What causes mesothelioma?

We know that exposure to asbestos causes mesothelioma. This has been proven in the research laboratory, as well as in animal experiments and in studies of exposed human beings. Recently researchers at Mt. Sinai Hospital in New York City reviewed the autopsies of 2,015 patients who died between 1883 and 1910. This review did not reveal any cases of tumors that resembled mesothelioma, apparently due to the fact that asbestos was not in generalized use during this period of time. This adds to the mounting evidence that asbestos is a key factor in the development of this disease. 

We have no evidence regarding the necessary level of asbestos for an individual to be exposed to in order to develop a mesothelioma. We only know that people who end up with this disease usually have had some type of previous exposure to asbestos. When asbestos is inhaled, it can travel and eventually lodge itself in tissue. It is thought that this leads to inflammation and or irritation. It is not fully understood if asbestos fibers themselves cause the cells to release cytokines (body chemicals that induce cells to become cancerous) or if the tissues when injured lead to the release of chemicals (cytokines) that direct the cells to become malignant. It is hypothesized that asbestos fibers are inhaled and first travel through the upper air passages, which include the throat, trachea (windpipe), and large bronchi (large breathing tubes of the lungs). Normally if an irritant is detected, we have a cough reflex to clear secretions and foreign bodies. 

Asbestos fibers are long and thin and may not be detected by the system we rely on to protect the lungs from foreign material. Once asbestos fibers are imbedded in the pleura, they can cause injury, which leads to the development of pleural plaques (calcium containing platelike structures) or fibrosis (scar tissue). When the lung itself is injured, these damaged areas create scar tissue known as asbestosis. Asbestosis can be associated with lung cancer or mesothelioma, though patients with pleural plaques are thought to be at the highest risk for developing mesothelioma. In peritoneal mesothelioma, it is thought that these fibers travel via the lymph or blood stream, or are simply swallowed and end up in the abdomen. It is difficult to find these fibers when examining the tissues of the abdomen but oftentimes we see peritoneal patients with pleural plaques, which is irrefutable evidence of asbestos exposure. 

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