Ewing's sarcoma pathophysiology

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1];Associate Editor(s)-in-Chief: Suveenkrishna Pothuru, M.B,B.S. [2];Assistant Editor(s)-In-Chief:Michael Maddaleni, B.S.


Ewing's sarcoma may occur anywhere in the body, but most commonly occurs in the pelvis and proximal long tubular bones. The pathogenesis of Ewing's sarcoma include t(11;22) chromosomal translocation. On microscopic histopathological analysis, the presence of small round cells that have a high nuclear to cytoplasmic ratio, vacuolated cytoplasm, and faded boundaries are characteristic findings of Ewing's sarcoma.


Ewing's sarcoma may occur anywhere in the body, but most commonly in the pelvis and proximal long tubular bones. The diaphyses of the femur are the most common sites, followed by the tibia and the humerus.


Ewing's sarcoma is the result of a translocation between chromosomes 11 and 22, which fuses the EWS gene of chromosome 22 to the FLI1 gene of chromosome 11.[1]

  • The EWSR1 gene is a member of the TET family [TLS/EWS/TAF15] of RNA-binding proteins. The FLI1 gene is a member of the ETS family of DNA-binding genes.
  • Characteristically, the amino terminus of the EWSR1 gene is juxtaposed with the carboxy terminus of the ETS family gene.
  • In most cases (90%), the carboxy terminus is provided by FLI1, a member of the family of transcription factor genes located on chromosome 11 band q24.
  • Other family members that may combine with the EWSR1 gene are ERG, ETV1, ETV4 (also termed E1AF), and FEV.
  • Rarely, TLS, another TET family member, can substitute for EWSR1.

The MIC2 gene product, CD99, is a surface membrane protein that is expressed in most cases of Ewing's sarcoma and is useful in diagnosing these tumors when the results are interpreted in the context of clinical and pathologic parameters. MIC2 positivity is not unique to Ewing's sarcoma, and positivity by immunochemistry is found in several other tumors, including synovial sarcoma, non-Hodgkin lymphoma, and gastrointestinal stromal tumors.

Microscopic pathology

Ewing's sarcoma belongs to the group of neoplasms commonly referred to as small, round, and blue-cell tumors of childhood:[1][2]

  • On microscopic histopathological analysis, Ewing's sarcoma consists of a homogeneous population of small round blue cells that have a high nuclear to cytoplasmic ratio.
  • The tumor cells are tightly packed and grow in a diffuse pattern without evidence of structural organization.
  • The individual cells of Ewing's sarcoma contain round-to-oval nuclei, with fine dispersed chromatin without nucleoli.
  • Occasionally, cells with smaller, more hyperchromatic, and probably degenerative nuclei are present, giving a light cell/dark cell pattern.
  • The cytoplasm varies in amount, but in the classic case, it is clear and contains glycogen, which can be highlighted with a periodic acid-Schiff stain.
  • The nuclei have intense color which make them easily visible.


  1. 1.0 1.1 Cellular Classification of Ewing's sarcoma.National cancer institute.http://www.cancer.gov/types/bone/hp/ewing-treatment-pdq#section/_15
  2. Iwamoto Y (2007). "Diagnosis and treatment of Ewing's sarcoma". Japanese Journal of Clinical Oncology. 37 (2): 79–89. doi:10.1093/jjco/hyl142. PMID 17272319. Retrieved 2012-01-04. Unknown parameter |month= ignored (help)

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