The purpose of this study is to select the best therapeutic strategy in studying the effectiveness of the association of a short duration hormonal therapy and radiotherapy compared with radiotherapy alone, in patients with a detectable PSA after radical prostatectomy.

Study the effectiveness of the association of a short duration hormonal therapy by degarelix (Firmagon ®) and radiotherapy, with radiotherapy alone on survival without events in the treatment of detectable PSA after radical prostatectomy.

122 patients should be included over a period of 2 years. Patients will be treated according to the following scheme:

• Arm A (61 patients) : Pelvic Radiotherapy: 46 Gy and prostate only boost up to 66 Gy
• Arm B (61 patients) : Arm A + hormonal therapy by degarelix during 6 months

Inclusion Criteria:

1. Patient with localized prostate adenocarcinoma treated with radical prostatectomy (whatever the initial prognostic stage)
2. R0 or R1
3. pN0 or pNx
4. Post prostatectomy PSA ≥0.2 ng/mL measured between 1 month and 4 months after surgery and increasing to a second test performed between 1 et 8 months after the post prostatectomy dosage
5. PSA ≤2 ng/mL at moment of the randomisation
6. No clinical signs of progressive disease (bone scan or PET scan or abdominal and pelvic scan or MRI): N0, M0
7. Neutrophils ≥1500/mm³; platelet count ≥100 000/mm³
8. Bilirubin ≤ upper limit of normal (ULN); alkaline phosphatase (ALP), aspartate aminotransferase (AST), and Alanine aminotransferase (ALT) ≤1.5 ULN
9. Creatinine <140 µmol/L (or clearance >60 mL/min)
10. Normal fasting glucose
11. Eastern Cooperative Oncology Group (ECOG) ≤1
12. Age >18 years
13. Life expectancy ≥10 years
14. Patients with invasive cancer in complete response for more than five years are eligible
15. Patients who have received the information sheet and signed the informed consent form
16. Patients with a public or a private health insurance coverage

Exclusion Criteria:

1. Prostate cancer histology other than adenocarcinoma
2. Patients pN1, N1 and M1
3. History of pelvic radiotherapy
4. Contraindication to pelvic irradiation (eg, scleroderma, chronic inflammatory bowel disease, etc.)
5. Testosterone ≤0.5 ng/mL
6. History of surgical castration
7. Previous treatment by hormonotherapy
8. Antineoplastic treatment in progress
9. History of another invasive cancer within 5 years before inclusion (with the exception of a basal cell skin carcinoma treated)
10. Known pituitary adenoma
11. Severe hypertension uncontrolled by appropriate treatment (160 mm Hg systolic and/or 90 mm Hg diastolic)
12. Patient with a corrected QT interval (using Fridericia correction) greater than 450 msec
13. Individual deprived of liberty or placed under the authority of a tutor
14. Unable to undergo medical monitoring test for geographical, social or psychological reasons
15. Known hypersensitivity to the treatment in test
16. Administration of an investigational therapeutic within 28 days prior to the screening visit or more if treatment is likely to influence the outcome of this

Individual Participant Data will not be shared at an individual level. Those data will be part of the study database including all enrolled patients.