Diabetes Drug May Help Fight Breast Cancer

CancerWise - September 2008

Clinical trial results suggest that metformin, the drug most often prescribed for Type 2 diabetes, also may help fight breast cancer, according to a study presented in June at the annual meeting of the American Society of Clinical Oncology.

Significance of study

This is the first study involving metformin as a possible cancer-fighting agent for diabetics with cancer.

More than 35 million prescriptions are filled each year for the oral medication, one of the most-prescribed drugs in this country. It is known by several brand names, including Glucophage®. Metformin is prescribed most often for diabetic patients who are obese or have insulin resistance.

"Metformin works by decreasing the amount of insulin resistance in diabetics, and insulin seems to be a growth factor for cancer," says the study’s principal investigator, Ana Maria Gonzalez-Angulo, M.D., assistant professor in
M. D. Anderson's Department of Breast Medical Oncology.

Background

Researchers decided to study metformin after a large epidemiologic study published in 2007 showed that patients with diabetes who took metformin had lower incidences of cancer, as well as better outcomes, Gonzalez-Angulo says.

Recent studies have shown that metformin activates the AMP kinase pathway, a potentially important pathway for the development of cancer, she says.

Research methods

Using the M. D. Anderson Breast Medical Oncology database, a record of patients who have been treated for breast cancer at M. D. Anderson, researchers identified 2,529 women who had breast cancer and received chemotherapy before surgery.

The patients included:

• 87 diabetics taking metformin
• 68 diabetics not taking metformin
• 2,374 nondiabetics

Ages of patients ranged from 21 to 87 years old, with a median age of 49. Sixty percent of the patients had stage I or II breast cancer; 40% had stage III. A total of 64% of the tumors were hormone-receptive (HR), and 25% were HER2-positive.

Research results

The cancer-free rate was highest in diabetic women who were taking metformin. The patients were cancer-free after chemotherapy and before surgery.

The cancer-free patients included:

• 24% of the diabetics on metformin
• 8% of the diabetics not taking metformin
• 16% of the nondiabetics

What’s next?

Researchers caution that while these results are exciting, the findings are early. They say further investigation with metformin is needed.

"We need to study the mechanism of the drug,” Gonzalez-Angulo says. ”It may be the decrease in insulin levels that causes better outcomes, or it may be that the drug has an anti-tumor effect.”

M. D. Anderson plans to open a clinical trial with metformin in combination with hormonal therapy for metastatic breast cancer patients who are obese.

— Adapted by Dawn Dorsey from an M. D. Anderson news release

M. D. Anderson resources:

• Breast cancer
• Nellie B. Connally Breast Center