Prognostic Value of FDG-PET/CT Metabolic Parameters in patients with biochemical or structure incomplete response differentiated thyroid cancer.

Objectives: Prognostic Value of FDG-PET/CT Metabolic Parameters in patients with biochemical or structure incomplete response differentiated thyroid cancer.

Introduction: Metabolic parameters of 18F-FDG PET/CT such as standardized uptake value (SUVmax), metabolic tumor volume (MTV) and total lesion glycolysis (TLG) could predict the risk of recurrence and death of many cancers such as lung cancer, breast cancer and lymphoma etc. There is less research using these parameters for predicting the prognosis of DTC patients with biochemical or structure incomplete response, so this study aims to explore the prognostic value of SUVmax, MTV and TLG on disease-free survival (DFS) and overall survival (OS) in such patients.

Methods: DTC patients with biochemical or structure incomplete response who undergoing 18F-FDG PET/CT were included from Dec, 2010 to Oct, 2018. All they had received at least one radioiodine treatment. SUVmax, MTV and TLG values of whole-body tumor were calculated from PET-CT images with a threshold of SUVmax equaling to 2. The optimal cutoff value of SUVmax, MTV and TLG were obtained by ROC curve analysis. The Kaplan-Meier method and Log-rank test were used to perform univariate survival analysis, while Cox proportional hazards model was done for multivariate analysis.

Results: 95 patients were included in this study, including 37 males and 58 females, mean age 48.6±13.2 years old(15-75), 82 patients with papillary thyroid cancer and 13 patients with follicular thyroid cancer. Until to Sep.2019, 37.9%(36/95)patients progressed with median PFS 55 months,7.4%(7/95) patients died for DTC, with median OS 68 months. The cutoff value of SUVmax, MTV and TLG for PFS was 3.9,3.0 and 8.4, with area under curve(AUC) 0.79( 95%CI 0.69~0.89), 0.75( 95%CI 0.65~0.86) and 0.76( 95%CI 0.65~0.86), respectively( all P value was 0.000). The cutoff value of SUVmax, MTV and TLG for OS was 6.7, 23.9 and 131.0, with AUC 0.82( 95%CI 0.73~0.91) , 0.75( 95%CI 0.65~0.85) and 0.76( 95%CI 0.66~0.86), respectively( all P value was 0.000). In the univariate analysis, prognostic factors for PFS were radioiodine refractory( P=0.006), SUVmax (P = 0.004), MTV (P = 0.001), and TLG (P = 0.000); prognostic factors for OS were MTV(P=0.049)and TLG (P=0.040). However,in the multivariate analysis, only TLG was the independent prognostic factors for PFS.

Conclusions: TLG reflecting whole body tumor metabolic burden is a prognostic factor for PFS of DTC patients with biochemical or structure incomplete response. However, there is no metabolic parameter for predicting OS, it indicates the study may need longer follow up.