Response to chemotherapy estimates by FDG PET is an important prognostic factor in patients with Ewing sarcoma.

Abstract

Response to chemotherapy is a prognostic factor in patients with Ewing sarcoma (ES); the role of FDG PET to predict response in these patients has not been thoroughly investigated. We evaluated the diagnostic accuracy and the potential of FDG PET to predict response to chemotherapy (CHT). We analyzed data of 50 patients with ES (median age 12.6 years). All patients were treated with neoadjuvant CHT, and underwent surgery for local control. All patients had (18)F-FDG PET/CT at diagnosis and after induction CHT, prior to local control. We compared response assessed by histopathology with FDG PET using standard uptake values (SUVs). Median SUV at diagnosis (SUV I) was 5 (range 1.2-17), and median SUV after neoadjuvant chemotherapy (SUV II) was 1.8 (range 0-8.4). Median SUV II/I ratio was 0.3 (range 0-1). SUV at diagnosis was significantly lower in patients with good histological response than in patients with poor histological response (median 3.8 vs. 7.2, p 0.02). We found a significant correlation between SUV II and outcome; the positive predictive value of an SUV II ≤ 2.5 for favorable response was 84.21 %, and the median SUV II was significantly higher in patients with disease progression (2.3 vs. 1.6, p = 0.04). In multivariate analysis, necrosis and SUV II were significant predictors of outcome. (18)F-FDG PET demonstrates high diagnostic accuracy for response to initial chemotherapy in patients with ES and it correlates with outcome. The role of FDG PET in predicting response and outcome should be further investigated.