Inclusion Criteria:

- ≥ 18 years of age

- ECOG ≤ 1

- Histologically confirmed prostate cancer of early or locally advanced stage, or
metastatic prostate cancer with bone involvement only (≤ 5 sites of bone metastases
only)

- Plan to receive ≥ 6 months continuous androgen deprivation therapy by a GnRH agonist

- Patients who are to receive antiandrogens with GnRH agonists are not excluded from
the study. But the form, dose and duration of antiandrogen treatment should be
recorded.

- Adequate renal function (Creatinine ≤ 177mMol/L and GFR >30 mls/min )

- Adequate hepatic function (Bilirubin must be ≤ 1.5 x upper limit of normal range, ALT
and ALP must be ≤ 2.5 x upper limit of normal)

Exclusion Criteria:

- Visceral involvement

- > 5 sites of bone metastases

- History of confirmed diabetes mellitus (patients with impaired fasting glucose or
impaired glucose intolerance will not be excluded) 12

- Treatment with medications that may alter glucose or insulin level within 3 months
(including insulin, oral hypoglycemic agents, systemic corticosteroid of any dosage,
atypical antipsychotic drugs of any dose)

- Malignant disease other than prostate cancer at the time of enrolment

- Bilateral orchiectomy

- Previous androgen deprivation therapy by a GnRH agonist or anti-androgen within last
12 months(patient who had a GnRH agonist more than 12 months ago are allowed if their
testosterone levels are in the normal range at the time of recruitment)

- Chemotherapy within 6 months

- History of lactic acidosis

- Cardiac or respiratory insufficiency, severe infection that is likely to increase the
risk of lactic acidosis

- Medical or psychiatric conditions that compromise the patient's ability to give
informed consent