Origin and Incidence of Ewing Sarcoma
Studies using immunohistochemical markers, cytogenetics,[5,6] molecular genetics, and tissue culture  indicate that Ewing sarcoma is derived from a primordial bone marrow-derived mesenchymal stem cell.[8,9] Older terms such as primitive neuroectodermal tumor, Askin tumor (Ewing sarcoma of chest wall), and extraosseous Ewing sarcoma (often combined in the term Ewing sarcoma family of tumors) refer to this same tumor.
The incidence of Ewing sarcoma is approximately three cases per 1 million per year and has remained unchanged for 30 years. Data from the U.S. National Cancer Institute (NCI) Surveillance, Epidemiology, and End Results (SEER) registries report an overall incidence of Ewing sarcoma of one case per 1 million in the U.S. population. The incidence in patients aged 10 to 19 years is between nine and ten cases per 1 million. The same analysis suggests that the incidence of Ewing sarcoma in the United States is nine times greater in Caucasians than in African Americans.
The median age of patients with Ewing sarcoma is 15 years, and more than 50% of patients are adolescents. Well-characterized cases of Ewing sarcoma in neonates and infants have been described.[12,13] Based on data from 1,426 patients entered on European Intergroup Cooperative Ewing Sarcoma Studies (EI-CESS), 59% of patients are male and 41% are female. Primary sites of bone disease include the following:
- Lower extremity (41%).
- Pelvis (26%).
- Chest wall (16%).
- Upper extremity (9%).
- Spine (6%).
- Hand and foot (3%).
- Skull (2%).
For extraosseous primary tumors, the most common primary sites of disease include the following:
- Trunk (32%).
- Extremity (26%).
- Head and neck (18%).
- Retroperitoneum (16%).
- Other sites (9%).[15,16]
Approximately 25% of patients will have metastatic disease at diagnosis.
The SEER database was used to compare patients younger than 40 years with Ewing sarcoma who presented with skeletal and extraosseous primary sites. Patients with extraosseous Ewing sarcoma were more likely to be older, female, nonwhite, and have axial primary sites and were less likely to have pelvic primary sites when compared with patients with skeletal Ewing sarcoma.