Diabetes drug metformin, a new weapon against cancer

Metformin, commonly used as the front-line treatment for type 2 diabetes, may be on the brink of a second career.

Evidence from two new studies from the Perelman School of Medicine at the University of Pennsylvania suggest that metformin improves survival for some breast cancer patients and shows promise as a treatment for patients diagnosed with endometrial hyperplasia.

In one study, researchers examined clinical outcomes for 1,215 patients who were diagnosed and underwent surgical treatment for breast cancer between 1997 and 2013. Ninety-seven patients examined reported using metformin before their diagnosis, and 97 reported use of the drug after diagnosis.

Results of the study showed that patients who used metformin before being diagnosed with breast cancer were more than twice as likely to die than patients who never used the drug, while patients who began using metformin after their cancer diagnosis were almost 50 percent more likely to survive than non-users.

"Using metformin as a cancer prevention strategy has been controversial and results have been inconsistent, but our analysis reveals that use of the drug is time-dependent, which may explain the disparity. While use of the drug may have a survival benefit for some breast cancer patients, those who developed breast cancer while already using Metformin may have more aggressive cancer subtypes," said lead author Yun Rose Li.

She added that the study also illustrates the complex interaction between underlying metabolic risks and breast cancer outcomes and underscore the importance of a multi-system approach to cancer treatment.

In the second study, the team examined the effectiveness of using metformin as a treatment for women newly diagnosed with endometrial hyperplasia, a condition that occurs when there is a hormonally related unbalanced overgrowth of the uterine lining. If left untreated, patients are at a significantly higher risk of developing uterine cancer.

Eighteen participants were enrolled in a multi-institutional trial and treated with metformin for three months. Results showed 56 percent of patients responded to treatment, defined as complete resolution of the hyperplasia. The effect was seen especially in women with simple hyperplasia without additional complications or irregularities.

"The results of our study may present an alternative treatment for particular forms of endometrial hyperplasia, in contrast to standard progesterone-based therapies or hysterectomy," said lead author Emily Ko. "Future prospective studies may better identify women for which metformin may be most beneficial, as well as the most effective dosing regimens."

The work will be presented at the American Society of Clinical Oncology (ASCO) Annual Meeting.