Phase Ib/II Trial of Pembrolizumab (MK-3475) Combination Therapies in Metastatic Castration-Resistant Prostate Cancer (mCRPC) (KEYNOTE-365)

• Has treated or de novo neuroendocreine metastatic prostate cancer defined by ≥1% neuroendocrine cells that are located in discrete regions of a recent biopsy specimen from a metastasis as determined by the investigational site and confirmed by central histology review prior to enrollment
• Must provide a core or excisional biopsy from soft tissue or a bone biopsy. For de novo metastatic neuroendocrine prostate participants, biopsies must be performed within 1 year of screening. Participants with bone metastasis only must provide an archival tumor tissue specimen.
• Has prostate cancer progression within 6 months prior to screening, as determined by the investigator, by means of one of the following: PSA progression as defined by a minimum of 2 rising PSA levels with an interval of ≥1 week between each assessment where the PSA value at screening should be ≥2 ng/mL; radiographic disease progression in soft tissue based on Response Evaluation Criteria In Solid Tumors Version 1.1 criteria with or without PSA progression; radiographic disease progression in bone defined as the appearance of 2 or more new bone lesions on bone scan with or without PSA progression. Participants with de novo neuroendocrine prostate cancer will not need to provide evidence of progression within 6 months
• Has ongoing androgen deprivation with serum testosterone <50 ng/dL
• Patients receiving bone resorptive therapy must be on stable doses
• ECOG PS 0-1
• Participants must have received prior treatment with androgen deprivation therapy (ADT) for metastatic disease. Participants must also have received prior treatment with an NHA (eg, abiraterone acetate, apalutamide, darolutamide, enzalutamide, or other NHA) or docetaxel for mHSPC or mCRPC. Prior treatment with up to a total of 2 chemotherapies for mCRPC is allowed, as well as up to 2 second-generation hormonal manipulations for mCRPC. Participants who received prior ketoconazole for metastatic disease may be enrolled. Docetaxel for mHSPC is allowed in addition to docetaxel for mCRPC. If docetaxel chemotherapy is used more than once (eg, once for metastatic hormone-sensitive and once for mCRPC), it will be considered as 1 therapy. A limited number of de novo neuroendrcine CRPC patients will be allowed to enroll with consultation with the study team.
• No immunodeficiency or systemic steroid use
• No autoimmune disease within last 2 years
• No known HIV/HBV/HCV
• No known CNS mets
• No superscan bone scan
• No symptomatic ascites or pleural effusion

• Primary
  • Percentage of patients with decrease in PSA by >/=50%
  • AE
  • ORR
• Secondary
  • DCR
  • OS
  • DOR
  • ORR based on PCWG3- modified RECIST
  • Time to PSA progression
  • Radiographic PFS
  • Composite Response Rate (PFS, PSA)