Lung cancer does not only occur in smokers – approximately 10 to 20 percent of cases are diagnosed in non-smokers[1][2][6]. In the United States, the American Cancer Society estimates that approximately 20 percent of people who have never smoked die of lung cancer each year[1]. In Asian countries, the share of non-smokers with lung cancer is even higher - they make up 30 to 40 percent of patients[2]. Scientists from the Mayo Medical School discovered that the cause of lung cancer in non-smokers may be a change in the activity of the GPC5 gene, which has up to 50 percent lower activity in adenocarcinoma than in healthy lung tissue[2]. Lung cancer in non-smokers is increasingly occurring in younger people and women, with the predominant type being adenocarcinoma[1]. Other risk factors for non-smokers include genetic predispositions, passive smoking, radon and air pollution[5]. Some cases of lung cancer in non-smokers occur without known risk factors and may be sporadic or accidental[1].