Metformin for Rising PSA Remote Trial

Inclusion Criteria:

* Histologically confirmed adenocarcinoma of the prostate. (\*in situations where pathology reports documenting prostate cancer are no longer available such as when the initial biopsy or prostatectomy was performed in the remote past, a documented history of prior prostate cancer and prostate cancer treatment in prior medical records will be sufficient)
* Biochemical disease progression after radical prostatectomy and/or radiation therapy (external-beam radiation therapy and/or brachytherapy), and no radiographic evidence of metastases.

  * Men with history of radical prostatectomy are required to have baseline PSA \> 0.5 ng/mL (Prior treatment with neoadjuvant, adjuvant, or salvage radiation therapy is allowed, again, with screening PSA greater than or equal to 0.5 ng/mL required for eligibility).
  * Men treated with primary radiation therapy are required to have baseline PSA ≥ 1.0 ng/mL above their post radiation nadir for men who were treated with primary radiation therapy (external beam and/or brachytherapy). Men who had primary radiation therapy followed by salvage prostatectomy are eligible if screening PSA is greater than or equal to 0.5 ng/mL.
  * Men with previous neoadjuvant adjuvant hormone therapy are eligible if testosterone level at screening is non-castrate (≥ 50 ng/dl). Men previously treated with intermittent hormonal therapy are also eligible if level of testosterone at screening is non-castrate (≥ 50 ng/dl).
* Eastern Cooperative Oncology Group (ECOG) performance status less than or equal to 2 (Karnofsky greater than or equal to 60%).
* Subjects must have normal organ as defined below:

  * AST(SGOT)/ALT(SGPT) less than or equal to 1.8 X institutional upper limit of normal
  * Serum bilirubin ≤ ULN (except for subjects with Gilbert's Disease who are eligible despite elevated serum bilirubin level)
  * Creatinine ≤ 1.5 mg/dL and/or creatinine clearance \> 60 ml/min
* English speaking

Exclusion Criteria:

* Concurrent use of other investigational agents or other prostate cancer therapies (e.g., androgen deprivation therapy)
* Currently taking metformin, sulfonylureas, thiazolidinedione, insulin, or other antidiabetic drugs for any reason.
* Known hypersensitivity or intolerance to metformin
* Condition associated with increased risk of metformin-associated lactic acidosis:

  * New York Heart Association Class III or IV Heart Failure
  * Intake of 3 or more alcoholic beverages per day
  * Known history of lactic acidosis