Asbestos as a risk factor for malignant mesothelioma
The likelihood of developing malignant mesothelioma relates to how long an individual has been exposed to asbestos (duration), how much they were exposed to (severity of exposure) and the type of asbestos. However, unlike other conditions associated with asbestos (which are associated with cumulative exposure), mesothelioma can follow very short-term exposures. In fact, in about 3% of cases, workers had less than 3 months exposure to asbestos. After exposure, there is a very long latent period between first exposure and development of malignant mesothelioma, usually of 30-45 years.

There are two main forms of asbestos: serpentine and amphibole. Chrysotile (or white asbestos) is the only form of serpentine asbestos; it is curly and flexible and accounts for 90% of commercial asbestos. There are various types of amphibole asbestos, which occur as microscopically thin, sharp rods that can penetrate deeply into the lungs. The risk of developing malignant mesothelioma is greatest with crocidolite (blue asbestos) and amosite (brown asbestos), and least with tremolite and chrysotile. There is some suggestion that chrysotile has only a low association with malignant mesothelioma, and that the disease occurs in chrysotile workers either when there are high levels or because of contamination with the more dangerous forms.

Amongst the non-exposed, malignant mesothelioma is very rare, affecting 2-17 people per million; however the risk increases more than 1000 times in those exposed to asbestos. The life-time risk in the heavily exposed is 7-10%. In all, 1 in 10 asbestos workers die from malignant mesothelioma (pleural or peritoneal) -- although 1 in 5 die from the more common bronchogenic lung cancer.

Men are more at risk for malignant mesothelioma, because they were more typically involved in industries mining or using asbestos. The male-to-female ratio is thus around 3 to 1. Race is not a factor in the development