Lung cancer refers to several different types of cancer which begin in the linings of the lungs. Lung cancer is currently the deadliest cancer, killing 1.3 million people per year. The five-year survival rate for lung cancer is less than 15%. Fortunately, however, lung cancer is also one of the most easily prevented of the major cancers. By far the most significant risk factor for lung cancer is tobacco use, including cigarette smoking.

Lung cancer is caused by cigarette smoke - both among smokers, and to a much lesser extent among nonsmokers exposed to secondhand smoke on a regular basis - more than by any other factor. Indeed, until the rise of cigarette smoking in the twentieth century, first among men and then among women, lung cancer was a comparatively rare form of cancer. Although the lifetime risk of lung cancer in the general population is only a little over 1%, the risk for smokers is nearly 12% for female smokers and over 17% for male smokers. The female lung cancer rates will continue to rise as more lifetime female smokers grow into middle and old age. Overall, only about one in ten people diagnosed with lung cancer in America is a nonsmoker.

Aside from smoking, other airborne chemicals are also known carcinogens and account for much of the remaining cases of lung cancer. The first of these is asbestos, which accounts for about one in thirty cancer cases. Asbestos was previously used as a common compound in building insulation, but developed countries have now generally banned this use because of health risks. (This results in the strange feature of old, asbestos-equipped buildings requiring expensive chemical hazard containment measures when undergoing renovations.) Canada still mines and exports asbestos to developing countries, where building regulations are more lax.

The second chemical which causes lung cancer is radon. Radon gas has no colour or odour, and seeps up from the Earth's crust, potentially through household basements. Concerns about radon gas are higher in some areas than others - for instance, Iowa in America and Cornwall in England have larger concentrations of radon gas. Overall, a small percentage of homes have excess radon gas. In major cities, particulate matter associated with pollution likely also results in a measurable increase in lung cancer over what would have been the incidence of the disease in a pollution-free environment.

Finally, according to the Centers for Disease Control (CDC), family history and diet also play some role as risk factors for lung cancer. People with a family history of lung cancer are at greater risk of developing lung cancer themselves, especially if they also have one or more other risk factors. In addition, there is conflicting information about the consequences of diet, although it is generally accepted that high-fat, high-cholesterol, low-fruit, and low-vegetable diets increase the risk of a range of cancers, including lung cancer.

Overall, however, family history and diet are not significant compared to the negative health consequences of smoking, or the positive benefits of quitting. Lung function begins to recover within just a few months of a person's last cigarette. People who quit smoking by age 30 almost entirely reduce their risk of lung cancer and other smoking-related diseases as they age. People who quit by age 50 cut their chances of premature death in half, and even people who quit after age 60 have longer life expectancies than those who never do.

If you have one or more risk factors for lung cancer and are concerned about contracting the disease, you should discuss your concerns with your doctor, who can help reduce your risk level.

American Cancer Society: "What are the Risk Factors for Non-Small Cell Lung Cancer?"

Centers for Disease Control (CDC): "Lung Cancer Risk Factors"

Mayo Clinic: "Lung Cancer: Risk Factors"

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