Ewing Sarcoma

John P. Christodouleas and Moody D. Wharam, Jr.

 Background

What is the annual incidence of Ewing sarcoma (EWS) in the U.S.? How common is it relative to other bone tumors?

200 cases/yr of EWS in the U.S.; 2^nd most common bone tumor (osteosarcoma #1)

What is the median age of presentation of EWS?

The median age of EWS is 14–15 yrs.

Is EWS associated with congenital Dz?

No. However, it can occur as a 2^nd malignant neoplasm.

What is the racial and gender predilction?

EWS is more common in whites (>90% of cases) and among males (1.5:1).

What is the embryologic tissue of origin in EWS?

Neuroectodermal tissue is the embryonic tissue of origin for EWS.

What is the most common genetic change seen in EWS?

t(11:22) in 90%, FLI1(11): EWS(22). Other minor translocations include t(21,22) and t(7,22).

What other neoplasms are associated with the EWS translocation?

PNET, malignant melanoma of soft parts, and desmoplastic small round cell tumor (DSRCT)

Which exon fusion in t(11,22) is most common, and why is this important?

The most common fusion is exon 7 of EWS and exon 6 of FLI1 in 60% of cases. It is associated with a lower proliferative rate and better prognosis.

What type of cell morphology is expected to be seen in EWS?

Small round blue cells should be seen in EWS.

What constitutes the Ewing family of tumors?

EWS (osseous and extraosseous), PNET, DSRCT, and Askin tumor

What other tumors also have small round blue cells?

1. 
   

   Lymphoma

   
   
2. 
   

   Ewing

   
   
3. 
   

   Acute lymphoblastic leukemia

   
   
4. 
   

   Rhabdomyosarcoma

   
   
5. 
   

   Neuroblastoma (NB)

   
   
6. 
   

   Neuroepithelioma

   
   
7. 
   

   Medulloblastoma

   
   
8. 
   

   Retinoblastoma

(Mnemonic: LEARN NMR)

What markers help differentiate EWS from other small round blue tumors?

Markers that differentiate EWS:

1. 
   

   Vimentin

   
   
2. 
   

   HBA-71

   
   
3. 
   

   β2-microglobulin

   
   
4. 
   

   ↑c-myc (vs. n-myc in NB)

How is PNET similar to and different from EWS histologically?

PNET and EWS have similar translocations and are both CD99 (MIC2)+ and vimentin+. However, PNET is NSE+, S100+, more differentiated, and has more neuroendocrine features. EWS is NSE– and S100 variable.

What major factors have been classically associated with a poor prognosis in EWS?

1. 
   

   Male gender

   
   
2. 
   

   Age >15 yrs (>17 yrs in some)

   
   
3. 
   

   Pelvic/axial Site or rib origin

   
   
4. 
   

   Size (>8 cm per St. Jude or >100 cc per CESS-81)

   
   
5. 
   

   Stage (metastatic)

   
   
6. 
   

   ↑ LDH

   
   
7. 
   

   Poor response to chemo (>10% viable tumor)

(Mnemonic: MASSSive LDH response)

What is Askin tumor?

Askin tumor is nonosseous PNET of the chest wall (worse prognosis than other sites).

What % of EWS pts present with mets?

20%–25% of EWS pts present with mets. Mets typically occur in the lung (40%–50%) > bone

Where do mets typically occur?

(25%–40%) ≥ BM (~25%) and LNs (<10%).

What % of pts with localized Dz vs. lung mets have BM micromets?

25% (localized) vs. 40% (lung mets)

 Workup/Staging

What is the typical clinical presentation with EWS?

Pain (96% of cases) and swelling (63% of cases) are most common → fever (21%) and fractures (16%).

What Sx at presentation portends a particularly poor prognosis in EWS?

Pts who present with fever (21% of cases) tend to have a poor prognosis.

What is the most commonly involved site in EWS at presentation?

Extremities (53%) > axial skeleton (47%). The lower extremity is the most common region, and the femur is most common site (~20% of cases).

If an EWS tumor presents centrally, what is the most common site?

The pelvis (20% of cases) is more common than the axial skeleton (12% of cases).

List the general workup for a pt who presents with an extremity mass.

Extremity mass workup: H&P, plain x-ray, MRI/CT primary, and core needle Bx or incisional Bx. Once a Dx of a sarcoma (EWS) is confirmed, complete the workup with CBC, BMP, LDH, ESR, LFTs, CXR, CT chest, bone scan or PET/CT, and BM Bx.

What are the characteristic findings on plain x-ray in EWS? How does this compare to osteosarcoma?

Classically, EWS shows an “onion skin” reaction on plain films, whereas osteosarcoma is associated with a “sunburst” appearance. The Codman triangle, an area of new subperiosteal bone as a result of periosteal lifting by underlying tumor, can be seen in both EWS and osteosarcoma.

How is EWS staged?

No standard staging system

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