[18F]Fluorodeoxyglucose Positron Emission Tomography Predicts Outcome for Ewing Sarcoma Family of Tumors

Purpose Response to neoadjuvant chemotherapy is a significant prognostic factor for the Ewing sarcoma family of tumors (ESFTs). [18F]fluorodeoxyglucose (FDG) positron emission tomography (PET) is a noninvasive imaging modality that accurately predicts histopathologic response in several malignancies. To determine the prognostic value of FDG PET response for progression-free survival (PFS) in ESFTs, we reviewed the University of Washington Medical Center experience. Patients and Methods Thirty-six patients with ESFTs were evaluated by FDG PET. All patients received neoadjuvant and adjuvant chemotherapy. FDG PET standard uptake values before (SUV1) and after (SUV2) chemotherapy were analyzed and correlated with chemotherapy response, as assessed by histopathology in surgically excised tumors. Thirty-four patients had both SUV1 and SUV2. Results The mean SUV1, SUV2, and ratio of SUV2 to SUV1 (SUV2:1) were 7.9 (range, 2.3 to 32.8), 2.1 (range, 0 to 4.3), and 0.36 (range, 0.00 to 1.00), respectively. Good FDG PET response was defined as SUV2 less than 2.5 or SUV2:1 ≤ 0.5. FDG PET response by SUV2 or SUV2:1 was concordant with histologic response in 68% and 69% of patients, respectively. SUV2 was associated with outcome (4-year PFS 72% for SUV2 < 2.5 v 27% for SUV2 ≥ 2.5, P = .01 for all patients; 80% for SUV2 < 2.5 v 33% for SUV2 ≥ 2.5, P = .036 for localized at diagnosis patients). SUV2:1 ≤ 0.5 was not predictive of PFS. Conclusion FDG PET imaging of ESFTs correlates with histologic response to neoadjuvant chemotherapy. SUV2 less than 2.5 is predictive of PFS independent of initial disease stage.