Spotlight on diabetes medications and cancer risks

The risks of cancer in patients taking medication for diabetes were analyzed by 2 recent studies.

In the first, a meta-analysis of 20 publications including more than 13,000 patients with cancer published in The Oncologist on Nov. 20, researchers compared the use of metformin with cancer-specific survival and overall survival. They found that patients taking metformin had significantly improved survival rates compared to those who didn't take metformin (hazard ratio, 0.66 for overall survival [95% CI, 0.55 to 0.79] and 0.62 for cancer survival [95% CI, 0.46 to 0.84]). The finding could be due to both the tumor-suppressing activities of metformin and the tumor-promoting effects of other diabetes medications, the authors suggested, concluding that metformin may be the drug of choice for patients with concurrent cancer and diabetes. The study was limited, however, by the fact that diabetes treatment often includes more than one drug and changes over time, the authors noted.

A second study looked at the cancer risks associated with some of those other diabetes medications. Published online Dec. 5 by Diabetes Obesity and Metabolism, the retrospective analysis included more than 25,000 patients from the Cleveland Clinic Diabetes Registry, studied over 8 years. Overall, 892 cancer cases were identified, and for men, no association was found between use of a particular oral diabetes therapy and cancer risk. However, women who used a thiazolidinedione had significantly lower risk of cancer than those taking a sulphonylurea (hazard ratio, 0.68; 95% CI, 0.48 to 0.97). In general, use of an insulin sensitizer (biguanide or thiazolidinedione) was associated with lower cancer risk than use of an insulin secretagogue (sulphonylurea or meglitinide), with a hazard ratio of 0.79 (95% CI, 0.64 to 0.98). The results are consistent with previous research finding a connection between elevated insulin levels and malignancy, the authors concluded, calling for further research on the topic, especially the apparent gender-specific effect.

In other good news for thiazolidinedione users, the FDA recently announced that updated data do not show an increased risk of heart attack with rosiglitazone compared to metformin or sulfonylureas. Therefore, the agency is removing the prescribing and dispensing restrictions that were put in place in 2010. Although some scientific uncertainty about the cardiovascular safety of rosiglitazone still remains, concern is substantially reduced, an FDA press release said.