1. Cigarette smoking: smokers have a 10 –25 times higher risk when compared to non-smokers.

Janerich et al suggested that 20% of all lung cancers in non-smokers are the result of passive smoking at home during childhood and young adulthood.

2. People exposed to air pollution in urban centres have a 2 x higher risk of developing lung cancer than people living in rural areas.

3. Chronic obstructive lung diseases (COPD) lead to cancer proneness of the squamous cell type, superimposed on the effect of smoking. Scar tissue may lead to the development of adenocarcinomas; lung cysts and idiopathic lung fibrosis are associated with a higher incidence of adenocarcinoma and bronchoalveolar cell carcinoma.

4. Exposure to asbestos, glass-wool and ceramic fibres increases the risk for lung cancer.

5. Genetic factors (see next slide).

6. It is suggested that dietary factors may also play a role. Ethanol is associated with an increased incidence, while dietary consumption of lettuce, broccoli and black tea may be associated with decreased incidence.