Joining FORCEs Newsletter

Joining FORCES is the FORCE newsletter with news, views and supportive information for individuals concerned about hereditary breast and ovarian cancer.


Does a Common Diabetes Medication Also Fight Cancer?

by Margaret Snow, MD

“Equally exciting is the fact that metformin already has FDA approval…”

The most common medication used to treat type 2 diabetes is showing some potential that it may also inhibit breast cancer cell growth. Several studies found that diabetics who were treated with the oral drug metformin were less likely to develop cancer than those who did not take the medication. Increasingly, evidence is mounting that metformin not only reduces blood sugar and insulin levels, but also may improve breast cancer outcomes.

One interesting and promising aspect of the research is that the drug may target cancer stem cells, a small population of cells believed to cause tumor growth and recurrence, and that resist conventional chemotherapies. In laboratory tests at Harvard Medical School, researchers who examined the metformin response in four distinct types of breast cancer cells found that the drug acts direct ly on cancer stem cells, reducing tumor s and prolonging remission after chemotherapy. Some tests were conducted on breast cancer cultures, while others were performed in mice. The combination of metformin and doxorubicin, a standard chemotherapy agent, was particularly powerful, preventing cancer cell growth and selectively destroying both estrogen-sensitive and triple-negative cancer stem cells. The authors reported the addition of metformin to the doxorubicin “has a dramatic effect on prolonging remission, and indeed may even represent a cure of these… tumors.”

The Harvard study differed from other tissue culture experiments: an important finding was that metformin did not appear to affect growth of healthy cells. This suggests metformin acts specifically on cancer cells.

Another recent study at M.D. Anderson Cancer Center involved diabetic patients with early-stage breast cancer who had neoadjuvant chemotherapy (chemotherapy given to shrink a tumor before it is surgically removed). In this study, diabetic patients who took metformin were more likely to have a complete response to chemotherapy (where the cancer shrank completely) than those who did not.

If metformin studies on larger groups and more non-diabetic patients prove that the drug acts as a cancer cell fighter, it could eventually become a component of breast cancer treatment, and may ultimately be used preventively to decrease risk of developing cancer. Equally exciting is the fact that metformin already has FDA approval for treating people with diabetes, and we know its safety profile from its use in that population. If future research with metformin is positive, the drug might more quickly become a standard treatment than a medication with an unknown safety profile.


Hirsch HA, Iliopoulous D, Tsichlis PN and Struhl K. "Metformin selectively targets cancer stem cells, and acts together with chemotherapy to block tumor growth and prolong remission." Cancer Research. October 2009;69(19):7507-7511.

Jiralerspong S, Palla SL, Giordano SH, et al. "Metformin and pathologic complete responses to neoadjuvant chemotherapy in diabetic patients with breast cancer." Journal of Clinical Oncology. July 2009;27(20):3297-3302.

Evans JM, Donnelly LA, Emslie-Smith AM, et al. "Metformin and reduced risk of cancer in diabetic patients." British Medical Journal. June 2005;330(7503):1304-1305.

Metformin Clinical Trials

Several clinical trials are now using metformin to treat early-stage breast cancer, while another trial is testing it as a metastatic cancer treatment. Information about these studies can be found on the National Institutes of Health clinical trials website.


We welcome your feedback. Please send your comments to Sue Friedman or fill out our Newsletter Feedback Form.

FORCE:Facing Our Risk of Cancer Empowered