Merck (MSD) on Tuesday announced that it will stop the Phase 3 KEYLYNK-010 trial investigating KEYTRUDA, Merck’s anti-PD-1 therapy, in combination with LYNPARZA, a PARP inhibitor, for the treatment of patients with metastatic castration-resistant prostate cancer (mCRPC) who progressed after treatment with chemotherapy and either abiraterone acetate or enzalutamide.

Merck is discontinuing the study following the recommendation of an independent Data Monitoring Committee (DMC) after the DMC reviewed data from a planned interim analysis. At the interim analysis, the combination of KEYTRUDA and LYNPARZA did not demonstrate a benefit in overall survival (OS), one of the study’s dual primary endpoints, compared to the control arm of either abiraterone acetate or enzalutamide.

The trial’s other dual primary endpoint, radiographic progression-free survival (rPFS), was evaluated at an earlier interim analysis and did not demonstrate improvement compared to the control arm. The safety profile of KEYTRUDA in combination with LYNPARZA in this trial was consistent with that observed in previously reported studies for the individual therapies; however, the combination was associated with a higher incidence of grade 3-5 adverse events and drug-related serious adverse events, compared to the control arm. Merck will inform study investigators of the recommendation from the DMC and advise patients in the study to speak to their physician regarding treatment. Data from this study will be presented at an upcoming scientific congress.

Dr. Roy Baynes, senior vice president and head of global clinical development, chief medical officer, Merck Research Laboratories said:

There remains a significant unmet need for patients diagnosed with advanced prostate cancer, who have a poor prognosis after not responding to initial therapy. Merck continues to evaluate the combination of KEYTRUDA and LYNPARZA in a range of cancers and to research other KEYTRUDA-based combinations for patients with advanced prostate cancer. We are grateful to the patients, their families and the investigators who made this study possible.

Merck has an extensive clinical development program in prostate cancer evaluating KEYTRUDA as monotherapy and in combination with LYNPARZA and other anti-cancer therapies.

In collaboration with AstraZeneca, Merck is evaluating LYNPARZA in combination with abiraterone in the Phase 3 PROpel trial. As previously AstraZeneca and Merck reported, Lynparza has been approved in the US for the adjuvant treatment of patients with germline BRCA-mutated (gBRCAm) HER2-negative high-risk early breast cancer.