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

• Has treated or de novo neuroendocrine  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 RECIST 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, etc.) 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 patients may enroll after consultation with the sponsor.
• No prior treatment with Radium or Lutitium
• No immunodeficiency or systemic steroids
• No autoimmune disease within the last 2 years
• No known HIV/HBV/HCV
• No known CNS mets
• No superscan bone scan
• No active cardiovascular disease
• No active hemoptysis

• Primary
  • Percentage of patients with decrease of >/=50% in PSA
  • AE
  • ORR
• Secondary
  • DCR
  • OS
  • DoR
  • ORR based on PCWG-3 RECIST
  • Time to PSA progression
  • Radiographic PFS
  • Composite Response rate (PSA, PFS)