A Pilot Presurgical Trial of REGN5678 (Anti-PSMA x CD28) in Patients With High-risk, Localized Prostate Cancer Followed by Radical Prostatectomy

This study tests a drug called REGN5678 — which activates the immune system to attack prostate cancer cells — in men with high-risk, localized (non-metastatic) prostate cancer before they undergo surgery (radical prostatectomy). The goal is to see if the immune treatment can shrink or weaken the tumor before removal. **You may be eligible if...** - You are a man 18 or older with high-grade prostate cancer (Gleason score 8 or higher) confirmed by biopsy - Your cancer is localized or locally advanced but appears operable (no distant spread) - You have not received any prior treatment for prostate cancer - Your overall health is good (ECOG 0 or 1) - Your blood counts and organ function are within required ranges - You are willing to use contraception during treatment and for 3 months after **You may NOT be eligible if...** - You have previously received hormone therapy, surgery, or radiation for prostate cancer - You are enrolled in another interventional clinical trial - You have a known active autoimmune disease (except mild conditions like vitiligo or well-controlled thyroid disease) - You have active serious infection (HIV with detectable viral load, active hepatitis, fungal infection) - You have a history of significant heart disease (heart attack, serious arrhythmia, stroke, or heart failure) within the past 6 months - You have a history of interstitial lung disease or active pneumonitis Talk to your doctor to see if this trial is right for you.