Metformin intervention against ovarian toxicity during chemotherapy for early breast cancer: Study protocol for a randomized double-blind placebo-controlled trial

Metformin and Breast Cancer: Where Are We Now?

Breast cancer is the most prevalent cancer and the leading cause of cancer-related death among women worldwide. Type 2 diabetes–associated metabolic traits such as hyperglycemia, hyperinsulinemia, inflammation, oxidative stress, and obesity are well-known risk factors for breast cancer. The insulin sensitizer metformin, one of the most prescribed oral antidiabetic drugs, has been suggested to function as an antitumoral agent, based on epidemiological and retrospective clinical data as well as preclinical studies showing an antiproliferative effect in cultured breast cancer cells and animal models. These benefits provided a strong rationale to study the effects of metformin in routine clinical care of breast cancer patients. However, the initial enthusiasm was tempered after disappointing results in randomized controlled trials, particularly in the metastatic setting. Here, we revisit the current state of the art of metformin mechanisms of action, critically review past and current metformin-based clinical trials, and briefly discuss future perspectives on how to incorporate metformin into the oncologist’s armamentarium for the prevention and treatment of breast cancer.

Efficacy of Metformin in Patients With Breast Cancer Receiving Chemotherapy or Endocrine Therapy: Systematic Review and Meta-analysis

BACKGROUND

Previous studies have suggested that metformin might improve survival outcomes in patients with breast cancer. However, findings on the efficacy of metformin with chemotherapy or endocrine therapy are inconsistent.

OBJECTIVE

To clarify the efficacy of metformin with chemotherapy or endocrine therapy in breast cancer patients according to the treatment setting, including neoadjuvant, adjuvant, and metastasis/recurrence.

METHODS

We systematically searched for randomized controlled trials (RCTs) in MEDLINE, CENTRAL, and EMBASE from inception through July 2020. Overall survival (OS), progression-free survival (PFS), and hypoglycemia rate were the primary outcomes. Secondary outcomes included severe adverse events (SAEs) and relapse-free survival. We used the Grading of Recommendations Assessment, Development, and Evaluation approach and performed a meta-analysis to evaluate the efficacy and safety of metformin with chemotherapy and endocrine therapy in patients with breast cancer.

RESULTS

Our systematic review included 412 participants from 5 trials. Metformin showed little to no difference in OS (hazard ratio [HR] = 1.13; 95% CI = 0.71-1.81; certainty of evidence [COE], moderate) and PFS (HR = 1.14; 95% CI = 0.86-1.50; COE, moderate) in patients with metastasis/recurrence. The evidence was very uncertain about the effect of metformin on survival outcomes in patients who received metformin with neoadjuvant or adjuvant treatment. Metformin showed little to no difference in hypoglycemia and SAEs.

CONCLUSION AND RELEVANCE

Metformin should be discouraged routinely in nondiabetic patients with metastatic/recurrent breast cancer. Further RCTs are needed to verify whether metformin with chemotherapy or endocrine therapy results in significant clinical benefits in the neoadjuvant or adjuvant setting.