Women's College Research Institute

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Metformin does not significantly improve breast cancer survival in older women with diabetes

The drug’s ability to improve breast cancer survival not shown in older patients

July 2013

Past research has shown that metformin, a drug that regulates blood sugar in people with type 2 diabetes, may also reduce breast cancer incidence by a remarkable 30 per cent in diabetic patients.

As a practicing endocrinologist, Women’s College research fellow Dr. Iliana Lega was eager to add to this body of research, by exploring how well metformin improves long-term survival in women with diabetes and breast cancer.

“Unfortunately, our study found that metformin use did not significantly improve overall survival or survival from breast cancer in older women with diabetes,” says Lega.

Lega emphasizes that the women studied had a mean age of 77 at time of diagnosis with breast cancer.

“Because we studied older women, our results cannot be generalized to all women with breast cancer and diabetes,” says Lega.

Lega and her team studied 2,361 women 66 years of age and older diagnosed with diabetes and breast cancer over a 10 year period. The study is one of the first population-based studies to examine the use of metformin in diabetic women with breast cancer, and it is the first to consider the duration of metformin use.

“The results of this study suggest that an older diabetic woman with breast cancer may not benefit from using metformin over another drug to control her blood sugar,” says Lega. “More research is needed to clarify the impact of metformin on breast cancer outcomes in different breast cancer populations, including younger women.”

The study was published in Diabetes Care, and was supported by funding provided by Cancer Care Ontario and the Ontario Institute for Cancer Research (through funding provided by the Ministry of Health and Long-Term Care and the Ministry of Research & Innovation of the Government of Ontario).

Read study abstract

Back to Impact July 2013

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