Introduction Definiton a distinctive small blue cell malignant tumor (sarcoma) Epidemiology commonly seen in Caucasian male adolescents typically found in patients from 5-25 years of age second most common bone tumor in children Location ~50% are found in the diaphysis of long bones the most common locations include pelvis, femur, tibia, and humerus Genetics t(11:22) translocation found in all cases leads to the formation of a fusion protein (EWS-FLI1) mnemonic 11+ 22 = 33 (Patrick Ewing's jersey number) Symptoms Presentation pain often accompanied by fever often mimics an infection can present as extremely aggressive with early metastases yet, is responsive to chemotherapy Physical exam swelling and local tenderness Imaging Radiographs large destructive lesion in the diaphysis or metaphysis with a moth-eaten appearance lesion may be purely lytic or have variable amounts of reactive new bone formation periosteal reaction may give "onion skin" or "sunburst" appearance Evaluation Labs ESR is elevated WBC is elevated anemia is common lactic dehydrogenase Bone marrow biopsy required as part of workup for Ewing to rule out metastasis to the marrow Histology Characteristic findings sheets of monotonous small round blue cells prominant nuclei and minimal cytoplasm may have pseudo-rosettes (circle of cells with necrosis in center) Treatment Operative chemotherapy and limb salvage resection Differentials & Groups Small-round-cell tumor differential (by age) < 5 yrs: neuroblastoma or leukemia 5-10 yrs: eosinophilic granuloma 5-30 yrs: Ewing sarcoma >30 yrs: lymphoma > 50 yrs: myeloma