Inclusion Criteria:

- Men will be eligible to this study if they are diagnosed with a histologically
confirmed organ-confined adenocarcinoma of the prostate (PCa) treatable by
prostatectomy and have a current prostate-specific antigen (PSA) less than 50 ng/ml

- Have not received chemotherapy and/or radiation for any malignancy (excluding
non-melanoma skin cancer and cancers confined to organs with removal as only
treatment) in the past 5 years

- Eastern Cooperative Oncology Group (ECOG) performance status 0-1 (Karnofsky >= 70%)

- Leukocytes >= 3,000/μL

- Absolute neutrophil count >= 1,500/μL

- Platelets >= 100,000/μL

- Total bilirubin =< 1.5 times institutional upper limits of normal (ULN)

- Aspartate aminotransferase (AST) (serum glutamic oxaloacetic transaminase
[SGOT])/alanine aminotransferase (ALT) (serum glutamic pyruvate transaminase[SGPT])
=< 1.5 times institutional ULN

- Creatinine within normal institutional limits

- Willing to use adequate contraception (barrier method, abstinence, subject has had a
vasectomy or partner is using effective birth control or is postmenopausal) for the
duration of study participation

- Ability to understand and the willingness to sign a written informed consent document

Exclusion Criteria:

- Type I or type II diabetic patients on treatment with any drug for diabetes or
participants with fasting glucose >= 126 mg/dL

- History of impaired liver or kidney function

- Participants with a current history of high alcohol consumption (> 3 standard
drinks/day) or binge drinking (5 or more drinks) in one session of 1-3 hours

- History of lactic acidosis or at increased risk for lactic acidosis such as patients
with unstable or acute congestive heart failure who are at risk of hypoperfusion with
hypoxemia

- Participants may not be receiving any other investigational agents

- History of allergic reactions attributed to compounds of similar chemical composition
to metformin

- Uncontrolled intercurrent illness including, but not limited to, ongoing or active
infection, symptomatic congestive heart failure, unstable angina pectoris, cardiac
arrhythmia, or psychiatric illness/social situations that would limit compliance with
study requirements

- Plan to undergo radiologic studies involving intravascular administration of
iodinated contrast materials

- No concurrent use of cationic drugs (e.g., amiloride, digoxin, morphine,
procainamide, quinidine, quinine, ranitidine, triamterene, trimethoprim, or
vancomycin)

- History of acute or chronic metabolic acidosis

- Concurrent use of non-study metformin or other biguanides