The use of metformin in standard cancer therapy may improve both overall and cancer-specific survival of patients with diabetes and breast cancer, a new study published online ahead of print in the journal The Oncologist has shown.1

Although patients with diabetes and breast cancer receiving metformin and adjuvant chemotherapy achieve a higher pathologic complete response rate than those not receiving metformin, there have been inconsistent data surrounding patients receiving salvage treatment.

Therefore, researchers sought to evaluate the impact of adding metformin to standard therapy on the prognosis of patients with breast cancer and diabetes.

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For the meta-analysis, researchers analyzed data from 11 studies that included a total of 5,464 patients with breast cancer and diabetes. Of those, 2,760 had received metformin and 2,704 had not.

Results showed that metformin use was associated with improved overall survival times (HR = 0.53; 95% CI: 0.39–0.71) and cancer-specific survival times (HR = 0.89; 95% CI: 0.79–1.00).

In subgroup analyses, researchers found that after adjusting for hormone receptor expression, metformin improved overall survival by 65% (HR = 0.35; 95% CI: 0.15–0.84), and metformin use after breast cancer diagnosis was still associated with improved overall survival.

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“Taking metformin after the diagnosis of breast cancer was still associated with prolonged overall survival. The findings of this study highlight the potential usage of metformin in diabetic patients with breast cancer,” the authors concluded.

Studies have also demonstrated that metformin may be beneficial in patients with prostate cancer and at reducing colorectal cancer risk.


  1. Xu H, Chen K, Jia X, et al. Metformin use is associated with better survival of breast cancer patients with diabetes: a meta-analysis [published online ahead of print October 7, 2015]. Oncologist. doi: 10.1634/theoncologist.2015-0096.