Clinico-pathological factors and 18 F-FDG PET/CT metabolic parameters for prediction of progression-free survival in Radioiodine Refractory Differentiated Thyroid Carcinoma

Abstract Objective Identifying prognostic markers for clinical outcomes is crucial for selecting appropriate treatment options for patients with radioiodine-refractory (RAI-R) differentiated thyroid carcinoma (DTC). The aim of this study was to investigate the prognostic value of clinico-pathological features and quantitative ¹⁸F-FDG PET/CT metabolic parameters in predicting progression-free survival (PFS) in DTC patients with RAI-R. Patients and Methods : This prospective cohort study included 110 consecutive RAI-R DTC patients referred for ¹⁸F-FDG PET/CT imaging. The maximum lesion SUV (Standard Uptake Value: SUVmax, SUVmean, SULpeak), total metabolic tumor volume (tMTV), and total lesion glycolysis (tTLG) were measured. Disease progression was assessed using the Response Evaluation Criteria in Solid Tumors (RECIST) 1.1 and/or Positron Emission Tomography Response Criteria in Solid Tumors (PERCIST) criteria. PFS curves were plotted using Kaplan–Meier analysis. Univariate and multivariate Cox analyses were conducted to determine the prognostic factors for PFS. Results ¹⁸F-FDG PET/CT metabolic parameters have predictive value for PFS in RAI-R DTC patients, with sensitivity ranging from 70.7–81% and specificity from 75–92.3% (p < 0.001). PFS was worse in patients with SUVmax > 6.39 g/ml, SUVmean > 3.68 g/ml, SULpeak > 3.14 g/ml, tTLG > 4.23 g/ml × cm³, and tMTV > 1240 ml. Clinico-pathological factors age > 55, aggressive variant and follicular histological subtype, extra-thyroidal extension of the primary tumor, stage III – IV disease at initial DTC dianogsis, distant metastases on ¹⁸F-FDG PET/CT findings, and metabolic parameters of ¹⁸F-FDG PET/CT associate with PFS in univariate analysis (p < 0.01). In multivariate analysis, extra-thyroidal extension (HR: 2.25; 95% CI: 1.22–4.16; p = 0.01), distant metastases on ¹⁸F-FDG PET/CT (HR: 2.98; 95%CI: 1.62–5.5; p = 0.000), and tMTV > 1240 ml (HR: 4.17; 95% CI: 2.02–8.6; p = 0.000), were independent prognostic factors for PFS. Conclusions In addition to classic clinico-pathological factors, the quantitative ¹⁸F-FDG PET/CT metabolic parameters can be used for dynamic risk stratification for progression in RAI-R DTC patients. Furthermore, extra-thyroidal extension of the primary tumor, distant metastases, and tMTV > 1240 ml are independent prognosticators for PFS.