99mTc-depreotide scintigraphy versus 18F-FDG-PET in the diagnosis of radioiodine-negative thyroid cancer

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

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

Patients and methods: Ten radioiodine-negative patients with suspicion of recurrent or metastatic thyroid Cancer were investigated with (99m)Tc-depreotide scintigraphy and (18)F-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 (99m)Tc-depreotide scintigraphy and in seven patients (70%) with (18)F-FDG-PET. (99m)Tc-depreotide scintigraphy gave better results in terms of detection of recurrent or metastatic disease compared with (18)F-FDG-PET in three patients, whereas (18)F-FDG-PET identified metastatic disease that was not seen with (99m)Tc-depreotide in only one patient. (99m)Tc-depreotide scintigraphy portrayed lesions in three patients with negative morphological imaging.

Conclusions: Results indicate a potential value of (99m)Tc-depreotide scintigraphy for the diagnosis of thyroid Cancer in the setting of detectable thyroglobulin and negative radioiodine scan. Furthermore, (99m)Tc-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.