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^99mTc-Depreotide Scintigraphy Versus ¹⁸F-FDG-PET in the Diagnosis of Radioiodine-Negative Thyroid Cancer

University Clinic for Nuclear Medicine (M.R., M.Ga., D.H., I.V.), A-6020 Innsbruck, Austria; Institute of Nuclear Medicine (M.R., M.Gr.), Hietzing Hospital, A-1130 Vienna, Austria; and Department of Nuclear Medicine (S.L.), Medical University of Vienna, A-1090 Vienna, Austria

Address all correspondence and requests for reprints to: Dr. Margarida Rodrigues, University Clinic for Nuclear Medicine, Anichstrasse 35, A-6020 Innsbruck, Austria. E-mail: rodriguesradischat{at}hotmail.com.

Background: Papillary and follicular thyroid cancer were found recently to express somatostatin receptors (SSTRs). ^99mTc-depreotide binds with high affinity to SSTRs 2, 3, and 5.

Aim: The aim of this study was to evaluate the feasibility of applying ^99mTc-depreotide scintigraphy to search for radioiodine-negative thyroid cancer; comparison is made to a standard approach using ¹⁸F-fluorodeoxyglucose-positron emission tomography (¹⁸F-FDG-PET).

Patients and Methods: Ten radioiodine-negative patients with suspicion of recurrent or metastatic thyroid cancer were investigated with ^99mTc-depreotide scintigraphy and ¹⁸F-FDG-PET, performed with a time interval that ranged from 1–8 wk. Locoregional recurrence and metastases were confirmed by ultrasonography and/or computed tomography, together with cytology or histological examination in selected cases.

Results: True-positive results were obtained in nine patients (90%) with ^99mTc-depreotide scintigraphy and in seven patients (70%) with ¹⁸F-FDG-PET. ^99mTc-depreotide scintigraphy gave better results in terms of detection of recurrent or metastatic disease compared with ¹⁸F-FDG-PET in three patients, whereas ¹⁸F-FDG-PET identified metastatic disease that was not seen with ^99mTc-depreotide in only one patient. ^99mTc-depreotide scintigraphy portrayed lesions in three patients with negative morphological imaging.

Conclusions: Results indicate a potential value of ^99mTc-depreotide scintigraphy for the diagnosis of thyroid cancer in the setting of detectable thyroglobulin and negative radioiodine scan. Furthermore, ^99mTc-depreotide adds complementary information regarding the SSTR status of lesions, which may be helpful for individual therapy planning in this group of patients, which is hard to manage clinically.