Mesothelioma is a cancer
that occurs in the mesothelium, a thin membrane encompassing the body’s
internal organs and cavities. Mesothelioma is caused by asbestos exposure.
Asbestos fibers that are inhaled through the mouth and nose may
eventually become embedded in the lining of the lungs, causing harmful
inflammation of the pleura and resulting in mesothelioma or asbestosis (scar tissue formation in the lungs). It has also been found that swallowing asbestos fibers could contribute to a form of the malignancy originating in the abdomen known as peritoneal mesothelioma.
Mesothelioma generally results from occupational asbestos exposure,
but there are instances of environmental exposure that can also cause the disease. Oftentimes a family member can be affected indirectly by second hand exposure from an asbestos worker’s soiled work clothes.
Asbestos was an effective insulation material. It was used liberally in commercial and industrial products
in the United States until being regulated in a joint effort between
the Consumer Product Safety Commission and the Environmental Protection
Agency in 1989. Occupational exposure was common among workers who
encountered these products in many industries including shipbuilding,
power plants, and other industrial settings.
Asbestos insulation workers appear to have the highest rate of
asbestos related disease. One study reports that almost six percent of
asbestos workers fall victim to mesothelioma or experience respiratory symptoms.
Asbestos insulation workers are over 300 times more likely to be
diagnosed with mesothelioma than those with no exposure history.
How does exposure to asbestos cause mesothelioma?
Asbestos fibers are microscopic, though they are also quite durable.
For this reason, asbestos was used in a number of different industrial
compounds to enhance strength and resistance to temperature extremes-
two properties at which the mineral is highly adept. Asbestos exposure
most often occurred among individuals who worked extensively with asbestos
or asbestos-containing materials. Friable asbestos (meaning loose or
airborne fibers) is easily inhaled- often without the exposed person
realizing.
When inhaled, asbestos lodges easily in the outer lung tissue and within the mesothelium. The mesothelium
is a thin membrane of cells which produces a lubricating fluid on the
surface of the organs. This lubricant allows the lung and other internal
structures to expand, contract, and move freely without friction in the
body cavity. There is a great deal of latency associated with mesothelioma between exposure to asbestos and the onset of symptoms.
Pleural mesothelioma is the most common variety of the disease and
forms on the pleural membrane, which surrounds the lung and chest
cavity. Peritoneal mesothelioma is less common and forms on the surface
of the peritoneum, a thin membrane surrounding the abdominal cavity.
Pericardial mesothelioma is the least common variety of the disease and
forms in the cardiac cavity that envelops the heart, a mesothelial
membrane known as the pericardium.
Inhaled asbestos fibers are known to be the cause of pleural mesothelioma,
whereas ingested asbestos fibers are the cause of peritoneal
mesothelioma. While the exact causal nature between asbestos and
pericardial mesothelioma is not known, physicians and cancer researchers
surmise asbestos fibers in the blood stream lodge in the outer layers
of the heart’s ventricles and lodge in the pericardium. Once asbestos
fibers reach the surface of the peritoneum or pericardium, the
inflammation process is essentially the same as it is on the surface of
the pleura.
Primary workplace exposure to the mineral was common in naval
shipyards, power plants, railroad infrastructure, and other industrial
jobsites. However, asbestos-related mesotheliomas have also been
diagnosed in spouses or children of those exposed to asbestos. Workers
often brought home dangerous asbestos fibers on their clothing, hair, or
person. Those who came into contact with these fibers on the person or
their clothing have developed mesothelioma as a result.
Other Contributing Factors
Mesothelioma is also causally associated with a few other factors,
but many of these are attributed to the development of mesothelioma in
conjunction with exposure to asbestos.
Smoking
Those who smoke are at a higher risk of mesothelioma, though smoking
is more commonly associated with traditional lung carcinomas. Smoking
tends to enhance risk even further in those who were also exposed to
asbestos.
Radiation Exposure
While extremely rare, some mesothelioma patients attribute their
diagnosis to exposure to radiation rather than exposure to asbestos.
Radiation tends to transform and mutate cell growth patterns and is more
commonly associated with brain and blood cancers.
Carbon Nanotubes
Research is extremely preliminary in this study, but some laboratory
studies indicate a molecular similarity between asbestos mineral fibers
and carbon nanotubes. Tests indicate a pronounced risk of mesothelioma
in some laboratory animals implanted with carbon nanotubes.