Changes in smoking use and subsequent lung cancer risk in the ATBC study

Background Reducing cigarettes/day may lower the risk of lung cancer compared with continuing to smoke at the same intensity. Other changes in smoking behaviors, such as increasing cigarette consumption or quitting for a period and relapsing, may also affect lung cancer risk. Methods We examined changes in smoking status and cigarettes/day among 24,613 Finnish male smokers aged 50-69 years who participated in the Alpha-Tocopherol, Beta-Carotene Cancer Prevention (ATBC) Study. Longitudinal data on smoking were collected during study follow-up visits three times a year (approximately every 4 months) between 1985 and 1993. Incident lung cancer cases through 2012 were identified by the Finnish Cancer Registry. Risk ratios (RRs) and 95% confidence intervals (95%CI) were estimated using Cox proportional hazards regression. Results Compared with smoking 20 cigarettes/day continuously across the intervention period, reducing an average of 5 cigarettes/day per year while smoking was associated with a 20% lower risk of lung cancer (95%CI : 0.71 to 0.90). A substantially lower risk of lung cancer was also observed when participants smoked at 50% (RR = 0.72; 95%CI : 0.57-0.90) and 10% (RR = 0.55; 95%CI : 0.36-0.83) of study visits, relative to smoked at 100% of study visits. Conclusions Smokers may lower their risk of lung cancer by reducing smoking intensity (cigarettes per day while smoking) and the time they smoke. However, quitting smoking completely is the most effective way for smokers to reduce their risk of lung cancer.