Effect of Smoking Cessation Duration on Lung Cancer Incidence: A Nationwide Retrospective Cohort Study in Korea

While smoking cessation is known to reduce lung cancer risk, the extent to which smoking cessation duration mitigates lung cancer risk remains unclear. This study aimed to analyze the association between smoking cessation duration and the reduction in lung cancer incidence using large-scale health insurance data from Korea.

In this retrospective cohort study, we utilized the cohort from the Korea National Health Insurance Corporation. Approximately 50% of the adults aged ≥50 years who underwent health examinations in 2009-2013 were randomly sampled and followed using medical and health examination records. The participants were classified into three groups: never-smokers, former smokers, and current smokers, and the incidence rates of lung cancer were compared among these groups.

We analyzed 165,512 individuals selected through propensity score matching (82,756 never-smokers, 41,378 former smokers, and 41,378 current smokers). Lung cancer risk significantly decreased after two years of smoking cessation (2-3 years after cessation: hazard ratio 0.760, p<0.001) but remained higher than that of never-smokers for up to 10 years. Subgroup analyses revealed similar tendencies among males, whereas no consistent patterns were observed among females. Moreover, a longer duration of smoking cessation was generally required for heavy smokers (≥20 pack-years) than for light smokers (<20 pack-years).

This nationwide cohort study highlights the significant impact of smoking cessation duration on lung cancer risk, emphasizing the substantial benefits of even short-term cessation regardless of prior smoking history.