A Study of Adding Apalutamide to Radiotherapy and LHRH Agonist in High-Risk Patients With Prostate-Specific Membrane Antigen-Positron Emission Tomography (PSMA-PET) Positive Hormone-Sensitive Prostate Cancer Participants

Inclusion Criteria:

Histologically confirmed adenocarcinoma of the prostate
Previously treated with radical prostatectomy with or without lymph node dissection and any post-operative prostate-specific antigen (PSA) measurement of less than (<) 0.1 nanogram/milliliter (ng/mL) between Week 6 and Week 20
Be able to swallow whole the study drug tablets or follow the instructions for admixing with apple sauce
Prostate specific membrane antigen-positron emission tomography (PSMA-PET) must be performed at screening: Patients who are PSMA-PET-positive for at least one loco-regional (pelvic) lesion with or without distant (extra-pelvic) lesions at screening, as determined by Blinded Independent Central Review (BICR), will be eligible to be randomized to either arm of the Interventional Cohort.The investigators will be blinded to the location of the PSMA-PET lesions after randomization and patients who are PSMA-PET-negative for any prostate cancer lesions (that is no loco-regional lesion and no distant lesion) at screening, as determined by BICR, will be eligible for inclusion in the Observational Cohort
Biochemically recurrent prostate cancer after RP with a high risk of developing metastasis defined as pathological Gleason score greater than or equal to (>=) 8 evaluated from prostate tissue specimen at radical prostatectomy, OR PSADT less than or equal to (<=) 12 months at the time of screening
No evidence of prostate cancer metastases on screening CT/MRI of the chest/abdomen/pelvis, Technetium 99m [99mTc] whole-body bone scan. Participants with a single bone lesion on 99mTc whole-body bone scan should have confirmatory imaging by CT or MRI; if the confirmatory scan confirms the bone lesion, the patient should be excluded from the study. Conventional images (99mTc-bone scan and CT/MRI) from the screening will be sent to BICR for confirmation of non-metastatic prostate cancer before randomization
Eastern Cooperative Oncology Group Performance Status Grade 0 or 1

Exclusion Criteria:

History of pelvic radiation for malignancy
Previous treatment with androgen deprivation therapy (ADT) for prostate cancer
Previously treated for biochemical recurrence (BCR) prostate cancer (previous surgical treatment of one or more loco-regional lesions is allowed)
Prior treatment with a CYP17 inhibitor (example, oral ketoconazole, orteronel, abiraterone acetate, galeterone) or any androgen receptor (AR) antagonist including bicalutamide, flutamide, nilutamide, apalutamide, enzalutamide or darolutamide and any other medications that may lower androgen levels (estrogens, progestins, aminoglutethimide, etc.), including bilateral orchiectomy
Known or suspected contraindications or hypersensitivity to apalutamide, Luteinizing Hormone-Releasing Hormone (LHRH) agonist or any of the components of the formulations
Prior chemotherapy for prostate cancer
Any evidence of prostate cancer metastasis on computed tomography/magnetic resonance imaging (CT/MRI) of the chest/abdomen/pelvis or 99mTc whole-body bone scan, at any time prior to screening