Decrease in risk of lung cancer death in males after smoking cessation by age at quitting: Findings from the JACC study

To evaluate the impact of smoking cessation in individuals and populations, we examined the decrease in risk of lung cancer death in male ex-smokers b y age at quitting in the Japan Collaborative Cohort Study for Evaluation of Cancer Risk Sponsored by Monbusho (JACC Study), which was initiated from 1 988 to 1990 in Japan. For simplicity, subjects were limited to male nonsmok ers, and former/current smokers who started smoking at ages 18-22, and 33 6 54 men aged 40-79 years were included. We modeled the mortality rates in no n-smokers and current smokers, and compared the rates in ex-smokers with th ose expected from the model if they had continued smoking. During the mean follow-up of 8.0 years, 341 men died from lung cancer. The mortality rate r atio for current smokers, compared to non-smokers, was 5.16, and those for ex-smokers who had quit smoking 0-4, 5-9, 10-14, 15-19 and greater than or equal to 20 years before were 4.84, 3.19, 2.03, 1.29 and 0.99, respectively . The functions of 3.20x10(-7)(age)(4.5) and 1.96x10(-5)x(age-29.6)(4.5) fi tted the observed mortality rates (per 100 000 person-years) in non-smokers and continuing smokers, respectively. A greater decrease in lung cancer mo rtality was estimated among those who quit smoking at younger ages. Stoppin g smoking earlier in life appears preferable to keep the individual risk lo w. The absolute rate, however, substantially decreased after smoking cessat ion even in those who quit at ages 60-69, reflecting the high mortality rat e among continuing smokers in the elderly.