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. It is unclear how much of this risk is due to shared environmental factors (like a smoking household) and how much is related to genetic risk. People who inherit certain genes, like genes that interfere with DNA repair, may be at greater risk for several types of cancer. Tests to identify people at increased genetic risk of lung cancer are not yet available for routine use.

Lung diseases

    The presence of certain diseases of the lung, notably chronic obstructive pulmonary disease (COPD), is associated with an increased risk (four- to six-fold the risk of a nonsmoker) for the development of lung cancer even after the effects of concomitant cigarette smoking are excluded. Pulmonary fibrosis (scarring of the lung) appears to increase the risk about seven-fold, and this risk does not appear to be related to smoking.

Prior history of lung cancer

    Survivors of lung cancer have a greater risk of developing a second lung cancer than the general population has of developing a first lung cancer. Survivors of non-small cell lung cancers (NSCLCs, see below) have an additive risk of 1%-2% per year for developing a second lung cancer. In survivors of small cell lung cancers (SCLCs, see below), the risk for development of second lung cancers approaches 6% per year.

Air pollution

    Air pollution from vehicles, industry, and power plants can raise the likelihood of developing lung cancer in exposed individuals. Up to 1%-2% of lung cancer deaths are attributable to breathing polluted air, and experts believe that prolonged exposure to highly polluted air can carry a risk for the development of lung cancer similar to that of passive smoking.

Exposure to diesel exhaust

    Exhaust from diesel engines is made up of gases and soot (particulate matter). Many occupations, such as truck drivers, toll booth workers, forklift and other heavy machinery operators, railroad and dock workers, miners, garage workers and mechanics, and some farm workers are frequently exposed to diesel exhaust. Studies of workers exposed to diesel exhaust have shown a small but significant increase in the risk of developing lung cancer.