Overweight, obesity and the risk of gallbladder and extrahepatic bile duct cancers: A meta-analysis of observational studies.

Epidemiological studies have repeatedly investigated the association between excess body weight and the risk of biliary tract cancer with inconsistent results. The objective of this study was to quantitatively assess the associations between overweight and obesity and the risk of biliary tract cancer.

A comprehensive search of PubMed, Embase, Web of Science, and China National Knowledge Infrastructure databases up to August 2015 was conducted, and the reference lists of retrieved articles for additional relevant studies were manually searched.

Fourteen prospective cohort studies and 15 case-control studies were included in this meta-analysis. These studies included 11,448,397 participants (6,733 patients with gallbladder cancer [GBC] and 5,798 patients with extrahepatic bile duct cancer [EBDC]) with follow-up durations ranging from 5 to 23 years. Among overweight adults, the pooled RR was 1.17 (95% CI, 1.07-1.28) for GBC and 1.26 (95% CI, 1.14-1.39) for EBDC, and among people with obesity, the pooled RR was 1.62 (95% CI, 1.49-1.75) for GBC and 1.48 (95% CI, 1.21-1.81) for EBDC. Visual inspection of the funnel plots and the Begg's and the Egger's tests did not show enough evidence of publication bias.

Integrated evidence from this meta-analysis suggests that excess body weight is associated with a significantly increased risk of GBC and EBDC.