F-18-Fdg-Pet/Ct Imaging To Assess Response To Treatment With Cabozantinib At 4 Weeks Versus 8 Weeks Of Therapy In Patients (Pts) With Metastatic Urothelial Carcinoma (Muc).

317Background: This study investigates whether changes in 18F-FDG-PET/CT correlate with response to cabozantinib at an early time point (4 wks) versus the conventional time point of restaging (8 wks) in pts with mUC, using Positron Emission Tomography Response Criteria in Solid Tumors (PERCIST). Methods: 68 pts with mUC in a single arm phase II clinical trial of cabozantinib underwent FDG-PET/CT scans at baseline, 4 and 8 wks. Up to 5 lesions with the highest Standard Uptake Value (SUV) were designated as target lesions. Response was determined using 2 versions of PERCIST (1 lesion vs top 5 lesions with highest FDG uptake) for FDG-PET/CT at 4 and 8 wks. PERCIST response classifications were compared to RECIST v1.1 at 8 wks. Results: 54 pts had evaluable disease. The single lesion 4 wk response by PERCIST showed 40% partial metabolic response (PMR), 33% stable metabolic disease (SMD), and 27% progressive metabolic disease (PMD). The single lesion 8 wk response by PERCIST showed 31% PMR, 31% SMD, and 38% PM...