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Causes of cancer Epidemiologists had identified many important causes of cancer by the early of 1980s. Many types of cancer vary in incidence by more than an order of magnitude between different populations and every type is rare in some part of the world. Many specific causes cancer are now known, the most common are by smoking, obesity and a few oncogenic viruses, but a large proportion of global variation for common cancers such as breast, prostate, colon and rectum remains unexplained (Peto J. , 2001). According to Richard Doll and Richard Peto, pollution accounts for 2% of all cancer cases and geophysical factors account for another 3% while 80% to 90% of cancers are caused by “environmental factors”. Environmental factors are the non-genetic factors which are smoking, diet, occupational exposure to chemicals and geophysical factors (naturally occurring radiation, man-made radiation, medical drugs and radiation and pollution. Source: Doll and Peto “ The Causes Of Cancer”. According to Doll and Peto, tobacco use accounts for about 30% of all annual cancer deaths while dietary choices account for 35% of the annual deaths. Bruce Ames and Lois Swirsky Gold also argued that smoking cause about a third of all cancers. They underline the importance of diet by pointing out that quarter of the population eating the fewest fruits and vegetables had double the cancer incidence than those eating the most. They concluded that there is no evidence that is convinced enough saying chemical pollutants were the main cause of human cancer (Logomasini, N.A). Environmental and lifestyle causes cancer. Carcinogenic effect of tobacco. Carcinogenic effect of tobacco was the most important discovery in the history of cancer epidemiology. Lung c... ... middle of paper ... ...cers of the throat, kidney esophagus and gallbladder but the evidence is still inconclusive. The cancer risks also caused by long-established activities such as working in an oil refinery or living near a high voltage power line are not large. Apart from skin cancers due to sunlight, the only substantial and widespread cancer risk known to be caused by an avoidable environmental factor in developed countries is the further increase in lung cancer among smokers caused by indoor radon escaping from the ground or from building materials, although both indoor and outdoor air pollution from fossil fuels may also contribute to the risk in smokers. The risk to non-smokers is relatively trivial in developed countries, but burning fossil fuels indoors without adequate ventilation certainly contributes to the high lung cancer rates even in non-smokers seen in parts of China.