Efficacy Study of Switching to a Lutenizing Hormone-releasing Hormone (LHRH) Antagonist From a LHRH Agonist to Treat Progressive Castrate Resistant Prostate Cancer (CRPC)

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