• Etiology: unclear but thought to be derived from either reticuloendothelial cells or undifferentiated mesenchymal cells of the bone marrow.

• Age of onset: 75% are under the age of 20 years; 90% are under the age of 30 years.

• Epidemiology: male > female (3:2); 95% are Caucasian

• Location: Younger patients tend to have the tumor arise in tubular bones whereas older patients tend to have tumor arise in axial skeleton, pelvis and shoulder girdle.

• Signs/Symptoms: localized pain and swelling, pyrexia and elevated ESR, weight loss, anemia; usually involves a single bone with extensive involvement of the diaphysis, as exemplified in this case. However, 25% arise primarily in the metaphysis. Bones commonly involved are the femur (most common), tibia and humerus, as well as marrow-rich sites such as the pelvis and ribs

• Radiologic features: Destructive bone lesion with extensive periosteal reaction. Tumor rapidly traverses the cortex and expands in the subperiosteal region. Erosion of the outer cortex occurs, producing so called ‘saucerization’ as mentioned in the findings in this case. Also classic is the ‘onion-peel’ appearance that is formed from episodic growth and repair by the tumor. This feature was not readily apparent in these films. The permeative pattern is produced by infiltration of cortical bone as the tumor spreads through the haversian canals.

• Differential diagnosis: in the early stages includes osteomyelitis or trauma. Both of which produce a periosteal reaction with little bone destruction. Other tumors in the differential include lytic osteosarcoma, primary lymphoma, secondary neuroblastoma, and eosinophilic granuloma.

• Prognosis: 15-30% have metastasis at time of presentation (most commonly to lung). Current treatment protocols report up to a 79% disease-free survival. For patients with recurrence, survival is half of that number. Nonresectable central lesions, particularly those in the pelvis have a worse prognosis, large lesion exceeding 8 cm are also more likely to present with metastasis and/or recur. Other adverse prognostic indicators include older age, elevated ESR and elevated leukocyte count at the time of presentation.

• Treatment: Multiagent chemotherapy (vincristine, dactinomycin, and cyclophosphamide) is used prior to radiation or surgery therapy. In this case, the patient will receive all three treatments (chemo, radiation and surgery)