Metformin Associated With Lower Cancer Risk

Allan S. Brett, MD

Journal Watch 

Abstract and Introduction

Abstract

Compared with sulfonylurea users, metformin users had a 10% lower incidence of cancer.

Introduction

During the past decade, observational studies have suggested associations between cancer and type 2 diabetes (or insulin therapy). Although several plausible mechanisms exist (e.g., cancer cells express insulin receptors that when activated could promote cell proliferation in type 2 diabetic patients with hyperinsulinemia), the association remains controversial (CA Cancer J Clin 2010; 60:207). In some studies, metformin has been associated with decreased cancer risk.

In a population-based retrospective study, Dutch researchers recorded the incidence of cancer in 85,000 type 2 diabetic patients who initiated metformin or sulfonylurea monotherapy. During up to 10 years of follow-up, metformin users were less likely to receive cancer diagnoses than sulfonylurea users (hazard ratio, 0.9; 95% confidence interval, 0.88–0.91) after adjustment for age, sex, and several other variables. This 10% reduction was modest in relative terms but highly statistically significant. Metformin-associated lower risks were noted for cancers of the esophagus, stomach, colon, liver, pancreas, lung, breast, and prostate.

Comment

If hyperinsulinemia really does promote cancer, metformin theoretically could lower cancer risk in type 2 diabetic patients because it lowers circulating glucose and insulin levels in patients with insulin resistance and hyperinsulinemia. Unrecognized confounders could have affected the results of this study, but its intriguing results reinforce metformin as first-line therapy for type 2 diabetes.

References

  • Ruiter R et al. Lower risk of cancer in patients on metformin in comparison with those on sulfonylurea derivatives: Results from a large population-based follow-up study. Diabetes Care 2012 Jan; 35:119.