The purpose of this study is to determine whether treatment with Zactima (vandetanib) in combination with Docetaxel and Prednisolone is more effective than the standard Docetaxel and Prednisolone alone for prostate cancer, in patients with Hormone refractory prostate cancer who have not previously received chemotherapy.

Inclusion Criteria:

• Metastatic hormone refractory prostate cancer defined as those patients with evidence of progression of disease in spite of castrate levels of testosterone indicated by rising levels of PSA
• No previous chemotherapy although those patients that have received estramustine can enter the study provided the estramustine was stopped 3 weeks before dosing of study drug
• screening PSA values >20ng/ml. this must be confirmed by two separate measurements at least 2 weeks apart

Exclusion Criteria:

• Treatment within 4 weeks before randomization and/or whilst on study, treatment with the following: 1)non-approved or experimental drug, 2)treatment with a drug with similar mechanism of action to ZD6474
• concurrent treatment with other anticancer agents, othr than docetaxel and prednisolone as defined in the protocol