Risk Factors for Mesothelioma

Risk Factors for Mesothelioma

Mesothelioma is a rare but deadly cancer that affects the linings of various organs. Asbestos exposure is the No. 1 risk factor for mesothelioma, but other risk factors also have been identified. Mesothelioma is a deadly cancer that affects the mesothelium. The mesothelium is the membrane, like a net, that covers many organs in the body, such as the lungs and the heart. It has two layers: One covers the organ, the other acts like a sac, letting the organ move, if necessary.

People who develop mesothelioma have usually been exposed to a substance that infiltrated the mesothelium.

Mesothelioma Risk Factors: Long-Term Asbestos Exposure

Among the risk factors for mesothelioma, exposure to asbestos dust is by far the most important. About 70 percent to 80 percent of mesothelioma patients report a history of asbestos exposure at work.

And because asbestos was widely used in industry, car manufacturing, and construction until just a few decades ago, millions of U.S. workers had long-term exposure to asbestos and still are at risk for the disease. Leading the list are:

• Asbestos miners
• Shipyard workers
• Makers of asbestos products and textiles
• Workers in the heating and construction industries

Mesothelioma Risk Factors: Short-Term Asbestos Exposure

Many more people with shorter or less intensive exposure to asbestos face reduced but still real risks. For instance, demolition workers, firefighters, drywall removers, asbestos removal workers, and automobile workers may also be exposed to asbestos fibers. Even family members of asbestos workers may be exposed to asbestos dust because the workers bring it home on their clothing.

One particular group that may be at elevated risk are the crews involved in the cleanup of the World Trade Center in New York City after 9/11. Asbestos was used in the construction of the North Tower and it is estimated that hundreds of tons of asbestos were among the debris.

The risks posed by asbestos exposure can be hard to quantify, but in general risk depends on:

• The quantity of asbestos the person was exposed to
• The length of time the person was exposed
• The size, shape, and chemistry of the asbestos fibers
• Personal risk factors, such as smoking

There are two main forms of asbestos, amphibole (straight fibers) and chrysotile (curly fibers). Although all asbestos is dangerous, recent studies suggest that exposure to amphibole asbestos may pose a greater risk of mesothelioma than chrysotile asbestos because amphibole fibers remain in the lungs longer.

Mesothelioma Risk Factors: Genetic Possibilities

While it is clear that the risks climb with more intensive exposure over longer periods of time, some people have gotten mesothelioma after only brief exposure to asbestos, while others who were intensively exposed do not.

"There is a lot of work being done to try to find links to genetic predisposition to the disease," says Timothy Winton, MD, an associate professor of surgery, and division director of thoracic surgery, of the University of Alberta in Edmonton, Canada. "There is also often a co-morbid history of smoking or a genetic predisposition to smoking-related problems. With many cancers — and mesothelioma is one of them — you may need multiple hits from different carcinogens before you develop the disease."

Mesothelioma Risk Factors: Simian Virus 40 (SV40)

In the 1950s some polio vaccines were contaminated with SV40, which has been shown to cause mesothelioma in laboratory animals. In humans, an association between SV40 and mesothelioma has been suggested because SV40 has been found in human mesothelioma tumors, but no clear connection has been established.

Mesothelioma Risk Factors: Thorium Dioxide and X-Ray Imaging

Some studies have linked the use of the X-ray radioactive contrast medium thorium dioxide (Thorotrast) to an increased incidence of cancer, including mesothelioma.

One study found that a group exposed to thorium dioxide had a cumulative incidence of peritoneal mesothelioma (the peritoneum lines the stomach cavity) as much as 0.6 percent higher than asbestos-exposed workers. Thorium dioxide has not been used in X-ray imaging for many years.

Mesothelioma Risk Factors: Zeolites

Zeolites are minerals found naturally in volcanic rock and ash that contain hydrated aluminum and silicon. In synthetic forms, zeolites are used in detergents, for water and air purifications, and in other uses. Exposure to airborne zeolite dust has been associated with high incidence of mesothelioma in Turkey. In one Turkish village, a form of zeolite used to whitewash houses caused pleural mesothelioma incidence to soar to 440.9 per 100,000 for women and 298.1 per 100,000 for men.(source everydayhealth)