Mesothelioma causes

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]Associate Editor(s)-in-Chief: Parminder Dhingra, M.D. [2]

Overview

The most common cause of mesothelioma is asbestos-fibre exposure. Less common causes of mesothelioma include erionite-fibre exposure, Simian virus 40, and radiation exposure.

Causes

Mesothelioma is caused by:

• Asbestos-fibre exposure: causes majority of cases
• Erionite-fibre exposure: naturally occurring mineral used in building, particularly in Turkey
• Simian virus 40 (SV40)
• Radiation exposure

Asbestos

The strongest and most common risk factor for mesothelioma is occupational exposure to asbestos, which has been widely used in building materials and many industries.

Asbestos is the name of a group of minerals that occur naturally and can be separated into long, thin fibres. Asbestos fibres are very fine. When they are breathed in (inhaled), they can make their way to the smallest airways of the lung and the mesothelium. The fibres get into the lung and settle in the pleura where they can eventually cause pleural mesothelioma. If they are coughed up and then swallowed, asbestos fibres can also settle in the peritoneum. This is probably the cause of peritoneal mesothelioma.

The link between asbestos and mesothelioma has been well known for many years. According to the International Agency for Research on Cancer (IARC) and the US National Toxicology Program, all forms of asbestos are known to cause cancer. Most people with mesothelioma have a history of asbestos exposure. Mesothelioma has a long latency period, which means it usually doesn’t develop for 15–40, or more, years after exposure to asbestos.

There are 2 types of exposure to asbestos:

Direct exposure affects people who come into contact with asbestos directly. This may include: workers in asbestos mines or mills producers of asbestos products or asbestos-based products construction workers, carpenters and painters shipyard workers manufacturers of cement insulation workers electricians and heating tradespeople plumbers demolition workers automotive industry workers, including brake and clutch repair workers people who live near an asbestos factory or mine people who worked in buildings where asbestos was present and was disturbed Indirect exposure affects people who come in contact with asbestos in other ways. This may include: family members who are exposed to asbestos from fibres brought home on a worker’s clothing people living close to a mine who may be exposed to asbestos in dust The risk of exposure to asbestos is highest for people who mine and export asbestos or those who work with it in manufacturing. The risk of developing mesothelioma is related to how much asbestos a person was exposed to and how long the exposure lasted. People exposed at an early age, for a long period of time and to greater amounts of asbestos are more likely to develop mesothelioma.

Occasionally, mesothelioma develops in people who have never been exposed to asbestos.

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Erionite

Erionite is a known human carcinogen that is linked to the development of pleural and peritoneal mesothelioma. It is a naturally-occurring mineral that belongs to a group of minerals called zeolites. Zeolites are chemically related to asbestos and erionite has asbestos-like fibres. Erionite is common in the soil in parts of Turkey and materials made with erionite are used in construction in these regions. High rates of mesothelioma in these areas are due to exposure to this mineral.

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Ionizing radiation

The risk of mesothelioma increases for people who have been exposed to medical radiation.

People who have been treated with radiation therapy to the chest or abdomen for lymphoma, breast cancer, lung cancer or other cancers have an increased risk for mesothelioma. Although the risk of mesothelioma is higher in people who have been treated with radiation therapy, mesothelioma is likely to occur in only a very small number of these people. There have been reports linking mesothelioma to Thorotrast (thorium dioxide). Thorotrast is a contrast medium contrast medium A substance used in some diagnostic procedures to help parts of the body show up better on x-rays or other imaging tests. once used for imaging tests, but it is no longer used.

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Possible risk factors

The following factor has some association with mesothelioma, but there is not enough evidence to say it is a known risk factor. Further study is needed to clarify the role of this factor for mesothelioma.

simian virus 40 – Researchers are studying the simian virus 40 (SV40) as a possible risk factor for mesothelioma. Some studies suggest that infection with SV40 might increase the risk of developing mesothelioma. Between 1955 and 1963, some polio vaccines were contaminated with SV40, which may have contributed to some cases of mesothelioma. It is thought that SV40 may act as a co-factor with asbestos in causing mesothelioma.

Exposure

Asbestos was known in antiquity, but it wasn't mined and widely used commercially until the late 1800s. Its use greatly increased during World War II. Since the early 1940s, millions of American workers have been exposed to asbestos dust. Initially, the risks associated with asbestos exposure were not publicly known. However, an increased risk of developing mesothelioma was later found among shipyard workers, people who work in asbestos mines and mills, producers of asbestos products, workers in the heating and construction industries, and other tradespeople. Today, the U.S. Occupational Safety and Health Administration (OSHA) sets limits for acceptable levels of asbestos exposure in the workplace, and created guidelines for engineering controls and respirators, protective clothing, exposure monitoring, hygiene facilities and practices, warning signs, labeling, recordkeeping, and medical exams. By contrast, the British Government's Health and Safety Executive (HSE) states formally that any threshold for mesothelioma must be at a very low level and it is widely agreed that if any such threshold does exist at all, then it cannot currently be quantified. For practical purposes, therefore, HSE does not assume that any such threshold exists. People who work with asbestos wear personal protective equipment to lower their risk of exposure.

Occupational

Exposure to asbestos fibres has been recognised as an occupational health hazard since the early 1900s. Several epidemiological studies have associated exposure to asbestos with the development of lesions such as asbestos bodies in the sputum, pleural plaques, diffuse pleural thickening, asbestosis, carcinoma of the lung and larynx, gastrointestinal tumours, and diffuse mesothelioma of the pleura and peritoneum.

The documented presence of asbestos fibres in water supplies and food products has fostered concerns about the possible impact of long-term and, as yet, unknown exposure of the general population to these fibres. Although many authorities consider brief or transient exposure to asbestos fibres as inconsequential and an unlikely risk factor, some epidemiologists claim that there is no risk threshold. Cases of mesothelioma have been found in people whose only exposure was breathing the air through ventilation systems. Other cases had very minimal (3 months or less) direct exposure.

Commercial asbestos mining at Wittenoom, Western Australia, occurred between 1945 and 1966. A cohort study of miners employed at the mine reported that while no deaths occurred within the first 10 years after crocidolite exposure, 85 deaths attributable to mesothelioma had occurred by 1985. By 1994, 539 reported deaths due to mesothelioma had been reported in Western Australia.

Paraoccupational Secondary Exposure

Family members and others living with asbestos workers have an increased risk of developing mesothelioma, and possibly other asbestos related diseases. This risk may be the result of exposure to asbestos dust brought home on the clothing and hair of asbestos workers. To reduce the chance of exposing family members to asbestos fibres, asbestos workers are usually required to shower and change their clothing before leaving the workplace.

Asbestos in buildings

Many building materials used in both public and domestic premises prior to the banning of asbestos may contain asbestos. Those performing renovation works or diy activities may expose themselves to asbestos dust. In the UK use of Chrysotile asbestos was banned at the end of 1999. Brown and blue asbestos was banned in the UK around 1985. Buildings built or renovated prior to these dates may contain asbestos materials.

Environmental Exposure

Incidence of mesothelioma had been found to be higher in populations living near Naturally Occurring Asbestos (NOA).

References

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