The Promise of Metformin

Metformin, a drug commonly used in the treatment of type 2 diabetes, is showing promise in the treatment of certain types of hormone-stimulated cancers, such as breast cancer and prostate cancer. If current research validates previous studies, experts say, metformin could become an invaluable weapon in the arsenal against cancer—especially among patients who are overweight.

Obesity is a known risk factor for type 2 diabetes and also a risk factor for several types of cancer. The fact that metformin may be useful in the treatment of both conditions is a lucky find.

Among individuals with type 2 diabetes, metformin lowers insulin and glucose levels, explains Michael Pollak, MD, director of the cancer prevention research unit at McGill University in Montreal, Canada. This same action may also make certain cancers behave less aggressively.

According to Pollak, metformin works by reducing the output of glucose from the liver, which then leads to a reduction in the levels of insulin and other hormones that have the capacity to stimulate the growth of certain tumors. “The reduction in the hormone levels may be more important in controlling prostate cancer than the reduction of glucose,” he notes.

Numerous studies have suggested a favorable impact of metformin in breast cancer. In one study published in the Journal of Clinical Oncology, diabetic patients with breast cancer receiving metformin and neoadjuvant chemotherapy were found to have a higher pathologic complete response compared to diabetics not receiving metformin.

Another study, published in Diabetes Care, a publication of the American Diabetes Association, found that long-term use of metformin may lower the risk of breast cancer among women with type 2 diabetes. The Canadian researchers are planning a large randomized trial of metformin to test its ability to lower the risk of recurrence after treatment for early-stage breast cancer. New studies are also evaluating its effectiveness against prostate cancer and colon cancer.

In addition, there is also some indication that metformin can make cancer treatment more effective. “In laboratory studies, there have been favorable interactions between metformin and standard treatments,” Pollak notes. He is quick to add, however, that clinical trials will be required to confirm such action. “We cannot make any definite forecasts,” Pollak says, “except to say that those questions are definitely on the radar screen.”

As for the future, Pollak is cautiously optimistic. “I think it certainly deserves research; it certainly might be helpful,” he says. “But it probably will only be helpful in those cancer patients where high insulin levels are to blame. In cases in which insulin levels are normal, metformin probably will have less to offer.”

Obesity is a known risk factor for type 2 diabetes and also a risk factor for several types of cancer. The fact that metformin may be useful in the treatment of both conditions is a lucky find.