Association of gallstone disease with risk of colorectal cancer: a systematic review and meta-analysis of observational studies

Numerous studies have assessed the association of gallstones or cholecystectomy (CE) with risk of colorectal cancer (CRC). However, the findings are mixed.To systematically review and meta-analyse the association between the presence of gallstone disease (GD), or CE and the incidence of CRC. Secondary endpoints were the risk based on type of exposure, study design, tumour subsites and sex.PubMed and EMBASE were searched from September 2020 to May 2021. The protocol was registered on the Open Science Foundation Platform. We identified and classified studies according to their design into prospective cohort, population-based case-control, hospital-based case-control and necropsy studies reporting CRC incidence among individuals with diagnosed GD or after CE (or both). Among 2157 retrieved studies, 65 (3%) met the inclusion criteria. We followed the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) reporting guidelines. Data were extracted by two independent reviewers. We evaluated the quality of the study according to the Newcastle-Ottawa Scale and only studies with a score of 6 and above were included in the final analyses. We pooled log-transformed odds ratios/risk ratios from the available adjusted models to estimate a summary relative risk (RR) and 95% confidence interval (CI) in a random-effects model. The primary outcome was overall CRC incidence. We also conducted secondary analyses according to sex and CRC subsites (proximal colon, distal colon and rectum). The outcome was measured by RRs with 95% CIs.The overall association of GD and/or CE with CRC was RR = 1.15 (1.08; 1.24), primarily driven by hospital-based case-control studies [RR = 1.61 (1.29; 2.01)], whereas a more modest association was found in population-based case-control and cohort studies [RR = 1.10 (1.02; 1.19)]. Most hospital-based case-control and necropsy studies reported estimates that were adjusted for age and sex only, leaving room for residual confounding; therefore we restricted to population-based case-control and cohort studies for our subsequent analyses. Similar associations were found for women [RR = 1.21 (1.05; 1.4) and men (RR = 1.24 (1.06; 1.44)]. When assessed by CRC subsites, GD and CE were primarily associated with higher risk of proximal colon cancer [RR = 1.16 (1.07; 1.26)] but not distal colon cancer [RR = 0.99 (0.96; 1.03)] or rectal cancer [RR = 0.94 (0.89; 1.00)].Gallstones are associated with a modestly increased risk of colon cancer, primarily in the proximal colon.