Biomarkers for Neoadjuvant Pembrolizumab in Non-Metastatic Prostate Cancer Positive by 18FDG-PET Scanning

Inclusion Criteria: * Male Age≥ 18 years old * Non-metastatic prostate cancer with histologically confirmed Gleason sum ≥8 * Eligible for radical prostatectomy with a delay of 6 to 9 weeks * Intraprostatic maximum standardized uptake value (SUVmax) ≥4 at 18-FDG-PET/CT exam. * Not be castrated or under androgen deprivation therapy * Not have received prior neo adjuvant hormonotherapy. * Provided archival formalin-fixed, paraffin embedded tumor biopsy of the prostate tumor lesion not previously irradiated * Performance status of Eastern Cooperative Oncology Group 0 to 1 * Adequate organ function Exclusion Criteria: * Has received prior therapy with an anti-PD-1, anti-PD-L1, or anti-PD-L2 agent or with an agent directed to another stimulatory or co-inhibitory T-cell receptor (eg, CTLA-4 (Cytotoxic T-lymphocyte-Associated Protein 4), OX-40, CD137). * Has received prior systemic anti-cancer therapy including investigational agents within 4 weeks prior to allocation. * Has received prior radiotherapy to the prostate or other organs within 2 weeks of start of study treatment. * Has received a live vaccine within 30 days prior to the first dose of study drug. * Is participating or has participated in a study of an investigational agent or has used an investigational device within 4 weeks prior to the first dose of study treatment. * Has a diagnosis of immunodeficiency or is receiving chronic systemic steroid therapy or any other form of immunosuppressive therapy within 7 days prior to the first dose of study drug * Other primary cancer within 3 years * Has severe hypersensitivity (≥Grade 3) to pembrolizumab and/or any of its excipients. * Has active autoimmune disease that has required systemic treatment in the past 2 years (i.e. with use of disease modifying agents, corticosteroids or immunosuppressive drugs). Replacement therapy (eg., thyroxine, insulin, or physiologic corticosteroid replacement therapy for adrenal or pituitary insufficiency, etc.) is not considered a form of systemic treatment. * Has a history of (non-infectious) pneumonitis that required steroids or has current pneumonitis. * Has an active infection requiring systemic therapy. * Has a known history of Human Immunodeficiency Virus (HIV). * Has a known history of Hepatitis B or known active Hepatitis C virus infection. Note: no testing for Hepatitis B and Hepatitis C is required unless mandated by local health authority. * Has a history or current evidence of any condition, therapy, or laboratory abnormality that might confound the results of the study, interfere with the subject's participation for the full duration of the study, or is not in the best interest of the subject to participate, in the opinion of the treating investigator. * Has known psychiatric or substance abuse disorders that would interfere with cooperation with the requirements of the trial. * Is expecting to father children within the projected duration of the study, starting with the screening visit through the date of prostatectomy.