[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

Abstract

Objective: The application of [¹⁸F]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 SUV_max as a referral parameter, although with heterogeneous results. The aim of this retrospective study was to evaluate the diagnostic accuracy of [¹⁸F]FDG PET/CT volumetric parameters (metabolic tumour volume (MTV) and total lesion glycolysis (TLG)) as compared to SUV_max 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 [¹⁸F]FDG PET/CT scan before (PET₁) and after induction chemotherapy (PET₂) were enclosed in the analysis. Values of PET metrics (SUV_max, MTV, TLG) at diagnosis and after neoadjuvant chemotherapy as well as the percentage change between PET₁ and PET₂ (ΔSUV, ΔMTV and ΔTLG) were correlated to histological response and to progression-free survival (PFS).

Results: ΔTLG (cut-off: -60%) is the best predictor for histologic response with 100% sensitivity and 77.8% specificity. MTV₁ > 33.4 cm³ and TLG₁ > 112 were also associated with a favourable histologic response (sensitivity 80% and specificity 77.8% for both). On multivariate analysis, SUV₂ (> 3.3) and ΔTLG (< -18%) were independent predictors of worse PFS.

Conclusions: [¹⁸F]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.

Key points: • The variation of the PET parameter tumour lesion glycolysis (TLG) can predict the histologic response to induction chemotherapy (sensitivity 100%, specificity 77.8%), in patients with Ewing sarcoma. • The percentage variation of TLG and the value of the SUVmax at PET scan after chemotherapy show a prognostic role for future disease relapse. The combination of both the parameters identifies three prognostic classes of patients with low, intermediate and high risk of disease relapse.

Keywords: Ewing sarcoma; Fluorine-18-fluorodeoxyglucose; Induction chemotherapy; PET/CT scan; Patient outcome assessment.