Type 2 diabetes and risk of cancer

Over the past 50 years, numerous studies have linked diabetes, in particular type 2 diabetes, to an increased risk of cancer. In 2010, a consensus report by the American Diabetes Association and American Cancer Society concluded that type 2 diabetes is convincingly associated with an increased risk for several cancers (colorectal, breast, endometrial, liver, pancreatic, and bladder), while the evidence is less conclusive for others (such as kidney cancer, leukemia, and esophageal cancer).1

In a linked article, Tsilidis and colleagues (doi:10.1136/bmj.g7607) present an umbrella review of 27 meta-analyses summarizing the associations between type 2 diabetes and cancer.2 This review represents one of the most comprehensive efforts to summarize an important, albeit complex, question in epidemiology. In their review, Tsilidis and colleagues confirmed robust associations between type 2 diabetes and the risk of breast, colorectal, intrahepatic cholangiocarcinoma, and endometrial cancer. For most other cancer sites, however, they concluded that the associations with type 2 diabetes were not convincing, despite clinically and statistically significant summary estimates from the meta-analyses. A main reason for this largely negative conclusion is the use of a number …