There appears to be an association between use of sulfonylureas or insulin and an increased risk of cancer in patients with type 2 diabetes, compared with patients treated with metformin,
However, senior investigator Dr. Jeffrey A. Johnson said that, "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."
Dr. Johnson of the University of Alberta and colleagues note that numerous studies have suggested an association between type 2 diabetes and cancer.
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 mean age was 63.4 years.
Over an average follow-up of 5.4 years, cancer mortality was 3.5% in metformin users, 4.9% in those on sulfonylurea monotherapy and 5.8% in insulin users.
After adjustment, compared to the metformin cohort, the hazard ratio for cancer-related mortality was 1.3 in the sulfonylurea group and 1.9 in the insulin group.
Regardless of the underlying causes for these differences, concluded Dr. Johnson, "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."
Diabetes Care 2006;29:254-258.