Smoking is well known to be a predominant risk factor for the development of lung cancer, but lung cancers occurring in never smokers has increased in recent times . It is also shown that the increase in the incidence of lung cancer in never smokers is higher in east Asia than the US or European countries . These findings suggest that factors other than smoking may be etiological and risk factors for lung cancer. Some environmental agents, such as radon, asbestos and cooking fumes, have also been implicated in its development [1,2]. However, to date, a large fraction of lung cancers have not been definitively associated with such environmental risk factors, highlighting the need for additional epidemiological research.
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