Trial Outcomes & Findings for Study of Pembrolizumab (MK-3475) Plus Enzalutamide Versus Placebo Plus Enzalutamide in Participants With Metastatic Castration-resistant Prostate Cancer (mCRPC) (MK-3475-641/KEYNOTE-641) (NCT NCT03834493)

Of the 1244 participants that were randomized to trial, 1235 received treatment. At the time of the primary analysis data cut-off, 635 participants are ongoing in the study.

Study of Pembrolizumab (MK-3475) Plus Enzalutamide Versus Placebo Plus Enzalutamide in Participants With Metastatic Castration-resistant Prostate Cancer (mCRPC) (MK-3475-641/KEYNOTE-641)

OS was defined as the time from randomization to death due to any cause. The OS for all participants is presented.

rPFS was defined as the time from randomization to the first documented progressive disease (PD) per PCWG-modified RECIST 1.1 based on blinded independent central review or death due to any cause, whichever occurred first. The rPFS per PCWG-modified RECIST for all participants is presented.

TFST was defined as time from randomization to initiation of the first subsequent anti-cancer therapy or death, whichever occurs first. The TFST for all participants is presented.

PSA response rate was defined as percentage of participants in the analysis population who have a negative change (decrease) in PSA level of ≥50% measured twice ≥3 weeks apart. The analysis was performed on participants who had baseline PSA measurements.

PSA undetectable rate was defined as percentage of participants in the analysis population with PSA \<0.2 ng/mL during study treatment. The analysis was performed on participants who had baseline PSA measurements.

OR was defined as the percentage of participants with complete response (CR: disappearance of all target lesions per RECIST 1.1; and no evidence of disease (NED) on bone scan per PCWG) or partial response (PR: at least a 30% decrease in the sum of diameters of target lesions per RECIST 1.1; and non-progressive disease, non-evaluable \[NE\], or NED on bone scan or CR with non-progressive disease or NE bone scan per PCWG).

DOR was defined as the time from first documented evidence of complete response (CR) or partial response (PR) per PCWG and RECIST 1.1 criteria until progressive disease (PD) or death. PD per RECIST 1.1 was defined as at least a 20% increase in the sum of diameters of target lesions. In addition to the relative increase of 20%, the sum must also demonstrate an absolute increase of at least 5 mm. PD per PCWG was the appearance of ≥2 new bone lesions on bone scan, that have been confirmed to not represent tumor flare, and were persistent for ≥6 weeks. The DOR was calculated using the product-limit (Kaplan-Meier) method for censored data. If a participant had not progressed, the participant was censored at the date of last disease assessment.

Time from randomization to PSA progression. PSA progression date is defined as the date of 1) ≥25% increase and ≥2 ng/mL above the nadir, confirmed by a second value ≥3 weeks later if there is PSA decline from baseline, or 2) ≥25% increase and ≥2 ng/mL increase from baseline beyond 12 weeks if there is no PSA decline from baseline.

Time from randomization to radiographic soft tissue progression per PCWG-modified RECIST 1.1

Time from randomization to pain progression. In this study, pain progression was assessed by participant responses to Item 3 of the BPI-SF and participant AQA Scores which are both assessed by participants daily for 7 consecutive days.

Time from randomization to the first SSRE. SSRE is defined as radiation to prevent or relieve skeletal symptoms, occurrence of new symptomatic pathological fracture, spinal cord compression, or surgery to bone.

An AE is defined as any untoward medical occurrence associated with the use of a drug in a participant, whether or not considered drug related. An AE can therefore be any unfavorable and unintended sign (including an abnormal laboratory finding), symptom, or disease (new or exacerbated) temporally associated with the use of a medicinal product and does not imply any judgment about causality. The number of participants who experienced an AE is presented.

An AE is defined as any untoward medical occurrence associated with the use of a drug in a participant, whether or not considered drug related. An AE can therefore be any unfavorable and unintended sign (including an abnormal laboratory finding), symptom, or disease (new or exacerbated) temporally associated with the use of a medicinal product and does not imply any judgment about causality. The number of participants who discontinued study treatment due to an AE is presented.