Relation between diabetes, metformin treatment and the occurrence of malignancies in a Belgian primary care setting.

BACKGROUND: Associations between type 2 diabetic patients and a higher risk of developing cancer have been reported worldwide. Recently, a protective effect of metformin has been described.

AIM: To examine in the Belgian primary care population the relation between presence of type 2 diabetes with and without metformin treatment and the occurrence of malignancies.

DESIGN OF STUDY: Retrospective cohort study, based on the Intego database, an ongoing Belgian general practice-based morbidity registry, covering 90 general practitioners and including about 1.5 million patient-years between 1994 and 2008.

METHOD: Cox proportional hazard analysis comparing emergence of malignancy in patients with and without type 2 diabetes, and among patients with diabetes comparing emergence of malignancy in those treated with various antidiabetic drugs.

RESULTS: Malignancies occurred more in type 2 diabetic patients compared to non-diabetic controls (HR=1.84; 95% CI=1.51-2.24), adjusted for age, gender and weight. Treatment with both metformin and 'other' antidiabetic agents was related to decreased cancer risk (HR=0.24 and 0.22) compared to diet only in men but not in women.

CONCLUSION: In this Belgian primary care setting, diabetic patients have higher cancer prevalences than non-diabetic patients. Moreover, in diabetic men, not only metformin but also other antidiabetic agents were associated with lower cancer risks.