Abstract
The clinical and prognostic role of 2-deoxy-2-[18F]fluoro-D-glucose positron emission tomography/computed tomography (2-[18F]FDG PET/CT) in the study of patients affected by differentiated thyroid carcinoma (DTC) with positive serum thyroglobulin (Tg) level and negative [131I] whole-body scan ([131I]WBS) has already been demonstrated. However, the potential prognostic role of semi-quantitative PET metabolic volume features, such as metabolic tumor volume (MTV) and total lesion glycolysis (TLG), has not yet been clearly investigated. The aim of this retrospective study was to investigate whether the main metabolic PET/CT parameters may predict the prognosis. We retrospectively included 122 patients with a positive 2-[18F]FDG PET/CT for DTC disease after a negative [131I]WBS with Tg > 10 ng/mL. The maximum and mean standardized uptake value (SUVmax and SUVmean), MTV and TLG of the hypermetabolic lesion, total MTV (tMTV) and total TLG (tTLG) were measured for each scan. Progression-free survival (PFS) and overall survival (OS) curves were plotted according to the Kaplan–Meier analysis. After a median follow up of 53 months, relapse/progression of disease occurred in 87 patients and death in 42. The median PFS and OS were 19 months (range 1–132 months) and 46 months (range 1–145 months). tMTV and tTLG were the only independent prognostic factors for OS. No variables were significantly correlated with PFS. The best thresholds derived in our sample were 6.6 cm3 for MTV and 119.4 for TLG. In patients with negative WBS and Tg > 10 ng/mL, 2-[18F]FDG PET/CT metabolic volume parameters (tMTV and tTLG) may help to predict OS.
Highlights
Differentiated thyroid cancer (DTC) is the most frequent endocrine cancer and it is a disease with optimal survival [1], except in cases with distant metastases and iodine-refractory states [2,3]
Patients with a high total MTV (tMTV) (>6.6 cm3) had a significantly shorter overall survival (OS) compared to patients with a lower tMTV (≤6.6 cm3), with a presence of bone metastases were significantly related to survival curves (Figure 4, Table 3)
Progression-free survival (PFS): progression-free survival; OS: overall survival; HR: hazard ratio; CI: confidence interval; N◦ : number; SUV: standard uptake value; MTV: metabolic tumor volume; TLG: total lesion glycolysis. * Variables dichotomized using cutoff values after receiver operating characteristic (ROC) analysis reported in Despite the overall optimal prognosis, a reduced group of DTC patients lost the ability to take up radioiodine and shifted into an aggressive behavior, which may usually manifest with a high level of Tg but negative or less positive [131 I]WBS
Summary
Differentiated thyroid cancer (DTC) is the most frequent endocrine cancer and it is a disease with optimal survival [1], except in cases with distant metastases (mainly bone) and iodine-refractory states [2,3]. The initial therapy for DTC consists of surgery (thyroidectomy with/without lymphadenectomy) followed by postoperative risk-adapted sodium iodide ([131 I]) therapy if indicated [1,2,3,4,5]. The goal to identify the patients who will have a more aggressive disease would be shareable, especially in an early stage. In this clinical scenario, the combination of the serum thyroglobulin (Tg) level and [131 I] whole-body scan ([131 I]WBS) findings may help to recognize patients who have not have benefited from [131 I] therapy. In the presence of negative [131 I]WBS and detectable Tg, iodine refractory disease is defined [8,9]
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