A Study of Apalutamide (Adjuvant Treatment) and Androgen Deprivation Therapy (ADT) in Participants Who Have Undergone Radical Prostatectomy (RP) for Non-metastatic Prostate Cancer and Who Are at High Risk for Metastases

A Multi-center, Open-label, Single-arm Phase 2 Study of the Adjuvant Treatment of Apalutamide and Androgen Deprivation Therapy (ADT) in Treatment-naïve Participants Who Have Undergone Radical Prostatectomy (RP) for Non-metastatic Prostate Cancer and Who Are at High Risk for Metastases

Main Study: The purpose of main study is to assess if the combination of apalutamide and androgen deprivation therapy (ADT) in participants with high-risk localized prostate cancer improves the biochemical recurrence (BCR) free rate.

Sub-study: The purpose of the sub-study is to assess if the co administration of apalutamide and relugolix is able to maintain castrate levels of testosterone.

Inclusion Criteria:

• A candidate for radical prostatectomy (RP) or status post RP. Eligible to receive study intervention between Day 29 and Day 90 post-RP. Post RP prostate-specific antigen (PSA) of <= 0.2 nanograms per milliliter (ng/mL). Has not received other treatment for prostate cancer
• Have recovered from RP procedure and have had no worsening in cardiac risk in the peri-operative period per the clinical judgement of the investigator
• Adequate organ function (hepatic, renal, hematologic and cerebral) determined at the discretion of the treating physician
• Eastern Cooperative oncology Group (ECOG) Performance Status Score of 0 or 1
• Histologically confirmed adenocarcinoma of the prostate and categorized as high risk for recurrent prostate cancer. High risk can be defined based on PSA alone or biopsy or RP specimen as follows: PSA greater than or equal to (>=) 20 ng/ml or; Gleason Score >= 9 in any core on biopsy or; Gleason Score >= 8 (4+4 or 5+3) in greater than (>) 80 percentage (%) of 2 cores on biopsy or; Gleason Score = 8 (4+4 or 5+3) in 1 core as long 5 or more other cores with minimum Gleason Score of 4+3 on biopsy. The determination of high risk may be based on pathology report of biopsy or equivalent criteria from radical prostatectomy

Exclusion Criteria:

• History or presence of soft tissue/bone metastasis or metastasis in distant lymph nodes (pelvic lymph nodes below the iliac bifurcation that are less than (<) 2 centimeter (cm) in diameter [short axis] either radiographically or pathologically are allowed.)
• History of bilateral orchiectomy
• Received an investigational intervention <= 4 weeks before the planned first dose of study intervention
• History of seizure or any condition that in the opinion of the investigator may predispose to seizure or treatment with drugs known to lower the seizure threshold within 4 weeks prior to starting treatment with apalutamide
• Allergy or hypersensitivity to apalutamide, or excipients, unable or unwilling to take androgen deprivation therapy (ADT)