[ 18F]-FDG-PET/CT correlates with the response of radiorefractory thyroid cancer to lenvatinib and patients' survival

Introduction [18F]-FDG-PET/CT positive metastatic lesions in radioiodine-refractory differentiated thyroid cancer (RAI-R DTC) have a poor prognosis and lenvatinib represents the best therapy. We investigated the role of [ 18F]-FDG-PET/CT in the evaluation of metabolic response and prediction of the outcome of RAI-R DTC patients treated with lenvatinib. Materials and methods Thirty-three progressive metastatic RAI-R DTC patients treated with lenvatinib were investigated at baseline and during follow-up with biochemical (Tg/TgAb), morphological (whole-body CT scan) and metabolic evaluation ([ 18F]-FDG-PET/CT). Results Nineteen of thirty-three (57.6%) patients showed the greatest metabolic response at the first [ 18F]-FDG-PET/CT scan, performed after 4 weeks of lenvatinib, while 5/33 (15.1%) patients had this response later. Moreover, 66.7% of patients had both a metabolic response at the first [ 18F]-FDG-PET/CT scan and a morphological response at the first CT scan. We observed a correlation between the metabolic response at [ 18F]-FDG-PET/CT scan performed after 4 weeks of treatment and the biochemical response at the same time in 60.6% of patients. The median overall survival (OS) was significantly longer in patients with either a metabolic response at last [ 18F]-FDG-PET/CT (40.00 vs 8.98 months) or a morphological response at last CT scan (37.22 vs 9.53 months) than in those without response. Moreover, the OS was longer in patients with a metabolic response at [ 18F]-FDG-PET/CT performed after 4 weeks of treatment (36.53 vs 11.28 months). Conclusions Our data show that [ 18F]-FDG-PET/CT can early predict the response to lenvatinib and correlates with the OS of RAI-R DTC patients treated with this drug.