Type 2 diabetes mellitus and risk of gallbladder cancer: a systematic review and meta-analysis of observational studies

AimsIncreasing evidence suggests that a history of type 2 diabetes mellitus (type 2 DM) may be involved in the development of various sites of cancer. However, the association with risk of gallbladder cancer remains unclear. MethodsWe identified studies by a literature search of MEDLINE and EMBASE through 31 August 2014 and by searching the reference lists of pertinent articles. All data were independently extracted by two investigators using a standardized data abstraction tool. Summary relative risks (SRRs) with 95% confidence intervals (CIs) were calculated with a random effects model. ResultsA total of 20 studies (eight case-control studies and 12 cohort studies) were included in this meta-analysis. Analysis of these 20 studies found that compared with non-diabetic individuals, diabetic individuals had an increased risk of gallbladder cancer (SRR=1.56, 95% CI: 1.36-1.79). There was evidence of moderate heterogeneity among these studies (p=0.010 and I-2=43.5%). This increased risk relationship is independent of smoking, body mass index and a history of gallstones. However, whether or not controlled for, alcohol use may be one of the potential confounders that significantly affect the association between type 2 DM and the risk of gallbladder cancer. Diabetic women and men had a similarly increased risk of gallbladder cancer associated with type 2 DM. ConclusionsThese findings of this systematic review indicate that compared with non-diabetic individuals, both men and women with type 2 DM had an increased risk of gallbladder cancer. Copyright (c) 2015 John Wiley & Sons, Ltd.