Lower Risk of Cancer in Patients on Metformin in ComparisonWith Those on Sulfonylurea Derivatives Results From a Large Population-based Follow-up Study

OBJECTIVEdNumerous studies have suggested a decreased risk of cancer in patients with diabetes on metformin. Because different comparison groups were used, the effect magnitude is difficult to estimate. Therefore, the objective of this study was to further analyze whether, and to what extent, use of metformin is associated with a decreased risk of cancer in a cohort of incident users of metformin compared with users of sulfonylurea derivatives. RESEARCH DESIGN AND METHODSdData for this study were obtained from dis-pensing records from community pharmacies individually linked to hospital discharge records from2.5million individuals in theNetherlands. The association between the risk of cancer in those using metformin compared with those using sulfonylurea derivatives was analyzed using Cox proportional hazard models with cumulative duration of drug use as a time-varying determinant. RESULTSdUse of metformin was associated with a lower risk of cancer in general (hazard ratio 0.90 [95 % CI 0.88–0.91]) compared with use of sulfonylurea derivatives. When specific cancers were used as end points, similar estimates were found. Dosage-response relations were identified for users of metformin but not for users of sulfonylurea derivatives. CONCLUSIONdIn our study, cumulative exposure to metformin was associated with