A Study of Pre-operative Metformin in Prostate Cancer

Inclusion Criteria: 1. 1\. Patients with histologically confirmed prostate cancer involving at least 20% of at least one unfragmented biopsy core; 2. Over the age of 18 and under the age of 75; 3. Ability to read and understand the consent form, either alone or with the aid of a translator 4. ECOG performance status less than or equal to 2 (Karnofsky greater than or equal to 60%); 5. Patients must have their TRUS biopsy performed at UHN (or at an outside institution if tissue accession can be arranged) in the last 3 months; 6. Patients must have normal organ and marrow function as defined by the following criteria: 1. Absolute neutrophil count greater than or equal to 1,500/uL 2. Platelets greater than or equal to 100,000/uL 3. Total bilirubin less than or equal to 1.5 X institutional ULN 4. AST(SGOT)/ALT(SGPT) less than or equal to 1.5 X institutional ULN 5. Creatinine less than or equal to 1.4 X institutional ULN Exclusion Criteria: 1. Patients who on initial assessment are found to be on treatment with any drug used for the treatment of any form of diabetes, or patients that begin treatment for any form of diabetes during the course of the study; 2. Patients may not be receiving any other investigational, herbal or anticancer agents while on study; 3. Uncontrolled intercurrent illness including, but not limited to, ongoing or active infection, congestive heart failure (NYHA Class 3 or greater), cirrhosis with a Child-Pugh level of B or greater or evidence of cardiac dysfunction, unstable angina pectoris, cardiac arrhythmia, active peptic ulcer disease, clinically significant gastrointestinal conditions (e.g. Crohns disease, ulcerative colitis), COPD or psychiatric illness/social situations that would limit compliance with study requirements; 4. Active malignancy at any other site excluding squamous cell or basal cell carcinomas of the skin 5. Radiotherapy within the past 4 weeks; 6. Patients with a current history of alcohol intake (\>2 standard drinks/day) or binge drinking (5 or more drinks (male), or 4 or more drinks (female)) in one session of 1-3 hours; 7. Past history of lactic acidosis or risk factors for lactic acidosis such as congestive heart failure (NYHA Class 3 or greater), hypoxia (resting PO2 \< 91%) or renal insufficiency (eGFR \< 60 mls/min) 8. Patients taking systemic glucocorticoids or estrogenic compounds. 9. Patients with known hypersensitivity or allergy to metformin or any of its excipients. 10. Patients with a history of impaired liver or kidney function.