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Epidemiology, pathology, and molecular genetics of the Ewing sarcoma family of tumors

Thomas F DeLaney, MD
Francis J Hornicek, MD, PhD
Stephen L Lessnick, MD, PhD
Henry J Mankin, MD
Section Editors
Alberto S Pappo, MD
Robert Maki, MD, PhD
Deputy Editor
Diane MF Savarese, MD


Ewing sarcoma (ES) and peripheral primitive neuroectodermal tumor (PNET) were originally described as distinct clinicopathologic entities:

In 1918, Stout described a tumor of the ulnar nerve with the gross features of a sarcoma, but composed of small round cells focally arranged as rosettes; this entity was subsequently designated neuroepithelioma, and then PNET [1].

ES was described by James Ewing in 1921 as an undifferentiated tumor involving the diaphysis of long bones that, in contrast to osteosarcoma, was radiation-sensitive. Although most often a primary bone tumor, ES was also reported to arise in soft tissue (extraosseous Ewing sarcoma [EES]) [2].

However, over the last several decades, it has become clear that these entities comprise the same spectrum of neoplastic diseases known as the Ewing sarcoma family of tumors (EFT), which also includes malignant small-cell tumor of the chest wall (Askin tumor) [3], and atypical ES [4,5]. Because of their similar histologic and immunohistochemical characteristics and shared nonrandom chromosomal translocations, these tumors are considered to be derived from a common cell of origin, although the histogenic origin of this cell is debated [6-13]. (See 'Histogenesis' below and "Diseases of the chest wall", section on 'Malignant neoplasms'.)

The EFT can develop in almost any bone or soft tissue, but the most common site is in a flat or long bone, and patients typically present with localized pain and swelling. Although overt metastatic disease is found in fewer than 25 percent at the time of diagnosis, subclinical metastatic disease is assumed to be present in nearly all patients because of the 80 to 90 percent relapse rate in patients undergoing local therapy alone. As a result, systemic chemotherapy has evolved as an important component of treatment.


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