The purpose of this research study is to find out if a certain type of hormone therapy, gonadotropin-releasing hormone agonist (GnRH agonist), affects the way the body produces and responds to insulin. The investigators will evaluate the changes in insulin sensitivity during and after GnRH agonist treatment for prostate cancer. The investigators are assessing the possibility that treatment-related insulin resistance may contribute to the risk of diabetes and/or cardiovascular disease in men with prostate cancer.

• The study will be divided into 2 groups: one group (Cohort A) will consist of men undergoing GnRH agonist therapy for at least 24 months. The second group (Cohort B) will consist of men undergoing the same treatment but who are scheduled to receive only 6 months of treatment.
• The following tests and procedures will be performed when the participant joins the study, then at 3, 6, 12 and 24 months thereafter. (All visits will take place at the General Clinical Research Center (GCRC) at the Massachusetts General Hospital.) Height and weight; blood and urine samples; Oral Glucose Tolerance Test (OGTT), Dual energy X-ray Absorptiometry scan; medical history; and physical examinations.

Inclusion Criteria:

• Adenocarcinoma of the prostate, clinical stage M0
• Scheduled to initiate GnRH agonist therapy with intended treatment duration of greater than 24 months (Group A)
• Scheduled for radiation therapy and neoadjuvant GnRH agonist therapy with intended 6 month duration of treatment (Group B)
• Karnofsky Performance Status 90 or 100
• Local or local-regional disease (Group B)

Exclusion Criteria:

• Prior hormone therapy (GnRH agonist or antiandrogen)
• History of bilateral orchiectomy
• Known diabetes mellitus or glucose intolerance
• Current treatment with anabolic agents or metabolic agents known to affect insulin or glucose levels

Men with prostate cancer scheduled to undergo GnRH agonist therapy with intended treatment duration of 6 or 24 months.