Risk Factors

Before cigarettes became popular in the beginning of the 20th century, lung cancer was rare. This year, lung cancer is expected to strike up to 174,470 Americans, and about 162,460 are expected to die from it. The disease usually appears 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.

Smokers and Those Exposed to Cigarette Smoke

Smoking appears to be the primary risk factor in 85% to 90% of lung cancers. About 15% of all people who smoke develop lung cancer. 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.

An elevated risk for lung cancer can persist for more than 20 years after quitting smoking, although the risk drops significantly even in the first year after quitting. And, there are benefits to quitting smoking even for people who are well into middle age.

Second-Hand Smoke. The Environmental Protection Agency has classified second-hand smoke as a carcinogen (cancer-causing chemical). A number of studies have suggested that exposure to second-hand tobacco smoke may increase the risk of lung cancer in the nonsmoker by about 25%. Still, other studies suggest that the effects of second-hand smoke on adults may be highly over-estimated. A 2003 study in California on smokers and their spouses, for example, found no significant relationship between second-hand smoke and a higher risk for tobacco-related deaths, heart disease, or lung cancer. It should be strongly stressed, however, that the harmful effects of parental smoking on children are fairly well established, and that no one should smoke.

Ethnic Differences

There appears to be some ethnic differences in lung cancer risk. For example, African Americans face a risk that is two to four times higher than that in Caucasians, regardless of smoking status. 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, an estimated 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. A 2001 study reported that 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.

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 One study suggests that people with intense or prolonged exposure to radon in their homes do indeed face the same risk as miners exposed to similar levels of radon. 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 awhile in areas with high radon levels. People with homes that have high radon levels and those who sleep or spend many hours to days in basements with detectable but moderate levels should consider taking protective measures.

Workers Highly Exposed to Carcinogens. An estimated 9,000 to 10,000 men and 900 to 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, a 2000 study suggests that agricultural workers' exposure to endotoxin may be responsible. Endotoxin is a component of common bacteria found in soil and animals and may have cancer-preventing effects on the immune system.

Exposure to Smoke from Grills. Grilling and high-heat frying emit chemicals called heterocyclic amines, which are known to be carcinogenic. A 2000 study of Chinese women found that smokers who stir-fried meat daily and inhaled cooking fumes had a higher risk of lung cancer than did those who stir-fried meat less frequently. No higher risk was found among nonsmokers.

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, including a major analysis of vital statistics in 2002, have found an association between increased risk for lung cancer and long-term exposure to very small particulates, especially sulfates, present 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. In one study, people with parents or siblings with respiratory tract cancers had a 30% higher risk for lung cancer than people without a family history, and women with mothers or sisters with lung cancer had triple the risk. A higher risk occurred in both smokers and nonsmokers. There was no association between a history of other cancers and lung cancer. Both genetic factors and secondary smoke appeared 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.