Prospective Comparison of ⁶⁸Ga-FAPI versus ¹⁸F-FDG PET/CT for Tumor Staging in Biliary Tract Cancers

Background Gallium 68-labeled fibroblast-activation protein inhibitor (68Ga-FAPI), an imaging agent for detecting tumors, represents a promising alternative to fluorine 18 fluorodeoxyglucose (18F-FDG). Purpose To compare the potential efficacy of 68Ga-FAPI PET/CT with that of 18F-FDG PET/CT for detecting primary tumor and nodal and distant metastases in biliary tract cancer (BTC) and to explore the impact (tumor staging) of 68Ga-FAPI compared with 18F-FDG on clinical management of BTC. Materials and Methods This single-center prospective clinical study was performed at the Affiliated Hospital of Southwest Medical University between June 2020 and June 2021. Participants with BTC underwent both 68Ga-FAPI and 18F-FDG PET/CT. Histopathologic examination, morphologic imaging, and/or follow-up imaging served as the reference standard. The maximum standardized uptake value (SUVmax) of the primary tumor and nodal and distant metastases between 18F-FDG and 68Ga-FAPI PET/CT were compared using the paired-sample t test. Results Eighteen participants with primary or recurrent BTC were evaluated (mean age, 61 years ± 10 [SD]). The sensitivity of 68Ga-FAPI PET/CT was higher than that of 18F-FDG PET/CT for detecting primary tumors (16 of 16 [100%] vs 13 of 16 [81%]), nodal metastases (41 of 42 [98%] vs 35 of 42 [83%]), and distant metastases (99 of 99 [100%] vs 78 of 99 [79%]). 68Ga-FAPI PET/CT resulted in new oncologic findings in 10 of 18 participants and upgraded tumor staging or restaging in five of 18 participants compared with 18F-FDG PET/CT. 68Ga-FAPI PET/CT demonstrated higher sensitivity than 18F-FDG PET/CT in inflammatory processes secondary to tumor-related obstruction (seven of eight [88%] vs one of eight [13%]). 68Ga-FAPI showed lower average SUVmax in inflammatory processes than in oncologic lesions (4.9 ± 2.6 vs 10.0 ± 4.6, respectively; P = .003). Conclusion Gallium 68-labeled fibroblast-activation protein inhibitor PET/CT for tumor staging showed potential for more accurate staging of biliary tract cancer, thereby improving treatment decision making. Clinical trial registration no. ChiCTR2100044131 © RSNA, 2022 Online supplemental material is available for this article. See also the editorial by Choyke in this issue.