 - Chemotherapy: patients must have received prior docetaxel based chemotherapy either as a single agent or in combination. Patients must have evidence of progression while receiving docetaxel based chemotherapy or within 6 months after the completion of docetaxel based chemotherapy. Prior adjuvant or neoadjuvant chemotherapy is permitted provided therapy was completed 12 months prior to registration. Prior therapy with mitoxantrone or experimental non-cytotoxic chemotherapy is permitted e.g. monoclonal antibodies, vaccine therapy, receptor tyrosine kinase inhibitors. 