Diabetes drug metformin has been shown in previous studies to reduce the risk of cancer in healthy patients, and even to improve survival in certain cancer patient populations, but a new population-based study published in Diabetes Care suggests that the drug has no impact on the survival rates of older women with breast cancer and diabetes.

The team of Canadian researchers recruited 2,361 women, aged 66 and older, who had been diagnosed with diabetes and breast cancer from 1997 to 2008. They found no significant association between the cumulative duration of their metformin usage, used to treat their diabetes, on either their all-cause or cancer-related mortality rate.

"Our findings failed to show an association between improved survival and increased cumulative metformin duration in older breast cancer patients who had recent-onset diabetes," the team wrote. "Further research is needed to clarify this association, accounting for effects of cancer stage and BMI in younger populations or those with differing stages of diabetes as well as in nondiabetic populations."

Although previous studies have been done on metformin's anticancer effects, this is the first time a study has been conducted on the cumulative effects of the drug on diabetic breast cancer patients, according to lead author Iliana Lega in a Women's College Hospital press release. "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," she said. "The findings will help physicians inform treatment plans for patients with diabetes."