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

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.