Men with castrate resistant prostate cancer who are switched from a luteinizing hormone-releasing hormone (LHRH) antagonists from a LHRH agonist will experience a fall in prostate-specific antigen (PSA).

To determine the proportion of patients with castrate resistant Prostate Cancer who have a PSA decline of ≥50% from baseline PSA when switched from an LHRH agonist to an LHRH antagonist.

Inclusion Criteria:

• histologically confirmed adenocarcinoma of the prostate
• currently receiving LHRH agonist
• Anti-androgen oral therapy is permitted but will be discontinued upon enrollment
• PSA > 2 ng/ml
• rising PSA despite LHRH agonist
• patients may or may not have clinical evidence off metastases. If metastases are present, they must be asymptomatic and in bone or lymph node only
• Prior chemotherapy allowed
• ECOG performance status 0-1

Exclusion Criteria:

• Patients with a history of other active malignancies, except: adequately treated non-melanoma skin cancer, superficial bladder cancer, or other solid tumours curatively treated with no evidence of disease for ≥ 3 years.
• Other serious illness, psychiatric or medical condition that would not permit the patient to be managed according to the protocol including: i)Significant cardiovascular condition including but not limited to: uncontrolled hypertension, unstable angina, significant congestive heart failure or myocardial infarction, deep venous thrombosis, pulmonary embolus or cerebrovascular attack within the last 6 months. ii) History of significant neurological disorder that would impair the ability to obtain consent