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Efficacy and Safety of Pembrolizumab (MK-3475) Plus Enzalutamide Plus Androgen Deprivation Therapy (ADT) Versus Placebo Plus Enzalutamide Plus ADT in Participants With Metastatic Hormone-Sensitive Prostate Cancer (mHSPC) (MK-3475-991/KEYNOTE-991)

StatusTerminated
PhasePhase 3
Started2020-02-12
View on ClinicalTrials.gov ↗

Amendment history

The 49 most recent of 80 record versions are listed below. See every version on ClinicalTrials.gov ↗

2026-09-29
Reclassified as terminated (was completed)
Trial terminated: The study stopped due to futility
2026-04-15
Study Status v79
Trial completed
Completion dateestimated 2026-03-27→confirmed 2026-04-08
2026-03-06
Study Status v78
Completion date2026-02-02→2026-03-27
2025-08-27
Study Status, Contacts/Locations v77
Study sites213→234
2025-05-14
Study Identification, Study Status, IPDSharing v76
Completion date2025-12-03→2026-02-02
Show 45 earlier versions
2025-01-31
Study Status v75
Completion date2026-06-15→2025-12-03
2024-11-14
Study Identification, Study Status, References v74
Re-verified, no change to tracked fields
2024-05-20
Study Status, Outcome Measures (Results) v73
Completion date2026-02-02→2026-06-15
2023-11-16
Study Status, Study Description, References, Outcome Measures (Results) v72
Results first postednot stated→2023-11-18
2023-10-11
Study Identification, Study Status, Study Description, Arms and Interventions, Outcome Measures, Eligibility, Document Section, Participant Flow, Baseline Characteristics, Outcome Measures (Results), Adverse Events, More Information v71
InterventionsAndrogen Deprivation Therapy (ADT) (Procedure), Enzalutamide (Drug), Pembrolizumab (Biological), Placebo (Other)→Androgen Deprivation Therapy (ADT) (Drug), Enzalutamide (Drug), Pembrolizumab (Biological), Placebo (Other)
Eligibility criteria+109 characters
[...] c resonance imaging (CT/MRI) Willing to maintain continuous Androgen Deprivation Therapy (ADT) with a luteinizing-hormone releasing hormone (LHRH) agonists or antagonists during study treatment or have a hi [...] ), anti-programmed cell death-ligand 1 (anti-PD-L1), or anti-programmed cell death-ligand 2 (anti PD-L2) agent or with an agent directed to another stimulatory or c [...]
Secondary endpoints12 entries, revised
Time to First Symptomatic Skeletal-Relatedrelated Event (TTSSRE) Time to Radiographic Soft Tissue Progression Per Soft Tissue Rules of ProstatePCWG-Modified Cancer Working Group (PCWG)-modified Response Evaluation Criteria in Solid Tumors Version 1.1 (RECIST 1.1) as Assessed by Blinded Independent Central ReviewBICR Time to Pain Progression (TTPP) as Assessed by Brief Pain Inventory-Short Form (BPI-SF) Item #3 ("Worst Pain in 24 Hours") and Opiate Use Time fromFrom Randomization to Disease Progression as Determined by Investigator Assessment afterAfter Next-line of Therapy or Death fromFrom An [...] [...]
Primary endpoints2 entries, revised
Radiographic Progression-free Survival (rPFS) Per Prostate Cancer Working Group (PCWG)-modifiedModified Response Evaluation Criteria in Solid Tumors Version 1.1 (RECIST 1.1) as Assessed by Blinded Independent Central Review (BICR)
2023-06-02
Study Identification, Study Status, Study Description, Outcome Measures v70
Completion date2026-09-01→2026-02-02
Secondary endpointsdetails revised at 12 of 12 entries
2023-05-03
Study Status, Study Design, References v69
Primary completion dateestimated 2026-07-02→confirmed 2022-10-31
Enrollment targetestimated 1232→confirmed 1251
2022-08-18
Study Identification, Study Status v68
Re-verified, no change to tracked fields
2021-07-06
Recruiting→Active, Not Recruiting Study Status, Contacts/Locations v67
Trial statusRecruiting→Active, Not Recruiting
Study sitesdetails revised at 213 of 213 sites
2021-06-24
Study Status, Contacts/Locations v66
Study sitesdetails revised at 1 of 213 sites
2021-06-18
Study Status, Contacts/Locations v65
Study sites212→213
2021-06-11
Study Status, Contacts/Locations v64
Study sitesdetails revised at 6 of 212 sites
2021-06-04
Study Status, Contacts/Locations v63
Study sites209→212
2021-05-28
Study Status, Contacts/Locations v62
Study sites209 entries, revised
CHUV (centre hospitalier universitaire vaudois) ( Site 2002)
2021-05-21
Study Status, Contacts/Locations v61
Study sites209 entries, revised
CHU de QuebecCHUQ-UniversiteUniv Laval-Hotel Dieu de Quebec ( Site 0101)
2021-05-13
Study Status, Contacts/Locations v60
Study sitesdetails revised at 5 of 209 sites
2021-05-07
Study Status, Contacts/Locations v59
Study sites207→209
2021-04-30
Study Status, Contacts/Locations v58
Study sites207 entries, revised
Sociedad de Investigaciones MedicasMédicas LimitadasLtda.-Clinical Reaserch Unit ( Site 2401)
2021-04-22
Study Status, Contacts/Locations v57
Study sitesdetails revised at 3 of 207 sites
2021-04-17
Study Status, Contacts/Locations v56
Study sites205→207
2021-04-09
Study Status, Contacts/Locations v55
Study sitesdetails revised at 4 of 205 sites
2021-04-02
Study Status, Contacts/Locations v54
Study sitesdetails revised at 2 of 205 sites
2021-03-26
Study Status, Contacts/Locations v53
Study sitesdetails revised at 3 of 205 sites
2021-03-19
Study Status, Contacts/Locations v52
Study sites202→205
2021-03-05
Study Status, Contacts/Locations v51
Study sites201→202
2021-02-26
Study Status, Contacts/Locations v50
Study sites200→201
2021-02-19
Study Status, Contacts/Locations v49
Study sites197→200
2021-02-04
Study Status, Contacts/Locations v48
Study sitesdetails revised at 4 of 197 sites
2021-01-29
Study Status, Contacts/Locations v47
Study sites194→197
2021-01-13
Study Status, Contacts/Locations v46
Study sites192→194
2020-12-30
Study Status, Contacts/Locations v45
Study sitesdetails revised at 2 of 192 sites
2020-12-23
Study Status, Contacts/Locations v44
Study sites188→192
2020-12-09
Study Status, Contacts/Locations v43
Study sites187→188
2020-12-02
Study Status, Contacts/Locations v42
Study sites182→187
2020-11-25
Study Status, Contacts/Locations v41
Study sites178→182
2020-11-20
Study Status, Contacts/Locations v40
Study sites173→178
2020-11-12
Study Status, Contacts/Locations v39
Study sites170→173
2020-11-05
Study Status, Contacts/Locations v38
Study sites166→170
2020-10-29
Study Status, Contacts/Locations v37
Study sites161→166
2020-10-23
Study Status, Contacts/Locations v36
Study sites157→161
2020-10-16
Study Status, Contacts/Locations v35
Study sites154→157
2020-10-08
Study Status, Contacts/Locations v34
Study sites148→154
2020-10-01
Study Status, Contacts/Locations v33
Study sites145→148
2020-09-25
Study Status, Contacts/Locations v32
Study sites140→145
2020-09-18
Study Status, Contacts/Locations v31
Study sites138→140
Merck (MSD)
401 trials monitored
See 24 trials at risk
Prostate Cancer
2,471 trials monitored
See 156 trials at risk
This study will assess the efficacy and safety of pembrolizumab plus enzalutamide plus Androgen Deprivation Therapy (ADT) versus placebo plus enzalutamide plus ADT in participants with mHSPC. The primary hypothesis is that in participants with mHSPC, the combination of pembrolizumab plus enzalutamide plus ADT is superior to placebo plus enzalutamide plus ADT with respect to 1) radiographic progression-free survival (rPFS) per Prostate Cancer Working Group (PCWG)-modified Response Evaluation Criteria in Solid Tumors (RECIST) 1.1 as assessed by blinded independent central review (BICR) and 2) overall survival (OS). As of 19-JAN-2023, the study was unblinded and all study participants stopped ongoing treatment with pembrolizumab/placebo and will continue to receive Standard of Care treatment until meeting protocol-specified discontinuation criteria if deriving clinical benefit. Safety analysis will be performed at the end of the study; there will be no further analyses for efficacy and electronic patient-reported outcome (ePRO) endpoints collected from participants beyond the IA1 cutoff date. All study participants will stop ongoing treatment with pembrolizumab/placebo. Exceptions may be requested for study participants who, in the assessment of their study physician, are benefitting from the combination of enzalutamide and pembrolizumab, after consulting with the Sponsor. All other study participants should be discontinued from study and be offered standard of care (SOC) treatment as deemed necessary by the Investigator. If enzalutamide as SOC is not accessible off study to the participant, central sourcing may continue. As of Amendment 04, disease progression will no longer be centrally verified, participants will only be assessed locally. As of Amendment 4, Second Course treatment is not an option for participants. There are currently no participants in the Second Course Phase.
Trial Details
NCT Number NCT04191096
Lead Sponsor Merck Sharp & Dohme LLC
Conditions Metastatic Hormone-Sensitive Prostate Cancer
Enrollment 1,251 participants
Start Date 2020-02-12
Primary Completion 2022-10-31 (estimated)
Study Completion 2026-04-08 (estimated)
Updated on ClinicalTrials.gov 2026-09-28