Cutaneous Ewing sarcoma
Primary cutaneous Ewing sarcoma (PCES); cutaneous primitive neuroectodermal tumour (PNET) — older descriptive term, since merged with Ewing sarcoma family; superficial Ewing sarcoma
Primary cutaneous Ewing sarcoma is a rare superficial variant of the Ewing sarcoma family of tumours, defined molecularly by the recurrent EWSR1-FLI1 gene fusion (~85%) — or less commonly EWSR1-ERG, EWSR1-FEV or other variants — and morphologically by sheets of small round blue cells with strong membranous CD99 positivity. While the visceral and osseous Ewing sarcomas of children and young adults are aggressive systemic diseases, the primary cutaneous / superficial subcutaneous form has a substantially better prognosis (5-year overall survival 80–90%) and tends to occur in older children, adolescents and young adults. Multimodality therapy (wide local excision, multi-agent chemotherapy, ± radiotherapy) following established Ewing sarcoma protocols delivered through a paediatric or sarcoma MDT is standard.
Clinical features
- Rapidly growing dermal / subcutaneous nodule, usually painless.
- Most common on the trunk and extremities (paraspinal, lower limb).
- Median age 15–25; both sexes; rare in children <5 (where infantile fibrosarcoma differential applies) and uncommon >40.
- Often misdiagnosed as cyst, lipoma or haematoma; diagnostic delay common.
- B symptoms (fever, weight loss, fatigue) are uncommon in superficial disease and should prompt staging for systemic involvement.
Histology & molecular
- Sheets of monotonous small round blue cells with scant cytoplasm, fine chromatin and high N:C ratio; "Homer-Wright rosettes" (rosette formation around a central neuropil) in the more PNET-like end of the spectrum.
- Brisk mitotic activity; tumour necrosis variable.
- Immunohistochemistry — strong membranous CD99 (MIC2) positivity (the diagnostic hallmark, though not specific); FLI-1 nuclear positive; NKX2.2 positive; cytokeratin focal in 20–30% (mimicking carcinoma).
- Negative for melanoma markers (S100, SOX10, Melan-A) and lymphoid markers (CD20, CD3, TdT — though differential includes lymphoblastic lymphoma).
- EWSR1 rearrangement by FISH or RT-PCR / RNA-seq; partner most often FLI1 (chromosome 11q24 ↔ 22q12), less commonly ERG, FEV, ETV1, ETV4.
- Differential: alveolar rhabdomyosarcoma (myogenin/MyoD1+); lymphoblastic lymphoma (TdT+); cutaneous Merkel cell carcinoma (CK20+ paranuclear dot); BCC; small-cell melanoma; metastatic neuroblastoma in young children.
Staging & workup
- Refer to paediatric / TYA / adult sarcoma MDT — Ewing sarcoma is treated through dedicated regional services in the UK.
- MRI of the affected region.
- CT chest (lung is the commonest metastatic site).
- PET-CT for systemic staging.
- Bone marrow biopsy at presentation (per Ewing protocols) — although superficial Ewing rarely involves marrow.
- Echocardiogram and audiometry pre-chemotherapy (anthracycline / cisplatin baseline).
Management
- Multimodality, protocol-based treatment (UK paediatric / TYA sarcoma protocols, e.g. iEuro-Ewing 2012 / EE2012).
- Induction chemotherapy — UK current standard is VDC/IE per EE2012 / iEuro-Ewing 2012 (vincristine-doxorubicin-cyclophosphamide alternating with ifosfamide-etoposide). VIDE (vincristine, ifosfamide, doxorubicin, etoposide) was the EE99 induction regimen and is historic.
- Local control — wide local excision with adequate margins (clear of fascia / deep planes) is the cornerstone for superficial disease; reconstruction with skin graft, local or free flap.
- Adjuvant radiotherapy for incomplete margins, large size or anatomically constrained lesions where wide excision is not feasible.
- Adjuvant chemotherapy — typical 8 cycles of vincristine, doxorubicin, cyclophosphamide alternating with ifosfamide and etoposide (VDC/IE), consistent with the EE2012 backbone, or risk-adapted intensification.
- Relapsed / refractory disease — high-dose chemotherapy + autologous stem-cell rescue, irinotecan/temozolomide combinations, regorafenib, clinical trials of EWSR1-FLI1-targeted therapies.
Prognosis
Substantially better than osseous Ewing sarcoma — 5-year overall survival 80–90% for primary cutaneous / superficial Ewing with multimodality therapy, compared with 60–70% for visceral / osseous disease and 20–30% for metastatic disease at presentation. Adverse factors: large tumour size (>8 cm), poor histological response to neoadjuvant chemotherapy, primary metastatic disease, axial / pelvic site (less applicable to true cutaneous disease).
References
- Chow LT et al. Cutaneous and subcutaneous Ewing sarcoma — clinicopathologic study. J Am Acad Dermatol; 2009.
- Brennan B et al. Outcome of patients with localised Ewing sarcoma treated on iEuro-Ewing 2012. Lancet Oncol; 2024.
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