Cigarette Smoking and Esophageal Cancer Risk: An Evaluation Based on a Systematic Review of Epidemiologic Evidence Among the Japanese Population

Abstract

Although cigarette smoking is considered as an important risk factor for esophageal cancer, the magnitude of the association might be varied among geographic areas. Therefore, we reviewed epidemiologic studies on the association between cigarette smoking and esophageal cancer among the Japanese population. Original articles were obtained from MEDLINE searched using PubMed or from searches of the Ichushi database, complemented by 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 for Research on Cancer. We identified four cohort studies and 11 case-control studies. All cohort studies and eight case-control studies showed strong positive associations between esophageal cancer and cigarette smoking. All cohort studies and five case-control studies showed that cigarette smoking had dose-response relationships with esophageal cancer. Meta-analysis of 12 studies indicated that the summary estimate for ever smokers relative to never smokers was 3.01 (95% confidence interval: 2.30-3.94). Summary relative risk for current and former smokers relative to never smokers was 3.73 (2.16-6.43) and 2.21 (1.60-3.06), respectively. We conclude that there is convincing evidence that cigarette smoking strongly increases the risk of esophageal cancer in the Japanese population.