Sometimes breast cancer is treated with chemotherapy BEFORE surgery to help shrink the cancer before it's removed. Chemotherapy given before surgery is called neoadjuvant chemotherapy.
The study reviewed here looked at women diagnosed with diabetes who also were being treated for breast cancer. The women who were taking the medicine metformin (brand names: Fortamet, Glucophage, Glucophage XR, Glumetza, Riomet) for diabetes were more likely to respond to breast cancer chemotherapy before surgery than women not taking metformin.
The researchers looked at the medical records of 2,500 women who got neoadjuvant chemotherapy for breast cancer. Most of the women didn't have diabetes and weren't treated with metformin. The researchers found 155 women who did have diabetes. Of these 155 women, 68 were being treated with metformin.
The researchers looked at how each of the 2,500 breast cancers responded to the neoadjuvant chemotherapy. The response was determined by a pathologist who looked at breast issue removed during biopsy. Women with diabetes who were taking metformin were more likely to have a complete response to the neoadjuvant chemotherapy than women without diabetes. Women who had diabetes but weren't taking metformin were less likely to have a complete response to chemotherapy than women without diabetes.
A complete response means that after chemotherapy, there was no cancer found in the breast or lymph nodes.
About 3 years after breast cancer was diagnosed:
Women without diabetes had better survival rates than women with diabetes in this study, whether or not the diabetic women were taking metformin.
It's not clear why metformin seems to improve the benefits of neoadjuvant chemotherapy. Other research has shown that metformin can stop breast cancer cells from growing in a lab. While the results of this study seem promising, they are EARLY results. The women in this study were taking metformin already when breast cancer was diagnosed. None of the women started taking metformin at the same time they started breast cancer treatment and none of the women without diabetes took metformin.
Much more research is needed before doctors will figure out if metformin might be part of a breast cancer treatment plan. Still, finding better ways to treat breast cancer often starts with studies like this.
Stay tuned to Breastcancer.org for the latest news on research that may lead to better ways to prevent, diagnose, and treat breast cancer.
CHICAGO, June 6 -- Diabetic patients with breast cancer had significantly higher rates of response to neoadjuvant chemotherapy if they taking metformin, data from a small retrospective analysis suggest.
Patients on the antidiabetic agent had a three-fold increased rate of pathologic complete response compared with diabetic patients not treated with metformin, and a 50% higher response rate compared with nondiabetic patients, Sao Jiralerspong, M.D., of the University of Texas M.D. Anderson Cancer Center in Houston, reported at the American Society of Clinical Oncology meeting.
The findings add to epidemiologic evidence that diabetic patients treated with metformin have a reduced risk of cancer and cancer-related mortality.
"This was a retrospective, hypothesis-generating study," said Dr. Jiralerspong. "Nonetheless, the results warrant further studies to evaluate the potential of metformin as an antitumor agent."
Laboratory studies have shown metformin inhibits the growth of breast cancer cells by activating AMP kinase and inhibiting the mTOR pathway and associated protein translation, said Dr. Jiralerspong.
The evidence provided a basis for the hypothesis that metformin's antiproliferative effect might enhance the efficacy of systemic neoadjuvant therapy in diabetic patients with breast cancer.
To examine the hypothesis in the clinical setting, Dr. Jiralerspong and colleagues retrospectively reviewed records on more than 2,500 breast cancer patients treated with neoadjuvant systemic therapy. The study population included 155 diabetic patients, 68 treated with metformin.
The primary outcome was pathologic complete response, defined as no residual disease in the breast or lymph nodes.
Among nondiabetic patients, 16% had a pathologic complete response, and diabetic patients not treated with metformin had a pathologic complete response rate of 8%.
In contrast, 24% of diabetic patients who were also taking metformin had pathologic complete responses (P=0.02 overall, P=0.007 versus diabetic patients without metformin, P=0.099 versus nondiabetic patients).
In a multivariate analysis adjusted for diabetes, treatment with metformin independently predicted an increased likelihood of pathologic complete response (OR 3.2, P=0.023).
At a median follow-up of 37 months, recurrence-free survival did not differ among the three groups.
However, nondiabetic patients had a significantly better (P=0.020) overall survival (85.9%) compared with diabetic patients treated with metformin (80.9%) or without metformin (77.6%).
American Society of Clinical Oncology 2008 Annual Meeting; Abstract 528
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