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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

Vural, Gulin Ucmak MD*; Akkas, Burcu Esen MD*; Ercakmak, Nur MD*; Basu, Sandip MD; Alavi, Abass MD, PhD

Clinical Nuclear Medicine:
doi: 10.1097/RLU.0b013e31825b2057
Original Articles
Abstract

Aims: This study aimed (a) to determine the clinical and histopathologic factors that are related to FDG avidity in the recurrence/metastases of patients with differentiated thyroid carcinoma (DTC) who present with elevated thyroglobulin (Tg) levels and negative 131I whole-body scans (WBSs), (b) to clarify Tg cutoff levels in this setting, and (c) to evaluate the impact of PET/CT on patient management strategies and hence to critically look into the importance of PET/CT in combination with Tg in clinical decision making.

Methods: A total of 105 patients with DTC with negative 131I WBS and neck ultrasound but elevated Tg, who underwent FDG PET/CT for the suspicion of recurrent/metastatic disease, were included in this analysis. All patients had previously undergone total thyroidectomy and radioiodine ablation/therapy. PET/CT results were correlated with Tg levels and clinical and histopathologic characteristics of the primary tumor compared with the follow-up data.

Results: PET/CT was true-positive in 69 patients (of which 23 had surgically amenable disease), true-negative in 20, false-positive in 6 patients and false-negative in 10 patients. Extrathyroidal spread was an independent risk factor related to FDG-avid recurrence. Tumor size was significantly higher in PET-positive patients than others, 2.25 (1.8) versus 1.5 (1.1) cm, P = 0.02. Significant correlation was observed between PET positivity and high Tg levels (P = 0.0001). Receiver operating characteristic curve analysis demonstrated a Tg cutoff of 1.9 ng/mL under thyroid-stimulating hormone suppression, 38.2 ng/mL with thyroid-stimulating hormone stimulation. Among PET-negative patients, no recurrence was detected in patients with undetectable/suppressible Tg in on-therapy state.

Conclusions: PET positivity correlated with extrathyroidal spread, and elevated Tg in recurrent/metastatic DTC. FDG PET/CT in combination with Tg levels was crucial in defining management strategies in patients with DTC with negative 131I WBS. A negative FDG PET/CT scan predicts a favorable prognosis and lack of recurrence on follow-up in patients with “suppressible Tg” levels in the on-therapy state despite significant elevation of Tg in the off-therapy state.

Author Information

From the *Department of Nuclear Medicine, Ankara Oncology Education and Research Hospital, Ankara, Turkey; †Radiation Medicine Centre, Bhabha Atomic Research Centre, TMH Annexe, Parel, Mumbai, India; and ‡Department of Radiology, Hospital of the University of Pennsylvania, Philadelphia, PA.

Received for publication December 15, 2011; revision accepted March 5, 2012.

Conflicts of interest and sources of funding: none declared.

Reprints: Burcu Esen Akkas, MD, Department of Nuclear Medicine, Ankara Oncology Research and Training Hospital, Ankara, Turkey. E-mail: drgulin@yahoo.com.

© 2012 Lippincott Williams & Wilkins, Inc.