18 F-FPPRGD 2 PET/CT in patients with metastatic renal cell cancer Abstract Purpose The usefulness of positron emission tomography/computed tomography (PET/CT) using (18F)-2-fluoropropionyl-labeled PEGylated dimeric arginine-glycine-aspartic acid peptide [PEG3-E{c(RGDyk)}2] (18F-FPPRGD2) in patients with metastatic renal cell cancer (mRCC) has not been evaluated; therefore, we were prompted to conduct this pilot study. Methods Seven patients with mRCC were enrolled in this prospective study. 18F-FPPRGD2 and 2-deoxy-2-(18F)fluoro-D-glucose (18F-FDG) PET/CT images were evaluated in a per-lesion analysis. Maximum standardized uptake value (SUVmax) and tumor-to-background ratio (T/B) were measured for all detected lesions, both before and after starting antiangiogenic therapy. Results Sixty lesions in total were detected in this cohort. SUVmax from 18F-FPPRGD2 PET/CT was lower than that from 18F-FDG PET/CT (4.4 ± 2.9 vs 7.8 ± 5.6, P < 0.001). Both SUVmax and T/B from 18F-FPPRGD2 PET/CT decreased after starting antiangiogenic therapy (SUVmax, 4.2 ± 3.2 vs 2.6 ± 1.4, P = 0.003; T/B, 3.7 ± 3.2 vs 1.5 ± 0.8, P < 0.001). Average changes in SUVmax and T/B were − 29.3 ± 23.6% and − 48.1 ± 28.3%, respectively. Conclusions 18F-FPPRGD2 PET/CT may be an useful tool for monitoring early response to antiangiogenic therapy in patients with mRCC. These preliminary results need to be confirmed in larger cohorts.