Farmer RE, et al. – In this study, researchers examined the impact of metformin on cancer risk compared with risk in patients with type 2 diabetes (T2DM) taking no medication via the use of marginal structural models (MSMs) with inverse probability of treatment weights (IPTW) to correctly adjust for confounders. They used a database of electronic health records derived from primary care in the United Kingdom and identified patients with incident T2DM. They assessed the impact of metformin on all cancers (including and excluding non-melanoma skin cancer) and breast, prostate, lung, colorectal and pancreatic cancers. Follow-up was split into 1-month intervals. At study entry, 55,629 T2DM patients were alive and cancer-free. Incident cancer was reported in 2,530 patients during a median follow-up time of 2.9 years. Using the MSM approach, the hazard ratio for all cancers, comparing treatment with metformin with no glucose-lowering treatment, was 1.02 (0.88–1.18). Overall, findings did not support a causal association of metformin with cancer risk.