Weekly Health Update: Breast Cancer & Metformin (Glucophage)

Health Report:

Breast Cancer & Metformin (Glucophage)

"A critical weekly review of important new
research findings for health-conscious readers..."

By, Robert A. Wascher, MD, FACS

Last Updated: 07/12/2009

The information in this column is intended for informational purposes only, and does not constitute medical advice or recommendations by the author. Please consult with your physician before making any lifestyle or medication changes, or if you have any other concerns regarding your health.

Breast Cancer & Metformin (Glucophage)

Patients with diabetes are thought to be at increased risk of developing certain types of cancer, as well as being at an increased risk of developing a recurrence of previously diagnosed cancers. For example, an increased risk of recurrent breast cancer has, specifically, been linked to obesity and diabetes in women. Among other possible explanations, elevated levels of insulin are thought to act as a stimulus for cancer cells to
grow and divide. Other diabetes-associated molecules also appear to cause increased cancer cell proliferation, or growth, including insulin-like growth factor (IGF).

Metformin, also known as Glucophage, has become the most commonly prescribed oral medication for the treatment of diabetes. Previous laboratory and public health studies have suggested that metformin may also be able to suppress cancer cell proliferation, and to reduce the risk of death due to cancer. However, thus far, there has been very little direct clinical research evidence available to support this hypothesis.

A new clinical research study, just published in the Journal of Clinical Oncology, sheds further light on the potential role of metformin as a possible new treatment for breast cancer. In this retrospective clinical study from the M.D. Anderson Cancer Center, the
medical records of 2,529 patients who received chemotherapy as initial treatment
(neoadjuvant chemotherapy) for their early stage breast cancers, between 1990 and 2007, were reviewed. This group of breast cancer patients included 68 diabetic patients who were taking metformin, 87 diabetic patients who were not taking metformin, and
2,374 nondiabetic patients. All 2,529 patients subsequently went on to have surgery for their breast cancers, and the researchers then assessed the response of each woman’s breast cancer to their initial chemotherapy.

A pathological complete response to chemotherapy occurs when the pathologist can no longer find any evidence of residual cancer after surgical removal of the original cancer site. (In general, a pathological complete response to neoadjuvant chemotherapy is associated with a better prognosis.) The incidence of pathological complete response to neoadjuvant chemotherapy was then evaluated in each of the three groups of women involved in this clinical study.

In this study, the diabetic women who were taking metformin were found to have three times the rate of pathological complete response to neoadjuvant chemotherapy when compared to the diabetic women who were not taking metformin (there was no statistically significant difference between the diabetic women taking metformin and the nondiabetic women, although there was still a trend towards improved pathological complete response in the metformin group).

While the retrospective nature of this study, and the relatively small numbers of diabetic women included in the study, significantly limits the conclusions that can be drawn, these results are consistent with other previous research findings. Taken together, this data strongly suggests that metformin may be able to, at a minimum, counteract the
proliferative effects of diabetes on breast cancer cells. This finding raises the question as to whether or not diabetic women who are diagnosed with breast cancer should be routinely placed on metformin as part of their overall cancer treatment program. Since this clinical study also detected a non-significant improvement in pathological complete response rates among diabetic women taking metformin, when compared to nondiabetic women, larger prospective clinical research studies may also help us to understand whether or not metformin might be clinically useful in treating breast cancer in women who do not have diabetes, as well.

Currently, there are several prospective clinical research trials underway, looking at the role of metformin in the management of breast cancer (and at least one such clinical trial for prostate cancer, as well). Hopefully, one or more of these prospective clinical research trials will help us to better understand the role, if any, for metformin as a potential breast cancer therapy in diabetic women (and, perhaps, in nondiabetic women as well). Meanwhile, if you are a breast cancer survivor with diabetes, and you are not taking metformin, you might be well advised to discuss this data with your Oncologist.

Disclaimer: As always, my advice to readers is to seek the advice of your physician before making any significant changes in medications, diet, or level of physical activity

Dr. Wascher is an oncologic surgeon, a professor of surgery, a widely published author, and the Physician-in-Chief for Surgical Oncology at the Kaiser Permanente healthcare system in Orange County, California