Ewing sarcoma

Epidemiology
2nd most common pediatric bone tumor (after osteosarcoma)
200 cases per year

Risk factors
57% males
Ages 8 - 25
Rare in blacks

Pathology
t11;22 (EWS gene) or t11;21 (ERG gene)
c-myc amplified
Staining: PAS+, S-100+, vimentin+, neuron specific enolase-, cytokeratin-

Clinical
Most common sites are pelvis (25%) and lower extremity (30%)
Diaphysis of the bone
On imaging: Onion-skinning = subperiosteal involvement; moth eaten bone
25% have mets at diagnosis

Prognostic factors
Unfavorable: tumor in pelvis or trunk, large mass, older age, poor chemo response, mets, unresectable tumor, VEGF+, p53, p16, p14 mutations

Therapy
1) Induction chemo: cyclophosphamide, adriamycin, vincristine, dactinomycin, ifosfamide, etoposide
Response to chemo is highly predictive of the ultimate outcome
2) Surgery: if at all possible
3) RT indications (always given with concurrent chemo)
 -Unresectable tumor (55.8Gy)
 -Positive or close margins
 -Incomplete histologic response

RT technique:
 -Whole bone RT is not necessary
 -Typical field encompasses the pre-chemo volume + 2-4cm to 36-45Gy then boost residual disease/tumor bed to 50.4Gy or 55.8Gy (residual/unresectable tumor)
 -Whole lung RT to 18Gy can be given for mets