Sex differences in risk of smoking-related 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 risk of lung cancer associated with smoking by sex. Altogether 585,583 participants from three Norwegian cohorts (Norwegian Counties Study, 40 Years Study and CONOR) were followed until December 31, 2013 through linkage of data to national registries. We used Cox proportional hazards models and 95% confidence intervals (CIs). 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 men and women current smokers who smoked ≥16 pack-years had a hazard ratio for lung cancer of 27.24 (95% CI: 22.42, 33.09) and 23.90 (95% CI: 20.57, 27.76) respectively, (Pheterogeneity = 0.30). In contrast, for current smokers, in the model of 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-years increment, (Pheterogeneity < 0.01). Our results suggest that women have an increased susceptibility to lung cancer compared to men, given the same lifetime smoking exposure