Diabetes mellitus and increased risk of cholangiocarcinoma: a meta-analysis.

Diabetes mellitus (DM) has been reported to be associated with an increased risk of several types of cancers. However, its relationship with cholangiocarcinoma (CC), which includes intrahepatic cholangiocarcinoma (ICC) and extrahepatic cholangiocarcinoma (ECC), remains unclear. We conducted a meta-analysis to assess the association between diabetes and the risk of CC (including ICC and ECC). We identified studies by a literature search of Medline (from 1 January 1966) and Embase (from 1 January 1974), through 30 November 2010, and by searching the reference lists of pertinent articles. Summary relative risks (RRs) with corresponding 95% confidence intervals (CIs) were calculated with a random-effects model. A total of 15 articles (10 case-control and five cohort studies) were included in this study. The number of reports on DM and risk of specific cancer were as follows: CC (n=5), ECC (n=9), and ICC (n=9). Compared with those without diabetes, individuals with diabetes had an increased risk of CC (summary RRs, 1.60; 95% CI, 1.38-1.87; P=0.992 for heterogeneity), ECC (summary RRs, 1.63; 95% CIs, 1.29-2.05; P=0.005 for heterogeneity), and ICC (summary RRs, 1.97; 95% CIs, 1.57-2.46; P=0.025 for heterogeneity). The funnel plot revealed no evidence for publication bias concerning diabetes and the risk of CC (including ICC and ECC). These findings strongly support the positive link between DM and the increased risk of CC (including ICC and ECC).