Metformin Does Not Improve Survival in High-Risk Breast Cancer

Incidence rate of invasive disease-free survival events and incidence rates for death did not differ with addition of metformin, placebo
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MONDAY, June 6, 2022 (HealthDay News) -- For patients with high-risk nonmetastatic breast cancer receiving standard therapy, the addition of metformin does not improve invasive disease-free survival, according to a study published in the May 24/31 issue of the Journal of the American Medical Association.

Pamela J. Goodwin, M.D., from the University of Toronto, and colleagues examined whether administration of adjuvant metformin improves outcomes among patients with breast cancer without diabetes. A total of 3,649 patients with high-risk nonmetastatic breast cancer receiving standard therapy were enrolled between August 2010 and March 2013, with follow-up to October 2020.

The researchers found that after a second interim analysis, futility was declared for patients who were estrogen receptor and/or progesterone receptor (ER/PgR)-negative, so the primary analysis was conducted among 2,533 ER/PgR+ patients, with a median follow-up of 96.2 months. Invasive disease-free survival events occurred in 465 ER/PgR+ patients. The incidence rates for invasive disease-free survival events were 2.78 and 2.74 per 100 patient-years in the metformin and placebo groups, respectively; the corresponding incidence rates for death were 1.46 and 1.32 per 100 patient-years.

"Among patients with high-risk operable breast cancer without diabetes, the addition of metformin versus placebo to standard breast cancer treatment did not significantly improve invasive disease-free survival," the authors write.

Several authors disclosed financial ties to the pharmaceutical industry; Apotex Canada provided in-kind donations of placebo and metformin.

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