Background
Gallium 68 (68Ga)-labeled fibroblast activation
protein inhibitor (FAPI) has been proposed as a potential radiotracer for visualizing cancerous lesions, but its utility for identifying metastatic differentiated
thyroid cancer (DTC) is not well established in the literature. Purpose To evaluate the clinical utility of
68Ga-FAPI PET/CT for detecting metastatic DTC and to compare the results with those of
fluorine 18 (
18F) fluorodeoxyglucose (FDG) PET/CT. Materials and Methods Participants with clinically suspected or confirmed metastatic DTC were prospectively enrolled and underwent paired
68Ga-FAPI and
18F-FDG PET/CT from May to August 2020. Histopathologic results and clinical follow-up (mean, 12 months ± 0.7 [SD]; range, 11-13 months) were used as reference standards for the final diagnosis.
18F-FDG and
68Ga-FAPI uptake was compared by using the Wilcoxon signed-rank test. The McNemar test was used to compare the diagnostic accuracy of the two techniques, and the influence of various clinicopathologic characteristics on
18F-FDG and
68Ga-FAPI uptake was evaluated with Mann-Whitney and Kruskal-Wallis tests. Results In total, 35 participants (median age, 44 years; IQR, 28-58 years; 18 [51%] men) were evaluated. In all 35 participants, the 68Ga-FAPI-derived maximum standardized uptake value (SUVmax) was higher than the 18F-FDG-derived SUVmax in the metastatic lateral compartment (6.0 vs 3.5; P = .001), axillary (8.5 vs 4.3; P = .01), mediastinal lymph nodes (9.1 vs 5.0; P = .001), and pulmonary
metastases (1.7 vs 1.1; P = .004).
68Ga-FAPI PET/CT had a higher sensitivity than
18F-FDG PET/CT for depicting neck lesions (83% [65 of 78; 95% CI: 73, 90] vs 65% [51 of 78; 95% CI: 54, 75], P = .01) and distant
metastases (79% [87 of 110; 95% CI: 71, 86] vs 59% [65 of 110; 95% CI: 50, 68], P < .001). Conclusion
Gallium 68-labeled fibroblast activation
protein inhibitor PET/CT was superior to
fluorine 18 fluorodeoxyglucose PET/CT for depicting metastatic differentiated
thyroid cancer, especially in lymph nodes and pulmonary
metastases. Published under a CC BY 4.0 license. Online supplemental material is available for this article.