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Lung cancer is the leading cause of cancer death for women in the United States, accounting for almost twice as many deaths as breast cancer.It is estimated that in 2008 that there will be 114,690 new cases of lung cancer diagnosed in men and 100,330 in women.Unlike men, a greater percentage of women who develop lung cancer have never smoked and roughly 20% of lung cancer deaths in women occur in lifelong nonsmokers.A significant controversy exists as to whether or not the relative risk for lung cancer attributed to smoking differs by sex.Large case control analyses have found higher risk for lung cancer development in women compared with men with similar cigarette pack-year exposure.Certain studies suggest that pathways involved in etiology of lung cancer may indeed differ between the sexes.SEER database from 1975 to 1999 confirmed that lung cancer patients with who are younger than 50 are more likely to be women and women are more likely to develop adenocarcinoma and SCLC.Genetic variation may account for differences in susceptibility, and hormonal and biologic factors may play a role in carcinogenesis.