Causes

Table 1 summarises the risk factors for lung cancer. Smoking is by far the most important cause, accounting for 90% of cases in men and 80% in women. Tobacco smoke contains more than 7000 chemicals, at least 70 of which are known to cause cancer in humans or animals (see chapters 8 and 9). People who smoke are 15–30 times more likely to be diagnosed with lung cancer or die from it than those who do not smoke, and the risk increases with the quantity and duration of smoking. Chronic obstructive pulmonary disease (COPD) is also a risk factor for lung cancer and patients with airflow limitation are more likely to develop lung cancer than those with normal airway function, independent of smoking status. Asbestos exposure is another important risk factor, with lung cancer developing in 20–25% of heavily exposed asbestos workers (see chapters 7 and 24). Asbestos is particularly found in insulation, pipe lagging and brake pads. Exposure to radon, chromium, arsenic and beryllium are further risk factors, and recently, diesel exhaust was added to the list. Other factors that may predispose to lung cancer include pulmonary fibrosis and a medical history of cancer of the head and neck or oesophagus. Genetic susceptibility plays a contributory role in the development of lung cancer, especially in those who develop the disease at a younger age and those who are nonsmokers. A family history of lung cancer has been implicated in conferring a higher risk. Smokers who have previously had lymphoma or breast cancer treated with thoracic radiotherapy also appear to be at increased risk.

Risk factors for lung cancer  
Smoking COPD Asbestos
Radon Chromium Arsenic
Beryllium Diesel exhaust Pulmonary fibrosis
Head/neck/oesophageal cancer Genetic susceptibility Lymphoma or breast cancer treated with thoracic radiotherapy
Family history of lung cancer Air pollution Coal smoke, indoor emissions from other fuels
Table 1 – Lung cancer risk factors. COPD: chronic obstructive pulmonary disease.

See the entire Lung Cancer Chapter