Diabetes and cancer links evaluated

Links between diabetes and cancer were assessed in a consensus report released last week by experts from the American Diabetes Association and the American Cancer Society.

Epidemiologic data have shown a higher risk for some cancers among diabetes patients, the report found. The risk of liver, pancreas or endometrial cancer is about doubled, while there is a 1.2- to 1.5-fold increased risk of colon/rectal, breast or bladder cancer. Diabetes has actually been associated with a lower risk of prostate cancer. Mortality from cancer may also be higher in diabetics, but it's not clear if that is true independent of the mortality risk of diabetes in general. The report was published online on June 16 by CA: A Cancer Journal for Clinicians.

It is also unclear whether the association between diabetes and cancer is direct, or whether diabetes is a marker of underlying biologic risk factors, the experts said. The association could also be due to one of the common risk factors between the two diseases, the list of which the experts reviewed in the report. The possible biologic mechanisms that could explain the link include hyperglycemia, hyperinsulinemia and inflammation.

The report also reviewed the association of diabetes therapies with cancer risk. Observational trials have found a reduced risk of cancer and cancer mortality in patients treated with metformin, but sulfonylureas have been associated with an increased risk. The effect of thiazolidinediones on cancer is unclear, with no definitive human data available on these relatively new drugs. Animal studies have found cancer risks with some incretin-based therapies, but no data on human cancer incidence have been reported yet.

The experts noted that the progressive nature of diabetes makes it very difficult to determine the effect of any individual medication on cancer. They called for additional research, particularly observational trials, on this issue, as well as others addressed in the consensus report.