Ewing Sarcoma
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Direct answer
Ewing sarcoma is a small round blue cell tumour of bone and soft tissue, mostly in children and young adults, defined by a translocation most often t(11;22) that fuses EWSR1 with FLI1. It typically arises in the diaphysis of a long bone or the pelvis, with lytic destruction and onion-skin periosteal reaction on radiograph. Fever, raised ESR and anaemia can mimic osteomyelitis, so biopsy is needed first.
What you must remember
- Age: mostly children and adolescents, with a peak in the second decade.
- Genetics: t(11;22)(q24;q12) with the EWSR1-FLI1 fusion in most cases, confirmed by molecular testing on tissue.
- Site: the diaphysis of long bones, the pelvis, ribs and chest wall, rather than the epiphysis.
- Radiograph: moth-eaten lytic destruction with onion-skin periosteal reaction and a large soft-tissue mass.
- Systemic features: fever, raised ESR, anaemia and sometimes leucocytosis, which can mislead towards infection.
- Markers: CD99 positivity on immunohistochemistry, with PAS-positive glycogen on staining.
- Treatment: multi-agent chemotherapy in alternating blocks, with local control by surgery or radiotherapy.
- Prognosis: metastases at diagnosis, especially to lung or bone, carry the worst outlook.
Ewing sarcoma and osteomyelitis side by side
Osteomyelitis is the mimic examiners most often pair with Ewing sarcoma, because both destroy bone, provoke a periosteal reaction and cause fever. The comparison below shows where they split and which feature should prompt a biopsy rather than another course of antibiotics. Once the diagnosis is confirmed, chest imaging and a bone scan complete the staging.
| Feature | Ewing sarcoma | Osteomyelitis |
|---|---|---|
| Age | Child or adolescent | Any age, commonly a child |
| Site | Diaphysis, pelvis or chest wall | Metaphysis, spreading to the diaphysis |
| Periosteal reaction | Onion-skin, with moth-eaten lysis | New bone with sequestrum and involucrum |
| Blood picture | Anaemia, raised ESR, fever | Raised CRP and neutrophilia |
| Confirmation | Biopsy with EWSR1 fusion testing | Culture from aspirate or biopsy |
Each feature alone is non-specific, but a lytic diaphyseal lesion that fails to respond to antibiotics is the signal to biopsy. Repeated antibiotic courses without a diagnosis delay the one test that settles the question. Imaging alone seldom separates the two with certainty, so tissue confirmation is always required.
Where the exam tries to catch you
The traps lie in the look-alikes and in assuming that normal systemic signs exclude the tumour.
- Trap: labelling every lytic diaphyseal lesion in a child as osteomyelitis Correct: Ewing sarcoma is the key mimic, and a lesion that does not respond to antibiotics needs biopsy.
- Trap: choosing surgery alone because the local tumour looks limited Correct: Ewing sarcoma is chemosensitive and needs systemic chemotherapy even when the local disease appears small.
- Trap: assuming a normal temperature and ESR exclude Ewing sarcoma Correct: systemic features are common but not invariable, so the diagnosis rests on the lesion and the biopsy.
Frequently asked questions
Which translocation is characteristic of Ewing sarcoma?
Ewing sarcoma is characteristically associated with the t(11;22)(q24;q12) translocation, which fuses EWSR1 with FLI1. The fusion is found in most cases and is confirmed by molecular testing on tissue.
How does Ewing sarcoma look different from osteomyelitis on X-ray?
Ewing sarcoma shows permeative, moth-eaten lysis with onion-skin periosteal reaction, typically in the diaphysis. Osteomyelitis shows new periosteal bone, sequestrum and involucrum, usually starting in the metaphysis.
How is Ewing sarcoma treated?
Ewing sarcoma is treated with multi-agent chemotherapy given before and after local control, combined with surgery or radiotherapy to the primary site. The tumour is sensitive to both chemotherapy and radiotherapy.
What worsens the prognosis of Ewing sarcoma?
Metastases at diagnosis, especially to the lungs or bone, are the most important adverse prognostic factor in Ewing sarcoma. A poor response to induction chemotherapy also worsens the outlook.