Mesothelioma Causes

Contact with asbestos is the leading cause of mesothelioma cancer, as nearly every patient diagnosed with this aggressive cancer came in contact with it at some point. Mesothelioma caused by asbestos exposure commonly occurs occupationally, environmentally or as a result of secondhand exposure.

Mesothelioma — a cancer that most commonly attacks the lungs and abdomen — was profoundly rare until industrial and commercial companies expanded the use of asbestos during the 20th century. After spending decades investigating the disease and its causes, medical researchers identified one primary culprit: Exposure to asbestos.

Medical research studies gradually pointed to the fact that breathing in minuscule asbestos fibers starts a chain of physical and metabolic events that lead to the development of several types of cancers or an incurable breathing disorder called asbestosis.

In March 2011, the International Agency for Research on Cancer (IARC) presented an update on the link between asbestos and cancer at a World Health Organization conference in Spain. The IARC explained the scientific evidence of this link has only strengthened over time, and there is overwhelming proof asbestos is cancerous to humans — regardless of the type or fiber length.

In March 2009, the International Agency for Research on Cancer reconfirmed that asbestos exposure is the leading cause for mesothelioma and all forms of asbestos cause the disease.

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Risk Factors for Mesothelioma

While exposure to asbestos is the leading cause for mesothelioma, other elements can play a significant role in this cancer’s development. Doctors call these elements risk factors, and they include any factors that increase a person’s likelihood of developing cancer.

Factors that Increase the Risk of Mesothelioma:

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Working at an asbestos mine or asbestos processing plant

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Working in a high-risk occupational setting, such as the construction or automotive industries

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Serving on military ships or facilities built with products containing asbestos

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Living in a residential area near an asbestos mine

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Disturbing asbestos products during a home renovation without proper safety measures

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Other Factors That May Increase the Risk of Developing Mesothelioma

Apart from risk factors associated with asbestos, exposure to minerals with similar properties to asbestos, a person's age and gender and other elements may increase the likelihood of developing the disease.

  • Exposure to Mineral Fibers

    Exposure to zeolites, a class of fibrous minerals chemically similar to asbestos, may also increase the risk for mesothelioma. High rates of mesothelioma in a region of Turkey suggest that those living in that area and others working with a zeolite building material called erionite may be at risk for developing the disease.

  • Radiation Exposure

    Exposure to radiation may increase mesothelioma risk, but evidence is rare and inconsistent. Several studies have shown the risk for mesothelioma slightly increases after a person receives radiation therapy as a treatment for other cancers.

  • Polio Vaccines and Simian Virus 40

    Some studies suggest people who received a polio vaccine between 1955 and 1963 may have an increased risk of developing mesothelioma. Tens of millions of polio vaccines during that nine-year span were infected by the simian virus 40 (SV40). Although the largest studies did not find a link between the virus and increased mesothelioma risk, the topic remains controversial as studies continue.

  • Genetics

    Because only a small number of people exposed to asbestos develop mesothelioma, scientists believe genetics can affect a person's risk for the cancer. Researchers have confirmed a mutation in a gene called BAP1 increases the likelihood of developing mesothelioma and melanoma of the eye.

  • Age and Gender

    Mesothelioma is more commonly diagnosed in men than women, and rarely affects people younger than 45. This is because mesothelioma often takes decades to develop, and men are more likely to work in jobs where asbestos exposure occurs.

  • Is Smoking a Risk Factor?

    Studies have shown that smoking is not a risk factor for mesothelioma. However, people who smoke and have been exposed to asbestos are much more likely to develop lung cancer. Some studies reveal that those who smoke are as much as 90 percent more likely to develop lung cancer if they also were exposed to asbestos.

    Researchers also found that smoking can weaken lungs and reduce the body's ability to dispense of asbestos fibers trapped inside. Smoking also aggravates asbestosis, an incurable breathing disorder also caused by asbestos exposure.

  • Causes vs. Risk Factors

    It is important to understand that a risk factor for mesothelioma is not necessarily a cause. Although research shows men are much more likely to develop mesothelioma than women, gender alone cannot cause the cancer. The same may be true for other risk factors.

    The link between asbestos exposure and mesothelioma is so strong that it can be difficult for researchers to tell if any known risk factors can cause mesothelioma on their own. Although scientists continue to study this topic, exposure to asbestos remains the most clearly defined cause for mesothelioma.

Where Does Asbestos Exposure Occur?

Asbestos once filled countless U.S. homes and businesses in the form of insulation and heat-protecting materials. Throughout the massive construction boom following World War II, it was a key element in thousands of industrial and household products, including drywall, wiring, glues and adhesives, ceiling tiles, cements and shingles.

Some of these asbestos products remain in old structures and are usually harmless — as long as they're not disturbed. Workers usually were exposed to the harmful natural mineral while on the job, but others, including their family members, also faced secondary exposures at home and environmental exposures in communities that mined or processed asbestos.

Occupational Exposure

Most harmful exposures occurred at work. The risk for asbestos-related illnesses is highest for people who worked directly with the raw mineral or with asbestos-containing products on a daily basis. Some of the most prevalent occurrences of asbestos exposure that cause mesothelioma were in the following occupations:

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Risk Factors in Construction and Craft Jobs

Construction workers and craftspeople are most likely to experience harmful exposures, especially while working on older homes and buildings constructed with contaminated materials. Exposures can happen during a renovation or demolition. If asbestos insulation is disturbed, fibers can become airborne and contaminate anyone who inhales them.

Fast Fact: Removing asbestos is a highly regulated endeavor, and the government fines people and businesses who ignore the regulations. Even though the U.S. government restricted the use of asbestos during the 1970s, workplace exposures still can occur.

Secondary Exposure

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When the asbestos industry was booming, families of workers were at great risk. Workers often came home with asbestos fibers on their hair, work clothes and tools — exposing family members to the toxic substance and increasing their risk for related diseases.

The National Institute of Occupational Safety and Health (NIOSH) presented a Workers' Home Contamination Study to Congress that showed "families of asbestos-exposed workers have been at increased risk of pleural, pericardial, or peritoneal mesothelioma, lung cancer, cancer of the gastrointestinal tract, and nonmalignant pleural and parenchymal abnormalities as well as asbestosis."

Environmental Exposure

Because asbestos is a naturally occurring mineral, people living near areas of large deposits, like hilly or mountainous regions, also face possible exposures. Minimal amounts of the mineral can fill the air in these regions, but environmental exposure is most dangerous near asbestos mines.

Two of the most recognized cities for asbestos exposure problems are Libby, Montana, and El Dorado Hills, California.

Libby was home to a vermiculite mine contaminated by naturally occurring asbestos. The mine, controlled by W.R. Grace & Company and operated from 1923 to 1990, is responsible for several hundred asbestos-related deaths. The U.S. Environmental Protection Agency (EPA) in June 2009 declared a public health emergency at the city.

The EPA said asbestos levels in El Dorado Hills were "of concern," according to the agency's report on the 450-plus air samples gathered there in 2004.

Although asbestos mines are no longer in operation in the U.S., people living near them continue to develop mesothelioma.

In February 2015, reports of exposures to naturally occurring asbestos in southern Nevada made national headlines. Geologists found asbestos in 150 soil samples from Nevada and Arizona, and epidemiology research showed an increased incidence of mesothelioma in the area sampled. Geologists suspect natural erosion and commercial development of asbestos-contaminated land sent asbestos fibers airborne.

Geological studies show the asbestos in Nevada is much like the asbestos found in Libby, Montana, and an asbestos deposit runs from Nevada into Arizona. The state of Nevada has responded by taking measures to protect workers on projects that involve areas contaminated with asbestos.

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How Does Mesothelioma Develop?

A number of studies have explored how asbestos causes mesothelioma. In 2012, mesothelioma expert Michele Carbone co-wrote a scientific article that discusses multiple different ways asbestos may damage the body and lead to mesothelioma, including by creating inflammatory chemicals and by causing direct genetic damage.

It usually takes heavy, repeated exposures to asbestos for a related cancer to develop, but even minor exposures can be harmful. Exposure occurs when raw asbestos is inhaled, or activities disturb materials containing asbestos and release toxic fibers into the air.

Mesothelioma has a dose-response relationship to asbestos, which means higher doses of asbestos exposure lead to a greater risk of developing mesothelioma. When it comes to asbestos, high concentrations of fibers and long durations of exposure amount to a greater risk of developing an asbestos-related disease.

Once inhaled, the body has a hard time getting rid of the sharp, sometimes jagged fibers, and they build up in the lungs or abdomen over time. Many years after the first exposure, these fibers may cause cancerous changes. Cancer starts in mesothelial cells, which make up the protective membranes that cover our lungs, abdomen and heart.

Possible Theories for How Asbestos Fibers Cause Tumors to Develop

Inflamed cells

Fibers inflame and irritate mesothelial cells, which leads to irreversible scarring, cellular damage and cancer.

Genetic changes

Fibers enter mesothelial cells and disrupt their life cycle. This can cause genetic changes that lead to cancer.

Cancerous mutations

Asbestos causes the production of free radicals, molecules that damage DNA and cause healthy cells to undergo cancerous mutations.

Uncontrolled Growth

The fibers can trigger the production of oncoproteins, which block genes that protect cells from growing uncontrollably and forming tumors.

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The common ground of these theories: Asbestos causes damages that change a cell's natural cycle. Every healthy cell has genes that safeguard against cancer. Once asbestos blocks this function, cells can divide uncontrollably, spreading throughout the body and forming tumors. These tumors are a patient's main source of symptoms.

While all types of asbestos cause mesothelioma, certain types, like crocidolite and amosite, are more carcinogenic than others. Researchers believe the varying chemical composition of the different asbestos types is what makes one type more carcinogenic than another.

Keep in mind that about 20 percent of people occupationally exposed to asbestos will go on to develop a related health condition. The vast majority of people who work with asbestos will not develop a disease. Individual factors like genetics play a role in mesothelioma development, while factors such as smoking cigarettes play a role in the development of lung cancer.

Prevention

The best way to prevent mesothelioma is to take a proactive stance on your health. If you think a past job or home repair project exposed you to asbestos, you should seek regular medical exams to check for signs of related diseases.

If you or a loved one has a history of asbestos exposure — especially in the workplace — don't wait for symptoms to show up. Instead, be proactive and ask your doctor. Early detection offers the best opportunity for effective treatment.

Additional Resources


Karen Selby is a registered nurse and a Patient Advocate at The Mesothelioma Center. She worked in several subspecialties within nursing before joining Asbestos.com in 2009.

  1. National Cancer Institute. (2009, May 1). Asbestos exposure and cancer risk. http://www.cancer.gov/about-cancer/causes-prevention/risk/substances/asbestos/asbestos-fact-sheet
  2. Straif, K. (2011, March 17). Update of the Scientific Evidence on Asbestos and Cancer. Retrieved from http://www.who.int/phe/news/events/international_conference/Session2_DrStraif.pdf
  3. Dodson, R. and Hammar, S. (2011). Asbestos: Risk Assessment, Epidemiology, and Health Effects. Taylor & Francis: Boca Raton.
  4. Castleman, B. (2005). Asbestos: Medical and Legal Aspects. Aspen Publishers: New York.
  5. Webster, P. (2005). White Dust Black Death. Trafford: Canada.
  6. Robinson, B., Musk, A., Lake, R. (2005). Malignant Mesothelioma. The Lancet; 366(9483): 397-408.
  7. Yang, H, Rivera, Z, Jube, S, et al. (2010, July 13). Programmed necrosis induced by asbestos in human mesothelial cells causes high-mobility group box 1 protein release and resultant inflammation. PNAS; 107(28): 12611-12616. Retrieved from http://www.pnas.org/content/107/28/12611.full.pdf
  8. Carbone, M, Yang, H. (2012). Molecular pathways: Targeting mechanisms of asbestos and erionite carcinogenesis in mesothelioma. Clin Cancer Res; 18. Retrieved from https://clincancerres.aacrjournals.org/content/18/3/598.full
  9. Hodgson, JT, Darnton, A. (2000). The qualitative risk of mesothelioma and lung cancer in relation to asbestos exposure. Ann Occup Hyg; 44: 565-601. Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/11108782
  10. Blum, D. (2015, February 9). In Nevada, a controversy in the wind. Retrieved from http://www.nytimes.com/2015/02/10/science/a-controversy-in-the-wind.html?_r=0

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