Predictive and prognostic value of 18F-DOPA PET/CT in patients affected by recurrent medullary carcinoma of the thyroid.

INTRODUCTION: Medullary thyroid carcinoma (MTC) is a malignancy accounting for about 5-8% of thyroid cancers. Serum calcitonin and carcinoembryonic antigen (CEA) levels are widely used to monitor disease progression. However, prognostic factors able to predict outcomes are highly desirable. We, therefore, aimed to assess the prognostic role of 18 F-DOPA PET/CT in patients with recurrent MTC.

MATERIALS AND METHODS: 60 patients (mean age 64 ± 13 years, range 44-82) with recurrent MTC were eligible from a multicenter database. All patients underwent a restaging 18 F-DOPA PET/CT, performed at least 6 months after surgery. CEA/calcitonin levels, local recurrences, nodal involvement and metastases at PET/CT were recorded. SUVmax, SUVmean (also normalized to mediastinal uptake) and metabolic tumor volume were automatically calculated for each lesion, by placing a volume of interest around the lesion with 40% of peak activity as threshold for the automatic contouring. The patients were clinically and radiologically followed up for 21 ± 11 months. Rate of progression-free survival (PFS), disease-specific survival (DSS) and incremental prognostic value of 18 F-DOPA PET/CT over conventional imaging modalities were assessed by Kaplan-Meier curves and Log-Rank test. Cox regression univariate and multivariate analyses were performed for assessing predictors of prognosis.

RESULTS: 18 F-DOPA PET/CT showed abnormal findings in 27 patients (45%) and resulted unremarkable in 33 (55%). PFS was significantly longer in patients with an unremarkable PET/CT scan (p = 0.018). Similarly, an unremarkable PET/CT study was associated with a significantly longer DSS (p = 0.04). 18 F-DOPA PET/CT added prognostic value over other imaging modalities both for PFS and for DSS (p < 0.001 and p = 0.012, respectively). Neither semiquantitative PET parameters nor clinical or laboratory data were predictive of a worse PFS and DSS in patients with recurrent MTC.

CONCLUSION: 18 F-DOPA PET/CT scan has an important prognostic value in predicting disease progression and mortality rate.