The purpose of this study is to assess the efficacy and safety of the combination of the polyadenosine 5'-diphosphoribose poly(ADP-ribose) polymerase (PARP) inhibitor olaparib and pembrolizumab in the treatment of participants with mCRPC who have failed to respond to either abiraterone acetate or enzalutamide (but not both) and to chemotherapy. The primary study hypotheses are that the combination of pembrolizumab plus olaparib is superior to abiraterone acetate or enzalutamide with respect to: 1. Overall Survival (OS) and 2. Radiographic progression-free survival (rPFS) per Prostate Cancer Working Group (PCWG)-modified Response Evaluation Criteria in Solid Tumors Version 1.1 as assessed by blinded independent central review (BICR)



Eligible Ages
Over 18 Years
Eligible Genders
Accepts Healthy Volunteers

Inclusion Criteria

  • Has histologically- or cytologically-confirmed adenocarcinoma of the prostate without small cell histology
  • Has prostate cancer progression while receiving androgen deprivation therapy (or post bilateral orchiectomy) within 6 months prior to screening
  • Has current evidence of metastatic disease documented by bone lesions on bone scan and/or soft tissue disease shown by computed tomography/magnetic resonance imaging (CT/MRI)
  • Has received prior treatment with abiraterone acetate OR enzalutamide, but not both
  • Have disease that progressed during or after treatment with abiraterone acetate for either metastatic hormone-sensitive prostate cancer (mHSPC) or mCRP or enzalutamide for mCRPC for at least 8 weeks (at least 14 weeks for participants with bone progression)
  • Participants that received abiraterone acetate for mHSPC may not have received abiraterone acetate or enzalutamide for mCRPC
  • Have received docetaxel chemotherapy regimen for mCRPC and have had progressive disease during or after treatment with docetaxel
  • Has ongoing androgen deprivation with serum testosterone <50 ng/dL (<2.0 nM)
  • If receiving bone resorptive therapy, including but not limited to bisphosphonates or denosumab, must have been receiving stable doses prior to randomization
  • Must agree to refrain from donating sperm during the intervention period and for at least 180 days thereafter PLUS Be abstinent from heterosexual intercourse OR Agree to use contraception unless confirmed to be azoospermic AND Also agree to use a male condom when engaging in any activity that allows passage of ejaculate to another person of any sex
  • Has provided tumor tissue from a fresh core or excisional biopsy (obtained within 12 months of screening) from soft tissue not previously irradiated. Samples from tumors progressing at a prior site of radiation are allowed. Participants with bone-only or bone-predominant disease may provide a bone biopsy sample
  • Has an Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1 assessed within 7 days of randomization

Exclusion Criteria

  • Has a known additional malignancy that is progressing or has required active treatment in the last 3 years
  • Has an active autoimmune disease that has required systemic treatment in the past 2 years
  • Has a history of (noninfectious) pneumonitis requiring steroids, or has current pneumonitis
  • Has known active human immunodeficiency virus (HIV), hepatitis B virus (e.g., hepatitis B surface antigen reactive) or hepatitis C virus (HCV) infection (e.g., HCV RNA [qualitative] is detected)
  • Has known active central nervous system (CNS) metastases and/or carcinomatous meningitis
  • Has a history of seizure or any condition that may predispose to seizure
  • Has a history of loss of consciousness within 12 months of screening
  • Has myelodysplastic syndrome (MDS)/acute myeloid leukemia (AML) or has features suggestive of MDS/AML
  • Has a diagnosis of immunodeficiency or is receiving chronic systemic steroid therapy
  • Has (≥Grade 3) hypersensitivity to pembrolizumab and/or any of its excipients
  • Has known hypersensitivity to the components or excipients in olaparib, abiraterone acetate, prednisone or prednisolone, or enzalutamide
  • Has symptomatic congestive heart failure (New York Heart Association Class III or IV heart disease)
  • Has received an anticancer monoclonal antibody (mAb) prior to randomization
  • Has received prior treatment with olaparib or any other PARP inhibitor
  • Has received prior treatment with apalutamide or darolutamide
  • Has received prior treatment with enzalutamide or apalutamide for metastatic hormone-sensitive prostate cancer
  • Has used herbal products that may have hormonal anti-prostate cancer activity and/or are known to decrease PSA (e.g., saw palmetto) prior to the date of randomization
  • Has received prior treatment with radium or other therapeutic radiopharmaceuticals for prostate cancer
  • Has received prior treatment with an anti-PD-1, anti-PD-L1, or anti PD-L2 agent, or with an agent directed to another stimulatory or co-inhibitory T-cell receptor (e.g., CTLA-4, OX-40, or CD137)
  • Is currently receiving either strong or moderate inhibitors of cytochrome P450 [CYP] (CYP3A4) that cannot be discontinued for the duration of the study
  • Has received a previous allogenic bone marrow transplant or double umbilical cord transplantation (dUCBT) or a solid organ transplant
  • Has received a live vaccine within 30 days prior to the date of randomization
  • Is currently participating in or has participated in a study of an investigational agent, or has used an investigational device, within 4 weeks prior to the date of randomization
  • Has a bone "superscan"
  • Is expecting to father children within the projected duration of the study, starting with the screening visit through 180 days after the last dose of study intervention

Study Design

Phase 3
Study Type
Intervention Model
Parallel Assignment
Primary Purpose
None (Open Label)

Arm Groups

ArmDescriptionAssigned Intervention
Pembrolizumab + Olaparib
Participants receive olaparib 600 mg as two 150 mg oral tablets twice daily (BID) continuously until progression PLUS on Day 1 of each 21-day cycle, pembrolizumab 200 mg by intravenous (IV) infusion for up to 35 cycles (approximately 2 years).
  • Biological: Pembrolizumab
    IV infusion
    Other names:
    • MK-3475
  • Drug: Olaparib
    Oral tablets
    Other names:
    • MK-7339
    • AZD-2281
Active Comparator
Abiraterone + Prednisone or Enzalutamide
Participants receive abiraterone acetate (participants previously treated with enzalutamide) 1000 mg as two 500 mg or four 250 mg oral tablets once daily (QD) PLUS prednisone 10 mg as one 5 mg tablet BID until progression OR Participants receive enzalutamide (participants previously treated with abiraterone acetate) 160 mg as four 40 mg oral tablets or capsules QD until progression.
  • Drug: Abiraterone acetate
    Oral tablets
    Other names:
    • ZYTIGA®
    • CB-7630
    • JNJ-212082
  • Drug: Prednisone
    Oral tablets
  • Drug: Enzalutamide
    Oral tablets or oral capsules
    Other names:
    • XTANDI®
    • MDV-3100
    • ASP-9785

Recruiting Locations

Tulane Cancer Center ( Site 0066)
New Orleans, Louisiana 70112
Study Coordinator

More Details

Merck Sharp & Dohme Corp.

Study Contact

Toll Free Number


Study information shown on this site is derived from ClinicalTrials.gov (a public registry operated by the National Institutes of Health). The listing of studies provided is not certain to be all studies for which you might be eligible. Furthermore, study eligibility requirements can be difficult to understand and may change over time, so it is wise to speak with your medical care provider and individual research study teams when making decisions related to participation.