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 [18F]FDG PET/CT. 68Ga-labeled fibroblast activation protein inhibitor-([68Ga]Ga-DOTA-FAPI)-PET/CT impresses with sharp contrasts in terms of high tumor uptake and low background noise leading to clear delineation. [18F]FDG PET/CT has limited accuracy in bladder cancer due to high background signal. Therefore, we sought to evaluate the diagnostic potential of [68Ga]FAPI in patients with bladder cancer.
This retrospective analysis consisted of 8 patients (median age 66), 7 of whom underwent both [68Ga]FAPI and [18F]FDG PET/CT scans with a median time interval of 5 days (range 1-20 days). Quantification of tracer uptake was determined with SUVmax and SUVmean. Furthermore, the tumor-to-background ratio (TBR) was derived by dividing the SUVmax of tumor lesions by the SUVmax of adipose tissue, skeletal muscle, and blood pool.
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, [68Ga]FAPI demonstrated significant uptake in the primary tumor located in the bladder wall. [68Ga]FAPI-PET/CT demonstrated significantly higher uptake compared to [18F]FDG PET/CT with higher mean SUVmax (8.2 vs. 4.6; p = 0.01). Furthermore, [68Ga]FAPI detected additional 30% (n = 9) lesions, missed by [18F]FDG. TBR demonstrated favorable uptake for [68Ga]FAPI in comparison to [18F]FDG. Significant differences were determined with regard to metastasis/blood pool ([68Ga]FAPI 5.3 vs [18F]FDG 1.9; p = 0.001).
[68Ga]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 [18F]FDG in a small patient cohort. Thus, this so far assumed potential has to be confirmed and extended by larger and prospective studies.
Molecular imaging and biology. 2022 Mar 29 [Epub]
E Novruzov, K Dendl, H Ndlovu, P L Choyke, M Dabir, M Beu, F Novruzov, E Mehdi, F Guliyev, S A Koerber, I Lawal, G Niegisch, J Debus, U Haberkorn, M Sathekge, F L Giesel
Department of Nuclear Medicine, Medical Faculty, Heinrich-Heine-University, University Hospital Dusseldorf, Dusseldorf, Germany., Department of Nuclear Medicine, University of Pretoria & Steve Biko Academic Hospital, Pretoria, South Africa., Molecular Imaging Branch, National Cancer Institute, Bethesda, MD, USA., Nuclear Medicine Department, National Centre of Oncology, Baku, Azerbaijan., Department of Uro-Oncology, National Centre of Oncology, Baku, Azerbaijan., Department of Radiation Oncology, Heidelberg University Hospital, Heidelberg, Germany., Department of Urology, University Hospital Duesseldorf, Duesseldorf, Germany., Department of Nuclear Medicine, University Hospital Heidelberg, Heidelberg, Germany., Department of Nuclear Medicine, Medical Faculty, Heinrich-Heine-University, University Hospital Dusseldorf, Dusseldorf, Germany. .