Metformin Seems to Enhance Power of Chemotherapy

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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.

A study 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.

  • 24% of women with diabetes taking metformin had a complete response
  • 16% of women without diabetes (so weren't taking metformin) had a complete response
  • 8% of women with diabetes but not taking metformin had a complete response

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:

  • 86% of women without diabetes were alive
  • 81% of women with diabetes who were taking metformin were alive
  • 78% of women with diabetes who weren't taking metformin were alive

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.

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