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.