Mesothelioma Risk Factors

The exposures to elements, substances, conditions as well as lifestyle choices and genetic factors that make a person more or less likely to contract a disease are known as risk factors. For example, to have unprotected sexual relations with a variety of partners is a risk factor for syphilis, AIDS and other venereal diseases. Family history, obesity and a sedentary lifestyle are risk factors for diabetes and heart disease.

Cancer has probably been around as long has life has existed on earth; paleontologists have discovered signs of cancer in the fossils of many prehistoric animals, including dinosaurs. There is no one risk factor for all forms of cancer, although a single risk factor in combination with others can potentially give rise to a variety of cancers, or increase the likelihood of such cancers developing. Excessive sun exposure can lead to skin cancer; use of tobacco products has long been associated with cancer of the lung as well as the mouth, throat and other organs. Genetics and family history also constitute risk factors.

On the other hand, there are people having one or more risk factors that never develop cancer.

Mesothelioma and Asbetos

Mesothelioma (mez-oh-thee-lee-OH-muh) is a specific type of cancer which attacks the internal lining of the chest and abdomen as well as that of internal organs, particularly the lungs. This lining is called the mesothelium, from which the disease derives its name.

Asbestos exposure has been shown to be the main risk factor in contracting mesothelioma. This substance is actually a group of six different naturally-occurring minerals, known as silicates, that was once used in construction materials, automotive applications and anything requiring a heat-resistant or fire-proof barrier.

Most uses of asbestos were outlawed by the Environmental Protection Agency (EPA) under the George H.W. Bush Administration in 1989. A decline in mesothelioma cases appears to have resulted from this ban; nonetheless, there are still some eight million people in the U.S. who have had dangerous exposure to asbestos. While the number of men contracting the disease has fallen, the number of women patients has stayed level, indicating that exposure occurs in locations other than the workplace.

Although asbestos is present in the atmosphere, the concentration is extremely low. People having the highest risk of developing mesothelioma from asbestos exposure are construction and demolition workers, miners, factory and railroad workers, and those working in ship building and dismantling. In addition, families of such workers may be at risk, since asbestos fibers can be carried in the hair and on clothing.

EPA estimates indicate that there may be nearly three-quarters of a million public buildings in the U.S. that still contain asbestos insulation and/or flooring. This includes up to 15% of all public school buildings in the nation.

How Asbestos Affects the Respiratory System

Asbestos is used in one of two forms. Serpetine fibers, consisting of the mineral chrysotile, is curly and quite flexible. It is the most common form of asbestos.
Amphiboles are similar to long, needle-like fibers. These are made from any one of five silicates: crocidolite, amosite, anthrophylite, tremolite, and actinolyte. While any kind of asbestos can be a risk factor for mesothelioma, crocidolite amphiboles are considered the most dangerous.

Serpentine asbestos fibers that are inhaled are captured by mucous membranes in the respiratory system (nose, throat, trachea [windpipe] and bronchi [tubes in the lungs]). These fibers are usually coughed up and/or swallowed. This can result in peritoneal mesothelioma, which afflicts the inner lining of the abdomen.

Amphiboles on the other hand may reach the very ends of the airways, penetrating the aveoli (small air sacs in the lungs) and penetrating the pleural lining of the lung and inner surface of the chest. These fibers cause cell injury, which ultimately leads to the development of mesothelioma. However, the condition does not develop immediately after concentrated exposure to asbestos; it often takes years and even decades for symptoms to develop.

Other Causes and Effects

Another lung disease attributable to the inhalation of asbestos fibers is asbestosis. This is caused when asbestos fibers actually scratch and puncture the inner surfaces of the lung, resulting in the formation of scar tissue.

Lung cancer can also be attributed to asbestos exposure. In fact, the risk of lung cancer among those who have been exposed to asbestos can be up to 600% greater than that of the public at large.

By itself, tobacco use does not result in mesothelioma. However, in combination with asbestos exposure, it can increase the risk of lung cancer by as much as 8000% compared to the general population. In fact, more asbestos workers die from lung cancer than mesothelioma.

Mesotheliomas have been known to be caused by factors other than asbestos. Thorium dioxide, a radioactive material once used by medical personnel in x-ray procedures, has been implicated in cases of pleural and peritoneal mesothelioma. Zeolite is another silicate is found in abundance on the Anatolian Plateau of Turkey. The incidence of mesothelioma in this region is correspondingly high.

Recent studies also implicate SV40, a simian virus now known to have contaminated some polio vaccines between 1955 and 1963. Lab studies have shown that animals and animal cells treated with SV40 have a tendency to develop mesothelioma. SV40 is also found in biopsies taken from mesothelioma patients. While there may be a causal relation, some scientists believe that the presence of SV40 may be due to contamination of the sample under examination. This virus was found to be present in the tissues of healthy individuals who had not had the polio vaccination in question.

Up until now, studies have not conclusively demonstrated any causal connection between SV40 and mesothelioma among cancer patients who received contaminated vaccines in childhood. As most mesothelioma is diagnosed in individuals between the ages of 50 and 70, the issue may remain unresolved for the next two decades.

'Mesothelioma Risk Factors' Resources:
  1. American Cancer Society. “What Are the Risk Factors for Malignant Mesothelioma?”. Cancer.org. October, 19, 2006.