The incidence of lung cancer is highly correlated with smoking.^[4]

Cancer pathogenesis is traceable back to DNA mutations that impact cell growth and metastasis. Substances that cause DNA mutations are known as mutagens, and mutagens that cause cancers are known as carcinogens. Particular substances have been linked to specific types of cancer. Tobacco smoking is associated with many forms of cancer,^[5] and causes 90% of lung cancer.^[6]

Many mutagens are also carcinogens, but some carcinogens are not mutagens. Alcohol is an example of a chemical carcinogen that is not a mutagen.^[7] In Western Europe 10% of cancers in males and 3% of cancers in females are attributed to alcohol.^[8]

Decades of research has demonstrated the link between tobacco use and cancer in the lung, larynx, head, neck, stomach, bladder, kidney, esophagus and pancreas.^[9]Tobacco smoke contains over fifty known carcinogens, including nitrosamines and polycyclic aromatic hydrocarbons.^[10] Tobacco is responsible for about one in three of all cancer deaths in the developed world,^[5] and about one in five worldwide.^[10] Lung cancer death rates in the United States have mirrored smoking patterns, with increases in smoking followed by dramatic increases in lung cancer death rates and, more recently,^[when?] decreases in smoking followed by decreases in lung cancer death rates in men. However, the numbers of smokers worldwide is still rising, leading to what some organizations have described as the tobacco epidemic.^[11]

Cancer related to one's occupation is believed to represent between 2–20% of all cases.^[12] Every year, at least 200,000 people die worldwide from cancer related to their workplace.^[13] Currently,^[when?] most cancer deaths caused by occupational risk factors occur in the developed world.^[13] It is estimated that approximately 20,000 cancer deaths and 40,000 new cases of cancer each year in the U.S. are attributable to occupation.^[14] Millions of workers run the risk of developing cancers such as lung cancerand mesothelioma from inhaling asbestos fibers and tobacco smoke, or leukemia from exposure to benzene at their workplaces.^[13]