Ewing's s can occur in any bone in the body; the most common sites are the pelvis, thigh, lower leg, upper arm, and rib. The tumor is composed of small round blue cells. Ewing's sarcoma can also arise in soft tissue (extra-skeletal).

Osteosarcomas vary greatly in radiological and pathological features and therefore needs careful diagnosis to differentiate this from other bone tumors. Most are high grade intramedullary osteosarcomas, about 5% are low grade lesions, some are secondary osteosarcomas (for example those caused by radiation therapy).