A Pilot Study to Assess the Clinical Utility of 18F-Fluciclovine (Axumin) PET-CT for Detecting True-versus Pseudo-Progression of Brain Metastases on Immunotherapy

This pilot study is testing whether a special PET scan using a tracer called 18F-fluciclovine (Axumin) can help doctors tell the difference between true cancer progression and pseudoprogression (when a tumor looks like it's growing on a scan but is actually the immune system reacting to immunotherapy) in patients with brain metastases receiving immunotherapy. **You may be eligible if...** - You are 18 or older - You have documented brain metastases (cancer that spread to the brain) - You are currently receiving immunotherapy for your cancer - At least one brain lesion is suspected to be pseudoprogression (not definite tumor growth) on a standard scan - You are in reasonably good health (ECOG ≤2) with a life expectancy of at least 3 months - You are willing to undergo a follow-up Axumin PET scan within ~60 days **You may NOT be eligible if...** - You are under 18 - You have no brain metastases - You are not currently on immunotherapy - You are unable to undergo the additional PET scan or follow-up visits Talk to your doctor to see if this trial is right for you.