Diabetes mellitus and increased risk of biliary tract cancer: systematic review and meta-analysis

Epidemiological evidences indicate that diabetic individuals may have an increased risk of several cancers; however, the relationships between diabetes and risk of cancers of biliary tract or its subsites remain unclear. To provide a quantitative assessment of this relationship, we identified studies by a literature search of Medline (from 1 January 1966) and EMBASE (from 1 January 1974), through 31 July 2010, and by searching the reference lists of pertinent articles. Summary relative risks with corresponding 95% confidence intervals were calculated with a random-effect model. Analysis of 21 studies (8 case-control and 13 cohort studies) found that diabetes was associated with an increased risk of biliary tract cancer, compared with no diabetes (summary RRs = 1.43, 95% CI = 1.18-1.72), with significant heterogeneity among studies (p = 0.001). The positive association was also found between diabetes and risk of gallbladder cancer or extrahepatic cholangiocarcinoma, but not cancer of ampulla of Vater. No significant publication bias was found. These findings strongly support the link between diabetes and increased risk of cancer of biliary tract and its subsites: gallbladder cancer or extrahepatic cholangiocarcinoma, but not cancer of ampulla of Vater.