The connection between asbestos exposure and lung cancer was noted as early as 1925, and confirmed over the next 70 years by many epidemiologic studies of asbestos-exposed workers. The four main types of commercially used asbestos, chrysotile, amosite, anthophyllite, and mixtures containing crocidolite, have all been associated with an increased risk of lung cancer. About one in seven people who suffer from asbestosis, a lung disease resulting from high exposure to asbestos, eventually develop lung cancer.

There is a relationship between cigarette smoking and asbestos exposure in causing lung cancer, such is that asbestos workers who smoke face a much higher risk than asbestos workers who do not. According to the National Cancer Institute, evidence suggests that asbestos-exposed workers who quit smoking can reduce their risk of developing lung cancer by 50% within five years of quitting.

How common is lung cancer?

Lung cancer is responsible for the most cancer deaths in both men and women throughout the world. The American Cancer Society says about 174,000 new cases of lung cancer in the U.S. were diagnosed in 2004 with more than 160,000 deaths. Lung cancer was not common before the 1930s but increased dramatically over the following decades as tobacco smoking increased.

What causes lung cancer?

The most common cause of lung cancer is smoking, with about 90% of lung cancers arising from tobacco use. The risk of lung cancer increases with the number of cigarettes smoked over time.

Pipe and cigar smoking can also cause lung cancer, although the risk is not as high as with cigarette smoking.

Other causes include:

• Passive smoking, or inhalation of tobacco smoke from other smokers sharing living or working quarters. Nonsmokers who live with a smoker have a 24% increase in risk for developing lung cancer when compared with other nonsmokers. An estimated 3,000 lung cancer deaths occur each year in the U.S. are due to passive smoking.
• Asbestos fibers -- Today, asbestos use is limited or banned in many countries including the Unites States. Both lung cancer and a type of cancer of the lining of the lung called mesothelioma are associated with exposure to asbestos. Cigarette smoking drastically increases the chance of developing an asbestos-related lung cancer in exposed workers. Asbestos workers who do not smoke have a fivefold greater risk of developing lung cancer than nonsmokers, and those asbestos workers who smoke have a risk that is 50 to 90 times greater than nonsmokers.
• Radon gas -- Radon gas is a natural, chemically inert gas that is a natural decay product of uranium. It decays to form products that emit a type of ionizing radiation. Radon gas causes 15,000 to 22,000 lung cancer-related deaths annually in the U.S. As with asbestos exposure, smoking greatly increases the risk of lung cancer with radon exposure. Radon gas can travel up through soil and enter homes through gaps in the foundation, pipes, drains, or other openings. The U.S. Environmental Protection Agency estimates that one out of every 15 homes in the U.S. contains dangerous levels of radon gas. Radon gas is invisible and odorless but can be detected with simple test kits.
• Familial predisposition -- While the majority of lung cancers are associated with tobacco smoking, the fact that not all smokers eventually develop lung cancer suggests that other factors, such as individual genetic susceptibility, may play a role in the causation of lung cancer. Numerous studies have shown that lung cancer is more likely to occur in both smoking and nonsmoking relatives of those who have had lung cancer than in the general population.
• * Air pollution -- Air pollution from vehicles, industry, and power plants can raise the likelihood of developing lung cancer in exposed individuals. Up to 1% of lung cancer deaths are attributable to breathing polluted air.