Darolutamide Augments Standard Therapy for Localised Very High-Risk Cancer of the Prostate

Inclusion Criteria: 1. Men aged 18 years and older, with pathological diagnosis of adenocarcinoma of the prostate 2. EITHER planned for primary RT and judged to be at very high risk for recurrence based on any of the following: * Grade Group 5, OR * Grade Group 4 AND one or more of the following: clinical T2b-4 OR MRI with seminal vesicle invasion OR extracapsular extension OR PSA\* \> 20ng/mL, OR * Pelvic nodal involvement (involvement of lymph nodes (LNs) at or below the bifurcation of the aorta into the common iliac arteries) defined radiologically as greater than 10mm on short axis using standard CT or MRI, or pathologically confirmed (PSMA PET alone is not considered enough if ≤ 10mm) OR Post-radical prostatectomy ≤ 365 days prior to randomisation and planned for RT with PSA\* ≥ 0.1 ng/mL that has risen or remained stable (within ≤ 0.05 ng/mL) since a previous level at least 1 week earlier, judged to be at very high risk for recurrence based on any of the following: * Grade Group 5, OR * Grade Group 4 AND pT3a or higher, OR * Pelvic nodal involvement (involvement of LNs at or below the bifurcation of the aorta into the common iliac arteries) defined radiologically as greater than 10mm on short axis using standard CT or MRI, or pathologically confirmed (PSMA PET alone is not considered enough if ≤ 10mm) \* This PSA level must be measured within 60 days prior to randomisation. However, if a participant has already commenced endocrine therapy (ET) for prostate cancer, this PSA level must be measured within 180 days prior to commencing ET. 3. Adequate bone marrow function: Haemoglobin ≥ 100g/L, white cell count (WCC) ≥ 4.0x109/L, absolute neutrophil count (ANC) ≥ 1.5x109/L and platelets \> 100 x 109/L 4. Adequate liver function: alanine aminotransferase (ALT) \< 2 x upper limit of normal (ULN) and total bilirubin \< 1.5 x ULN, (or if total bilirubin is between 1.5 - 2 x ULN, they must have a normal conjugated bilirubin) 5. Adequate renal function: calculated creatinine clearance \> 30 mL/min (Cockroft-Gault) 6. Eastern Cooperative Oncology Group (ECOG) performance status of 0 - 1 7. Study treatment both planned and able to start within 7 days after randomisation 8. Willing to complete health-related quality of life (HRQL) questionnaires UNLESS is unable to complete because of literacy or limited vision 9. Willing and able to comply with all study requirements, including standard of care treatment such as EBRT, timing and/or nature of required assessments 10. Signed, written informed consent Exclusion Criteria: 11. Prostate cancer with predominant non-adenocarcinoma features (sarcomatoid or spindle cell or neuroendocrine small cell or squamous cell components or other non-adenocarcinoma) 12. Involvement of LNs by conventional CT imaging superior to the common iliac artery bifurcation, and/or outside the pelvis (distant LNs). LN involvement is defined by histopathological confirmation, or by a short axis measurement \> 10mm on standard imaging (CT or MRI, but not PET). 13. Evidence of metastatic disease. Minimum imaging requirements to exclude metastatic disease are diagnostic quality imaging of both the pelvis and the abdomen (CT or MRI), chest (CXR or CT), and a whole body radioisotope bone scan (WBBS). * If endocrine therapy (ET) had not started, imaging must be within 60 days prior to randomisation. * If ET has been started, imaging must have been performed no more than 60 days prior to starting ET and no more than 30 days after starting ET and prior to randomisation. 14. PSA \> 100 ng/mL at any time 15. Any prior use of new generation potent AR inhibition (abiraterone, enzalutamide, apalutamide, darolutamide or similar agents). 16. Prior endocrine therapy for prostate cancer except for the following which are allowed: * (i) LHRHA and/or (ii) a first-generation nonsteroidal antiandrogen (NSAA) are allowed if commenced no more than 90 days before randomisation. If an NSAA has been used, it must be stopped before starting study treatment with darolutamide/placebo; and * Prior use of 5-alpha reductase inhibitor is allowed and if used it must be stopped before starting study treatment with darolutamide/placebo 17. Bilateral orchidectomy 18. Prior pelvic brachytherapy or other radiotherapy that would result in an overlap of radiotherapy fields that would preclude the required RT 19. History of * Loss of consciousness or transient ischemic attack or stroke within 6 months prior to randomisation, or * Significant cardiovascular disease within 6 months prior to randomisation: including myocardial infarction, unstable angina, congestive heart failure (NYHA grade II or greater), ongoing arrhythmias of Grade \> 2 (CTCAE v5.0), thromboembolic events (e.g. deep vein thrombosis, pulmonary embolism), coronary artery bypass graft. Chronic stable atrial fibrillation on stable anticoagulant therapy is allowed. 20. Known gastrointestinal (GI) disease or GI procedure that could interfere with the oral absorption or tolerance of darolutamide, including difficulty swallowing tablets 21. History of another malignancy within 5 years prior to randomisation except for those malignancies treated with curative intent with a predicted risk of relapse of less than 10% including but not limited to non-melanoma carcinoma of the skin; or adequately treated, non-muscle-invasive urothelial carcinoma of the bladder (i.e. Tis, Ta and low grade T1 tumours). All such cases with a history of malignancy within the last 5 years are to be discussed with study team before randomisation. Melanoma in-situ and other adequately treated in-situ neoplasms are not considered malignancies for the purposes of eligibility assessment. 22. Concurrent illness, including severe infection that might jeopardise the ability of the participant to undergo the procedures outlined in this protocol with reasonable safety (HIV infection is not an exclusion criterion if it is controlled with anti-retroviral drugs that are unaffected by concomitant darolutamide) 23. Presence of any psychological, familial, sociological or geographical condition potentially hampering compliance with the study protocol and follow-up schedule, including alcohol dependence or drug abuse 24. Patients who are sexually active with women of child-bearing potential and not willing/able to use medically acceptable and highly effective forms of contraception during study treatment and for at least 4 weeks after completion of study treatment. Contraception must include: * Condom use (also required if sexual partner is pregnant), and * Additional birth control with low failure rate (less than 1% per year) when used consistently and correctly. E.g. combined (oestrogen and progestogen containing) hormonal contraception associated with inhibition of ovulation (oral, intravaginal, transdermal), progestogen-only hormonal contraception associated with inhibition of ovulation (oral, injectable, implantable), intrauterine device (IUD), intrauterine hormone-releasing system (IUS), bilateral tubal occlusion, vasectomised partner, true sexual abstinence. True sexual abstinence will only be an acceptable form of contraception when this is in line with the preferred and usual lifestyle of the subject. Periodic abstinence (e.g., calendar, ovulation, symptothermal, post-ovulation methods), declaration of abstinence for the duration of exposure to study treatment, and withdrawal are not acceptable methods of contraception. 25. Participation in other clinical trials of investigational agents for the treatment of prostate cancer or other diseases 26. Major surgery within 21 days prior to randomisation 27. Patients with history of hypersensitivity to the study treatment