Active and passive smoking in relation to lung cancer incidence in the Women's Health Initiative prospective cohort study.

Abstract

1504 Background: The relationship between both active and passive smoking and lung cancer incidence in post-menopausal women was examined in theWomen’s Health Initiative Observational Study (WHI-OS). Methods: The WHI-OS, a prospective cohort study conducted at 40 U.S. centers, enrolled women ages 50-79 from 1993-1998.Among 93,676 participants, 76,304 women with complete smoking and covariate data comprised the analytic cohort, in which the association of lung cancer incidence with active and passive (childhood, adult home, and work) smoking exposure was studied. Results: Over 10.5 meanyears of follow-up with 901 lung cancer cases, lung cancer incidence was higher in current smokers (HR 13.44, 95% CI 10.80-16.75) and former smokers (HR 4.20, 95% CI 3.48-5.08), compared to never smokers. This relationship was dose-dependent for both current and former smokers. Risk of all lung cancer subtypes, particularly small cell lung cancer (SCLC) and squamous cell carcinoma (SqCC), was higher in smokers. Among never smokers, any passive smoking exposure (HR 0.88, 95% CI 0.52-1.49) and most passive smoking categories did not significantly increase lung cancer risk, compared to no passive exposure; however, passive exposure as an adult at home for >=30 years was associated with increased risk, of borderline significance (HR 1.61, 95% CI 1.00-2.58). Current smokers had an annualized lung cancer incidence rate of 472.9 cases/100,000 person-years, compared to 158.1 for former smokers and 36.2 for never smokers (112.3 overall). Conclusions: To our knowledge, this is the first study to examine both active and passive smoking in relation to lung cancer incidence in a complete prospective cohort of U.S. women. Active smoking is associated with significant increases in incidence of all lung cancer subtypes in post-menopausal women, particularly SCLC and SqCC. Smoking cessation decreases lung cancer risk. Prolonged exposure as an adult at home may be the strongest passive smoking contributor to lung cancer risk in this cohort. The findings support continued need for investment in smoking prevention and cessation, research on passive smoking, and understanding of lung cancer risk factors other than smoking.