Cancer is mainly an environmental disease, as evidence in migrants suggests, with changes in risk that match those found in their new environment, sometimes even in first-generation immigrants. The IARC World Cancer Report addresses a number of risk factors for cancer.

Cancer is more often caused by the environment a person lives in, rather than his or her innate biology.

Cancer incidence age-standardized rates (world) per 100,000, circa 1970

Download High Res Text alternative: Cancer incidence rates per 100,000 in select countries in 1970

An estimated 1.3 billion people worldwide currently smoke tobacco, with the vast majority of these people smoking manufactured cigarettes.


An estimated 1.3 billion people worldwide currently smoke tobacco, with the vast majority of these people smoking manufactured cigarettes. All forms of tobacco are carcinogenic; smoking causes over 16 types of cancer and accounts for about one-fifth of global cancer deaths. Nearly 40% of the reductions in male cancer death rates between 1991 and 2003 in the USA are thought to be attributed to smoking declines in the last half-century.


According to a recent analysis, 16.1% of all cancers worldwide in 2008 were due to infectious agents. This fraction (the reduction in cancer if exposure to these infections was reduced to zero) was higher in less-developed countries (22.9%) than in more-developed countries (7.4%), and varied from 3.3% in Australia and New Zealand to 32.7% in Sub-Saharan Africa.

Text alternative: Smoking accounts for more than 20% of all cancer deaths worldwide

Smoking is associated with at least 16 types of cancers.

Smoking accounts for more than 20% of all cancer deaths worldwide

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The importance of occupational origin for a number of cancers, including mesothelioma, sinonasal, lung, nasopharynx, breast, non-melanoma skin cancer, bladder, esophagus, soft tissue sarcoma and stomach, has been highlighted in high-income countries. The carcinogens involved are asbestos, mineral oils, silica, diesel engine exhaust, coal tars and pitches, dioxins, environmental tobacco smoke, radon, tetrachloroethylene, arsenic and strong inorganic mists, and occupational exposures, including shift work, painting or welding. An emerging problem that needs to be addressed is that high-risk professions are now commonly exported to low-income countries.


Obesity is a risk factor for breast (post-menopausal), colorectal, endometrial, kidney, esophageal and pancreatic cancers, though the burden of such diseases explained by diet, weight, and body fat is still uncertain. Alcohol use is clearly associated with liver, aero-digestive tract, breast and colorectal cancers. Dietary recommendations on dietary cancer prevention have been issued by the World Cancer Research Fund.


Other known risk factors include reproductive factors, environmental pollutants, and ultraviolet (UV) exposure. The extent of exposure to environmental carcinogenic pollutants is unknown, particularly in low-income countries, though the burden adds up to several hundred thousand newly diagnosed cancers per year just for arsenic, air pollution, aflatoxin, polychlorinated biphenyls, and asbestos. Another environmental factor that is not man-made but is an important and preventable risk factor for skin cancer is excessive exposure to UV radiation, primarily from the sun, but also as a result of indoor tanning.

"The growing prevalence of obesity and overweight, seen in every corner of the world, is the warning signal that big trouble is on its way."

Margaret Chan, Director-General of the World Health Organization