Walking Away From Breast Cancer

Breast cancer incidence and metformin use associated

/ Author:  / Reviewed by: Robert Carlson, M.D

(RxWiki News) A drug used to treat diabetes to might work on different kinds of cancer. One day, that may include breast cancer.

In postmenopausal women with diabetes, metformin may help reduce the occurrence of breast cancer that has spread.

"If you have questions about diabetes, talk to your pharmacist."

A research team, headed by Rowan T. Chlebowski, MD, PhD, of the Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center, reviewed information about 68,000 postmenopausal women from the national Women's Health Initiative project, who were followed for roughly 12 years.

About 3,400 of the women had diabetes when they were enrolled in the study, and 3,273 were diagnosed with breast cancer during the study period.

New cases of diabetes were tracked throughout; researchers gathered medication information at the outset of the study and in years 1, 3, 6 and 9.

After taking into account other risk factors for the disease, investigators compared new cases of breast cancer diagnosed in women with diabetes who were being treated with metformin and those who were not. .

Diabetic women who weren't treated with metformin had a slightly higher incidence of breast cancer. Women with the disease who were receiving metformin had a lower incidence.

This trend was seen in breast cancers that were positive for both estrogen and progesterone receptors, but negative for HER2.

We asked Anthony J. Berdis, PhD, assistant professor of pharmacology at Case Western Reserve University, to explain the implications of this study.

"The study by Chlebowski and colleagues is to date the most comprehensive study showing that the use of the diabetes drug, metformin, is associated with a lower incidence of invasive breast cancer in postmenopausal women, Berdis said.

"This study is very important as it provides a possible new treatment for breast cancer, as well as suggesting some possible mechanisms linking metabolic diseases such as diabetes with cancer," Berdis told dailyRx in an email.

He concluded, "While more research is needed to verify both aspects, this study clearly raises some very important issues in cancer treatment using established drugs for other diseases,"

These findings, while impressive, don't show a cause-and-effect relationship. That is, the study didn't show that the use of metformin lowers the risk or incidence of breast cancer in women with diabetes.

More study is needed to establish that.

Meanwhile, metformin is approved by the U.S. Food and Drug Administration (FDA) only for the treatment of type 2 diabetes and nothing else.

This study was published in the June 11, 2012 issue of the Journal of Clinical Oncology.

No financial disclosures were publicly available.

Reviewed by: 
Review Date: 
June 18, 2012
Last Updated:
September 27, 2012