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

Abstract

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 [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. Material and Methods 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. 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, [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). Conclusion [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.

PET Imaging in Bladder Cancer: An Update and Future Direction

“…Generally, [ 68 Ga]Ga-FAPI-46-PET/CT demonstrated significantly higher uptake compared to [ 18 F]FDG PET/CT, with higher mean SUVmax (8.2 vs. 4.6; p = 0.01) and higher tumor-to-background ratio (metastasis/blood pool 5.3 with [ 68 Ga]Ga-FAPI-46 vs. 1.9 for [ 18 F]FDG; p = 0.001). Additionally, [ 68 Ga]Ga-FAPI-46 detected an additional 30% (n = 9) of lesions missed by [ 18 F]FDG [65]. Thus, early study results suggest that [ 68 Ga]Ga-FAPI-46PET may be useful in the management of BC.…”

PET in bladder cancer imaging

“…FAPI-PET exhibited a higher uptake in the primary tumour located in the bladder wall in comparison to FDG. In addition, 30% more lesions were detected with FAPI [22]. In a further study by Unterrainer et al , 15 patients with high-grade urothelial carcinoma underwent 68Ga-FAPI-PET/CT imaging with the primary tumour showing the highest uptake, followed by lymph node metastases.…”

Primäre und sekundäre Lebertumore – aus Sicht der Nuklearmedizin

“…Aufgrund der im Vergleich sehr hohen Urinaktivität zeigt die FAPI-PET im Vergleich zur FDG-PET darüber hinaus deutliche Vorteile in der Bildgebung von Urothelkarzinomen mit einem hohen Tumor-zu Nicht-Tumor-Verhältnis (▶ Abb. 7) [85].…”