[18F]FDG PET/CT quantitative parameters for the prediction of histological response to induction chemotherapy and clinical outcome in patients with localised bone and soft-tissue Ewing sarcoma

Objective The application of [F-18]FDG PET/CT in predicting histologic response to induction chemotherapy in patients with Ewing sarcoma (EWS) has been proposed using the values of pre-post treatment SUVmax as a referral parameter, although with heterogeneous results. The aim of this retrospective study was to evaluate the diagnostic accuracy of [F-18]FDG PET/CT volumetric parameters (metabolic tumour volume (MTV) and total lesion glycolysis (TLG)) as compared to SUVmax to predict response to chemotherapy and clinical outcome in patients with localised EWS of bone and soft-tissue. Methods Twenty-eight patients with non-metastatic EWS of bone (n = 20) and soft tissues (n = 8) who underwent a [F-18]FDG PET/CT scan before (PET1) and after induction chemotherapy (PET2) were enclosed in the analysis. Values of PET metrics (SUVmax, MTV, TLG) at diagnosis and after neoadjuvant chemotherapy as well as the percentage change between PET1 and PET2 (Delta SUV, Delta MTV and Delta TLG) were correlated to histological response and to progression-free survival (PFS). Results Delta TLG (cut-off: -60%) is the best predictor for histologic response with 100% sensitivity and 77.8% specificity. MTV1 > 33.4 cm(3) and TLG(1) > 112 were also associated with a favourable histologic response (sensitivity 80% and specificity 77.8% for both). On multivariate analysis, SUV2 (> 3.3) and Delta TLG (< -18%) were independent predictors of worse PFS. Conclusions [F-18]FDG PET/CT could accurately predict histologic response to neoadjuvant chemotherapy in patients with EWS, also showing a possible prognostic value for future disease relapse.