A Study to Assess the Safety of Continued Administration of MDV3100 in Subjects With Prostate Cancer Who Showed Benefit From Prior Exposure to MDV3100

Inclusion Criteria: * Has completed a prior study with MDV3100, can be enrolled in this extension study without any interruption in study drug * No new clinically significant abnormalities based upon physical examination, safety laboratory data, vital signs, ECG, and other clinical assessments noted from the last visit conducted during the subject's active MDV3100 study prior to initiation of this study * Male subjects and their female spouses/partners who are of childbearing potential must be using highly effective contraception1 consisting of two forms of birth control (one of which must be a barrier method) starting at Screening and continue throughout the study period and for 3 months after final study drug administration. Male subjects must not donate sperm starting at Screening and throughout the study period and for at least 3 months after final study drug administration. 1Highly effective contraception is defined as: * Established use of oral, injected or implanted hormonal methods of contraception. * Placement of an intrauterine device (IUD) or intrauterine system (IUS). * Barrier methods of contraception: Condom or occlusive cap (diaphragm or cervical/vault caps) with spermicidal form/gel/film/ cream/suppository * Subject agrees not to participate in another interventional study while on treatment Exclusion Criteria: Subject will be excluded from participation if any of the following apply: 1. Subject has a history of seizure or any condition that may predispose to seizure including, but not limited to underlying brain injury, stroke, primary brain tumours, brain metastases, or alcoholism. 2. Subject has a history of loss of consciousness or transient ischemic attack within 12 months prior to Day 1 of the completed preceding study. 3. Use of the following prohibited medication/therapies: * Concomitant medication that likely could cause clinically relevant drug-to-drug interactions with MDV3100. * Other (than MDV3100) androgen-receptor (AR) antagonists (bicalutamide, flutamide, nilutamide). * Investigational therapy other than MDV3100 or investigational procedures of any kind.