Asbestos is the "perfect carcinogen" as it acts as both a promoter and initiator of cancer. Studies by the National Cancer Institute have shown that exposure to asbestos may increase the risk of lung cancer and mesothelioma(a relatively rare cancer of the thin membranes that line the chest and abdomen). Although rare, mesothelioma is the most common form of cancer associated with asbestos exposure.
In addition to lung cancer and mesothelioma, some studies have suggested an association between asbestos exposure and gastrointestinal and colorectal cancers, as well as an elevated risk for cancers of the throat, kidney, esophagus, and gallbladder.
Asbestos exposure may also increase the risk of asbestosis (an inflammatory condition affecting the lungs that can cause shortness of breath, coughing, and permanent lung damage) and other non-malignant lung and pleural disorders, including pleural plaques (changes in the membranes surrounding the lung),pleural thickening, and benign pleural effusions (abnormal collections of fluid between the thin layers of tissue lining the lungs and the wall of the chest cavity). Although pleural plaques are not precursors to lung cancer, evidence suggests that people with pleural disease caused by exposure to asbestos may be at increased risk for lung cancer.
Evidence presented in 1907 to a government enquiry by Dr. Montague Murray described the first diagnosed case of fatal, non-tubercular, diffuse pulmonary fibrosis in an asbestos worker: asbestosis. Asbestosis is an irreversible and progressive lung condition which results from the inhalation of asbestos fibres over an extended period. In asbestosis, lung tissue is scarred and thickened by the abrasive action of the asbestos fibres in the alveoli (the air sacks). The latency period for asbestosis is usually at least ten years and the higher the exposure, the greater the chances of developing the disease. Asbestosis tends to be linked to heavy occupational exposure, although cases of asbestosis among those not occupationally exposed have been known.
An article which appeared in The Lancet in 1934 presented evidence of a link between asbestos and lung cancer. Dr. Richard Doll's landmark paper Mortality from Lung Cancer in Asbestos Workerswas published in 1955. Doll's research showed that the incidence of lung cancer among men at an asbestos factory in Rochdale was ten times the national norm. Asbestos related lung cancer can occur from occupational or environmental exposure: it is virtually incurable. The chances of recovery for those whose lung cancer is caused by asbestos are worse because the lungs may already be damaged by the dust. One type of lung cancer asbestos causes - undifferentiated, small-cell type - is the one with the least hope of treatment. The latency period for lung cancer associated with asbestos exposure is usually between fifteen and thirty-five years. An article in theJournal of the American Medical Association estimated that an asbestos insulation worker who smokes had ninety two times the chance of dying from lung cancer as a non-smoking, non-asbestos worker.
Mesothelioma is a formerly rare, but increasingly common cancer of the lung or the abdominal cavity; the only known cause of mesothelioma is exposure to asbestos. Malignant mesothelioma can be contracted from very low exposures to asbestos and accounts for the majority of victims who contract an asbestos-related disease through environmental exposure. The latency period for mesothelioma is generally between thirty to fifty years, although British courts have accepted a latency period as short as ten years. On average, mesothelioma patients survive for eighteen months to two years following diagnosis, although some people survive considerably longer. Currently, there is no known cure.