Systematic review of the relation between smokeless tobacco and cancer of the pancreas in Europe and North America

The present work reviews the available epidemiological data on the relationship of pancreatic cancer and smokeless tobacco used in North America and Europe. Meta-analytic methods were used to estimate the overall relative risk. Four cohort and seven case-control studies were identified. Two sets of estimates were selected for meta-analysis. The first meta-analysis was based on study-specific estimates for the overall population of smokers and nonsmokers combined, where they were available, otherwise on estimates for never smokers. The overall random-effects risk estimate was found to be 1.10 (95% confidence interval 0.73-1.65). Sub-group analyses by continent, study type, or type of smokeless tobacco also showed no increased risk. The second meta-analysis was based on study-specific estimates for never smokers, where they were available, otherwise on combined smokers/nonsmokers estimates. The overall random-effects risk estimate was found to be 1.15 (95% confidence interval 0.67-1.98). There were, however, some indications of increased risk in cohort studies, in studies conducted in Sweden or Norway, and in studies of snuff. As there are a number of weaknesses in the currently available studies, no definite conclusion can be drawn. Our results are less indicative of a causal relationship than other reviewers have suggested; additional studies will have to be conducted to clarify the situation.