Although the aetiology for lung cancer among never smokers is not always clear, risk factors include secondhand tobacco smoke, radon gas exposure, other environmental exposures and genetic factors.
Lung cancer is the leading cause of cancer death worldwide, causing about 1.8 million deaths per year.1 In Ireland, approximately 2,700 people are diagnosed with lung cancer every year.2 Exposure to tobacco smoke is the main aetiologic factor responsible for lung cancer, accounting for approximately two-thirds of cases worldwide and its importance is demonstrated by the decline in lung cancer incidence and mortality that has accompanied the decline in smoking.3-5Despite the preponderance of tobacco smoking as its predominant aetiology, lung cancer is also a health problem in those with no history of smoking, accounting for between 10-20% of cases5,6 and despite the general reduction in lung cancer rates, the rate of lung cancer in non-smokers has been noted to be increasing.5
The term “never smoker” refers to individuals who have smoked less than 100 cigarettes in their lifetime. The majority of lung cancers in non-smokers occur in Non-Small Cell Lung Cancers (NSCLC) and particularly in lung adenocarcinoma.6 A much smaller subset of lung tumours (2%) called carcinoid tumours also show no major relationship to previous smoking history.6 With advances in the understanding of the molecular biology of cancer, substantial differences have been found in the genetic and molecular characteristics of lung cancer in smokers versus non-smokers including clinically significant treatment differences and prognostic outcomes. Several studies have suggested that lung cancer in non-smokers is different enough from a biologic and epidemiologic perspective to be looked at as almost a completely different entity.7-10
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