• A rare tumor usually occurring in persons age 10-30 years
• Patients usually present with pain and swelling of variable duration
• Tumor most frequently located in distal femur and humerus, most are metaphyseal
• Lesion may be sclerotic or mixed osteolytic/osteosclerotic
• Permeative border and Codman’s triangle usually present
• Soft tissue mass present in majority of cases
• Histologically, sheets of small, round, blue cells observed
• Appearance is similar to that of Ewing sarcoma, but differs from Ewing in that these cells produce osteoid
  • Use of Ewing immunohistochemical markers and evaluation for an 11:22 chromosomal translocation useful to eliminate a diagnosis of Ewing sarcoma