Evaluation based on systematic review of epidemiological evidence among Japanese populations: Tobacco smoking and total cancer risk

Background: We evaluated the association between tobacco smoking and total cancer risk among Japanese populations based on a systematic review of epidemiological evidence. Methods: Original data were obtained from searches of MEDLINE using PubMed, complemented with manual searches. Evaluation of associations was based on the strength of evidence and the magnitude of association, together with biological plausibility as previously evaluated by the International Agency for Research on Cancer. Meta-analysis of associations was also conducted to obtain summary estimates of association. Results: A total of eight cohort studies were identified. In men, all studies consistently showed a moderately increased risk of total cancer in current smokers compared with never-smokers. In women, an increase in risk was seen but was weaker than in men. The summary relative risk was estimated as 1.53 (95% confidence interval 1.41-1.65). Conclusion: We conclude that there is convincing evidence that current tobacco smoking moderately increases the risk (, approximate to 1.5 times) of total cancer in the Japanese population compared with never-smoking Japanese.