People with type 2 diabetes who take sulfonylureas or insulin appear to be at increased risk of dying from cancer compared with their peers who take metformin, Canadian doctors report.

However, senior investigator Dr. Jeffrey A. Johnson of the University of Alberta told Reuters Health, “Our study on this relationship is very preliminary; it is still uncertain whether the increased risks of cancer-related mortality we observed are related to a protective effect of metformin or deleterious effects of sulfonylurea and insulin.”

Johnson and colleagues note that numerous studies have suggested an association between type 2 diabetes and cancer.

The so-called sulfonylureas boost production of insulin, while the drug metformin makes the body’s existing stores of insulin more effective.

To determine whether there might be a relationship with agents that increase insulin, the researchers examined information from Saskatchewan databases. The team identified more than 10,300 new users of metformin or sulfonylureas. Their average age was 63.

Over an average follow-up of 5.4 years, cancer mortality was 3.5 percent in metformin users, 4.9 percent in sulfonylurea users, and 5.8 percent in insulin users.

After adjustment for several factors, users of a sulfonylurea or insulin had a higher risk of cancer-related mortality than metformin users.

“What is apparent from our work - and others - is that how you lower blood sugar may be as important as how well you lower it,” Johnson concluded.

SOURCE: Diabetes Care, February 2006.