An 8 yr old child is having fever with pain and swelling in mid thigh. On Xray lamellated appearance and Codman's triangle is present. Histopathologic examination shows small round cells positive for MIC-2. What is the most likely diagnosis?

Child is showing features of Ewing's sarcoma. Ewing sarcoma is the fouh most common primary malignancy of bone, but it is the second most common (after osteosarcoma) in patients younger than 30 years of age and the most common in patients younger than 10 years of age. Features of Ewings sarcoma: Is a small round blue cell malignancy. It involves diaphysis of long bones. Patients usually presents with pain, with or without swelling and erythema. Radiologic features are similar to that of osteosarcoma such as Codman's triangle (periosteal new bone formation with lifting of bony coex). Biopsy shows sheets of undifferentiated cells with hyperchromatic nuclei, well-defined cell borders, and scanty cytoplasm. Positive immunoreactivity for CD99 (MIC2)is a hallmark of Ewing's sarcoma.