Ewing sarcoma

Ewing sarcoma is a highly aggressive, malignant small round cell neoplasm that arises predominantly in bone and, less commonly, in soft tissue.[1][2] It is the second most common primary malignant bone tumor in children and adolescents after osteosarcoma.[2][3] The tumor is genetically defined by balanced chromosomal translocations fusing a member of the FET gene family (most often EWSR1) with an ETS transcription factor, producing a chimeric oncoprotein that drives tumorigenesis.[1][2] In the jaws, Ewing sarcoma characteristically presents as a rapidly enlarging, poorly defined, permeative lytic lesion with aggressive periosteal reaction and an associated soft-tissue mass.[3][4] Management requires urgent multidisciplinary referral for neoadjuvant multiagent chemotherapy followed by surgery and/or radiotherapy.[5][6]

Current classification

The WHO Classification of Soft Tissue and Bone Tumours, 5th edition (2020), places Ewing sarcoma within the chapter on undifferentiated small round cell sarcomas of bone and soft tissue.[7][8] It is now strictly defined by FET::ETS gene fusions, distinguishing it from other round cell sarcomas that were formerly grouped under the umbrella term "Ewing sarcoma family of tumors".[7][8]

Accepted and obsolete names

• Ewing sarcoma — the current preferred term.[7]
• Primitive neuroectodermal tumor (PNET) — historically used for tumors showing greater neural differentiation; now subsumed under Ewing sarcoma when a FET::ETS fusion is confirmed.[5][9]
• Askin tumor — an obsolete designation for Ewing sarcoma of the chest wall.[9][10]
• Ewing sarcoma family of tumors (ESFT) — a former umbrella term that is no longer recommended, as the WHO 5th edition separates CIC-rearranged sarcoma, BCOR-altered sarcoma, and sarcomas with EWSR1–non-ETS fusions into distinct entities.[7][8]
• Ewing-like sarcoma — terminology no longer included in the WHO classification.[5][8]

• Age: Peak incidence at approximately 15 years; the majority of cases occur in the first two decades of life. In the jaws specifically, the median age at diagnosis is approximately 12 years.[1][2][6]
• Sex: Slight male predominance overall (male-to-female ratio ~1.3–1.6:1).[1][11]
• Ancestry: Markedly more common in persons of European ancestry, with an incidence nearly 10 times that observed in persons of African ancestry.[1]
• Frequency in the jaws: The head and neck region accounts for only 1%–9% of all Ewing sarcomas. Among head and neck sites, the jawbones are the second most commonly affected location after the respiratory tract. The mandible is involved far more often than the maxilla. Overall, jaw involvement represents approximately 1%–2% of all Ewing sarcomas.[3][6][11][12]

Presentation and symptoms

The clinical features of jaw Ewing sarcoma are nonspecific and frequently mimic odontogenic infection or other benign conditions, leading to diagnostic delay.[3][13]

• Swelling is the most common presenting sign — typically a rapidly enlarging, firm, fixed mass.[6][11]
• Pain is reported in roughly half of mandibular cases and is associated with significantly worse overall survival.[6]
• Dental symptoms include tooth loosening, toothache, and widening of the periodontal ligament space.[3]
• Paresthesia or anesthesia of the inferior alveolar nerve distribution may occur with mandibular lesions.[3]
• Loss of pulp vitality of involved teeth has been reported as an early symptom in maxillary cases.[14]
• Mucosal changes such as hyperemia, venous dilation, and overlying soft-tissue induration may be present.[3]

Tempo and red flags

The mean time from symptom onset to diagnosis is approximately 4 months but ranges widely.[11] Rapid growth, sensory nerve disturbance, and tooth mobility in a child or adolescent without an obvious infectious or traumatic cause should raise suspicion for a malignant process. Systemic symptoms (fever, weight loss, fatigue) may appear with advanced or metastatic disease.[1]

Location and distribution

Ewing sarcoma of the jaws arises centrally within the medullary cavity.[3][4] The mandible is affected far more frequently than the maxilla; the posterior body and ramus are the most common mandibular subsites.[3] Maxillary involvement typically centers on the alveolar process and may extend into the maxillary sinus.[14]

Periphery and shape

The lesion characteristically has poorly defined, irregular margins consistent with an aggressive growth pattern.[3][4] On conventional radiographs, the margin pattern corresponds to Lodwick–Madewell grade IIIB (moth-eaten to permeative osteolysis), reflecting the rapid, infiltrative nature of the tumor.[1][15] A well-defined border is occasionally reported in head and neck cases but should not diminish suspicion when other aggressive features are present.[11]

Internal architecture

The internal pattern is predominantly radiolucent (lytic), reflecting permeative medullary destruction without significant matrix mineralization.[3][4][11] Mixed radiolucent–radiopaque appearances are reported in a majority of head and neck cases on cross-sectional imaging, largely attributable to residual bone islands within the zone of destruction and periosteal new bone rather than tumor matrix production.[11] True tumoral calcification or osteoid formation is absent; the presence of mineralized tumor matrix should prompt consideration of osteosarcoma instead.

Periosteal reaction

Aggressive periosteal reaction is a characteristic feature of Ewing sarcoma and may take several forms:[1][15]

• Lamellated ("onion-skin") periosteal new bone — the classic pattern in long bones; however, this pattern is uncommon in the jaws because the thin cortex of flat bones provides insufficient substrate for multilayered periosteal response.[3][15]
• Spiculated (sunray/sunburst) periosteal reaction — occasionally seen in jaw lesions.[3][16]
• Codman triangle — representing elevated, disrupted periosteum at the margin of a soft-tissue mass — may be identified.[1][15]
• In the jaws, a spiculated pattern or Codman triangle is more likely to be the dominant periosteal finding than the lamellated pattern.[3][16]

Effects on teeth and adjacent structures

A distinctive feature of jaw Ewing sarcoma is displacement of teeth without root resorption, a finding that helps differentiate it from many odontogenic and other malignant jaw lesions.[4] Widening of the periodontal ligament space around involved teeth is common. Root resorption, while not the dominant pattern, has been reported occasionally — for example, in maxillary cases extending through the alveolar bone.[14] Tooth loosening and loss of vitality may occur as the tumor infiltrates the alveolar process and neurovascular structures.[3]

Extent and cortical involvement

Cortical destruction is common and often extensive, with focal breaches allowing continuity between the intraosseous tumor and an extraosseous soft-tissue mass.[3][10] The soft-tissue component is frequently large relative to the intraosseous component and may be the dominant finding on clinical and imaging examination.[3][10] Extension into the maxillary sinus, infratemporal fossa, or parotid region has been documented.[3][17] CBCT can delineate cortical perforation and the three-dimensional extent of bone destruction more precisely than panoramic radiography, though medical CT and MRI remain the standard for full staging.[18]

Recognized variants in imaging appearance

Occasional cases present as a predominantly expansile lesion mimicking an odontogenic cyst or benign tumor, particularly when the soft-tissue mass is not yet clinically apparent.[13] This deceptive appearance is a well-recognized diagnostic pitfall in the jaws.

Soft-tissue extent and marrow involvement

MRI is the preferred modality for evaluating the full extent of Ewing sarcoma in the jaws.[5][19] The tumor typically demonstrates low-to-intermediate signal on T1-weighted images and heterogeneous high signal on T2-weighted images, with avid contrast enhancement.[20] MRI is superior to CT for delineating intramedullary tumor extent, soft-tissue invasion, and the relationship to neurovascular structures and adjacent compartments (e.g., infratemporal fossa, orbit, skull base).[19][21] Subtle cortical channels connecting intraosseous and extraosseous tumor components are well depicted on both CT and MRI.[10]

Metastatic staging

FDG-PET/CT is the preferred whole-body staging modality and is recommended at initial workup to detect distant metastases to lung, bone, and bone marrow.[5][22] Chest CT is required for pulmonary metastasis evaluation, as PET/MRI and whole-body MRI are less sensitive for small lung nodules.[23] Bone scintigraphy is an alternative when PET/CT is unavailable.[5] Elevated FDG uptake (SUVmax) at diagnosis has been correlated with tumor burden and may carry prognostic significance.[22]

Ewing sarcoma of the jaws must be distinguished from other aggressive lytic lesions occurring in children and young adults. The permeative destruction, aggressive periosteal reaction, and large soft-tissue mass in a young patient narrow the differential, but considerable overlap exists with other small round blue cell tumors and aggressive jaw pathology.

The highest-risk diagnostic pitfall is misidentification of Ewing sarcoma as odontogenic infection or a benign cystic lesion, which delays definitive diagnosis.[3][13] Any rapidly progressive lytic jaw lesion in a child or adolescent warrants incisional or core biopsy with immunohistochemical and molecular confirmation rather than empiric treatment for infection.

Microscopic findings

Ewing sarcoma is composed of monotonous sheets of small, round, blue cells with high nuclear-to-cytoplasmic ratio, round-to-oval nuclei with finely dispersed chromatin, and inconspicuous nucleoli.[1] The cytoplasm is scant and often contains glycogen, which can be demonstrated with periodic acid–Schiff (PAS) staining.[2] Homer-Wright pseudorosettes (fibrillary cytoplasmic processes arranged around a central neuropil-like core) may be present, indicating neural differentiation.[9][24]

Immunohistochemistry

• CD99 (MIC2): Strong, diffuse membranous expression is characteristic and highly sensitive; its absence virtually excludes the diagnosis. However, CD99 is not specific and is expressed by lymphoblastic lymphoma, Merkel cell carcinoma, and other round cell tumors.[1][2][28]
• NKX2.2: Nuclear positivity is sensitive (80%–93%) and, when combined with CD99, achieves specificity approaching 95%–98%.[28][29]
• FLI1: Nuclear expression is seen in most cases but is also expressed by vascular tumors and some lymphomas.[3]
• PAX7: A recently validated marker with high sensitivity for Ewing sarcoma.[29][30]
• Negative staining for desmin, myogenin, MyoD1 (excluding rhabdomyosarcoma), CD45/LCA (excluding lymphoma), and cytokeratins (excluding carcinoma) is essential for differential exclusion.[3]

Molecular confirmation

Definitive diagnosis requires identification of a FET::ETS fusion gene.[1][5] The EWSR1::FLI1 fusion, resulting from t(11;22)(q24;q12), is present in approximately 85% of cases; EWSR1::ERG accounts for roughly 10%, with rare fusions involving ETV1, ETV4, or FEV.[2][31] Detection methods include FISH for EWSR1 rearrangement, RT-PCR for specific fusion transcripts, and next-generation sequencing (NGS)-based RNA panels.[28][32] FISH alone cannot identify the fusion partner and may yield false negatives; NGS or RT-PCR is recommended when FISH is negative and clinical suspicion persists.[5][28]

Radiologic–pathologic correlation

The permeative lytic pattern on imaging corresponds to the diffuse, highly infiltrative growth of small round cells through marrow spaces with minimal stroite reaction. The large soft-tissue mass reflects the tumor's propensity for cortical penetration through small channels, a finding confirmed on both cross-sectional imaging and gross pathologic examination.[10]

Workup and referral

Any jaw lesion with imaging features suggestive of Ewing sarcoma requires urgent referral to a multidisciplinary sarcoma team.[5][12] The NCCN-recommended workup includes:[5]

• Contrast-enhanced MRI (± CT) of the primary site
• Chest CT for pulmonary staging
• FDG-PET/CT (preferred) or bone scintigraphy for systemic staging
• Serum lactate dehydrogenase (LDH)
• Incisional or core biopsy with tissue submitted for immunohistochemistry and molecular/cytogenetic testing
• Consideration of bone marrow biopsy and/or screening MRI of spine and pelvis

Biopsy should be performed by the surgical team that will manage definitive resection to avoid compromising future surgical planes.[5][12] Fine-needle aspiration alone is often insufficient; core or open biopsy is preferred.[12]

Definitive treatment

Multimodal therapy is the standard of care:[5][6]

• Neoadjuvant chemotherapy — multiagent regimens (typically VDC/IE: vincristine, doxorubicin, cyclophosphamide alternating with ifosfamide and etoposide) for at least 9 weeks prior to local therapy (NCCN category 1).[5]
• Local control — surgical resection, radiotherapy, or both. In the jaws, surgical resection (segmental mandibulectomy or maxillectomy) is generally preferred when feasible, as surgery combined with chemotherapy is associated with the best survival outcomes. Radiotherapy is used when complete resection is not achievable or as adjuvant therapy for close or positive margins.[6][12][33]
• Adjuvant chemotherapy follows local control.[5]

Prognosis

• Localized disease: 5-year overall survival exceeds 70% with multimodal therapy; head and neck primary tumors may carry a somewhat more favorable prognosis than axial or pelvic sites, possibly due to earlier detection and smaller tumor volumes.[1][33]
• Mandibular Ewing sarcoma: Estimated 5-year overall survival of approximately 61%.[6]
• Metastatic disease: 5-year survival drops below 30%; metastasis at diagnosis is the single most important adverse prognostic factor.[1]
• Other prognostic factors: Pain at presentation, single-modality treatment, large tumor volume (≥200 mL), and elevated LDH are associated with worse outcomes.[1][6][33]

Surveillance

Post-treatment follow-up includes serial clinical examination, chest CT, and MRI of the primary site to monitor for local recurrence and pulmonary metastases.[5] FDG-PET/CT may be used for restaging.[5]

Molecular subclassification and Ewing-like sarcomas

The WHO 5th edition (2020) now recognizes several round cell sarcomas that were formerly classified within the Ewing sarcoma family but harbor non-ETS fusions (e.g., CIC::DUX4, BCOR::CCNB3, EWSR1::NFATC2).[7][8] These entities differ from true Ewing sarcoma in prognosis and chemosensitivity: CIC-rearranged sarcomas carry a markedly worse prognosis and respond poorly to standard Ewing sarcoma chemotherapy regimens, while BCOR-altered sarcomas may have somewhat more favorable outcomes.[7] Accurate molecular subclassification is therefore essential and should be pursued in all cases of undifferentiated small round cell sarcoma of the jaws.[5][25]

Adamantinoma-like Ewing sarcoma

A recently described variant, adamantinoma-like Ewing sarcoma, shows epithelial differentiation with cytokeratin expression and may arise in the head and neck region.[34] Awareness of this variant is important to avoid misdiagnosis as carcinoma.

Pediatric considerations

Because the majority of jaw Ewing sarcomas occur in children and adolescents, fertility preservation counseling should be offered before initiating chemotherapy.[5] Growth and development of the craniofacial skeleton may be affected by both surgical resection and radiotherapy, necessitating long-term reconstructive and rehabilitative planning.