Metformin in Early Breast Cancer: A Prospective Window of Opportunity Neoadjuvant Study

Breast Cancer Res Treat. 2012 Oct;135(3):821-30. doi: 10.1007/s10549-012-2223-1. Epub 2012 Aug 30.


Metformin may exert anti-cancer effects through indirect (insulin-mediated) or direct (insulin-independent) mechanisms. We report results of a neoadjuvant "window of opportunity" study of metformin in women with operable breast cancer. Newly diagnosed, untreated, non-diabetic breast cancer patients received metformin 500 mg tid after diagnostic core biopsy until definitive surgery. Clinical (weight, symptoms, and quality of life) and blood [fasting serum insulin, glucose, homeostasis model assessment (HOMA), C-reactive protein (CRP), and leptin] attributes were compared pre- and post-metformin as were terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) and Ki67 scores (our primary endpoint) in tumor tissue. Thirty-nine patients completed the study. Mean age was 51 years, and metformin was administered for a median of 18 days (range 13-40) up to the evening prior to surgery. 51 % had T1 cancers, 38 % had positive nodes, 85 % had ER and/or PgR positive tumors, and 13 % had HER2 overexpressing or amplified tumors. Mild, self-limiting nausea, diarrhea, anorexia, and abdominal bloating were present in 50, 50, 41, and 32 % of patients, respectively, but no significant decreases were seen on the EORTC30-QLQ function scales. Body mass index (BMI) (-0.5 kg/m(2), p < 0.0001), weight (-1.2 kg, p < 0.0001), and HOMA (-0.21, p = 0.047) decreased significantly while non-significant decreases were seen in insulin (-4.7 pmol/L, p = 0.07), leptin (-1.3 ng/mL, p = 0.15) and CRP (-0.2 mg/L, p = 0.35). Ki67 staining in invasive tumor tissue decreased (from 36.5 to 33.5 %, p = 0.016) and TUNEL staining increased (from 0.56 to 1.05, p = 0.004). Short-term preoperative metformin was well tolerated and resulted in clinical and cellular changes consistent with beneficial anti-cancer effects; evaluation of the clinical relevance of these findings in adequately powered clinical trials using clinical endpoints such as survival is needed.

Publication types

  • Clinical Trial
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Apoptosis / drug effects
  • Body Mass Index
  • Breast Neoplasms / drug therapy*
  • Breast Neoplasms / pathology
  • Breast Neoplasms / surgery*
  • Cell Proliferation / drug effects
  • Female
  • Humans
  • Hypoglycemic Agents / administration & dosage
  • Hypoglycemic Agents / adverse effects
  • Hypoglycemic Agents / therapeutic use*
  • Ki-67 Antigen / analysis
  • Metformin / administration & dosage
  • Metformin / adverse effects
  • Metformin / therapeutic use*
  • Middle Aged
  • Neoadjuvant Therapy
  • Preoperative Care
  • Quality of Life


  • Hypoglycemic Agents
  • Ki-67 Antigen
  • Metformin