Phase 2 Study of Neoadjuvant PEMbrolizumab Before Radical PROstatectomy in High-risk Prostate Cancer Patients

Inclusion Criteria: 1. Male participants who are at least 18 years of age on the day of signing informed consent with histologically confirmed diagnosis of prostate cancer. 2. The participant (or legally acceptable representative if applicable) provides written informed consent for the trial. 3. PCa detected at prostate biopsy (random biopsy with at least 12 cores taken ± target biopsy according to the mpMRI findings). 4. The participant should be fit and planned for RP and ePLND (according to clinical guidelines). 5. The participant should be affected by high-risk PCa defined as PSA ≥20 ng/ml and/or clinical stage ≥T3 at digital rectal examination and/or biopsy grade group 4-5. 6. No evidence of lymph node invasion (cN0) and metastatic disease (M0) at imaging (mpMRI, PSMA-PET/CT and bone scan). 7. Have provided archival tumour tissue sample or newly obtained core or excisional biopsy of a tumour lesion not previously irradiated. Formalin-fixed, paraffin embedded (FFPE) tissue blocks are preferred to slides. Newly obtained biopsies are preferred to archived tissue. 8. Have an Eastern Cooperative Oncology Group (ECOG) performance status of 0 to 1. Evaluation of ECOG is to be performed within 7 days prior to the date of allocation. 9. Have adequate organ function as defined in the following table (Table 1). Specimens must be collected within 10 days prior to the start of study treatment. 10. Willingness to use contraception during study treatment Exclusion Criteria: 1. 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, OX-40, CD137). 2. Has received prior systemic anti-cancer therapy including investigational agents within 4 weeks prior to allocation. 3. Has received prior surgery or radiotherapy for PCa. 4. Has received a live vaccine within 30 days prior to the first dose of study drug. Examples of live vaccines include, but are not limited to, the following: measles, mumps, rubella, varicella/zoster (chicken pox), yellow fever, rabies, Bacillus Calmette-Guérin (BCG), and typhoid vaccine. Seasonal influenza vaccines for injection are generally killed virus vaccines and are allowed; however, intranasal influenza vaccines (eg, FluMist®) are live attenuated vaccines and are not allowed. 5. Is currently participating in 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. Note: Participants who have entered the follow-up phase of an investigational study may participate as long as it has been 4 weeks after the last dose of the previous investigational agent. 6. Has a diagnosis of immunodeficiency or is receiving chronic systemic steroid therapy (in dosing exceeding 10 mg daily of prednisone equivalent) or any other form of immunosuppressive therapy within 7 days prior to the first dose of study drug. 7. Has a known additional malignancy that is progressing or has required active treatment within the past 3 years. Note: Participants with basal cell carcinoma of the skin, squamous cell carcinoma of the skin, or carcinoma in situ (e.g. breast carcinoma, cervical cancer in situ) that have undergone potentially curative therapy are not excluded. 8. Has known active CNS metastases and/or carcinomatous meningitis. Participants with previously treated brain metastases may participate provided they are radiologically stable, i.e. without evidence of progression for at least 4 weeks by repeat imaging (note that the repeat imaging should be performed during study screening), clinically stable and without requirement of steroid treatment for at least 14 days prior to first dose of study treatment. 9. 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. 10. Has a history of (non-infectious) pneumonitis that required steroids or has current pneumonitis. 11. Has an active infection requiring systemic therapy. 12. Has a known history of Human Immunodeficiency Virus (HIV). Note: No HIV testing is required unless mandated by local health authority. 13. Has a known history of hepatitis infection (defined as having a positive hepatitis B surface antigen \[HBsAg\] test at screening) or hepatitis C. Patients with past hepatitis B virus (HBV) infection or resolved HBV infection (defined as having a negative HBsAg test and a positive antibody to hepatitis B core antigen \[anti-HBc\] antibody test) are eligible. Patients positive for hepatitis C virus (HCV) antibody are eligible only if polymerase chain reaction (PCR) is negative for HCV RNA. 14. Has a known history of active TB (Bacillus Tuberculosis). 15. 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. 16. Has known psychiatric or substance abuse disorders that would interfere with cooperation with the requirements of the trial. 17. Has a history or current evidence of unstable cardiovascular disease 18. Has a history or current evidence of congestive heart failure 19. Severe hypersensitivity (Grade 3) to pembrolizumab and/or any of its excipients