Previous research has found that metformin was associated with an up to 30 percent reduction in new cancers in breast cancer patients without diabetes, noted study author Dr. Iliana Lega, a research fellow at Women's College Hospital in Toronto. Prior research has also tied use of the drug to slowed tumor growth.
"Metformin is a drug commonly used by diabetic patients to control the amount of glucose [sugar] in their blood," Lega explained in a hospital news release. "Although existing scientific literature suggests that the drug may prevent new cancers and death from breast cancer, our study found the drug did not significantly impact survival rates in our patients."
The study included more than 2,300 women, aged 66 and older, with diabetes who took metformin and were diagnosed with breast cancer between 1997 and 2008. The women were followed from the time of their diagnosis until their death or until early 2010.
Metformin use was not associated with any significant drop in breast cancer deaths, according to the study published online recently in the journal Diabetes Care.
"What makes our study so unique is that while the effects of metformin have been well documented, previous research has not examined the cumulative effects of the drug on patients, particularly breast cancer patients with diabetes," Lega said. "This is important given that diabetic patients may switch drugs over the course of their treatment."
She and her colleagues said further research is necessary in younger patients who have both breast cancer and diabetes.
"Understanding the effects of metformin on breast cancer patients is critical in helping address the gap in cancer outcomes in patients with and without diabetes," Lega explained. "The findings will help physicians inform treatment plans for patients with diabetes."