Abemaciclib Before 177Lu-PSMA-617 for the Treatment of Metastatic Castrate Resistant Prostate Cancer

This trial is testing whether a drug called abemaciclib (which slows cancer cell growth) can help prepare the body to respond better to a radioactive treatment called lutetium-177 PSMA-617 (Lu-PSMA) in men with advanced prostate cancer that has stopped responding to hormone therapy. The theory is that abemaciclib may make prostate cancer cells express more of a target (PSMA) that the radioactive drug attaches to. **You may be eligible if...** - You are 18 or older with confirmed metastatic castration-resistant prostate cancer (prostate cancer that kept growing despite hormone therapy) - Your cancer shows the PSMA target on a specialized PET scan - You have already tried at least one newer hormone therapy (like enzalutamide or abiraterone) - Your testosterone is at castrate levels (very low) - You are in good general health (ECOG 0–2) with at least 6 months life expectancy - Your blood counts and organ function are adequate **You may NOT be eligible if...** - You have certain types of prostate cancer other than adenocarcinoma - You have significant problems with your salivary glands - You have had prior treatment with Lu-PSMA or abemaciclib - You have active or uncontrolled infection, uncontrolled diabetes, or other serious medical conditions - You have significant kidney problems Talk to your doctor to see if this trial is right for you.