Prognostic Value Of Radioiodine And ¹⁸F-FDG Uptake In Lung Metastasis Of Differentiated Thyroid Cancer

Purpose:The lungs are the most frequent distant localization from differentiated thyroid cancer?DTC?.Positive ¹⁸F-fluorodeoxyglucose(¹⁸F-FDG)accumulation on PET scan has been proved to be a strong predictor of poor prognosis in DTC patients.However,the prognostic value of ¹⁸F-FDG PET for pulmonary metastases?PMs?from DTC is not clear and was investigated in the study.Methods:DTC patients with PMs treated with ¹³¹I from January 1994 to March 2016which met the following criteria were included.All patients were instructed to follow a low-iodine diet for at least 2 weeks before RAI treatment.And these patients achieved a sufficient hypothyroid state clinically with a serum TSH level of 30 mIU/ml after withdrawal of L-levothyroxine?L-T4?for 3-4 weeks.L-T4 therapy was administered72h after RAI treatment.The clinical data including¹⁸F-FDG PET/CT and ¹³¹I whole body scans were retrospectively collected and analyzed.Therapeutic response assessment was based on serum thyroglobulin?Tg?levels,and the comparisons of PMs size between pre-treatment and the last follow upon CT images were assessed using Response Evaluation Criteria in Solid Tumors?RECIST,version 1.1?.The mean follow-up period was 111.9±91.6 months.The progression-free survival was estimated by the Kaplan-Meier method.Results:In the 83 included patients,25?25/83,30%?showed ¹⁸F-FDG uptake in PMs of DTC.Significant difference in tumor size was found between ¹⁸F-FDG-positive and negative PMs of DTC?P=0.023?.RAI avidity is also the significant factor on therapeutic of RAI on PMs?P=0.0?.In ¹³¹I-avid lesions,no significant difference in response to ¹³¹I therapy was found between ¹⁸F-FDG positive and negative PMs based on CT and TG?P=0.35,0.47?.The presence of ¹³¹I uptake in the lung lesions and the absence of ¹⁸F-FDG uptake in these lesions were independently related to a better progression-free survival?P=0.00?.Conclusions:¹⁸F-FDG avidity may predicate poor therapeutic effect in terms of tumor size and high risk of disease progression and less favorable prognosis.PMs from DTC with ¹⁸F-FDG-avidity is not synonymous to refractory disease.The majority of patients with PMs were both ¹³¹I and ¹⁸F-FDG avid and responded to therapy.Our results indicated an inverse relationship and the heterogeneity of iodine and glucose metabolisms in PMs.Our results also indicated the heterogeneity of iodine and glucose metabolisms in DTC metastases from different organs and heterogeneity of therapeutic effects.¹⁸F-FDG avidity may predicate poor therapeutic effect by tumor size and high risk of disease progression and less favorable prognosis.¹³¹I-avidity remains the key factor suggesting therapeutic effect on PMs.