MEDICAL DICTIONARY
Ewing sarcoma : A type of bone tumor that occurs in children and adolescents, most often in the large bones of the arms and legs and the flat bones of the pelvis , spine and ribs. The tumor is caused by a chromosome abnormality, called a translocation (an exchange of material), most commonly between chromosomes 11 and 22 that occurs by chance alone in a single cell which divides to form the malignant clone (colony) of cells. The tumor is named after the American pathologist James Ewing (1866-1943).
Ewing's sarcoma is the second most common type of bone tumor (after osteosarcoma ) in children and adolescents. The disease tends to occur between ages 10 and 20 and almost always before age 30. It may metastasize (spread) to bones, the lungs or the bone marrow .
Treatment is chemotherapy + radiation therapy . The tumor is typically radiosensitive meaning it responds to radiation therapy. Sometimes, surgery is also done to remove the original tumor or to remove metastases from the lungs.
The overall chance of long-term survival with Ewing's sarcoma is currently about 60%. This is a composite figure. Survival is about 75% for patients with localized tumor (particularly if the tumor is located below the elbow or the midcalf) and about 25-30% with tumor that has spread.
Ewing's sarcoma develops from a type of primitive nerve cell and may occur in the soft tissues of the body as well as in bone. The Ewing's family of tumors includes Ewing's tumor of bone (ETB or Ewing's sarcoma of bone), extraosseus Ewing's (EOE), primitive neuroectodermal tumors (PNET or peripheral neuroepithelioma), and Askin's tumor (PNET of the chest wall). All of these tumors are derived from the same primordial stem cell , the primitive nerve cell.
About 90% of tumors in the Ewing's family have the translocation between chromosomes 11 and 22, called t(11;22)(q24;q12) that results in the fusion of the EWS gene in band 22q12 with the transcription factor gene FLI1 in band 11q24. This fusion leads to the production of a hybrid transcript and an chimeric protein . In a few tumors in the Ewing's family, the EWS gene is engaged in other types of translocations such as t(21;22)(q12;q12) and t(7;22)(p22;q12), leading to fusions EWS-ERG and EWS-ETV1, respectively. In all cases the chimeric protein is oncogenic. It is responsible for the malignancy .
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