Use of FDG PET in Staging, Restaging, and Assessment of Therapy Response in Ewing Sarcoma

Ewing sarcoma family tumors account for approximately 3% of all pediatric cancers, making them the second most common bone malignancies in children and adolescents. Advances in the treatment of localized disease have dramatically prolonged the survival of patients in whom Ewing sarcoma is diagnosed, but the prognosis for patients with metastatic or recurrent disease remains poor. Radiologic evaluation of Ewing sarcoma can help (a) detect and accurately assess the extent of disease prior to treatment, (b) determine whether metastatic or recurrent disease is present, and (c) monitor therapy response. Standard imaging evaluation of bone and soft-tissue sarcomas typically consists of conventional radiography, magnetic resonance (MR) imaging, computed tomography (CT), and bone scintigraphy. Positron emission tomography (PET) with 2-[fluorine-18]fluoro-2-deoxy-D-glucose (FDG) provides unique information with regard to the biologic activity of Ewing sarcomas. It represents a noninvasive means of estimating histologic tumor grade and can be used to detect progression or regression of disease prior to anatomic imaging. Such information can be used to optimize staging, restaging, and assessment of therapy response. Functional imaging with FDG PET can also potentially help predict patient prognosis both before and after neoadjuvant therapy. FDG PET does have inherent limitations that must be acknowledged to avoid potential diagnostic pitfalls and is optimally used in combination with correlative anatomic imaging modalities such as CT and MR imaging. Nevertheless, FDG PET provides unique physiologic information that often has important clinical implications.