Cigarette smoking and pancreas cancer risk: an evaluation based on a systematic review of epidemiologic evidence in the Japanese population.

OBJECTIVE Cigarette smoking has been recognized as an important risk factor for pancreas cancer, but the magnitude of the association may vary among geographical areas. Therefore, we reviewed epidemiologic studies on the association between cigarette smoking and pancreas cancer in the Japanese population. METHODS Original data were obtained from MEDLINE searched using PubMed or from searches of the Ichushi database, complemented with manual searches. Evaluation of associations was based on the strength of evidence ('convincing', 'probable', 'possible' or 'insufficient') and the magnitude of association ('strong', 'moderate', 'weak' or 'no association'), together with biological plausibility as previously evaluated by the International Agency of Research on Cancer. RESULTS We identified four cohort studies and three case-control studies. All cohort studies consistently showed positive associations between pancreas cancer and cigarette smoking, although statistical significance in each study is variable. Most of the cohort studies consistently showed that cigarette smoking had a dose-response relationship with pancreas cancer. One case-control study showed a strong positive association, but the rest did not show any association. Meta-analysis of seven studies indicated that a summary estimate for ever smoking relative to never smoking was 1.68 (95% confidence interval: 1.38-2.05). CONCLUSIONS We conclude that there is convincing evidence that cigarette smoking moderately increases the risk of pancreas cancer in the Japanese population.