THE COMBINED USE OF CALCITONIN DOUBLING TIME AND F-18-FDG PET/CT IMPROVES PROGNOSTIC VALUES IN MEDULLARY THYROID CARCINOMA: THE CLINICAL UTILITY OF F-18-FDG PET/CT

Abstract

Objective: Calcitonin and carcinoembryonic antigen (CEA) doubling times are established prognostic markers in medullary thyroid cancer (MTC). On the other hand, F-18-fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) shows an increased rate of detection with high blood tumor marker levels in several cancers. This study aimed to analyze the ability of F-18-FDG PET/CT to determine prognosis in the follow-up of patients with MTC. Methods: Medical records of 17 patients with MTC who underwent F-18-FDG PET/CT were analyzed retrospectively. All patients were classified into two groups: stable disease or progressive disease. Results: Eight patients presented with progressive disease, and all of them showed F-18-FDG uptake (100%), compared to only 3 of 9 patients who presented in stable condition (33%). F-18-FDG PET/CT results were able to distinguish progressive from stable disease (P = .009). Calcitonin levels >4,020 pg/mL (P = .0004), CEA levels >26.8 ng/mL (P = .04), and a calcitonin doubling time <24.1 months (P = .015) were associated with progressive disease in our cohort. The proportion of variance explained that predicted progressive disease was 32% for F-18-FDG uptake, 27.1% for a calcitonin doubling time of 24.1 months, and 41.2% for doubling time plus F-18-FDG PET/CT. Conclusion: F-18-FDG uptake was able to distinguish progressive from stable disease. However, this tool should not replace the validated calcitonin doubling time, but rather the combination of information could improve the clinical re-assessment and better identify high-risk patients who require more careful surveillance.