Metformin and Cancer Occurrence in Insulin-Treated Type 2 Diabetic Patients

OBJECTIVE: Metformin is associated with reduced cancer-related morbidity and mortality. The aim of this study was to assess the effect of metformin on cancer incidence in a consecutive series of insulin-treated patients. RESEARCH DESIGN AND METHODS: A nested case-control study was performed in a cohort of 1,340 patients by sampling, for each case subject, age-, sex-, and BMI-matched control subjects from the same cohort. RESULTS: During a median follow-up of 75.9 months, 112 case patients who developed incident cancer and were compared with 370 control subjects. A significantly lower proportion of case subjects were exposed to metformin and sulfonylureas. After adjustment for comorbidity, glargine, and total insulin doses, exposure to metformin, but not to sulfonylureas, was associated with reduced incidence of cancer (odds ratio 0.46 [95% CI 0.25–0.85], P = 0.014 and 0.75 [0.39–1.45], P = 0.40, respectively). CONCLUSIONS: The reduction of cancer risk could be a further relevant reason for maintaining use of metformin in insulin-treated patients.