The role of gallstones in gallbladder cancer in India: a Mendelian randomization study


Background:Past history of gallstones is associated with increased risk of gallbladder cancer (GBC) in observational studies. We conducted complementary observational and Mendelian Randomization (MR) analyses to determine whether history of gallstones is causally related to development of GBC in an Indian population. Methods: To investigate associations between history of gallstones and GBC, we used questionnaire and imaging data from a GBC case-control study conducted at Tata Memorial Hospital, Mumbai (cases=1170; controls=2525). We then used 26 genetic variants identified in a genome-wide association study of 27,174 gallstones cases and 736,838 controls of European ancestry in a Mendelian randomization approach to assess causality. The association of these genetic variants with both gallstones and GBC was examined in the GBC case-control study. Various complementary MR approaches were used to evaluate the robustness of our results in the presence of pleiotropy and heterogeneity, and to consider the suitability of the selected SNPs as genetic instruments for gallstones in an Indian population. Results: We found a strong observational association between gallstones and GBC using self-reported history of gallstones (OR=4.5, 95%CI=3.5-5.8) and with objective measures of gallstone presence using imaging techniques (OR=2.0, 95%CI=1.5-2.7). We found consistent causal estimates across all MR techniques, with odds ratios for GBC in the range of 1.3-1.6. Conclusions: Our findings indicate a causal relationship between history of gallstones and increased risk of GBC, albeit of a smaller magnitude to those found in observational analysis. Impact: Our findings emphasise the importance of gallstone treatment for preventing GBC in high risk individuals.

Cancer Epidemiology and Prevention Biomarkers