Longitudinal Changes in Smoking Behaviors and Cancer-Related Mortality Risk in Middle-Aged Korean Women

Purpose This study investigated association between smoking habit change and cancer-related mortality risk in Korean women. Materials and Methods Study population were women aged >= 40 years who underwent two biennial cancer screenings during 2009-2012 and were followed up until 2020. Participants were grouped into sustained nonsmokers, sustained quitters, new quitters, relapsers/smoking initiators, and sustained smokers. Outcomes included all-cause and cancer-related deaths. Cox regression and competing risk analysis was used to assess association between smoking habit change and mortality risk. Results Of 2,892,590 women, 54,443 death cases were recorded (median follow-up of 9.0 years). Compared with sustained nonsmokers, mortality risk from all causes and cancer-related causes increased in all other smoking groups. Cancer-related risk increased 1.22-fold among sustained quitters (95% confidence interval [CI], 1.10 to 1.36), 1.56-fold (95% CI, 1.40 to 1.75) in new quitters, 1.40-fold (95% CI, 1.21 to 1.62) in relapsers/smoking initiators, and 1.61-fold (95% CI, 1.46 to 1.78) in sustained smokers compared with sustained nonsmokers. Women who were sustained smokers with higher smoking intensity had a higher mortality risk in terms of hazard ratios compared to nonsmokers (< 5 pack-years 2.12-fold, 5-10 pack-years 2.15-fold, and > 10 pack-years 2.27-fold). Conclusion Quitting smoking earlier is critical for preventing death from all causes and cancer among female smokers.