Background: It is well known that the relative risk (RR) of lung cancer mortality decreases following smoking cessation compared with the risk in persons who continue to smoke. However, changes in the absolute risk of lung cancer death following smoking cessation are not well documented. Further, few studies have examined the effect of age at smoking cessation on subsequent lung cancer death risk.
Purpose: The purpose of this study was to examine and compare absolute and relative lung cancer death risks in former smokers as a function of age at cessation.
Methods: Using the American Cancer Society's Cancer Prevention Study II, a prospective cohort study with 6 years of follow-up, we modeled absolute risk of lung cancer mortality in individuals who had never smoked and in current and former smokers. The model was fit with the use of person-years logistic regression analysis.
Results: Similar patterns of absolute risk of lung cancer death by age were found for all ages of smoking cessation up to the mid-60s. Lower lung cancer death risk was observed for those quitting earlier in life, and the risk for all former smokers was significantly lower than that for current smokers. For those quitting between ages 30 and 49, lung cancer death risk rose gradually with age at a rate slightly greater than that for those who had never smoked. Lung cancer death risk for former smokers quitting between ages 50 and 64 leveled off near the risk attained at the time of quitting until around age 75, when it rose sharply. At age 75, the RR for former smokers compared with current smokers was approximately 45% for those quitting in their early 60s, approximately 20% for those quitting in their early 50s, and less than 10% for those quitting in their 30s. For those who had never smoked, the RR at age 75 is less than 5%.
Conclusions: In terms of reduced risk of lung cancer mortality, smoking cessation is beneficial at any age, with much greater benefits accruing to those quitting at younger ages. Unlike previous research, which has primarily examined the effects of cessation as a function of years since quitting, our results demonstrate that age at cessation has a major impact on subsequent lung cancer risks.
Implications: Smokers of all ages should be encouraged to quit because cessation at any age decreases lung cancer risk relative to that of current smokers.