Smoking is the most important risk factor for lung cancer

Approximately 90% of lung cancers are smoking-related. However, not all smokers develop lung cancer. There is a clear dose-response relationship between the number of cigarettes smoked per day, the duration of the smoking habit and the risk of lung cancer. A lifetime smoker has a 20-40 times greater risk of developing lung cancer than a non-smoker (Tyczynski et al., 2003).

The impact of environmental factors

Passive exposure to tobacco smoke or environmental tobacco smoke (ETS), increases the risk of lung cancer by 15-25% (Tyczynski et al., 2003).

Occupational exposure to substances such as asbestos, radon, tar, soot and metals, such as arsenic, cadmium and nickel, and to ionising radiation is known to increase the risk of lung cancer. The effects of asbestos, radon and arsenic on lung cancer development are synergistic with smoking. In general, the contribution of environmental factors, except for cigarette smoke, to the risk of lung cancer is small.

Gender, age, socio-economic status, genetics

Lung cancer is rarely diagnosed in those under 40 years, but incidence rises steeply thereafter, peaking between ages 75-84.The male/female ratio for lung cancer incidence, which was very high, has changed considerably in the past decades. Female rates are approaching male rates in some countries, as a result of the increase in smoking prevalence among women several decades ago.

The risk of lung cancer is associated with deprivation, including poverty and low educational levels, as is smoking.

Genetic factors may predispose to the development of lung cancer. It is well-documented that first-degree relatives of lung cancer patients have an increased risk of developing lung cancer. Recently, a major susceptibility locus influencing lung cancer risk has been identified (Bailey-Wilson et al., 2004).