Mesothelioma Causes and Risk Factors

Causes and Risk Factors
Kathryn E. Vinson, MS, CCRC

Earlier this week, we talked a bit about mesothelioma in Cancer Risk to our Veterans; however, this disease strikes people from all walks of life. According to mesotheliomahelp.org, the only known cause of this condition is asbestos exposure, although there are other risk factors that scientists are exploring.  Let’s take some time today to explore what asbestos is, how it is thought to cause mesothelioma, and other risk factors associated with the development of the disease.

If you’re like me, you probably think that asbestos is a weird material conjured up in a lab somewhere.  I mean, how else could something be so toxic.  Turns out that assumption is wrong.  Asbestos is a naturally occurring mineral, known as a silicate.  Its long fibers, resistance to tearing and burning, and ability to be woven into other materials, made it ideal for use in insulation, other construction materials,  and as fire retardants.  The first known use of asbestos was over 4,500 years ago, but large-scale mining of the mineral didn’t begin until the mid 19^th century.  By the beginning of the 20^th century, the use of asbestos was widespread, being used in applications such as:

• Fire retardant coatings
• Bricks
• Cement for fireplaces
• Gaskets
• Pipes
• Insulation
• Certain types of drywall, flooring, and roofing
• Outdoor furniture

In order to understand how asbestos causes mesothelioma, we need to first know a few things.  The mesothelium is simply the layer of epithelial cells that line the structures/organs in the chest, abdomen, and pelvis. As such, mesothelioma can be pleural (affecting the lungs), pericardial (around the heart), peritoneal (affecting the abdomen), or testicular.  The most well known and most common mesothelioma is pleural mesothelioma.  This happens when those long, stringy, asbestos fibers are inhaled, and travel into the lungs, then invade the pleura – the epithelial cells that line lungs and chest wall.  There, these fibers imbed in the tissue, and cause injury and scarring. It is thought that this damage is what leads to the abnormal cell growth that we know as cancer.  It is important to note that the original cancer growth in mesothelioma is in these epithelial cells – not the lung itself – differentiating it from lung cancer. This process is similar in peritoneal, pericardial, and testicular mesotheliomas.

We know that there are people that have worked in certain industries that are at a greater risk for developing mesothelioma due to their workplace exposure – military, shipyards, construction, and manufacturing to name a few – but what other risk factors exist?  You may be surprised to find out that family members of these workers are at a higher risk due to their passive exposure – that is the asbestos that was brought home on their clothing and bodies.

A few other risk factors have been explored in the literature.  Exposure to zeolites, a mineral chemically related to asbestos, is believed to be a risk.  Rarely, patients exposed to high levels of radiation to the chest and abdomen for the treatment of other cancers, have developed the disease as well.  In addition, a radioactive material known as Thorotrast, which was used in the 1950s as a diagnostic tool in x-rays has been linked to mesothelioma.  Thankfully, this product has not been used for many years as it is now a known carcinogen.

One interesting link that scientists are still studying is the simian virus 40 (SV40).  Between 1955 and 1963, some polio vaccines were contaminated with this virus.  To date, the largest human studies have not shown an increased incidence of mesothelioma in patients that received these contaminated vaccines; however, lab studies in mouse cells have shown that the virus increases cancerous growths in those cells.  Furthermore, “absbestos increases the cancer-causing effect of SV40 on those cells” (Cancer.org). Interestingly, researchers have identified SV40 DNA in mesothelioma tumors obtained from humans.  Researchers believe that they may not know the answer until the cohort of patients injected with the contaminated virus reach 50-70 years of age, the age of peak incidence for mesotheliomas.

Two other risk factors worth mentioning are age and gender.  Men are more likely to develop the disease, likely due to their increased chances of being exposed to asbestos on the job.  Increased age is also a factor, as the disease does not show symptoms until at least 15 years after exposure.

If you or a loved one are battling mesothelioma, we encourage you to look at the resources available at www.mesotheliomahelp.org.  Here you will find a multitude of educational material, as well as information on assistance, legal aid, and treatment options. Please also take a look at our page dedicated to Clinical Trials, as this may be an option for you to discuss with your doctor.