This is an open label non-comparative controlled randomized phase II study. The experimental arm is the group receiving ODM-201. The group receiving androgen-deprivation therapy (ADT) is included as an internal control. The primary trial objective is to demonstrate that ODM-201 produces prostate-specific antigen (PSA) response rates at 24 weeks (defined as ≥80% reduction compared to baseline) that are in the range of those achieved with 24 weeks of ADT. In total, this 1:1 randomized study will therefore require randomization of at least 250 patients, 125 to each arm.

ODM 201 will be administered as oral 300-mg tablets. The dose of study drug to be administered is 600 milligrams (mg) (2 x 300-mg tablets) twice daily (bid) for a daily dose of 1200 mg. It is recommended that ODM-201 be taken with food. Subjects who have clinical benefit at week 24 may continue to receive ODM-201 at the discretion of the investigator until disease progression, objective or clinical, or occurrence of an unacceptable toxicity. This includes those that will receive external beam radiation therapy. Any anti-cancer therapy other than the study drug given as single agent will not be considered part of the protocol treatment. The standard treatment for this stage of the disease is androgen deprivation therapy (ADT) by means of Luteinizing hormone-releasing hormone (LHRH) antagonist for 24 weeks or by LHRH agonist therapy for 24 weeks with 4 weeks of anti-androgen to prevent flare. This includes leuprolide, goserelin, triptorelin, and degarelix. Beyond week 24, the treatment will be left to the discretion of the treating physician. The primary trial objective is to demonstrate that ODM-201 produces prostate-specific antigen (PSA) response rates at 24 weeks (defined as ≥80% reduction compared to baseline) that are in the range of those achieved with 24 weeks of ADT. The secondary objectives are to: * To document the effects of ODM-201 compared to ADT in terms of patient-reported side effects of hormonal therapy, based on the Hormonal treatment (HTR) symptom scale of EORTC QLQ PR25 at 24 weeks; * To document the effects of ODM-201 compared to ADT in terms of patient-reported side effects of hormonal therapy, based on EORTC QLQ C30 and PR25 at 24 weeks; * To document the effect of ODM-201 on PSA complete response at 24 weeks (defined as ≥ 90% reduction from baseline); * To document the effect of ODM-201 on objective response rate at 24 weeks in patients with RECIST 1.1 measurable disease at baseline; * To document the safety and tolerability of ODM-201 vs. ADT in subjects who have not previously received hormone treatment for prostate cancer; * To document the effects of ODM-201 on androgen deprivations symptoms using the Aging male symptoms (AMS) questionnaires; * To document the proportion of patients who opted to continue treatment with ODM-201 beyond the protocolized 24 weeks The primary endpoint is the PSA response assessed at 24 weeks. PSA response is defined as a ≥ 80% decline in PSA measurement taken at week 24 relative to the measurement taken at baseline, in the ODM-201 study arm. The ADT arm is used as an internal control. Key secondary endpoints: * Change in hormone-treatment related symptoms scale of the EORTC QLQ-PR25 at 24 weeks compared to baseline in the ODM-201 study arm. A 10-point difference is regarded as a clinically meaningful benefit. * Objective response rate at 24 weeks in patients with RECIST 1.1 measurable disease at baseline * PSA response at 24 weeks defined as a ≥90% decline in PSA compared to baseline * Safety according to National Cancer Institute - Common terminology for adverse events (NCI-CTC) version 4.0