Define Ewing’s Sarcoma. Describe its clinical features, investigations, management and prognosis.

Definition & Epidemiology

Ewing’s sarcoma is a highly malignant small round-cell tumour of bone (and soft tissue), thought to arise from primitive neuroectodermal cells and characterised by the t(11;22) translocation (EWS-FLI1 fusion). It typically affects children and adolescents (5–15 years) — a slightly younger group than osteosarcoma — and arises in the diaphysis of long bones and in flat bones (pelvis, ribs, scapula).

Ewing’s sarcoma of the diaphysis with a laminated ‘onion-skin’ periosteal reaction and a permeative destructive pattern.

Clinical Features

Pain and a swelling, often with fever, malaise, weight loss and a raised ESR/WCC — a picture that can closely mimic osteomyelitis. The overlying tissues may be warm and tender. Presentation with metastatic disease is not uncommon.

Investigations

• Radiographs show a permeative (‘moth-eaten’) destructive diaphyseal lesion with a laminated ‘onion-skin’ periosteal reaction and often a large soft-tissue mass.
• MRI defines the extent (often larger than the radiograph suggests)
• staging includes CT chest, bone scan/pet and bone-marrow assessment.
• Biopsy shows sheets of small round blue cells (PAS-positive glycogen; CD99 positive) and the characteristic translocation confirms the diagnosis.

Management

Ewing’s is treated by a multimodal regimen: multi-agent chemotherapy (neoadjuvant and adjuvant) combined with local control by surgery and/or radiotherapy. Unlike osteosarcoma, Ewing’s is highly radiosensitive, so radiotherapy has a major role in local control, particularly for surgically inaccessible sites (e.g. Parts of the pelvis/spine); wide surgical excision is preferred where feasible.

Prognosis

Prognosis depends chiefly on the presence of metastases at diagnosis, tumour size/site and response to chemotherapy. Localised disease has a reasonable cure rate with modern multimodal therapy, but metastatic disease (lungs, bone, marrow) carries a much poorer outlook.

Differential Diagnosis

The main differentials are acute osteomyelitis (shared fever, warmth and raised inflammatory markers), other small round-cell tumours (metastatic neuroblastoma in young children, lymphoma of bone), and eosinophilic granuloma. Histology with CD99 immunostaining and demonstration of the EWS gene rearrangement is decisive, which is why tissue diagnosis is mandatory before committing to treatment.

• Malignant small round-cell tumour; t(11;22)/EWS-FLI1; children/adolescents.
• Diaphysis of long bones and flat bones; onion-skin periosteal reaction; permeative destruction.
• Mimics osteomyelitis (fever, ↑WCC/ESR) — biopsy resolves doubt; CD99 positive.
• Multimodal chemo + local control; highly radiosensitive (unlike osteosarcoma).
• Prognosis hinges on metastases at diagnosis and chemo response.