text_1: Participants who quit smoking reduce lung cancer risk by approximately 50%.
text_2: DESIGN, SETTING, AND PARTICIPANTS Observational population-based cohort study with up to 31 years of follow-up from the Copenhagen Centre for Prospective Population Studies, which administrates data from 3 longitudinal studies conducted in Copenhagen and suburbs, the Copenhagen City Heart Study, the Copenhagen Male Study, and the Glostrup Population Studies, Denmark.