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Four Must Read books for anyone diagnosed with pleural mesothelioma.

Causes & Risk Factors of Mesothelioma

Since doctors first found tumors on the lining of a patient’s lung in 1890, researchers have entertained several theories about what causes pleural mesothelioma. It wasn’t until 1960, however, that a scientist named J.C. Wagner clearly attributed this cancer to asbestos exposure.

Wagner’s team identified 33 cases of the disease over a four-year period; 32 had a history of asbestos exposure. (All but four of the exposed patients worked in or lived near the town’s asbestos mines.) Since then, multiple studies have confirmed the relationship between asbestos and pleural mesothelioma.

The asbestos industry continues to argue that certain types of asbestos do not cause pleural mesothelioma. However, researchers maintain that all types of asbestos — including amphibole and chrysotile — can cause cancer.

Types of Asbestos Exposure that Cause Pleural Mesothelioma

Patients with pleural mesothelioma have reported several sources of asbestos exposure. Many of the sources fall into one of the following categories:

Sources of exposure	Examples
Asbestos mines and processing plants	Jeffrey Asbestos Mine; WR Grace Vermiculite Plant
Industrial worksites (non-asbestos industry)	National Gypsum drywall factory; construction sites
Shipyards	Todd Shipyards; Hunters Point Naval Shipyard
Military facilities	USS Alabama; Fort Bragg; Brooklyn Navy Yard
Areas with active asbestos mines or naturally occuring deposits	Libby, Montana; Coalinga, California

By far, the majority of exposures occurred at industrial jobsites. Until the 1980s, asbestos heavily contaminated worksites like refineries and power plants. Many workers sustained long-term, high-dose exposure over the course of their careers. This type of exposure is the most likely to lead to disease.

Patients have also been exposed outside of the workplace — although on a less frequent basis. These exposures may have come from asbestos-contaminated consumer products, like loose-fill insulation , or asbestos that came home on the clothing or skin of an asbestos worker. In a handful of cases, patients encountered the fibers in the environment.

How Does Asbestos Cause Pleural Mesothelioma?

Pleural mesothelioma develops after a person inhales asbestos. As the long, thin fibers pass through the respiratory pathway, they can get trapped in the lining of the lung — known as the pleura.

Once trapped, the fibers can trigger a carcinogenic process that takes between 20 and 50 years to complete. Researchers aren’t completely sure how this process works, but they have several theories:

Cellular inflammation

"Observations support a scenario [where] mesothelial cells undergo a series of chronic injury, inflammation and proliferation," according to a 2013 study in the American Journal of Pathology.

Genetic mutations

Asbestos may cause genetic changes that can lead to cancer. These changes may include "mutations in genetic susceptibility or cell cycle genes," according to the American Journal of Pathology article.

Free radical-induced damage

Inside the body, asbestos may trigger free radical production. Some of these free radicals, known as reactive oxygen species, may intensify the toxicity of asbestos fibers, while triggering additional damage to mesothelial cells.

Growth pattern overrides

Asbestos may trigger the production of oncoproteins. These substances can override cell programming that controls growth, in turn allowing cells to divide too quickly and become cancerous

Certain factors may make people more likely to develop pleural mesothelioma after sustaining asbestos exposure. Smoking weakens the lungs and may make them more susceptible to developing asbestos-related lung cancer, but smoking does not increase the risk of mesothelioma in anyone with a history of asbestos exposure. Genetics may serve as a risk factor; research is underway to understand the genes and related biological processes that contribute to pleural mesothelioma. This genetic factor may help explain why some people develop pleural mesothelioma after exposure, while others who are exposed do not.

The level and duration of asbestos exposure can also affect someone’s risk of developing this pleural disease. Even low-level exposure to asbestos can cause pleural mesothelioma. Renowned asbestos researcher Gunnar Hillerdal reported in 1999: “There is no proof of a threshold value — that is, a minimal lower limit below which asbestos fibers cannot cause the tumor — and thus it is plausible that even such low exposure can cause mesothelioma (even if the risk is extremely low).”

A 1998 study by Iwatsubo et al. found an excess of pleural mesothelioma cases among the lowest exposure group participating in the study. Multiple studies demonstrate a dose-response relationship between asbestos exposure and pleural mesothelioma, meaning that as asbestos exposure increases so does the inhalation of asbestos fibers into the lungs, which in turn increases the risk of developing pleural mesothelioma.

Can Pleural Mesothelioma Be Unrelated to Asbestos?

On rare occasions, patients without a history of asbestos exposure have developed pleural mesothelioma. Most non-asbestos pleural mesothelioma cases come from exposure to minerals that closely resemble asbestos in structure, known as asbestiform minerals. Erionite and taconite are two examples of asbestiform minerals that have caused pleural mesothelioma.

Pleural mesothelioma rarely develops without a specific cause. However, pediatricians have reported a very small number of spontaneous cases in children.No cases of mesothelioma from home use of contaminated hairdryers has been reported.

Source

Chahinian, A., and Robinson, B. Mesothelioma. Martin Dunitz: London. 2002.
Wagner, J.C., Sleggs, C. A., & Marchand, P. (1960). Diffuse pleural mesothelioma and asbestos exposure in the North Western Cape Province. British Journal of Industrial Medicine, 17 (260). Retrieved from http://pubmedcentralcanada.ca/pmcc/articles/PMC1038078/pdf/brjindmed00208-0014.pdf
Dodson, R.F., & Hammar, S. P. (Eds.). (2006). Asbestos: Risk assessment, epidemiology, and health effects. Boca Raton, FL: Taylor & Francis Group.
Mossman, B. T., Shukla, A., Heintz, N. H., Verschraegen, C. F., Thomas, A., & Hassan, R. (2013). New insights into understanding the mechanisms, pathogenesis and management of malignant mesotheliomas. American Journal of Pathology, 182 (4). Retrieved from http://www.sciencedirect.com/science/article/pii/S0002944013000382
Baas, P., Schouwink, H., & Zoetmulder, F. A. N. (1998). Malignant pleural mesothelioma. Annals of Oncology, 9 (139-149). Retrieved from http://annonc.oxfordjournals.org/content/9/2/139.full.pdf
Hillerdal, G. (1999). Mesothelioma: cases associated with non-occupational and low dose exposures. Occupational Environmental Medicine, 56 (8), 505-513. Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/10492646
Iwatsubo, Y., Pairon, J.C., Coutin, C., Menard, O., Massin, N., Caillaud, D., … Brochard, P. (1998). Pleural mesothelioma: Dose-response relation at low levels of asbestos exposure in a French population-based case-control study. American Journal of Epidemiology, 148 (2), 133-142. Retrieved from http://aje.oxfordjournals.org/content/148/2/133