Exposure to asbestos is the primary cause of mesothelioma, a rare and aggressive cancer with no definitive cure. The risk factors for that exposure can be occupational, environmental or secondhand.
Mesothelioma was virtually unknown until industrial and commercial companies expanded its use during the 20th century. After spending decades investigating the disease and its causes, medical researchers identified one primary culprit: Asbestos.
Medical research studies proved inhaling or ingesting microscopic asbestos fibers can start a chain of physical and metabolic events that lead to the development of different cancers or 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 and 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. IARC explained the scientific evidence of this link has strengthened over time, and there is overwhelming proof asbestos is carcinogenic to humans, regardless of the type or fiber length.
Causes & Risks
A cause is the contributing factor that leads to a disease or health condition.
The inhalation or ingestion of microscopic asbestos fibers is responsible for most cases of mesothelioma.
In rare cases, radiation exposure and exposure to zeolite — another type of fibrous mineral similar to asbestos —have been identified as causes of mesothelioma.
A risk factor in this case is anything that increases the chances of developing mesothelioma or asbestos-related cancers.
Factors that increase the risk of mesothelioma from asbestos exposure include:
- Working at an asbestos mine or asbestos processing plant
- Working in a high-risk occupational setting, such as the construction or automotive industries
- Serving on military ships or facilities built with products containing asbestos
- Living in a residential area near an asbestos mine
- Disturbing asbestos products during a home renovation without proper safety measures
Apart from risk factors associated with asbestos, there are other factors that could increase your risk of developing mesothelioma or another asbestos-related disease.
Exposure to Mineral Fibers
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.
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 vaccine doses during that nine-year span were inadvertently 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.
Genetics
Because only a small number 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.
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 for Mesothelioma?
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, an incurable breathing disorder also caused by asbestos exposure.
Differences Between Causes & Risk Factors
A risk factor for mesothelioma is not necessarily a cause. Infrequent causes, such as radiation and zeolite exposure, could also be considered risk factors.
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.
Multiple risk factors can increase your risk for developing mesothelioma. The duration of exposure also plays a key role. While the World Health Organization says no amount of asbestos exposure is considered safe, it is usually heavy, repeated exposures over many years that lead to mesothelioma and other asbestos-related illnesses.
The link between asbestos exposure and mesothelioma is so strong that it can be difficult for researchers to tell if any other 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 construction boom following WWII, asbestos 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.
Occupations that are at high risk for exposure in older buildings include firefighters, contractors, demolition workers, electricians and plumbers.
Occupational Exposure
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 include:
- Shipyard Workers
- Construction Workers
- Power Plant Workers
- Chemical Plant Workers
- Industrial Workers
- Insulators
- Boiler Workers
- Auto Mechanics
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, remodeling or demolition. If asbestos insulation is disturbed, fibers can become airborne and contaminate anyone who inhales them.
Secondary 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.
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 in some 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 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 more than 200 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 400-plus air samples gathered there in 2004.
Although asbestos mines no longer operate in the U.S., people living near the defunct mines 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 to Arizona. Officials in Nevada responded by taking measures to protect workers on projects that involve areas contaminated with asbestos.
How Does Mesothelioma Develop?
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, including the creation of inflammatory chemicals that cause direct genetic damage.
It usually takes heavy, long-term exposures to asbestos for a related cancer to develop, but even minor exposures can be harmful. Activities that disturb asbestos-containing products 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 comprise the protective membranes that cover the lungs, abdomen and heart.
Possible Theories 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. This can cause 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 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.
The common ground of these theories: Asbestos causes damages that change a cell’s natural life cycle.
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. These 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 more carcinogenic than others. Researchers believe the varying chemical composition of the different asbestos types is what makes one type more carcinogenic than another.
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 asbestos-related 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 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 show up. Instead, be proactive and ask your doctor.
Early detection offers the best opportunity for effective treatment.