Mesothelioma is caused by inhaling asbestos. When microscopic asbestos fibers lodge in the pleura (the lining of the lungs), they can cause genetic changes that create cancer cells. Greater exposure to asbestos leads to a greater risk of developing the cancer.
Mesothelioma was virtually unknown until the 20th century. After decades investigating the disease, medical researchers identified the cause: Asbestos exposure. Mesothelioma rates rose as industries expanded the use of asbestos.
Research studies proved inhaling or swallowing microscopic asbestos fibers can start a chain reaction that leads to several types of cancer. The toxic dust can also cause asbestosis, an incurable breathing disorder.
In March 2009, the International Agency for Research on Cancer (IARC) reconfirmed asbestos exposure as the leading cause of mesothelioma. All forms of asbestos cause the disease.
Two years later, the IARC presented an update on the link between asbestos and cancer at a World Health Organization conference in Spain. They explained the scientific evidence has strengthened over time. There is now overwhelming proof asbestos is carcinogenic to humans, regardless of the type or fiber length.
Main Risk Factors for Mesothelioma
Working at an asbestos mine or asbestos-processing plant
Working in a high-risk occupation such as construction or heavy industry
Serving on military ships or facilities built with products containing asbestos
Living in a residential area near an asbestos mine or contaminated site
Disturbing asbestos products during a home renovation without proper safety measures
Apart from the risk factors associated with asbestos, a few other factors could increase your risk of developing mesothelioma.
Exposure to the fibrous mineral zeolite may increase the risk for mesothelioma. Previous studies have linked high rates of mesothelioma in remote villages in Turkey to building materials containing erionite — part of the zeolite family of minerals.
Exposure to radiation may also contribute to the development of mesothelioma, but the evidence is rare and inconsistent. Some studies show the risk for mesothelioma slightly increases after a person receives radiation therapy as a treatment for other cancers.
Other 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 vaccine doses during that nine-year span were contaminated with 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.
Because only a fraction of people exposed to asbestos develop mesothelioma, scientists believe genetics can play a role in a person’s risk. Researchers have confirmed a mutation in a gene called BAP1 increases the likelihood of developing mesothelioma and other cancers.
If someone else in your family has mesothelioma, genetic testing may suggest you have an increased risk for developing the cancer.
Mesothelioma is more common in men than women and it 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.
Studies show smoking is not a risk factor for mesothelioma, but those who smoke and are regularly exposed to asbestos are much more likely to develop asbestos-related lung cancer. Some studies reveal the combination of smoking and asbestos exposure raises the risk of lung cancer by approximately 90 percent.
Researchers also found smoking can weaken lungs and reduce the body’s ability to dispose of asbestos fibers trapped inside. Smoking also aggravates asbestosis.
Dr. Jacques Fontaine talks about the different people who are at risk of developing mesothelioma.
Differences Between Causes & Risk Factors
A risk factor is anything that increases the odds of developing a disease. A cause is the contributing factor that leads to a disease.
For example, although men are much more likely to develop mesothelioma than women, gender alone cannot cause the cancer.
Often, multiple risk factors are involved in the development of mesothelioma.
The duration of asbestos exposure plays a key role. While the World Health Organization says no amount of asbestos exposure is safe, it is usually heavy, repeated exposure over many years that leads to asbestos-related illnesses.
A study in the American Journal of Epidemiology found the longer someone works in a job that involves asbestos exposure, the higher their risk of mesothelioma becomes.
Years of Occupational Asbestos Exposure
Increase in Risk of Mesothelioma
1-7
1.7 times more likely
8-19
2 times more likely
20+
5.4 times more likely
Dose-Response Relation at Low Levels of Asbestos Exposure in a French Population-based Case-Control Study.
The link between asbestos exposure and mesothelioma is so strong that it can be difficult for researchers to tell if any other risk factors can cause mesothelioma on their own. Although scientists continue to study this topic, exposure to asbestos remains the most clearly defined cause.
Where Does Asbestos Exposure Occur?
Asbestos once filled countless U.S. homes and businesses in the form of insulation and fire-resistant materials.
Throughout the construction boom following WWII, asbestos was a key element in thousands of industrial and household products. Examples include drywall, wiring, glues and adhesives, ceiling tiles, cements and shingles.
Workers were exposed to the harmful natural mineral while on the job. Others, including workers’ family members, faced secondary exposure at home. Environmental exposure happened in communities that mined or processed asbestos.
Some asbestos products remain in old structures and are usually harmless — as long as they’re not disturbed. Firefighters, contractors, demolition workers, electricians and plumbers are at high risk of exposure to asbestos in old buildings.
Past Occupational Exposure
The risk for asbestos-related illnesses is highest for people who worked with the raw mineral or with asbestos-containing products on a daily basis. Some of the occupations with the highest risk include:
Asbestos removal is highly regulated, and the government fines people and businesses who ignore the rules. Workplace asbestos exposure is still a hazard at jobsites where safety procedures are not followed.
Risk Factors in Present-Day Jobs
Construction tradesmen and firefighters can be exposed to asbestos while working in old homes and structures built with contaminated materials. Exposure can happen during a renovation, demolition or disaster response.
When old buildings are destroyed without safety precautions, airborne asbestos fibers can contaminate the surrounding area.
Secondhand Exposure
When the asbestos industry was booming, families of workers were also 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.
In 1995, the National Institute of Occupational Safety and Health (NIOSH) presented a study of “Workers’ Home Contamination” to Congress.
They concluded “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 large deposits in hilly or mountainous regions also face possible exposure. Minimal amounts of the mineral can fill the air in these regions, but environmental exposure is most dangerous near former 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 hundreds of asbestos-related deaths.
In June 2009, the U.S. Environmental Protection Agency (EPA) declared a public health emergency in Libby.
In El Dorado Hills, the EPA said asbestos levels were “of concern,” according to the agency’s report on the 400-plus air samples gathered there in 2004.
Although asbestos mines no longer operate in the U.S., people living near defunct mines continue to develop mesothelioma.
In February 2015, reports of exposure 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. Officials in Nevada responded by taking measures to protect workers on projects that involve areas contaminated with asbestos.
“My father worked in steel mills for years and I remember washing his clothes which were covered in dust.”
A number of studies have explored how asbestos causes mesothelioma. In 2012, mesothelioma expert Dr. Michele Carbone, director of thoracic oncology at the University of Hawaii Cancer Center, co-wrote a scientific article detailing multiple ways asbestos may damage the body.
One way is through the creation of inflammatory chemicals that cause direct genetic damage.
Mesothelioma has a dose-response relationship to asbestos, which means higher doses of asbestos exposure lead to a greater risk of developing mesothelioma. High concentrations of fibers and long durations of exposure amount to a greater risk of developing an asbestos-related disease.
Once asbestos is 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 comprise the protective membranes that cover the lungs, abdomen and heart.
Spreading mesothelioma tumors may form a sheath around the lungs.
Possible Mechanisms for Asbestos-Related Tumor Development
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, causing genetic changes that lead to cancer.
Cancerous Mutations: Asbestos causes the production of free radicals, which are molecules that damage DNA and cause healthy cells to mutate.
Uncontrolled Growth: The fibers trigger the production of oncoproteins, which block genes that protect cells from growing uncontrollably and forming tumors.
Every healthy cell has genes that regulate growth and safeguard against cancer. Once asbestos blocks this function, cells can divide uncontrollably, causing malignant tumors to form locally and possibly metastasize — spreading throughout the body and forming metastatic tumors.
Metastatic tumors develop relatively late in the course of mesothelioma but may be a patient’s main source of symptoms.
While all types of asbestos cause mesothelioma, certain types such as crocidolite and amosite are especially dangerous. Researchers believe the varying chemical composition of the different asbestos types is what makes some more carcinogenic than others.
The vast majority of people who work with asbestos will not develop a disease. Individual factors such as genetics play a role in mesothelioma development, while smoking cigarettes can increase the risk of asbestos-related lung cancer.
Preventing and Detecting Mesothelioma
The best way to prevent mesothelioma is to follow workplace safety regulations. Be cautious of materials in old homes that may contain asbestos.
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 asbestos-related diseases.
If you or a loved one has a history of asbestos exposure — especially in the workplace — don’t wait for symptoms to arise. Instead, be proactive and talk to your doctor. Early detection offers the best opportunity for effective treatment.
Karen Selby joined Asbestos.com in 2009. She is a registered nurse with a background in oncology and thoracic surgery and was the director of a tissue bank before becoming a Patient Advocate at The Mesothelioma Center. Karen has assisted surgeons with thoracic surgeries such as lung resections, lung transplants, pneumonectomies, pleurectomies and wedge resections. She is also a member of the Academy of Oncology Nurse & Patient Navigators. Read More
Dodson, R., & Hammar, S. Asbestos: Risk Assessment, Epidemiology, and Health Effects. Taylor & Francis: Boca Raton, 2012.
Castleman, B. Asbestos: Medical and Legal Aspects. Aspen Publishers: New York, 2005.
Webster, P. White Dust Black Death. Trafford: Canada, 2005.
Robinson, B., Musk, A., & Lake, R. (2005). Malignant Mesothelioma. The Lancet, 366(9483), 397-408. doi: 10.1016/S0140-6736(05)67025-0
Yang, H. 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. doi: 10.1073/pnas.1006542107
Carbone, M., & Yang, H. (2012). Molecular pathways: Targeting mechanisms of asbestos and erionite carcinogenesis in mesothelioma. Clin Cancer Res., 18(3), 598-604. doi: 10.1158/1078-0432.CCR-11-2259.
Hodgson, J.T., & Darnton, A. (2000). The qualitative risk of mesothelioma and lung cancer in relation to asbestos exposure. Ann Occup Hyg., 44(8), 565-601. Retrieved from:
http://www.ncbi.nlm.nih.gov/pubmed/11108782
Farioli, A. et al. (2016). Radiation‐induced mesothelioma among long‐term solid cancer survivors: a longitudinal analysis of SEER database. Cancer Med., 5(5), 950–959. doi: 10.1002/cam4.656
Larson, D. et al. (2017). Abstract 5763: Investigating the carcinogenic potential of various types of mineral fibers in the development of mesothelioma. Cancer Research, 77(13), Supplement. doi: 10.1158/1538-7445.AM2017-5763
