The study will test metformin in patients with early breast cancer. Blood and tissue will be collected before and after the use of metformin.

Patients will take metformin twice a day for 3 weeks before surgery. The hypothesis is that metformin will reduce cell proliferation rates (Ki67) and increase apoptoses (TUNEL)in tumor tissue.

The study will collect and analyze pre- and post-treatment blood specimens for:

• Serum glucose
• Insulin levels
• Estradiol
• HOMA test
• Glycosylated haemoglobin

Inclusion Criteria:

• Invasive breast cancer T1 or T2, Nx
• Knowledge of the investigational nature of the study and ability to provide consent for study participation

Exclusion Criteria:

• Diabetes or baseline glucose or Glycosylated haemoglobin upper limit of normal for the institution
• Recent use of corticosteroids
• AST > 1.5 times upper limit of normal for the institution
• Pregnancy
• Serious clinical illness
• Prior or concurrent systemic neoadjuvant Breast Cancer therapy.