FAPI PET/CT provides higher uptake and better target to back ground in recurrent and metastatic tumors of patients with Iodine refractory papillary thyroid cancer compared with FDG PET CT

Abstract

Purpose The role of fibroblast activation protein inhibitor (FAPI) PET CT scan is not well documented in papillary thyroid cancer (PTC) patients. Patients with radioiodine refractory PTC and high thyroglobulin levels need PET/CT scan which is generally done by 18F FDG. In the current study, the diagnostic performance of 68Ga FAPI and FDG PET/CT scans were compared head to head in patients with radioiodine refractory PTC. Method Fourteen patients with negative whole body Iodine scans and high thyroglobulin levels underwent whole body PET scans with, respectively, 120–310 and 145–370 MBq 68Ga FAPI-46 and 18F FDG. SUVmax of the back ground in the blood pool and liver and the hottest, largest and average neck, mediastinum, lung and bone lesions were calculated and compared. Result Ten patients had at least one active (SUVmax>blood pool) lesion similarly in two scans. The liver and blood pool SUVmax values were 1.25(0.2) and 1.7(0.2) in FAPI and 2.65(0.2) and 2.0(0.2) in FDG PET images, respectively. The difference was significant (p=0.001). Standard SUV of the hottest lesion to liver was above 3 in all FAPI scans but in half of FDG scans. Target lesion number and intensity were similar between two PET studies but in a patient out of 5 pulmonary metastatic patients, pulmonary nodules were negative (SUVmax=0.9) in FDG while positive (SUVmax= 3.8) in FAPI images (i.e. 20% patient upstaged). Conclusion FAPI accumulates in the recurrent and metastatic lesions of patients with Iodine refractory PTC at least as well as FDG with particular privileges as lower injected activity and lower back ground.

FAPi-Based Agents in Thyroid Cancer: A New Step towards Diagnosis and Therapy? A Systematic Review of the Literature

“…The standard SUV of the hottest lesion to the liver was above 3 in all FAPI scans but in half of the FDG scans. The target lesion number and intensity were similar between the two PET studies, but in one out of five pulmonary metastatic patients, the pulmonary nodules were negative (SUVmax = 0.9) in the FDG but positive (SUVmax = 3.8) in the FAPI images, leading to up to 20% patient being upstaged [44].…”

“…In a recent comparative study from Nourbakhsh et al [44], fourteen PTC patients with negative whole-body iodine scans and high Tg levels underwent PET/CT with both [ 68 Ga]Ga-FAPI-46 and [ 18 F]FDG. The background SUVmax in the blood pool and liver; the hottest, largest, and average values in the neck; and the mediastinum, lung, and bone lesions were calculated and compared.…”

Advances in the Development of Positron Emission Tomography Tracers for Improved Detection of Differentiated Thyroid Cancer

“…In a study by Nourbakhsh et al (2024) involving 14 patients with TENIS syndrome, the performance of 18 F-FAPI-46 was compared to 18 F-FDG PET/CT imaging [28]. All the patients exhibited active lesions in both scans, with significantly lower SUVmax values in the liver and blood pool for the FAPI compared to the 18 F-FDG PET/CT (p = 0.001).…”