A Study of Apalutamide (JNJ-56021927, ARN-509) Plus Androgen Deprivation Therapy (ADT) Versus ADT in Participants With mHSPC

The purpose of this study is to determine if the addition of apalutamide to ADT provides superior efficacy in improving radiographic progression-free survival (rPFS) or overall survival (OS) for participants with mHSPC.

This is a randomized (study medication assigned to participants by chance), double-blind (neither the researchers nor the participants know what treatment the participant is receiving), placebo-controlled, multinational, multicenter study of apalutamide in participants with mHSPC. The study consists of 4 Phases: Screening Phase (up to 28 days before randomization), Treatment Phase (28 day treatment cycles until disease progression or the occurrence of unacceptable treatment related toxicity), an End of Treatment Phase (until 30 days after the last dose of study drug), and then a Survival Follow up Phase. In the event of a positive study result and notification of unblinding at either of the interim analyses or at the final analysis, participants in the treatment Phase will have the opportunity to enroll in an Open-label Extension Phase, which will allow participants to receive active drug (apalutamide) for approximately 3 years. Participants who are receiving apalutamide in the Open-label Extension Phase may continue receiving apalutamide in the Long-term Extension (LTE) Phase if they will continue to derive benefit from treatment (based on investigator assessment). Participants' safety will be monitored throughout the study.

Eligibility Criteria:
Inclusion Criteria:

* Diagnosis of prostate adenocarcinoma as confirmed by the investigator
* Metastatic disease documented by greater than or equal to (\>=) 1 bone lesions on 99mTc bone scan. Participants with a single bone lesion must have confirmation of bone metastasis by computed tomography (CT) or magnetic resonance imaging (MRI)
* Eastern Cooperative Oncology Group Performance Status (ECOG PS) grade of 0 or 1
* Participants who received docetaxel treatment must meet the following criteria: a) Received a maximum of 6 cycles of docetaxel therapy for mHSPC; b) Received the last dose of docetaxel \<=2 months prior to randomization; c) Maintained a response to docetaxel of stable disease or better, by investigator assessment of imaging and PSA, prior to randomization
* Other allowed prior treatment for mHSPC: a) Maximum of 1 course of radiation or surgical intervention; radiation therapy for metastatic lesions must be completed prior to randomization; b) Less than or equal to (\<=) 6 months of ADT prior to randomization
* Allowed prior treatments for localized prostate cancer (all treatments must have been completed \>= 1 year prior to randomization) a) \<= 3 years total of ADT; b) All other forms of prior therapies including radiation therapy, prostatectomy,lymph node dissection, and systemic therapies

Exclusion Criteria:

* Pathological finding consistent with small cell, ductal or neuroendocrine carcinoma of the prostate
* Known brain metastases
* Lymph nodes as only sites of metastases
* Visceral (ie, liver or lung) metastases as only sites of metastases
* Other prior malignancy less than or equal to 5 years prior to randomization with the exception of squamous or basal cell skin carcinoma or non-invasive superficial bladder cancer
* Prior treatment with other next generation anti-androgens or other CYP17 inhibitors, immunotherapy or radiopharmaceutical agents for prostate cancer
* History of seizures or medications known to lower seizure threshold