The effect of metformin use on gastric cancer in patients with type 2 diabetes: A systematic review and meta-analysis of cohort studies

Introduction: Gastric cancer is one of the main causes of cancer-related deaths in the world. Various studies have so far been conducted to determine the risk of gastric cancer in relation to taking metformin. Therefore, this systematic review and meta-analysis study aims to evaluate the relationship between the administration of metformin in type II diabetes patients and their risk of developing gastric cancer. Materials and Methods: All studies were cohorts. A comprehensive literature searches of the databases, including Cochrane, Web of Science, PubMed, Scopus, and Google Scholar web browser was conducted using standard keywords. Data analysis of this meta-analysis was conducted using STATA 14 software and P<0.05 was considered as a significant level for tests. Results: In a set of 17 cohort studies, including an overall number of 1383404 patients, it was concluded that metformin consumption had reduced the risk of gastric cancer in type II diabetes patients [OR: 0.80 (95% CI: 0.71-0.91)]. In these patients, the impact of metformin on overall survival rates was not statistically significant [OR: 0.71 (95% CI: 0.42-1.18)]. Data analysis revealed the effects of metformin on the risk of gastric cancer development, which involved a reduction [OR: 0.69 (95% CI: 0.44-1.07)] for those who had been taking metformin for less than five years, [OR: 1.04 (95% CI: 0.83-1.30)] for those who had been taking metformin for 5-10 years, and [OR: 0.71 (95% CI: 0.59-0.84)] for the patients who had a history of taking metformin for over 10 years. Conclusion: Metformin administration in type II diabetes patients resulted in the reduction of the risk of gastric cancer, but did not affect the overall survival rates. Furthermore, it was observed that type II diabetes patients, who had been treated by metformin for more than 10 years, had a 29% lower risk for gastric cancer.