A Phase III Trial to Test the Efficacy of ZD4054(Zibotentan), an Endothelin A Receptor Antagonist, Versus Placebo in Patients With Hormone Resistant Prostate Cancer (HRPC) and Bone Metastasis Who Are Pain Free and Mildly Symptomatic.

Enthuse M1 is a large phase III clinical trial studying the safety and efficacy of ZD4054 (Zibotentan) in patients with hormone resistant prostate cancer and bone metastases. * This clinical trial will test if the Endothelin A Receptor Antagonist ZD4054 (Zibotentan) can improve survival compared with placebo. * ZD4054(Zibotentan) is a new type of agent, which is thought to slow tumour growth and spread by blocking Endothelin A receptor activity. This trial will look at the effects of ZD4054 (Zibotentan) in hormone resistant prostate cancer patients with bone metastases. * All patients participating in this clinical trial will receive existing standard prostate cancer treatments in addition to trial therapy. * Half the patients will receive ZD4054 (Zibotentan), and half the patients will receive placebo in addition to standard prostate cancer therapy. By participating in this trial there is a 50% chance that patients will receive an agent that may slow the progression of the tumour. * No patients will be deprived of standard prostate cancer therapy.