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.

Keywords

papillary thyroid cancer - radioiodine - PET CT scan - Fibroblast activation protein

Publication History

Received: 05 April 2023

Accepted after revision: 25 September 2023

Article published online:
08 January 2024

• References

• 1 Cho SW. et al. Long-term prognosis of differentiated thyroid cancer with lung metastasis in Korea and its prognostic factors. Thyroid 2014; 24 (02) 277-286
• 2 Nervo A. et al. Bone metastases from differentiated thyroid carcinoma: current knowledge and open issues. J Endocrinol Invest 2021; 44 (03) 403-419
• 3 Asa S. et al. The role of FDG-PET/CT in differentiated thyroid cancer patients with negative iodine-131 whole-body scan and elevated anti-Tg level. Ann Nucl Med 2014; 28 (10) 970-979
• 4 Bannas P. et al. Can (18)F-FDG-PET/CT be generally recommended in patients with differentiated thyroid carcinoma and elevated thyroglobulin levels but negative I-131 whole body scan?. Ann Nucl Med 2012; 26 (01) 77-85
• 5 Kim SJ. et al. Diagnostic performance of PET in thyroid cancer with elevated anti-Tg Ab. Endocr Relat Cancer 2018; 25 (06) 643-652
• 6 Ora M. et al. The Utility of (18)F-Fluorodeoxyglucose Positron Emission Tomography/Computed Tomography in Differentiated Thyroid Cancer Patients with Biochemical Recurrence and Negative Whole-Body Radioiodine Scintigraphy and Evaluation of the Possible Role of a Limited Regional Scan. Indian J Nucl Med 2020; 35 (03) 203-209
• 7 Trybek T. et al. The role of 18F-Fluorodeoxyglucose Positron Emission Tomography in patients with suspected recurrence or metastatic differentiated thyroid carcinoma with elevated serum thyroglobulin and negative I-131 whole body scan. Nucl Med Rev Cent East Eur 2014; 17 (02) 87-93
• 8 Vural GU. et al. Prognostic significance of FDG PET/CT on the follow-up of patients of differentiated thyroid carcinoma with negative 131I whole-body scan and elevated thyroglobulin levels: correlation with clinical and histopathologic characteristics and long-term follow-up data. Clin Nucl Med 2012; 37 (10) 953-959
• 9 Zhu L. et al. Cancer-associated fibroblasts in papillary thyroid carcinoma. Clinical and experimental medicine 2023;
• 10 Huang R. et al. FAPI-PET/CT in Cancer Imaging: A Potential Novel Molecule of the Century. Front Oncol 2022; 12: 854658
• 11 Kratochwil C. et al. (68)Ga-FAPI PET/CT: Tracer Uptake in 28 Different Kinds of Cancer. J Nucl Med 2019; 60 (06) 801-805
• 12 Sgouros G. et al. Radiopharmaceutical therapy in cancer: clinical advances and challenges. Nature Reviews Drug Discovery 2020; 19 (09) 589-608
• 13 Fu H. et al. FAP-Targeted Radionuclide Therapy of Advanced Radioiodine-Refractory Differentiated Thyroid Cancer With Multiple Cycles of 177 Lu-FAPI-46. Clin Nucl Med 2022; 47 (10) 906-907
• 14 Fu H. et al. 68)Ga Fibroblast Activation Protein Inhibitor PET/CT in the Detection of Metastatic Thyroid Cancer: Comparison with (18. Radiology 2022; 304 (02) 397-405
• 15 Wu J, Ou L, Zhang C. Comparison of (68)Ga-FAPI and (18)F-FDG PET/CT in metastases of papillary thyroid carcinoma. Endocrine 2021; 73 (03) 767-768
• 16 Papaioannou C. et al. Lymph Node Metastasis and Extrathyroidal Extension in Papillary Thyroid Microcarcinoma in Cyprus: Suspicious Subcentimeter Nodules Should Undergo FNA When Multifocality is Suspected. J Thyroid Res 2020; 2020: 3567658
• 17 Song RY, Kim HS, Kang KH. Minimal extrathyroidal extension is associated with lymph node metastasis in single papillary thyroid microcarcinoma: a retrospective analysis of 814 patients. World Journal of Surgical Oncology 2022; 20 (01) 170
• 18 Mu X. et al. (18)F]FAPI-42 PET/CT in differentiated thyroid cancer: diagnostic performance, uptake values, and comparison with 2-[(18)F. Eur J Nucl Med Mol Imaging 2023; 50 (04) 1205-1215