Clinical and Biologic Effects of Metformin in Early Stage Breast Cancer

Inclusion criteria

• invasive T1-4 (if T1, ≥ 1cm), NX operable breast cancer confirmed on core biopsy
• < 70 years of age
• breast surgery scheduled at least 2 weeks after study entry at one of the participating institutions (metformin will be started no more than 3 weeks prior to scheduled surgery) for the current breast cancer
• patient and physician consent

Exclusion criteria

• on metformin for any reason during the preceding 4 weeks
• recent (within 4 weeks) antiestrogen or estrogen therapy
• prior or concurrent systemic neoadjuvant BC therapy of any type (chemotherapy, hormone therapy, biologic therapy)
• known diabetes or baseline fasting glucose > or = 7.0 mmol/L (specific treatment is required)
• current or recent (within 4 weeks) use of drugs that may influence insulin or insulin sensitivity including oral corticosteroids, insulin sensitizers, exogenous insulin or oral hypoglycemic agents
• serum creatinine above upper limit of normal for the institution
• history of lactic or other metabolic acidosis
• consumption of > 3 alcoholic beverages per day (on average)
• AST > 1.5 times upper limit of normal for the institution
• known hypersensitivity or allergy to metformin
• current or past congestive heart failure
• coagulopathy (including use of anti-coagulants) precluding biopsy
• pregnancy or lactation within 3 months.
• Serious psychiatric illness

• Note: Women with childbearing potential will be required to use an effective form of birth control (condom or other barrier method, tubal ligation or vasectomy - oral contraceptives are contra-indicated in breast cancer) and to have a negative pregnancy test prior to starting metformin.