Head-to-head Intra-individual Comparison of [(68)Ga]-FAPI and [(18)F]-FDG PET/CT in Patients with Bladder Cancer

AIM/PURPOSE: Fibroblast activation protein-(FAP)-ligands, a novel class of tracers for PET/CT imaging, demonstrated promising results in previous studies in various malignancies compared to standard [(18)F]FDG PET/CT. (68)Ga-labeled fibroblast activation protein inhibitor-([(68)Ga]Ga-DOTA-FAPI)-PET/CT impresses with sharp contrasts in terms of high tumor uptake and low background noise leading to clear delineation. [(18)F]FDG PET/CT has limited accuracy in bladder cancer due to high background signal. Therefore, we sought to evaluate the diagnostic potential of [(68)Ga]FAPI in patients with bladder cancer. MATERIAL AND METHODS: This retrospective analysis consisted of 8 patients (median age 66), 7 of whom underwent both [(68)Ga]FAPI and [(18)F]FDG PET/CT scans with a median time interval of 5 days (range 1–20 days). Quantification of tracer uptake was determined with SUV(max) and SUV(mean). Furthermore, the tumor-to-background ratio (TBR) was derived by dividing the SUV(max) of tumor lesions by the SUV(max) of adipose tissue, skeletal muscle, and blood pool. RESULTS: Overall, 31 metastases were detected in five patients including lymph node metastases (n = 23), bone metastases (n = 4), lung metastases (n = 3), and a peritoneal metastasis (n = 1). In one patient, [(68)Ga]FAPI demonstrated significant uptake in the primary tumor located in the bladder wall. [(68)Ga]FAPI-PET/CT demonstrated significantly higher uptake compared to [(18)F]FDG PET/CT with higher mean SUV(max) (8.2 vs. 4.6; p = 0.01). Furthermore, [(68)Ga]FAPI detected additional 30% (n = 9) lesions, missed by [(18)F]FDG. TBR demonstrated favorable uptake for [(68)Ga]FAPI in comparison to [(18)F]FDG. Significant differences were determined with regard to metastasis/blood pool ([(68)Ga]FAPI 5.3 vs [(18)F]FDG 1.9; p = 0.001). CONCLUSION: [(68)Ga]FAPI-PET/CT is a promising diagnostic radioligand for patients with bladder cancer. This first described analysis of FAP-ligand in bladder cancer revealed superiority over [(18)F]FDG in a small patient cohort. Thus, this so far assumed potential has to be confirmed and extended by larger and prospective studies. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s11307-022-01715-3.