Metformin and risk of cancer among patients with type 2 diabetes mellitus: A systematic review and meta-analysis

Aim: We carried out this meta-analysis on all published studies to estimate the overall cancer risk of the use of metformin in T2DM patients. Methods: We searched the PubMed, Embase and CNKI databases for all articles within a range of published years from 2007 to 2019 on the association between the use of metformin and cancer risk in T2DM patients. The odds ratio (OR) corresponding to the 95% confidence interval (95% CI) was used to assess the association using a random-effect meta-analysis. Results: Finally, 67 studies met the inclusion criteria for this study, with 10,695,875 T2DM patients and 145,108 cancer cases. Overall, For T2DM patients of ever vs. never metformin users, there was statistical evidence of significantly decreased cancer risk was found to be associated with ever metformin users (OR= 0.70, 95% CI = 0.65-0.76). Considering T2DM may be a specific and independent risk factor for various forms of cancer, due to its particular metabolic characteristics of glucose intolerance and hyperinsulinemia, we performed a comparison to estimate the effects of metformin on cancer risk with other anti-diabetes medications (ADMs), our results found significantly decreased cancer risk to be associated with the use of metformin (OR = 0.80, 95% CI = 0.73-0.87). Conclusion: Our meta-analysis indicated that metformin may be a independent protective factor for cancer risk in T2DM patients. (C) 2020 Primary Care Diabetes Europe. Published by Elsevier Ltd. All rights reserved.