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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.
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.
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:
Free radical-induced damage
Growth pattern overrides
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.
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.