Use of metformin is associated with lower incidence of cancer in patients with type 2 diabetes

Introduction: The objective of the study was to assess the influence of metformin on the prevalence of cancer and risk factors for the development of cancer, in patients with type 2 diabetes. Materials and methods: A total of 1063 patients, treated between October 2012 and March 2013 in the Diabetes and Endocrinology Centre in Bydgoszcz, were enrolled in the study. Only patients who were first diagnosed with diabetes and consecutively with cancer were included in the analysis. The final dataset compromised data from 1028 patients with type 2 diabetes, in whom retrospective analysis of the association between the occurrence of cancer and treatment with or without metformin was performed. Demographic data, medical history, physical assessment, diabetes history, diabetes complications, concomitant medication, and additional examination results were compared between two groups: those with cancer and those without cancer. Data were analysed using Student’s t-test, Chi-square test with Yates' continuity correction, and multiple logistic regression. Results: The most commonly observed cancer was breast cancer (24 patients; 22.5%), followed by uterine cancer (15 patients; 13.6%). Of the 75 diabetic patients with a cancer diagnosis, 18.7% were treated with metformin; of the 953 patients without cancer, 38% received metformin. Analysis of probability of cancer occurrence using Kaplan-Meier curves showed that the probability of cancer development was higher in groups of patients who were not treated with metformin (p = 0.006). Conclusions: Metformin treatment reduces the risk of cancer in type 2 diabetes patients.