Active Surveillance With or Without Apalutamide Treatment in Low Risk Prostate Cancer

Inclusion Criteria: 1. Out-patient aged ≥ 18 years old 2. With life expectancy of more than 5 years 3. With ECOG performance status = 0 or 1 4. Having read, understood, signed and dated the informed consent, 5. With a Localized prostate cancer diagnozes within less than 7 months and defined by: * Clinical Stage: T1c or T2a * Sampled biopsy with less of 3 positive cores and tumor length \< 3 mm per core (\<7 mm for targeted cores) * Gleason score \< 7 (3+4 for patients \>70years if small volume tumor) * PSA levels ≤ 10 ng/ml or PSA density \<0.2ng/ml/ml 6. Clinical laboratory values at screening: 1. Hemoglobin ≥9.0 g/dL, independent of transfusion and/or growth factors within 3 months prior to randomization 2. Platelet count ≥100,000 x 109/µL independent of transfusion and/or growth factors within 3 months prior to randomization 3. Serum albumin ≥3.0 g/dL 4. Serum creatinine \<2.0 × upper limit of normal (ULN) 5. Serum potassium ≥3.5 mmol/L 6. Serum total bilirubin ≤1.5 × ULN (Note: In subjects with Gilbert's syndrome, if total bilirubin is \>1.5 × ULN, measure direct and indirect bilirubin and if direct bilirubin is ≤1.5 × ULN, subject may be eligible) 7. Aspartate aminotransferase (AST) or alanine aminotransferase (ALT) \<2.5 × ULN 7. Medications known to lower the seizure threshold (see list in appendix 2) must be discontinued or substituted at least 4 weeks prior to study entry. 8. Agrees to use a condom (even men with vasectomies) and another effective method of birth control if he is having sex with a woman of childbearing potential or agrees to use a condom if he is having sex with a woman who is pregnant while on study drug and for 3 months following the last dose of study drug. Must also agree not to donate sperm during the study and for 3 months after receiving the last dose of study drug. 9. Having accepted the principle of active surveillance 10. Who is willing to participate to the study for a minimum period of 36 months 11. Able to swallow the study drug and comply with study requirements 12. Patient affiliated to the national "Social Security" regimen or beneficiary of this regimen. Exclusion Criteria: 1. Prior treatment for prostate cancer with surgery or radiotherapy or including 5-alpha reductase inhibitor (finasteride or dutasteride) and antiandrogen 2. Absolute neutrophil count \< 1,500/μL, 3. Seizure or known condition that may pre-dispose to seizure (including but not limited to prior stroke, transient ischemic attack, loss of consciousness within 1 year prior to randomization, brain arteriovenous malformation; or intracranial masses such as schwannomas and meningiomas that are causing edema or mass effect) 4. Any prior malignancy (other than adequately treated basal cell or squamous cell skin cancer, superficial bladder cancer, or any other cancer in situ currently in complete remission) within 5 years prior to randomization 5. Severe/unstable angina, myocardial infarction, symptomatic congestive heart failure, arterial or venous thromboembolic events (e.g., pulmonary embolism, cerebrovascular accident including transient ischemic attacks), or clinically significant ventricular arrhythmias within 6 months prior to randomization 6. Uncontrolled hypertension (SBP≥160 mmHg or DBP≥90 mmHg). Patients with a history of uncontrolled hypertension are allowed provided blood pressure is controlled by anti-hypertensive treatment. 7. Gastrointestinal disorder affecting absorption 8. Active infection (eg, human immunodeficiency virus \[HIV\] or viral hepatitis) or other medical condition that would make prednisone/prednisolone (corticosteroid) use contraindicated 9. Any other condition that, in the opinion of the Investigator, would impair the patient's ability to comply with study procedures 10. Mental deficiency or any other reason that may hinder the understanding or the strict application of the Protocol 11. Patient placed under judicial protection, tutorship, or curatorship 12. Patient unlikely to attend control visits 13. Patient currently enrolled in an investigational study or having participated to another investigational study within the past 3 months