Ewing sarcoma (ES)/primitive neuroectodermal tumor (PNET) is a malignant small round blue cell neoplasm of presumed neuroectodermal origin that affects bones and soft tissue in children and young adults. Nearly 80% of the patients are younger than 20 years. The tumor cells characteristically express CD99 (MIC2 antigen), a glycoprotein localized on cell membrane. The defining feature of ES/PNET ...
