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

Objective: Calcitonin and carcinoembryonic antigen (CEA) doubling times are established prognostic markers in medullary thyroid cancer (MTC). On the other hand, ¹⁸ F-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 ¹⁸ F-FDG PET/CT to determine prognosis in the follow-up of patients with MTC.
Methods: Medical records of 17 patients with MTC who underwent ¹⁸ F-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 ¹⁸ F-FDG uptake (100%), compared to only 3 of 9 patients who presented in stable condition (33%). ¹⁸ F-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 ¹⁸ F-FDG uptake, 27.1% for a calcitonin doubling time of 24.1 months, and 41.2% for doubling time plus ¹⁸ F-FDG PET/CT.
Conclusion: ¹⁸ F-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.
Abbreviations: CEA = carcinoembryonic antigen CT = computed tomography ¹⁸ F-FDG = ¹⁸ F-fluorodeoxyglucose MTC = medullary thyroid cancer PET = positron emission tomography PVE = proportion of variance explained sCT = serum calcitonin SUV = standard uptake value US = ultrasound.