Ewing Sarcoma - Primitive Neuroectodermal Tumor

The Ewing sarcoma family of tumors (ESFT) are small round blue cell neoplasms and include classic Ewing sarcoma (ES) of the bone, extraskeletal ES, small round-cell tumors of the thoracopulmonary region (Askin tumor), and peripheral-type primitive neuroectodermal tumors (pPNET).

  • Diagnosis
  • Monitoring
  • Background
  • Lab Tests
  • References
  • Related Topics
  • Videos

Indications for Testing

  • Tumor with initial histology at appropriate site (eg, bony tumor in childhood)


  • Densely packed homogeneous small round blue cells
    • Biopsy specimen may be difficult to assess because tumor cells resemble other similar sarcomatous or round-cell tumors (eg, lymphoma/leukemia, rhabdomyosarcoma, medulloblastoma, neuroblastoma, desmoplastic small round cell tumor [DSRCT], poorly differentiated carcinoma, poorly differentiated synovial sarcoma, melanoma)
  • Immunohistochemistry
    • CD99 (MIC2, also known as O13) – cell surface glycoprotein
      • Highly sensitive
      • Found in 85-95% of Ewing sarcoma (ES)
      • Not specific – expressed in acute lymphoblastic leukemia/lymphoma; synovial sarcoma and DSRCT; and other sarcomas
      • May be helpful in differentiating ES and peripheral primitive neuroectodermal tumors (pPNET) from other small round-cell neoplasms
    • Friend leukemia integration-1 (Fli-1) protein
      • Nuclear staining found in ~70% of ES
      • Not specific – found in acute lymphoblastic lymphomas, DSRCT, Merkel cell carcinoma, and synovial sarcoma
  • Molecular studies (PCR, FISH) – may be crucial if tumor is in unusual location; studies together may provide complementary information
    • EWSR1 rearrangements – supports diagnosis of ES
      • EWSR1-FLI1 fusion [t(11:22)(q24;q12)] – 85-90%
      • EWSR1-ERG fusion [t(21;22)(q22;q12)] – 5-10%
      • Other chimeric translocations are rare (most common listed below); for other fusions, see Sarcoma topic
        • EWSR1-ETV1 [t(7:22) (p22;q12)]
        • EWSR1-TVA [t(17;22) (q21;q12)]
        • EWSR1-FEV [t(2;22) (q35;q12)]

Imaging Studies

  • Plain radiographs – may show a lytic lesion of bone
  • MRI
    • Both bony and soft tissue components may coexist
    • “Onion skinning” of reactive periosteum
    • Saucerization – concave cortical defect in bone due to erosion of outer cortex
    • “Hair on end” – vertical form of periosteal reaction in bone
  • Bone scan or FDG-PET may be used for staging


  • Favorable
    • Normal serum LD
    • Distal site of primary disease
    • Absence of metastatic disease
  • Unfavorable
    • Metastatic disease – most significant adverse factor
      • ~25% present with metastatic disease
      • Lungs, other bones, bone marrow are most common sites
    • Elevated serum LD
    • Primary tumor in pelvic bone
    • Large tumor
    • Age – lower survival rate in adults

Differential Diagnosis

  • Similar-appearing sarcomatous tumors
    • DSRCT
    • Poorly differentiated synovial sarcoma
    • Alveolar rhabdomyosarcoma
    • Mesenchymal chondrosarcoma
    • Undifferentiated small round cell sarcomas with CIC-DUX4 or BCOR-CCNB3 fusions
    • Small cell osteosarcoma
    • Undifferentiated small round cell sarcoma/Ewing-like sarcoma
  • Other tumors
    • Neuroblastoma
    • Lymphoblastic lymphoma
    • Small cell carcinoma
    • Merkel cell carcinomas
    • Melanoma, small cell malignant variant
  • Tumor recurrence and/or distant spread
  • Increased risk of osteosarcoma secondary to radiotherapy
  • Increased risk (5-8%) of treatment-related leukemias and myelodysplastic syndromes secondary to chemotherapy


  • Incidence – 4/1,000,000 (SEER)
  • Age
    • Second most common neoplasm of the bone in children and adolescents
    • Peak incidence in second decade
    • Small percent in patients <10 years and >20 years; rare in >30 years
  • Sex – M>F, 1.5:1
  • Ethnicity – in U.S., more common in Caucasians; infrequent in African Americans


  • ES is characterized by fusion of EWS chromosome 22q12 with chromosome in the ETS gene family
    • ETS genes include FLI1ERGETV1ETV4FEV
  • EWSR1-FLI1 t(11;22)(q24;q12)
    • Found in 85-90% of ES
  • EWSR1-ERG t(21;22)(q22;q12)
  • EWSR1 gene is also rearranged in a variety of other tumors with a variety of other partners


  • Classic ES is a poorly differentiated, homogeneous population of small round cells with high nuclear-to-cytoplasmic ratio
  • Characterized by strong expression of glycoprotein CD99 (also known as O13)
  • Majority arise in bone; remainder in soft tissue
    • In bone – most frequent in diaphysis or metaphyseal region

Clinical Presentation

  • Symptoms based on location of tumor
  • Primary tumor sites include
    • Pelvis (26%)
    • Femur (20%)
    • Tibia/fibula (18%)
    • Chest wall (16%)
    • Upper extremity (9%)
    • Spine (6%)
    • Other (5%)
  • Pain may be intermittent and variable in intensity
    • Easily mistaken for bone growth or injury in children
  • Palpable mass/swelling at affected site
  • Constitutional – occasionally may present with fever, weight loss, fatigue
Tests generally appear in the order most useful for common clinical situations. Click on number for test-specific information in the ARUP Laboratory Test Directory.

EWSR1 (22q12) Gene Rearrangement by FISH 2007225
Method: Fluorescence in situ Hybridization


Results may be compromised if the recommended fixation procedures have not been followed (avoid decalcification)

Does not identify specific translocation partner

Chromosome FISH, Interphase 2002298
Method: Fluorescence in situ Hybridization

Ewing Sarcoma (O13) by Immunohistochemistry 2004055
Method: Immunohistochemistry


Insufficient for diagnosis as a stand-alone test

Lactate Dehydrogenase, Serum or Plasma 0020006
Method: Quantitative Enzymatic

Friend Leukemia Integration-1 (Fli-1) by Immunohistochemistry (Temporary Referral as of 10/09/17) 2003887
Method: Immunohistochemistry


Insufficient for diagnosis as a stand-alone test


NCCN Clinical Practice Guidelines in Oncology, Bone Cancer. National Comprehensive Cancer Network. Fort Washington, PA [Accessed: Apr 2017]

NCCN Clinical Practice Guidelines in Oncology, Soft Tissue Sarcomas, Version 2.2017. National Comprehensive Cancer Network. Fort Washington, PA [Accessed: Jun 2017]

Protocol for the Examination of Specimens From Pediatric Patients With Ewing Sarcoma (ES). Based on AJCC/UICC TNM, 7th ed. Protocol web posting date: Jun 2012. College of American Pathologists (CAP). Northfield, IL [Revised: Aug 2016; Accessed: Dec 2016]

General References

Balamuth NJ, Womer RB. Ewing's sarcoma. Lancet Oncol. 2010; 11(2): 184-92. PubMed

Bovée JV, Hogendoorn PC. Molecular pathology of sarcomas: concepts and clinical implications. Virchows Arch. 2010; 456(2): 193-9. PubMed

Choi EK, Gardner JM, Lucas DR, McHugh JB, Patel RM. Ewing sarcoma. Semin Diagn Pathol. 2014; 31(1): 39-47. PubMed

de Alava E, Lessnick S, Sorenson. Ewing Sarcoma, Ch 19. In Fletcher CDM, Bridge JA, Hogendoorn, Mertens F, eds. WHO Classification of Tumours of Soft Tissue and Bone, 4th ed. Lyon, France: World Health Organization, 2013.

Folpe A, Gown A. Immunohistochemistry for Analysis of Soft Tissue Tumors, Ch 7. In Goldblum JR, Folpe AL, Weiss SW, eds. Enzinger and Weiss's Soft Tissue Tumors, 6th ed. Philadelphia, PA: Elsevier, 2014.

Goldblum J, Folpe A, Weiss S. Approach to the Diagnosis of Soft Tissue Tumors, Ch 6. In Goldblum JR, Folpe AL, Weiss SW, eds. Enzinger and Weiss's Soft Tissue Tumors, 6th ed. Philadelphia, PA: Elsevier, 2014.

Goldblum J, Folpe A, Weiss S. Malignant Soft Tissue Tumors of Uncertain Type, Ch 33. In Goldblum JR, Folpe AL, Weiss SW, eds. Enzinger and Weiss's Soft Tissue Tumors, 6th ed. Philadelphia, PA: Elsevier, 2014.

Gulley ML, Kaiser-Rogers KA. A rational approach to genetic testing for sarcoma. Diagn Mol Pathol. 2009; 18(1): 1-10. PubMed

Ladanyi M, Fletcher J, Cin P. Cytogenetic and Molecular Genetic Pathology of Soft Tissue Tumors, Ch 4. In Goldblum JR, Folpe AL, Weiss SW, eds. Enzinger and Weiss's Soft Tissue Tumors, 6th ed. Philadelphia, PA: Elsevier, 2014.

Potratz J, Dirksen U, Jürgens H, Craft A. Ewing sarcoma: clinical state-of-the-art. Pediatr Hematol Oncol. 2012; 29(1): 1-11. PubMed

Puls F, Niblett AJ, Mangham C. Molecular pathology of bone tumours: diagnostic implications. Histopathology. 2014; 64(4): 461-76. PubMed

Slater O, Shipley J. Clinical relevance of molecular genetics to paediatric sarcomas. J Clin Pathol. 2007; 60(11): 1187-94. PubMed

References from the ARUP Institute for Clinical and Experimental Pathology®

Kikuchi K, Taniguchi E, Chen HH, Svalina MN, Abraham J, Huang ET, Nishijo K, Davis S, Louden C, Zarzabal LA, Recht O, Bajwa A, Berlow N, Suelves M, Perkins SL, Meltzer PS, Mansoor A, Michalek JE, Chen Y, Rubin BP, Keller C. Rb1 loss modifies but does not initiate alveolar rhabdomyosarcoma. Skelet Muscle. 2013; 3(1): 27. PubMed

Lewis TB, Coffin CM, Bernard PS. Differentiating Ewing's sarcoma from other round blue cell tumors using a RT-PCR translocation panel on formalin-fixed paraffin-embedded tissues. Mod Pathol. 2007; 20(3): 397-404. PubMed

Sangle NA, Layfield LJ. Telangiectatic osteosarcoma. Arch Pathol Lab Med. 2012; 136(5): 572-6. PubMed

Medical Reviewers

Last Update: October 2017