Impact of tobacco smoking on subsequent cancer risk among middle-aged Japanese men and women: data from a large-scale population-based cohort study in Japan--the JPHC study.

Background: The present study aimed to obtain a relevant epidemiological index of the impact of tobacco smoking on the subsequent risk of cancer in Japan.
Methods: We conducted a cohort analysis on the possible association between tobacco smoking habits and total cancer risk among a middle-aged Japanese population, using a large-scale population-based cohort of 92,792 subjects (44,521 men and 48,271 women) with 10-year follow-up.
Results: During 1990-2001, 4,922 cases of cancer (2,969 men and 1,953 women) were newly diagnosed. From the baseline questionnaire, 52.2% of men were current smokers and they presented a significantly increased hazard ratio (HR) of subsequent cancer occurrence compared with never-smokers [HR 1.64, 95% confidence interval (95% CI) 1.48-1.82]. Only 5.6% of women were current smokers and their HR also represented a significant increase (HR 1.46, 95% CI 1.21-1.75). The corresponding population attributable fraction (PAF) (%) of total cancer incidence in men was 22.4% (95% CI 15.7%-28.5%) and 7.0% (95% CI 3.7%-10.3%) in relation to current and past exposures to tobacco smoke. In women, the PAF was only 2.2% and 0.6% due to the low prevalence of current and former smokers.
Conclusions: Our results suggest that 29% of male cancer and 3% of female cancer would be preventable in Japanese middle-aged population by avoidance of tobacco smoking.