The Multitopic Blog

Mesothelioma remains a relatively rare cancer, in spite of the fact that the incidence of reported cases has increased in the past twenty years. One is every 1,000,000 persons is affected by mesothelioma while with high smoking the incidence rate of lung cancer is 1,000 for every 1,000,000. In industrialized Western countries the incidence of malignant mesothelioma ranges from 7 to 40 for every 1,000,000 depending on the exposure to asbestos and it has been estimated to have reached a high of 15 per 1,000,000 in the U.S in 2004. While the incidence is expected to increase constantly, it is more prevalent among men and risk increases with age but can appear at any age. Peritoneal mesothelioma accounts for one-fifth to one-third of all mesotheolima.

Approximately 27.5 million people were estimated to have been exposed to asbestos at work in the United States between 1940 and 1979 and between 1973 and 1984, the incidence of pleural mesothelioma has found to have increased threefold in Caucasian males. The casualties of Mesothelioma have increased by 50% from 2000 to 3000 per year in the U.S with men being four times more likely to acquire it than women. These figures however may not be entirely accurate since in many cases it is likely that mesothelioma has been mistakenly diagnosed as adenocarcinoman of the lung, which is similar and difficult to differentiate.

Risk factors

Constant contact with asbestos is a major risk factor for mesothelioma and exposure to asbestos is found in almost every reported case. However quite often, mesothelioma has also been reported in cases where there is no known exposure to asbestos. In sparingly few cases mesothelioma has also been found to have been caused by irradiation, intrapleural thorium dioxide and by inhaling other fibrous silicates such as erionite.

Asbetos is a group of minerals that occur naturally and in the form of masses of strong and flexible fibres that can be separated into thin threads and woven. It is this property of asbestos that makes it an oft-used material in industrial products such as cement, flooring products, textiles and for the purpose of insulation and in the form of brake linings and roof shingles. During the manufacturing process, tiny asbestos particles float in the air and such particles are liable to be swallowed or inhaled and can cause serious health hazards. In addition to causing mesothelioma, contact to asbestos can also increase the risk of lung cancer, asbestosis and cancers of the larynx and kidneys, among others.

Together smoking and exposure to asbestos can markedly increase the risk of a person developing cancer of the airways. Although by itself smoking cigarettes does not increase the risk of mesothelioma, a brand of cigarettes known as Kent was known to have used asbestos in its filters a few years in the 1950s and a few cases of mesothelioma were found to have been caused in persons who had smoked these cigarettes.

A few studies have lead to the belief that the simian virus 40 or SV40 may also play a contributing role in the development of mesothelioma.

Exposure

Though the properties of asbestos were known, it wasn’t until the late 1800s that the mining and commercial use of asbestos began. By the time of World War II it was used in great quantities and since the 1940s several million workers in America have been exposed to asbestos dust. However the risk of developing mesothelioma was first noticed among people who worked in shipyards, asbestos mines and mills and those who produced asbestos products and worked in heating and construction industries. The U.S Occupational Safety and Health Administration has set upper limits for asbestos exposure at the workplace and has laid down guidelines for engineering controls and respirators, putting up of warning signs, labeling, recordkeeping and the conducting of medical exams. The Health and Safety Executive (HSE), an initiative of the British Government however that made formal statements that the threshold for mesothelioma must be very low and that in case the threshold is very low, then it cannot be quantified at all. Therefore the assumption by the HSE is that a threshold does not exist at all. Thus people who come into contact with asbestos at work are required to wear protective gear to protect themselves from the risk of exposure.

Occupational

Since the beginning of the last century exposure to asbestos fibres has been regarded as and occupational hazard since it has been noted in various epidemiological studies that exposure to asbestos could be connected to the developing of lesions including asbestos bodies in the sputum, pleural plaques, diffusion of the pleural thickening and of mesothelioma of the pleura and peritoneum. Moreover asbestos has also been found to cause carcinoma of the lung and larynx.

The presence of asbestos fibred in food and water has given rise to concerns about the impact of long-term and in many cases unknown exposure of the population to asbestos. Though brief and transient exposure to these fibres has been considered to not be very harmful by many experts, some still believe that there is no known threshold of risk. People who have only breathed the air through air ventilation systems have been found to have mesothelioma as well as those who were direct exposure for a very minimal time period (3 months or less).

Between the years 1945 and 1966 commercial asbestos mining took place at Wittenoom in Western Australia. A longitudinal study of persons employed in the mine showed that while no deaths occurred within the first 10 years of crocidolite exposure, by 1985, 85 deaths and by 1994, 539 deaths caused due to mesothelioma had occurred.

Paraoccupational Secondary Exposure

The families of asbestos workers are at a much higher risk of developing asbestos related diseases since they are constantly exposed to asbestos dust which stays on the clothing and hair of an asbestos worker. To avoid exposing others to the risks of asbestos worker are requires to bathe and change their clothing prior to leaving the workplace.

Asbestos in buildings

Asbestos was used in building materials that was used to build both domestic as well as public premises prior to the banning of such material. People undertaking renovation or DIY activities are at a high risk of coming into contact with asbestos. The use of Chrysotile asbestos was banned in 1999 and brown and blue asbestos was banned around 1985 in the U.K. Buildings built or renovated prior to those dates however might have been built with asbestos containing materials.

Environmental Exposure

Mesothelioma has been found to occur at a higher rate among people living near areas with Naturally Occurring Asbestos or NOA.