Diagnostic Accuracy of 18F-FDG PET/CT in Patients With Biochemical Evidence of Recurrent, Residual, or Metastatic Medullary Thyroid Carcinoma

Objective Medullary thyroid carcinoma (MTC) is a rare malignancy. Location of residual, recurrent, or metastatic disease is crucial to treatment management and outcome. We aimed to evaluate the use of 18F-FDG PET/CT in localizing MTC foci in patients with biochemical relapse. Methods This is a retrospective cohort study. Review of 51 FDG PET/CT studies of 45 patients referred to restage MTC due to increased calcitonin (Ctn) and carcinoembryonic antigen (CEA) values at follow-up. FDG PET/CT diagnostic accuracy was determined through a patient-based analysis, using histology as criterion standard when available, or other imaging studies and clinical follow-up otherwise (mean, 4 years). Results There were 25 positive scans. Sensitivity, specificity, positive and negative predictive values, diagnostic accuracy, and positive likelihood ratio were 66.7%, 83.3%, 88.0%, 57.7%, 72.5%, and 4.0, respectively. Using a Ctn cutoff of 1000 pg/mL, sensitivity increased to 76.9%. There were significant differences of Ctn and CEA values between positive and negative FDG PET/CT (P

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