Review of Fluorine-18-2-Fluoro-2-Deoxy-D-Glucose Positron Emission Tomography (FDG-PET) in the Follow-Up of Medullary and Anaplastic Thyroid Carcinomas
October 2005, Vol. 12, No. 4
Authors: Nasim Khan, MD, PhD; Noboru Oriuchi, MD, PhD; Tetsuya Higuchi, MD, PhD; Keigo Endo, MD, PhD
Abstract
Background: The goal of posttreatment follow-up for medullary and anaplastic thyroid cancer (MTC and ATC) is the early diagnosis of recurrence or metastases. However, routine follow-up protocols, including physical examination and clinically oriented investigations, are not standardized, and their sensitivity in accurately detecting recurrent or metastatic disease is often suboptimal. A valuable addition to posttreatment follow-up of oncology patients is positron emission tomography using fluorine-18-2-fluoro-2-deoxy-D-glucose (FDG-PET).
Methods: We review the role of FDG-PET imaging in the follow-up of patients previously treated for MTC and ATC.
Results: Based on the encouraging literature data, FDG-PET appears to be useful in detecting recurrent or metastatic disease in patients with MTC and ATC, providing a higher sensitivity (66% to 100%) and specificity (79% to 90%) than conventional imaging methods. However, the PET technique is limited by less accurate spatial assignment of small lesions, especially in the lung and liver.
Conclusions: Supporting evidence indicates that FDG-PET has a significant role in the follow-up of patients with MTC and ATC.
Introduction
The primary treatment for most thyroid cancers is surgery. After the initial treatment, follow-up methods for patients with thyroid cancer differ according to the origin of their primary disease. The World Health Organization classifies the major types of primary thyroid carcinomas as papillary, follicular, medullary, and anaplastic.[1] Each of these morphologic patterns has a distinctive biology and clinical significance. Anaplastic thyroid carcinoma (ATC) and particularly medullary thyroid carcinoma (MTC) have the biological capability of secreting specific tumor markers that have been utilized for the diagnosis and follow-up of these malignancies.[2] Despite the availability of numerous imaging modalities, localization of recurrence or metastases in patients with MTC or ATC and elevated serum tumor marker levels is often problematic. Moreover, since curative outcome and patient survival depend on the surgical removal of all tumor tissue, early diagnosis of recurrence or metastases is important.
Many studies have demonstrated the clinical application of fluorine-18-2-fluoro-2-deoxy-D-glucose positron emission tomography (FDG-PET) in several types of cancers, including lung, head and neck, breast, and colorectal cancers, as well as lymphoma, melanoma, and brain tumors.[3,4] Although the use of FDG-PET to differentiate between benign and malignant tumors in the preoperative evaluation of thyroid nodules is controversial, it is a valuable diagnostic tool in the postoperative follow-up of differentiated thyroid cancer.[5-7] Also, supporting evidence indicates that FDG-PET has a significant role in the follow-up of patients with MTC and ATC.[8-10] The metabolic imaging findings by PET may precede the morphologic changes evidenced by computed tomography (CT) or magnetic resonance imaging (MRI) by several weeks or months. This difference provides the rationale to assess the role of FDG imaging in the posttreatment evaluation of thyroid cancer.
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