The Impact of Cigarette Smoking on the Incidence of Lung and Laryngeal Cancer

Background: Smoking has been identified as the most substantial risk factor for lung and laryngeal cancer; however, research on their histological classification remains scarce.Therefore, our research team conducted a prospective cohort analysis to investigate the relationship between smoking and incidence of small cell lung carcinoma, lung squamous cell carcinoma, lung adenocarcinoma, and laryngeal squamous cell carcinoma.Methods: This study investigated a prospective cohort of 159,844 participants included in The Korean Cancer Prevention Study-II who visited 18 nationwide health examination centers for screening purposes from 2004 to 2013.Incidence of cancer and chronic diseases among the study participants was confirmed by linking their data with those published in the National Cancer Center registry and National Health Insurance Service.After excluding cases with missing smoking duration and pack-years, the final cohort comprised 141,679 individuals.Using Cox proportional hazards models adjusting for sex, age, and alcohol consumption, relative risks for lung and laryngeal cancer according to histological subtype were calculated based on smoking duration and pack-years, along with attributable risks.Results: Mean follow-up period for the 141,679 participants was 12.9 years (standard deviation 1.6), accumulating a total of 1,827,451 person-years.Among current smokers, 19.7% had smoked for less than 30 years with at least 20 pack-years, whereas 9.4% had smoked for 30 years or more with at least 20 pack-years.Among all the participants, 741 developed lung cancer, with an incidence rate of 42.8 per 100,000 person-years.Histological subtypes included small cell lung carcinoma (43 cases), pulmonary squamous cell carcinoma (133 cases), pulmonary adenocarcinoma (489 cases), and laryngeal squamous cell carcinoma (45 cases).The relative risk of incident cancer among current smokers who had smoked for over 30 years with more than 20 pack-years was 41.2 (95% CI, 5.5-310), 28.4 (95% CI, 11.4-70.9),4.4 (95% CI, 2.9-6.8), and 6.8 (95% CI, 2.2-21.2) times greater among those with small cell lung cancer, pulmonary squamous cell carcinoma, pulmonary adenocarcinoma, and laryngeal squamous cell carcinoma, respectively, than among never smokers.Their attributable risks for cancer incidence were 97.5%, 96.4%, 77.2%, and 85.3%, respectively. Conclusion:This study provides evidence that smoking is a potent risk factor for lung cancer incidence, specifically for small cell lung cancer and pulmonary squamous cell carcinoma, wherein smoking contributes to over 96% of the risk.