Ewing's sarcoma and primitive neuroectodermal tumor are related neoplasms which consist of malignant round cells and are associated with 11:22 chormosomal translocation.
Ewing's sarcoma occurs most often between the ages of 10-15 and occurs in males more than females. Ewing's sarcoma is the second most common bone sarcoma in children.
The tumor appears in the medullary cavity in the diaphysis of the long bones such as femur as well as the pelvis.
Clinically, the tumor may present with bone pain, a warm tender soft tissue mass and swelling suggesting of infection. X-ray may reveal multilayering of the reactive bone around the tumor producing an onion-skin appearance.
Grossly, the tumor invades the periosteum and may produce a soft tissue mass.
Microscopically, the tumor consists of round cells. There is some evidence of neural differentiation in the neuroectodermal tumors. Some tumor cells are arranged as Homer-Wright pseudorosettes around a central fibrillary space. The tumor may exhibit foci of necrosis. The cells exhibit round nuclei and scant cytoplasm. Staining reveals presence of glycogen in the cytoplasm.