Causes of Mesothelioma
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Share ArticleMesothelioma is a rare, aggressive form of asbestos cancer that is typically fatal. It affects the mesothelium, a membrane which covers most of the body's internal organs, including the lungs and heart. There are several types of mesothelioma: pleural mesothelioma, which affects the lining of the chest wall; peritoneal mesothelioma, which affects the lining of the abdomen; pericardial mesothelioma, which affects the sac surrounding the heart; and, the rarest form, tunica vaginalis mesothelioma, which affects the tissue surrounding the testes in males.
There are several known risk factors for mesothelioma, including asbestos exposure and exposure to a mineral called Zeolite. Someone could have one or more risk factors and never develop the disease; others might have only minimal risk and develop it.
The most common cause of mesothelioma is exposure to asbestos, a commercial term which refers to a group of six minerals that occur naturally in the environment and can be mined (1). Asbestos consists of oxygen, silicon, hydrogen, and other metal cations (a positively charged ion). Asbestos is known for its cloth-like qualities; it is also resistant to fire and heat, and is known for being quite strong.
Such traits made asbestos a popular and prevalent material in many industrial processes from the late 1800's through the end of the twentieth century. Industries that involve exposure to asbestos include: aluminum plants; chemical plants; oil refineries; power plants; shipyards; steel mills; and construction sites. Asbestos was used in the construction of houses (e.g. in insulation and roofing materials) and buildings, such as schools. Asbestos has also been used to produce many common household items, such as hair dryers. In fact, one study estimated that asbestos has been used in over 3,000 products. Asbestos also occurs naturally in the environment and there are several geographic locations in which people can be exposed through the environment.
Asbestos becomes dangerous when it is damaged and its fibers are released into the air. It is at this point that its fibers can be either swallowed or inhaled. Fibers become embedded in tissue, such as lung tissue, and over time lead to mesothelioma. The fibers harden and become like scar-like tissue. When they are in the lungs, they impede airflow and reduce the amount of blood that reaches the lungs.
Once asbestos exposure occurs, an individual will always be at risk for developing malignant mesothelioma. The American Cancer Society states that “risk appears to be lifelong and undiminished.” A number of factors impact how an individual is affected by asbestos exposure, including: how much asbestos one was exposed to; how long one was exposed for; how often one was exposed; and the type of asbestos one was exposed to. It typically takes between fifteen to fifty years after the exposure for the disease to develop and a patient to be diagnosed with mesothelioma. It is important to note that "secondary" or "limited" exposure can also occur. For example, if someone who is directly exposed at work brings home clothing containing asbestos fibers, their family members could inhale these fibers in the home. There have been documented cases of secondary exposure leading to mesothelioma.
Estimates of the numbers of American exposed to asbestos range from 8 million to 27 million. Although the risks of asbestos exposure were first documented in the 1920's, industries as varied as shipbuilding companies, steel factories and the US Navy, withheld information about the risks of exposure from employees for many decades. It was not until the 1980's, in the face of intense public pressure, that industries began curbing the use of asbestos. Most uses of asbestos in the United States were banned by the Environmental Protection Agency in 1989, although it continues to be used under certain circumstances today.
Additional risk factors for mesothelioma are listed below.
Radiation: Research has shown that exposure to thorium dioxide has led to cases of peritoneal and pleural mesotheliomas. Also known as Thorotrast, this substance was used to perform types of x-ray tests. Thorium dioxide stopped being used once its risks was discovered.
Zeolite is, like asbestos, a silicate mineral. It is found naturally in the soil of a region of Turkey called Anatolia, a peninsula that sits between the Mediterranean Sea and the Black Sea (4). There are elevated cases of mesothelioma in this area.
Tobacco: Those who were exposed to asbestos and who smoked are at higher risk of developing lung cancer, which is another complication related to asbestos exposure. The American Cancer Society reports that those who worked with asbestos and smoked have a risk 50 to 90 times higher than the general population’s of developing lung cancer. It is strongly recommended that those who were exposed to asbestos exposure avoid smoke exposure and smoking.
SV40 Virus: In recent years, research has emerged linking mesothelioma to a polio vaccine that was used between 1955 and 1963. Some of these vaccines were contaminated with SV40, or simian virus 40 (which can also be transmitted naturally). It is estimated that anywhere between 10 and 30 million people were exposed to the virus through the vaccine. Research has found traces of SV40 DNA in biopsies of mesotheliomas; however this does not conclusively prove that the virus leads to the cancer. Other research has pointed to the combination of asbestos exposure and exposure to SV40 as increasing the risk of developing mesothelioma. Currently, researchers largely concur that this issue is unresolved and that further research is called for to conclusively determine whether or not exposure to SV40 increases the risk of contracting mesothelioma.
Individuals who believe they were exposed to asbestos, thorium dioxide, Zeolite, or SV40 are advised to work with a physician to closely monitor their health for signs and symptoms of mesothelioma, or other respiratory conditions. Common symptoms of conditions caused by exposure include shortness of breath, fatigue, and coughing up blood. Once mesothelioma is diagnosed, treatment often consists of surgery, chemotherapy, radiation, experimental therapies (such as immunotherapy) or some combination of these treatments. Mesothelioma is not considered curable and often leads to death within a year of the initial diagnosis.
- National Institute for Occupational Safety and Health. "Asbestos."
Accessed: 16 August 2007. - American Cancer Society. "What Are the Risk Factors for Malignant Mesothelioma?" 19 October 2006.
Accessed: 18 August 2007. - National Cancer Institute. "Asbestos Exposure: Questions and Answers." 1 February 2007.
Accessed: 18 August 2007.
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