ODM-201 Maintenance Therapy in Patients With mCRPC Previously Treated With Novel Hormonal Agents.

Inclusion Criteria: * Written informed consent according to Swiss law and ICH/GCP regulations before registration and prior to any trial specific procedures not part of normal medical care. * Histologically or cytologically confirmed diagnosis of adenocarcinoma of the prostate * Castration resistance: tumor progression after orchiectomy or during treatment with GnRH analogues (agonists or antagonists) * Metastatic disease, documented by imaging * Total testosterone ≤ 50 ng/dL (≤ 1.7 nmol/L) * Treatment with abiraterone AND/OR enzalutamide for at least 8 weeks prior to taxane based chemotherapy * No evidence of disease progression after chemotherapy with docetaxel (at least cumulative dose of ≥ 300 mg/m2 or total dose ≥ 600mg) or cabazitaxel (at least cumulative dose of ≥ 80 mg/m2 or total dose ≥ 160 mg) * No evidence of progression on imaging according to PCWG3 * No evidence of progression on PSA levels referred to the nadir since start of taxane treatment (PSA progression defined as \> 25% increase of PSA level or \>50% if PSA decrease under chemotherapy \>50% AND \> 5 ng/mL increase in the absolute PSA value) * Non-surgically castrated patient agrees on ongoing use of GnRH analogues (agonists or antagonists) during the trial * Planned start of trial treatment 2 to 8 weeks after last taxane dose * Male patient 18 years or older * WHO performance status of ≤2 * Laboratory values as specified below * alanine aminotransferase (ALT) ≤ 2.5 x ULN (except for patients with liver metastases ≤ 5.0 x ULN) * Total bilirubin ≤ 1.5 x ULN (except for patients with Gilbert's disease ≤ 3.0 x ULN) * Estimated creatinine clearance using the Cockcroft-Gault formula \> 30 mL/minute * Blood counts at screening: haemoglobin ≥ 90 g/L, absolute neutrophil count ≥ 1500/μl (1.5x109/L), platelet count ≥ 100,000/μl (100x109/L) (patient must not have received any growth factor or blood transfusion within 7 days of the haematology laboratory obtained at screening) * Adequate cardiac function: Left ventricular Ejection Fraction (LVEF) ≥ 40% as determined by echocardiography (ECHO) * Patient is able and willing to swallow trial drug as whole tablet * Sexually active male subjects must agree to use condoms as an effective barrier method and refrain from sperm donation, and/or their female partners of reproductive potential to use a method of effective birth control, during the study treatment and for 3 months after the end of the treatment. * Patient agrees to participate in the mandatory translational research project Exclusion Criteria: * Prior chemotherapy for prostate cancer except from chemotherapy with a taxane * Concurrent disease requiring higher doses of corticosteroid than the equivalent of 10 mg prednisone per day * Known CNS or leptomeningeal metastases * Clinical or radiological evidence of current spinal cord compression * History of hematologic or primary solid tumor malignancy, unless in remission for at least 2 years from registration with the exception of localized non-melanoma skin cancer or carcinoma in situ having undergone complete resection. * Prior therapy for mCRPC with modern anti-hormonal treatment except for enzalutamide or abiraterone * Concurrent treatment with other experimental drugs or treatment in a clinical trial within 30 days prior to trial entry (except clinical trial SAKK 96/12) * Concomitant use of other anti-cancer drugs or radiotherapy except for local pain control and GnRH analogues * Severe or uncontrolled cardiovascular disease * Acute exacerbations of chronic illnesses, serious infections, or major surgery within 4 weeks before expected start of treatment * ECG abnormalities of Q-wave infarction, unless identified ≥ 6 months prior to registration or QTc interval \>480 msec * Known gastrointestinal (GI) disease or GI procedure that could interfere with the GI absorption or tolerance of ODM-201 * Known hypersensitivity to trial drug or to any component of the trial drug * Any other serious underlying medical, psychiatric, psychological, familial or geographical condition, which in the judgment of the investigator may interfere with the planned staging, treatment and follow-up, affect patient compliance or place the patient at high risk from treatment-related complications.