BIMG-12. [18F]FLUCICLOVINE PET TO DISTINGUISH PSEUDOPROGRESSION FROM TUMOR PROGRESSION IN POST-TREATMENT GLIOBLASTOMA

PURPOSE: Differentiation of true tumor progression from pseudoprogression (PsP) is a major unmet need in patients with glioblastoma (GBM). [(18)F]Fluciclovine is a synthetic amino acid PET radiotracer that is FDA approved in the setting of biochemical recurrence in prostate cancer. The aim of this study was to assess the value of [(18)F]Fluciclovine PET in differentiation of true tumor progression and PsP in post-treatment of glioblastoma. METHODS: 15 patients with GBM with new contrast-enhancing lesions or lesions showing increased enhancement (>25% increase) on standard MRI after completion of radiation underwent 60-minutes dynamic [(18)F]Fluciclovine PET imaging. Patients subsequently (within 1 week) underwent resection of the enhancing lesion and the tumor percentage vs treatment-related changes were quantified on histopathology. Patients were considered true tumor progression if tumor represented ≥ 50% of the resected specimen and considered PsP if treatment-related changes represented ≥70% of the resected specimen. Summed 30- to 40-minute post-injection PET images were used to measure SUV(peak), SUV(max), and 50% threshold SUV(mean). RESULTS: 10 patients with true tumor progression and 5 patients with PsP were included. Patients who demonstrated true tumor progression had significantly higher SUV(peak) compared to patients with PsP (5.3±1.4 vs 3.1± 0.9, p=0.002, AUC=0.92, p<0.0001). SUV(peak) cut-off of 3.5 provided 100% sensitivity, 80% specificity and 93% accuracy for differentiation of true tumor progression from PsP. There was a moderate to strong correlation between SUV(peak) and tumor percentage on histopathology (Rho= 0.68, p=0.004). Alternative SUV measures had similar performance. DISCUSSION: Our preliminary results indicated that [(18)F]Fluciclovine PET imaging can accurately differentiate true tumor progression from PsP. Further studies are required to confirm these promising early results and determine the optimal criteria for interpreting [(18)F]Fluciclovine PET to distinguish PsP from true tumor progression.