Role of 18F-FDG-PET/CT in the initial staging of very high-risk Ewing Sarcoma in a prospective multicentric Phase II Study: Is there still a place for bone marrow sampling?

The Ewing Sarcoma Family of Tumors (ESFT) constitutes a group of rare malignancies, wherein approximately one-third of cases exhibit metastatic spread, particularly impacting prognosis when bone and/or bone marrow (BM) are involved. Primary extra-pulmonary metastatic ESFT often necessitates intensified therapeutic approaches. Accurate staging plays a pivotal role in clinical decision-making, with fluorine-18-fluorodeoxyglucose-positron emission tomography/computed tomography (PET/CT) currently serving as a non-invasive modality for assessing ESFT’s BM extent. In the French phase II COMBINAIR3 (NCT03011528) study, a comprehensive approach for patients with extra-pulmonary ESFT metastasis was evaluated. We prospectively compared the efficacy of PET/CT to BM aspiration and biopsy (BMAB) analysis in patients undergoing initial staging. Among the 42 patients analyzed (median age 14 y, 2:1 male/female ratio), 45% presented with pelvic primary tumors and 83% had bone/BM involvement at diagnosis. Our findings showed PET/CT had 100% specificity and 83.3% sensitivity in detecting initial BM involvement. Overall, PET/CT correctly classified 92.8% of patients, reaching 100% accuracy in patients identified with bone involvement, thus surpassing the standard BMAB. These results suggest that the conventional use of BMAB in the initial staging of high-risk ESFT patients can be omitted, promoting PET/CT as a non-invasive alternative, thus improving staging accuracy and treatment decisions in ESFT management.