Risk Factors:

Before cigarettes became popular in the beginning of the 20th century, lung cancer was rare. In 2009, lung cancer is expected to strike up to 219,440 Americans, and about 159,000 are expected to die from it. The disease usually occurs in people over 50 years old. Men have a significantly greater incidence of lung cancer compared to women. On the encouraging side, the rate of lung cancer in men has been declining significantly over the past decade. While lung cancer rates have been increasing dramatically in women (by 600% from 1950 to 2000), they now appear to be stabilizing. However, lung cancer deaths among female nonsmokers seem to be on the rise.

Smokers and Those Exposed to Cigarette Smoke

Smoking is the primary risk factor in 85 - 90% of lung cancers. The risk of lung cancer in smokers is about 20 times that of nonsmokers. The risk depends on the duration of the addiction and the number of pack years. (One pack year equals the number of packs of cigarettes smoked per day, multiplied by the number of years that the person has smoked.) Genetic damage in the lung occurs in nearly all chronic smokers, even if cancer has not developed.

People who smoked can be at increased risk for lung cancer more than 20 years after quitting, although the risk drops significantly even in the first year after quitting. There are benefits to quitting smoking, even for people who are well into middle age.

Secondhand Smoke. The Environmental Protection Agency has classified secondhand smoke as a carcinogen (cancer-causing chemical). Exposure to secondhand tobacco smoke increases the risk of lung cancer in the nonsmoker by about 20 - 30%. A 2006 Surgeon General report found that about 3,000 nonsmokers die each year of lung cancer resulting from exposure to secondhand smoke.

Ethnic Differences

There may be some ethnic differences in lung cancer risk. For example, African-American men have about a 45% higher risk of developing lung cancer than Caucasian men. It is not clear what factors are responsible for this higher risk. Some African Americans appear to have a genetic vulnerability to the harmful chemicals in cigarette smoke.

In China, about one-third of all young male smokers will eventually die because of tobacco-related illnesses. Their risk for lung cancer, however, is much less than it is for chronic lung disease, the opposite of the Western trend. The lower rate of lung cancer among Chinese people might be due to a slow rate of clearing nicotine, which results in smoking fewer cigarettes.

Socioeconomic Differences

Low income and a lack of education have been linked to an increased risk for lung cancer. Researchers say socioeconomic status is connected to other factors involved in lung cancer risk, such as smoking, diet, and exposure to cancer-causing chemicals in the workplace.

Environmental Factors

People with High Exposure to Radon. Studies have shown that radon raises the risk of lung cancer in underground miners by 40%. It is unclear whether the results of these studies would apply to people exposed to radon in their homes. A cumulative long-term exposure to radon and smoking also increases the danger. Most people move an average of 10 or 11 times over their lifetime, so the risk of developing lung cancer through radon exposure is very low in most individuals, even for those who lived for a while in areas with high radon levels. People with homes that have high radon levels and those who sleep or spend a long time in basements with detectable but moderate levels should consider taking protective measures.

Workers Highly Exposed to Carcinogens. An estimated 9,000 - 10,000 men and 900 - 1,900 women develop lung cancer each year because of occupational exposure to carcinogens. More than half of these cases are attributable to past exposure to asbestos, which has long been known to be a risk factor for mesothelioma (cancer of the pleura, the lining around the lung) and can increase the risk of lung cancer in smokers. With better protective measures, these rates are expected to fall in the future.

Other chemicals that put workers at risk for lung cancer include:

• Arsenic (insecticide and herbicide sprayers, tanners, oil refinery workers)
• Chloromethyl methyl ether (workers exposed to certain polymers, water repellents, or products using chloride and formaldehyde)
• Chromium compounds (workers using certain alloys, paints, pigments, and preservatives)
• Depleted uranium (soldiers exposed to weapons during battlefield conditions)
• Crystalline silica

By contrast, agricultural workers seem to have a lower lung cancer rate, despite their possible occupational exposures to risky chemicals. While this rate has traditionally been attributed to good health habits, including low tobacco use, agricultural workers' exposure to endotoxin may be responsible. Endotoxin is a component of common bacteria found in soil and animals, and it may have cancer-preventing effects on the immune system.

Air Pollution. Although any risk from air pollution is very small, it nevertheless may be a contributor to those lung cancers not obviously related to smoking. Some studies have found an association between increased risk for lung cancer and long-term exposure to very small particulates, especially sulfates, in polluted air. The risk, if any, is very small.

Family History

A family history of lung cancer may play a role in increasing susceptibility to this disease. Women who had mothers or sisters with lung cancer have triple the risk. The risk is higher in both smokers and nonsmokers. There is no association between a history of other cancers and lung cancer. Both genetic factors and secondhand smoke appear to contribute to the danger in these individuals.

Other Diseases that Increase Risk

Smokers with emphysema or chronic inflammatory lung diseases, such as asthma, are at increased risk for lung cancer. Both smokers and nonsmokers whose lungs are scarred from recurrent lung diseases, such as pneumonia or tuberculosis, are also at increased risk, particularly for bronchoalveolar lung cancer.