| Summary: | Background. Patients with treated thyroid cancer are followed routinely to look for metastatic disease. For most tumor types, patients can be followed by serum biomarkers, such as thyroglobulin for differentiated cancer or calcitonin for medullary cancer, which indicate the likely recurrence of thyroid cancer. To confirm and localize the tumor recurrence or metastasis an imaging study is used, such as 131I scintigraphy (WBS) for differentiated cancer or computed tomography, somatostatin receptor scintigraphy (SRS), or magnetic resonance imaging for medullary cancer. However, these standard imaging tests may be negative in the face of biochemical evidence of metastatic disease. Positron emission tomography (PET) has been proposed as a highly accurate test to detect metastatic disease in this setting. However, PET is expensive, is not commonly available, and may not be sensitive for metabolically inactive tumors. Questions of interest. 1. What is the test performance of PET for localization or staging of previously treated thyroid cancer suspected to be metastatic for which standard imaging modalities have failed to localize metastatic lesions or are thought not to be helpful to locate metastatic disease? 2. In the same population, what is the evidence that PET affects health outcomes or alters management? 3. What are the test performance and effect on clinical management of PET for initial, pre-treatment, staging of patients differentiated thyroid cancer types that commonly do not take up radioiodine?
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