The fraction of lung cancer attributable to smoking in the Norwegian Women and Cancer (NOWAC) Study.

BACKGROUND: We examined the association between active and passive smoking and lung cancer risk and the population attributable fraction (PAF) of lung cancer due to active smoking, in the Norwegian Women and Cancer Study, a nationally representative prospective cohort study. METHODS: We followed 142,508 women, aged 31-70 years, who completed a baseline questionnaire between 1991 and 2007, through linkages to national registries through December 2015. We used Cox proportional hazards models, to estimate hazard ratios (HRs) with 95% confidence intervals (CIs). We calculated PAF to indicate what proportion of lung cancer cases could have been prevented in the absence of smoking. RESULTS: During the more than 2.3 million person-years of observation, we ascertained 1507 lung cancer cases. Compared with never smokers, current (HR 13.88, 95% CI 10.18-18.91) smokers had significantly increased risk of lung cancer. Female never smokers exposed to passive smoking had a 1.3-fold (HR 1.34, 95% CI 0.89-2.01) non- significantly increased risk of lung cancer, compared with never smokers. The PAF of lung cancer was 85.3% (95% CI 80.0-89.2). CONCLUSION: More than 8 in 10 lung cancer cases could have been avoided in Norway, if the women did not smoke.

Sex Differences in Risk of Smoking-Associated Lung Cancer: Results From a Cohort of 600,000 Norwegians.

Whether women are more susceptible than men to smoking-related lung cancer has been a topic of controversy. To address this question, we compared risks of lung cancer associated with smoking by sex. Altogether, 585,583 participants from 3 Norwegian cohorts (Norwegian Counties Study, 40 Years Study, and Cohort of Norway (CONOR) Study) were followed until December 31, 2013, through linkage of data to national registries. We used Cox proportional hazards models and 95% confidence intervals to estimate risks. During nearly 12 million person-years of follow-up, 6,534 participants (43% women) were diagnosed with lung cancer. More men than women were heavier smokers. Compared with never smokers, male and female current smokers with ≥16 pack-years of smoking had hazard ratios for lung cancer of 27.24 (95% confidence interval (CI): 22.42, 33.09) and 23.90 (95% CI: 20.57, 27.76), respectively (P for heterogeneity = 0.30). In contrast, for current smokers, in a model with pack-years measured continuously, men had a hazard ratio of 1.43 (95% CI: 1.39, 1.48) and women a hazard ratio of 1.64 (95% CI: 1.57, 1.71) for each 10-pack-year increment of smoking (P for heterogeneity < 0.01). Our results suggest that women have an increased susceptibility to lung cancer compared with men, given the same lifetime smoking exposure.