Snapshot A 12-year-old boy presents to the pediatric emergency department with pain in his right lower extremity. He was recently playing in soccer, but he denies any trauma to the leg. Physical examination is notable for mild swelling in the right mid-tibia and tenderness to palpation. A radiograph of the leg demonstrate periosteal elevation and "onion skinning" concerning for malignancy. Introduction Overview neoplastic disease of the bone that most often arises in the long bones of the extremities pelvic bones Epidemiology Incidence children and adolescents are most commonly affected median age of diagnosis is 15 years of age ETIOLOGY Pathophysiology chromosomal translocation t(11;22) leads to the production of oncogenic fusion proteins (EWS-FLI1) that enhance cellular proliferation and malignant transformtion Genetics chromosomal translocation between Ewing sarcoma breakage region 1 (EWS) and erythroblast transformation-specific family transcription factors (FLI1), t(11;22) leads to the production oncogenic fusion proteins Symptoms Symptom constitutional symptoms (in 10-20% of cases) fever weight loss fatigue pain at the site of involvement Physical exam swelling and tenderness at the site of involvement Imaging Radiography indication inital imaging study findings "onion skin pattern" of osteolytic lesions commonly affecting the diaphysis of the bone can also involve the metaphysis Codman triangle periosteal elevation MRI indication to evaluate for the extent of disease provides an image with higher definition than radiography Radionuclide bone scan indication to survery the entire skeletion for the presence of metastasis Studies Invasive studies open or core needle biopsy indication confirms the diagnosis perform histology and molecular testing finding histology small, round, blue cells that are poorly differentiated neuroectodermal origin scant cytoplasm molecular testing chromosomal translocation of 11;22 Differential Osteosarcoma differentiating factors malignat osteoblasts lesions are most often found in the metaphysis typically has a rim of bone formation (uncommon in Ewing sarcoma) Treatment Medical chemotherapy indication typically initial treatment option in most cases radiation therapy indication may be used if surgical resection is not indicated Operative resection indication treatment option for local disease Complications Metastasis other bone sites bone marrow lungs