Ever-smokers in Norway and lung cancer: median time from self-reported smoking debut to lung cancer diagnosis in 11 prospective population studies (CONOR).

Background: Tobacco smoking patterns and lung cancer incidence are closely related, but with years of lag. Most smokers start smoking as teenagers, and lung cancer is diagnosed at a median age of 70 years. However, the median lag time between smoking consumption and lung cancer incidence and smoking-related mortality is commonly reported to be up to 40 years. Here we investigate the median lag time from smoking debut to lung cancer diagnosis in Norway. Methods: We used the Cohort of Norway (CONOR), consisting of linked data from 11 Norwegian prospective population-based cohorts (n=180 534). The study included 80 761 ever-smokers, where 1336 developed lung cancer. Median follow-up time from inclusion in the CONOR study was 11.9 years (0.0-20.8 years) and follow-up from self-reported smoking debut was 44.2 years (2.7-85.4 years). The time from smoking initiation to lung cancer diagnosis was calculated for all cases. Results: The median age of lung cancer diagnosis is 72.5 years. The mean and median time from smoking debut to lung cancer diagnosis are 51.9 (30.2-69.1) and 53.3 years, respectively. The median time from smoking debut until lung cancer diagnosis is >40 years (p<0.001). There is a shorter median lag time in women compared to men and in current smokers compared to former smokers, 48.6 Conclusion: The latency between smoking debut and lung cancer diagnosis in Norwegian ever-smokers is much longer than what has previously been reported. Women and current smokers have a shorter time to diagnosis than men and former smokers, respectively. This is important knowledge in the planning of future healthcare, lung cancer screening, and prevention measures.