Colon neoplasia in patients with type 2 diabetes on metformin: A meta-analysis

Background A growing body of evidence has suggested that metformin potentially reduces the risk of cancer. Objective We performed a meta-analysis of available studies to better define the effect of metformin on colon neoplasia (cancer and polyps) in patients with type 2 diabetes. Methods Medical literature searches for human studies were performed through December 2015, using suitable keywords. Pooled estimates were obtained using fixed or random-effects models. Heterogeneity between studies was evaluated with the Cochran Q test whereas the likelihood of publication bias was assessed by constructing funnel plots. Their symmetry was estimated by the Begg and Mazumdar adjusted rank correlation test and by the Egger's regression test. In addition subgroup and sensitivity analyses were performed. Results A total number of 709,980 patients, with type 2 diabetes, were included in 17 studies eligible for meta-analysis [1 RCT and 16 observational studies (13 cohort and 3 case–controls)]. The risk of colon neoplasia was significantly lower among metformin users than controls (non-metformin users) [pooled RRs (95% CI) = 0.75 (0.65–0.87), test for overall effect Z = − 3.95, p < 0.001]. This observation applied separately for colon cancer [0.79 (0.69–0.91), Z = − 3.34, p < 0.001] and for colon polyps [0.58 (0.42–0.80), Z = − 3.30, p < 0.001]. Conclusion This meta-analysis shows that the use of metformin in patients with type 2 diabetes is associated with significantly lower risk of colon neoplasia.