shown that family members of people exposed to asbestos at work have an increased risk of mesothelioma, too, because asbestos fibers are carried home on the clothes of the workers. Asbestos was used in the insulation of many older homes and public buildings around the country, including some schools. Because the asbestos is contained within the building materials, a large amount is not likely to be found in the air. The risk is thought to be much less unless the asbestos is somehow released into the air, such as when building materials begin to decompose over time, or during remodeling or removal.
    The risk of getting mesothelioma depends on how much asbestos a person was exposed to and for how long. Mesotheliomas take a long time to develop. The time between the first exposure and finding the disease is often between 20 and 50 years. Another important point about asbestos is that once you have been exposed, the risk of mesothelioma appears to be life-long and does not go down over time.
  • Radiation – There is some evidence linking thorium dioxide (Thorotrast) to mesothelioma. Thorotrast is a material that was once used in certain x-rays. It has not been used for many years.
  • SV40 virus – Some studies have suggested that infection with simian virus 40 (SV40) might increase the risk of mesothelioma. Some polio vaccines prepared between 1955 and 1963 were contaminated with SV40. Research into this question is still going on.

Source: Adapted from content provided by the American Cancer Society. Always consult a physician about specific medical problems.