Small Round Cell Tumor | Second Most Common Pediatric Bone Malignancy | Multimodal Treatment Required
ENNEKING STAGING
Critical Must-Knows
- Second most common primary bone malignancy in children (after osteosarcoma)
- EWS-FLI1 translocation t(11;22) present in 85% - diagnostic hallmark
- Onion-skin periosteal reaction classic radiographic finding
- Multimodal treatment mandatory: chemotherapy + surgery ± radiation
- Poor response to chemotherapy (under 90% necrosis) is worst prognostic factor
Clinical Pearls
- "Fever and elevated inflammatory markers mimic infection - biopsy essential
- "VDC-IE protocol: Vincristine, Doxorubicin, Cyclophosphamide alternating with Ifosfamide, Etoposide
- "Surgical margins more important than degree of necrosis for local control
- "Metastases to lung, bone, bone marrow - whole-body staging required
Clinical Imaging
Critical Ewing Sarcoma Exam Points
Diagnostic Hallmark
t(11;22) translocation creating EWS-FLI1 fusion. Present in 85% of cases. Small round blue cells on histology with CD99 strong diffuse membrane staining.
Classic Presentation
Adolescent with painful diaphyseal lesion, fever, elevated ESR. Mimics osteomyelitis. Femur and pelvis most common sites (60% of cases).
Treatment Paradigm
Neoadjuvant chemotherapy first, then surgery. VDC-IE protocol for 14-17 cycles. Surgery or radiation for local control. Response to chemo predicts survival.
Prognosis Factors
Tumor volume under 200ml, under 90% necrosis post-chemo, metastases at presentation. 5-year survival: 70% localized, 30% metastatic.
Quick Decision Guide: Ewing Sarcoma Management
| Clinical Scenario | Staging | Treatment | Key Pearl |
|---|---|---|---|
| Localized extremity tumor, good chemo response | IB or IIB, over 90% necrosis | Wide excision + reconstruction | Limb salvage in 85% - margins matter more than necrosis |
| Localized pelvic tumor, difficult location | IIB extracompartmental | Chemotherapy + radiation (surgery if resectable) | Radiation for unresectable sites - 55.8 Gy standard dose |
| Metastatic disease at presentation | Stage III with lung mets | Intensive chemotherapy + local control + lung surgery | Whole lung radiation if unresectable - survival drops to 30% |
EWINGEwing Sarcoma Diagnostic Features
| E | EWS-FLI1 fusion t(11;22) translocation in 85% - diagnostic hallmark |
| W | White race predominance Rare in African and Asian populations |
| I | Inflammatory presentation Fever, elevated ESR, mimics osteomyelitis |
| N | Necrosis post-chemo Over 90% necrosis predicts better survival |
| G | Glycogen-rich cells Small round blue cells, PAS positive, CD99 positive |
| E | EWS-FLI1 fusion t(11;22) translocation in 85% - diagnostic hallmark | N | Necrosis post-chemo Over 90% necrosis predicts better survival |
| W | White race predominance Rare in African and Asian populations | G | Glycogen-rich cells Small round blue cells, PAS positive, CD99 positive |
| I | Inflammatory presentation Fever, elevated ESR, mimics osteomyelitis |
Hook:EWING cells are small and angry - they look like infection but have the EWS-FLI1 fusion signature!
VDC-IEVDC-IE Chemotherapy Protocol
| V | Vincristine Microtubule inhibitor |
| D | Doxorubicin Anthracycline - cardiotoxicity risk |
| C | Cyclophosphamide Alkylating agent |
| I | Ifosfamide Alkylating agent - hemorrhagic cystitis risk |
| E | Etoposide Topoisomerase inhibitor - secondary leukemia risk |
| V | Vincristine Microtubule inhibitor | I | Ifosfamide Alkylating agent - hemorrhagic cystitis risk |
| D | Doxorubicin Anthracycline - cardiotoxicity risk | E | Etoposide Topoisomerase inhibitor - secondary leukemia risk |
| C | Cyclophosphamide Alkylating agent |
Hook:VDC-IE cycles: VDC for cycles 1,3,5 then IE for cycles 2,4,6 - alternating reduces resistance!
MELTSEwing Sarcoma Prognosis Factors
| M | Metastases at presentation Worst prognostic factor - drops survival to 30% |
| E | Extremity vs axial Extremity better prognosis than pelvis |
| L | Large tumor volume Greater than 200ml associated with worse outcomes |
| T | Tumor necrosis under 90% Poor response to chemotherapy predicts recurrence |
| S | Size over 8cm Larger tumors have worse prognosis |
| M | Metastases at presentation Worst prognostic factor - drops survival to 30% | T | Tumor necrosis under 90% Poor response to chemotherapy predicts recurrence |
| E | Extremity vs axial Extremity better prognosis than pelvis | S | Size over 8cm Larger tumors have worse prognosis |
| L | Large tumor volume Greater than 200ml associated with worse outcomes |
Hook:MELTS away your prognosis - avoid these factors!
Overview and Epidemiology
Why Ewing Sarcoma Matters
Ewing sarcoma is the second most common primary bone malignancy in children and adolescents (after osteosarcoma), representing 10-15% of all primary bone tumors. It is a highly aggressive small round cell tumor that requires urgent multimodal treatment. Before the advent of chemotherapy in the 1970s, 5-year survival was under 10%. Modern protocols combining chemotherapy, surgery, and radiation have improved survival to 70% for localized disease.
Demographics
- Peak age: 10-20 years (75% of cases)
- Second peak: 20-30 years (15% of cases)
- Rare over age 30: 10% of cases
- Gender: Male greater than Female (1.5:1 ratio)
- Race: 85% white, rare in African/Asian populations
Anatomic Distribution
- Femur: 25% (most common single site)
- Pelvis: 20% (worst prognosis due to size)
- Tibia/fibula: 15%
- Humerus: 10%
- Ribs: 10%
- Axial skeleton: 20% (vertebrae, scapula)
The diaphysis of long bones is involved in 90% of extremity cases, distinguishing Ewing from osteosarcoma (which favors metaphysis). Pelvic tumors are often large at presentation due to deep location and delayed symptoms.
Pathophysiology and Molecular Biology
EWS-FLI1 Translocation: Diagnostic Gold Standard
t(11;22)(q24;q12) translocation creates the EWS-FLI1 fusion oncogene in 85% of Ewing sarcoma cases. The remaining 15% have variant translocations (e.g., EWS-ERG). This fusion protein acts as an aberrant transcription factor, driving uncontrolled proliferation of primitive neuroectodermal cells. FISH or RT-PCR for EWS rearrangement is mandatory for diagnosis - this confirms Ewing sarcoma and distinguishes it from other small round cell tumors.
Cell of Origin
Primitive neuroectodermal cells (mesenchymal stem cells). Cells are small, round, and blue with high nuclear-to-cytoplasmic ratio. PAS-positive glycogen in cytoplasm. Cells express CD99 (MIC2) strongly - diffuse membrane staining pattern.
Growth Pattern
Highly aggressive. Permeative growth through bone marrow spaces. Extensive soft tissue extension common. Lytic destruction of cortex with periosteal reaction (onion-skin or sunburst pattern). Early hematogenous spread to lungs, bones, bone marrow.
| Ewing Sarcoma | Osteosarcoma | Lymphoma |
|---|---|---|
| Age: 10-20 years (peak 15) | Age: 10-20 years (peak 16) | Age: Bimodal (10-20, over 60) |
| Location: Diaphysis | Location: Metaphysis | Location: Metaphysis/diaphysis |
| Histology: Small round blue cells, CD99 positive | Histology: Pleomorphic, osteoid production | Histology: Lymphoid cells, CD20/CD3 positive |
| Genetics: EWS-FLI1 fusion (85%) | Genetics: Complex karyotype, TP53 mutations | Genetics: Various B/T-cell markers |
Classification and Staging
Enneking Surgical Staging System
Gold standard for bone sarcomas. Based on tumor grade, local extent, and metastases.
| Stage | Grade | Extent | Metastases | 5-Year Survival |
|---|---|---|---|---|
| IA | Low-grade | Intracompartmental | None | Not applicable (Ewing always high-grade) |
| IB | High-grade | Intracompartmental | None | 70-75% |
| IIA | Low-grade | Extracompartmental | None | Not applicable (Ewing always high-grade) |
| IIB | High-grade | Extracompartmental | None | 65-70% |
| III | Any grade | Any extent | Present (regional or distant) | 25-30% |
Ewing sarcoma is ALWAYS high-grade, so only stages IB, IIB, and III are relevant.
Compartment Definition
Intracompartmental: Tumor confined within bone cortex or within a single anatomic compartment (e.g., anterior thigh). Extracompartmental: Tumor extends beyond bone cortex into soft tissues OR crosses anatomic barriers (e.g., joint, neurovascular bundle). Most Ewing sarcomas at presentation are Stage IIB (high-grade, extracompartmental, no metastases).
Clinical Presentation
History
- Pain: Localized bone pain (90%) - progressive, worse at night
- Swelling: Palpable soft tissue mass (60%)
- Systemic symptoms: Fever (30%), weight loss, malaise
- Duration: Symptoms 2-6 months before diagnosis (average 3 months)
- Trauma history: 30% report antecedent trauma (coincidental, not causative)
Examination Findings
- Inspection: Visible swelling, skin erythema, venous distension
- Palpation: Warm, tender mass; soft tissue extension common
- Function: Limp if lower extremity; restricted ROM
- Neurovascular: Usually intact (invasion rare)
- Lymph nodes: Regional nodes rarely involved (unlike soft tissue Ewing)
Beware the Mimicker: Ewing Masquerading as Infection
30% of patients present with fever, elevated WBC, and elevated ESR, leading to initial misdiagnosis as osteomyelitis. Key distinguishing features: Ewing typically has a longer symptom duration (months vs weeks), diaphyseal location (osteomyelitis favors metaphysis), and large soft tissue mass. Always biopsy a suspected infection that does not respond to antibiotics within 48-72 hours.
Ewing Sarcoma vs Osteomyelitis: Clinical Distinctions
| Feature | Ewing Sarcoma | Osteomyelitis |
|---|---|---|
| Duration of symptoms | Months (average 3) | Days to weeks |
| Fever pattern | Low-grade, intermittent | High-grade, persistent |
| Bone location | Diaphysis | Metaphysis |
| Soft tissue mass | Large, firm | Small or absent |
| Response to antibiotics | None | Improves within 48-72 hours |
Differential Diagnosis: Small Round Blue Cell Tumours of Bone
| Diagnosis | Typical age | Distinguishing histology / IHC | Key genetics |
|---|---|---|---|
| Ewing sarcoma | 10-20 years | Uniform small round cells, PAS-positive glycogen, strong diffuse membranous CD99, NKX2-2 positive | EWSR1-FLI1 t(11;22) (85%); EWSR1-ERG variant |
| Osteosarcoma (small cell variant) | 10-20 years | Malignant osteoid production by tumour cells; SATB2 positive | Complex karyotype, TP53/RB1 alterations |
| Lymphoma of bone | Bimodal (older adults) | Larger cells, LCA/CD45 positive, CD20 (B) or CD3 (T) positive; CD99 negative | Various B/T-cell rearrangements |
| Metastatic neuroblastoma | Under 5 years | Rosettes, neuropil, PHOX2B / synaptophysin positive; raised urinary catecholamines | MYCN amplification |
| Rhabdomyosarcoma | Children | Rhabdomyoblasts; desmin, myogenin, MyoD1 positive | PAX3/7-FOXO1 (alveolar) |
| Acute osteomyelitis | Any | Neutrophilic inflammation, organisms on culture; no clonal tumour cells | Not applicable |
Investigations
Diagnostic Imaging Protocol
AP and lateral views of affected bone plus joint above and below. Classic findings: Permeative lytic lesion in diaphysis; moth-eaten bone destruction; onion-skin periosteal reaction (lamellated layers); Codman triangle (elevated periosteum); large soft tissue mass. Sunburst pattern less common than osteosarcoma.
Gold standard for local extent. Defines intramedullary involvement, soft tissue extension, neurovascular relationship, skip lesions. Essential for surgical planning. T1: Low signal in marrow. T2: High signal tumor and edema. Contrast: Heterogeneous enhancement of viable tumor.
High-resolution CT chest to detect pulmonary metastases. Present in 15% at diagnosis. Nodules may be small (under 5mm). Follow-up CT every 3 months during treatment.
PET-CT or bone scan to detect skeletal metastases. Bone metastases in 10% at diagnosis. PET-CT also useful for assessing response to chemotherapy (decreased SUV indicates good response).
Bilateral iliac crest marrow aspirate and biopsy to detect marrow involvement (5% at diagnosis). Presence of marrow disease portends poor prognosis (similar to metastatic disease).
Biopsy Technique: Get It Right the First Time
Biopsy planning is critical. Perform incisional or core needle biopsy along longitudinal axis of limb, in line with planned surgical incision. Avoid transverse incisions. Contaminated biopsy tract must be excised en bloc with tumor. Send fresh tissue for: 1) Cytogenetics (FISH for EWS rearrangement), 2) Flow cytometry, 3) Microbiology if infection suspected. Coordinate with oncology and pathology before biopsy.
Laboratory Investigations
- CBC: Anemia (30%), leukocytosis (25%)
- ESR/CRP: Elevated in 50% (non-specific)
- LDH: Elevated in 60% (prognostic marker)
- Alkaline phosphatase: Normal or mildly elevated
- Renal/hepatic function: Baseline for chemotherapy
Histopathology Gold Standard
- Morphology: Sheets of small round blue cells, uniform size
- PAS stain: Positive for glycogen (diastase-sensitive)
- CD99 (MIC2): Strong diffuse membrane staining (95%)
- Cytogenetics: EWS-FLI1 fusion by FISH or RT-PCR (85%)
- Differential: Negative for LCA (vs lymphoma), desmin (vs rhabdomyosarcoma)
Management: Multimodal Treatment Paradigm
Never Operate First: Chemotherapy Comes Before Surgery
Ewing sarcoma requires neoadjuvant chemotherapy FIRST. Surgery or radiation is performed after 10-14 weeks of induction chemotherapy. This approach: 1) Treats micrometastases early, 2) Reduces tumor size for easier resection, 3) Assesses chemotherapy response (over 90% necrosis = good prognosis). Operating first is a critical error that worsens survival and increases morbidity.
Multimodal Treatment Timeline
Biopsy confirmation. Complete staging (MRI, CT chest, PET-CT, bone marrow biopsy). Multidisciplinary tumor board review. Counsel patient and family. Central line placement.
VDC-IE protocol: Vincristine, Doxorubicin, Cyclophosphamide alternating with Ifosfamide, Etoposide. Typically 5-6 cycles over 10-14 weeks. Monitor for toxicity (cardiotoxicity, hemorrhagic cystitis, neutropenia). Restaging MRI at week 10 to assess response.
Preferred: Wide surgical excision with negative margins. Alternative: Radiation therapy (55.8 Gy) for unresectable tumors (pelvis, spine). Pathology assessment of percent necrosis (over 90% = good responder).
Continue VDC-IE for total of 14-17 cycles (approximately 48 weeks total treatment). If good response (over 90% necrosis): standard protocol. If poor response (under 90% necrosis): consider intensified regimen or clinical trial.
Years 0-2: CT chest and MRI local site every 3 months. Years 2-5: Every 6 months. After 5 years: Annual imaging. Monitor for late effects (cardiac, pulmonary, secondary malignancies).
Standard VDC-IE Protocol
VDC cycles (Weeks 1, 7, 13, etc.):
- Vincristine 2 mg/m² IV (max 2 mg) on Day 1
- Doxorubicin 75 mg/m² IV over 48 hours on Days 1-2
- Cyclophosphamide 1200 mg/m² IV on Day 1
IE cycles (Weeks 4, 10, 16, etc.):
- Ifosfamide 1800 mg/m² IV daily for 5 days (Days 1-5)
- Etoposide 100 mg/m² IV daily for 5 days (Days 1-5)
- Mesna (uroprotection for ifosfamide) 1800 mg/m² IV daily
Total duration: 48 weeks (approximately 14-17 cycles depending on protocol)
Chemotherapy Toxicity Monitoring
Doxorubicin cardiotoxicity: Monitor with ECHO or MUGA at baseline, 6 months, and end of treatment. Cumulative dose limit 450-550 mg/m². Ifosfamide hemorrhagic cystitis: Prevented with mesna (binds acrolein metabolite). Neutropenic fever: G-CSF support. Secondary malignancies: Etoposide increases risk of acute myeloid leukemia (AML) at 2-5 years.
Prognostic Factors
Prognostic Factors in Ewing Sarcoma
| Factor | Favorable | Unfavorable | Impact on 5-Year Survival |
|---|---|---|---|
| Metastases at diagnosis | Localized disease | Metastatic (lung, bone, marrow) | 70% vs 25-30% |
| Response to chemotherapy | Over 90% necrosis | Under 90% necrosis | 75% vs 50% |
| Tumor volume | Under 200 ml | Over 200 ml | 70% vs 50% |
| Tumor site | Extremity (distal) | Pelvis, axial skeleton | 75% vs 50% |
| Age at diagnosis | Under 15 years | Over 15 years | 70% vs 55% |
| LDH level | Normal | Elevated | 70% vs 55% |
Percent Necrosis: The Most Important Modifiable Prognostic Factor
Over 90% tumor necrosis after neoadjuvant chemotherapy is the single most important modifiable prognostic factor. Patients with over 90% necrosis have 75% 5-year survival vs 50% for under 90% necrosis. This finding guides adjuvant therapy: good responders continue standard protocol, poor responders may be enrolled in intensified regimens or clinical trials. However, surgical margins are more important than necrosis for local control.
Surgical Technique
Principles of Limb Salvage Surgery
Surgical Goals
Primary Objectives:
- Wide surgical margins (tumor-free tissue surrounding specimen)
- En bloc resection of tumor with intact pseudocapsule
- Reconstruction to restore function
- Facilitate adjuvant chemotherapy (wound healing)
Margin Classification (Enneking):
- Intralesional - through tumor (inadequate)
- Marginal - through reactive zone (high recurrence)
- Wide - through normal tissue (goal for cure)
- Radical - entire compartment (rarely needed)
Timing and Sequencing
Neoadjuvant Chemotherapy First:
- 10-12 weeks of chemotherapy before surgery
- Shrinks tumor, allows assessment of response
- May convert borderline cases to limb salvage
- Reduces micrometastatic disease
Surgical Timing:
- After recovery from chemotherapy toxicity
- When counts adequate (platelets greater than 100, WBC greater than 3)
- Usually 2-3 weeks after last chemotherapy cycle
- Coordinate with oncology team
Key Surgical Principles
Biopsy Tract Excision:
- Biopsy tract must be excised en bloc with specimen
- Prior incisional or needle biopsy site included in resection
- Contaminated tissue must not remain
Wide Margin Achievement:
- 2-3 cm soft tissue margin where possible
- Normal muscle cuff around tumor
- Sacrifice adjacent contaminated structures
- Neurovascular preservation if possible (if not encased)
Reconstruction Options:
- Endoprosthetic replacement - modular tumor prostheses
- Allograft reconstruction - structural allograft
- Allograft-prosthetic composite - combination
- Vascularized fibula - for intercalary defects
- Rotationplasty - specialized limb-sparing option
Clinical Pearl
Exam Viva Point: "What are the principles of surgical resection in Ewing sarcoma?" Answer: Wide en bloc resection with 2-3 cm margins. Include biopsy tract. Surgery performed after neoadjuvant chemotherapy (10-12 weeks). Limb salvage possible in 80-90% with modern techniques. Specimen assessed for percent necrosis.
Limb salvage surgery achieves equivalent oncological outcomes to amputation with modern techniques and multimodal therapy.
Complications
Chemotherapy Complications
| Complication | Incidence | Causative Agent | Management |
|---|---|---|---|
| Cardiomyopathy | 5-10% (clinical), 30% (subclinical) | Doxorubicin (cumulative dose) | Baseline and serial ECHO; dexrazoxane cardioprotection; limit cumulative dose |
| Hemorrhagic cystitis | 10-30% without mesna | Ifosfamide | Mesna uroprotection; aggressive hydration; monitor urinalysis |
| Neutropenic fever | 40-60% | Myelosuppression (all agents) | G-CSF support; prophylactic antibiotics; urgent admission if fever |
| Secondary malignancy (AML) | 1-2% at 10 years | Etoposide, alkylating agents | Long-term surveillance; no prevention available |
Surgical Complications
| Complication | Incidence | Risk Factors | Management |
|---|---|---|---|
| Infection | 5-15% | Chemotherapy-induced neutropenia, endoprosthesis | Antibiotics; irrigation and debridement; prosthesis retention vs removal |
| Local recurrence | 5-10% | Positive margins, poor chemo response | Re-excision or radiation; metastatic workup |
| Limb length discrepancy | Variable | Skeletally immature patients | Expandable prosthesis; contralateral epiphysiodesis |
Radiation Complications
- Growth arrest: Radiation to growth plates in skeletally immature patients
- Radiation-induced sarcoma: 1-2% at 10 years (latency 5-20 years)
- Pathologic fracture: Radiation-weakened bone (5-10%)
- Soft tissue fibrosis: Chronic pain, reduced ROM
Modern IMRT and proton therapy reduce these complications significantly compared to older techniques.
Postoperative Care
Immediate Postoperative Care
Wound Management
Early Wound Care:
- Closed suction drainage (remove when output less than 30 mL/24h)
- Daily wound inspection for hematoma, infection
- Chemotherapy may delay wound healing
- Avoid tension on closure
Infection Prevention:
- Perioperative antibiotics (24-48 hours)
- Clean dressing technique
- Monitor for signs of infection
- Higher infection risk due to immunosuppression
Rehabilitation
Early Mobilization:
- Weight-bearing as per reconstruction type
- Range of motion exercises when wound stable
- Physical therapy referral
- Occupational therapy for upper limb tumors
Prosthesis-Specific:
- Protected weight-bearing if endoprosthesis
- May need assistive devices initially
- Progress per surgeon protocol
Coordination with Oncology
Chemotherapy Resumption:
- Continue adjuvant chemotherapy 2-4 weeks post-surgery
- When wound healing adequate and counts recovered
- Coordinate timing with oncology team
- Total treatment duration approximately 12 months
Specimen Assessment:
- Histopathological analysis of resected tumor
- Percent necrosis reported (response to chemotherapy)
- Margin status documented
- Guides subsequent therapy
Clinical Pearl
Exam Viva Point: "What is the postoperative care after Ewing sarcoma surgery?" Answer: Wound management (higher infection risk). Resume adjuvant chemotherapy within 2-4 weeks when healed. Specimen assessed for percent necrosis (over 90% = good responder). Rehabilitation tailored to reconstruction. Ongoing surveillance for local recurrence and metastasis.
Postoperative care focuses on wound healing, rehabilitation, and seamless transition to adjuvant chemotherapy.
Outcomes
Survival Outcomes
Prognostic Factors
Factors Affecting Prognosis
| Factor | Good Prognosis | Poor Prognosis |
|---|---|---|
| Metastases at diagnosis | Localized disease | Metastatic disease (worst factor) |
| Tumor necrosis | Over 90% necrosis after chemo | Under 90% necrosis (poor responder) |
| Surgical margins | Wide negative margins | Positive or marginal margins |
| Tumor size | Under 8 cm | Over 8 cm |
| Location | Extremity (distal) | Axial (pelvis, spine) |
| Age | Younger patients | Older patients (over 18) |
Key Outcome Determinants:
- Metastatic disease at presentation is the single worst prognostic factor
- Percent tumor necrosis is the most important modifiable factor
- Surgical margins critical for local control
- Chemotherapy completion essential for systemic control
Clinical Pearl
Exam Viva Point: "What is the prognosis for Ewing sarcoma?" Answer: Localized disease: 70% 5-year survival. Metastatic at diagnosis: 25-30% (worst prognostic factor). Over 90% tumor necrosis post-chemotherapy associated with better outcomes. Complete multimodal therapy (chemo + surgery + radiation) is essential.
With modern multimodal therapy, most patients with localized Ewing sarcoma are cured, but metastatic disease remains a significant challenge.
Evidence Base and Key Trials
INT-0091 (Grier): Addition of Ifosfamide and Etoposide
- Multi-centre RCT: 518 eligible patients with Ewing sarcoma / PNET of bone
- Standard VACD (vincristine, doxorubicin, cyclophosphamide, dactinomycin) alternating with ifosfamide-etoposide (IE) vs VACD alone
- Non-metastatic disease (n=398): 5-year EFS 69% (IE arm) vs 54% (standard), P=0.005; OS 72% vs 61%, P=0.01
- No benefit from IE in the 120 patients with metastatic disease at diagnosis
CESS/EICESS: Local Therapy in Localised Ewing Tumours (Schuck)
- Pooled analysis of 1058 patients from CESS 81, CESS 86 and EICESS 92 trials
- Local failure: 7.5% after surgery (with or without post-operative RT) vs 26.3% after definitive radiotherapy (P=0.001)
- Pre-operative RT achieved 5.3% local failure (comparable to surgery)
- Irradiated patients were a negatively selected group with unfavourable (axial) sites
AEWS0031 (Womer): Interval-Compressed Chemotherapy
- RCT (Children's Oncology Group): 568 eligible patients with localised Ewing sarcoma randomised to standard (every 21 days) vs interval-compressed (every 14 days) VDC-IE
- 5-year EFS: 73% (compressed) vs 65% (standard), P=0.048
- Toxicity similar between the two arms with filgrastim support
- 10-year follow-up (Cash 2023) confirmed durable benefit: 10-year EFS 70% vs 61%, OS 76% vs 69%, no excess second malignancies
Picci: Chemotherapy-Induced Necrosis as Prognostic Factor
- 118 patients with localised extremity Ewing sarcoma treated with pre-operative chemotherapy then surgery
- Histological grading of response: grade III (no viable tumour) 5-year DFS 95% vs grade II 68% vs grade I (macroscopic viable tumour) 34% (P less than 0.0001)
- Histological response had the strongest correlation with outcome of all parameters tested
- Method identifies poor responders who may benefit from intensified adjuvant therapy
May: EWS-FLI1 is a Transforming Chimeric Transcription Factor
- The t(11;22) translocation fuses the EWS transactivation domain to the FLI1 DNA-binding (ETS) domain
- EWS-FLI1 transformed NIH 3T3 cells (focus formation, anchorage-independent growth) - demonstrating oncogenic activity
- Deletion of either the EWS domain or the FLI1 DNA-binding domain abolished transformation
- Established the molecular mechanism: a chimeric aberrant transcription factor drives tumourigenesis
Shi: Population-Based Risk Factors for Metastasis and Prognosis (SEER)
- Large SEER population-based cohort of Ewing sarcoma patients
- Pelvic primary (OR 2.49) and tumour over 8cm (OR 1.91) independently predicted metastasis at diagnosis
- Worse overall survival with older age, larger size, pelvic site, black race (HR 2.10) and metastatic extent (HR 3.26)
- Chemotherapy was strongly associated with improved survival (HR 0.47)
Exam Viva Scenarios
Use these scenarios to practise clinical reasoning and management decisions
Scenario 1: Initial Presentation and Diagnosis (~3 min)
"A 14-year-old boy presents with a 3-month history of progressive right thigh pain and swelling. He has had intermittent fevers. X-ray shows a permeative lytic lesion in the mid-femoral diaphysis with an onion-skin periosteal reaction and soft tissue mass. ESR is elevated. His GP started him on antibiotics 2 weeks ago with no improvement. What is your assessment and management?"
Scenario 2: Local Control Decision-Making (~4 min)
"A 16-year-old girl with biopsy-proven Ewing sarcoma of the distal femur has completed 14 weeks of VDC-IE chemotherapy. Restaging MRI shows excellent response with 60% reduction in soft tissue mass. The tumor remains 2cm from the distal femoral physis. She is skeletally immature (Risser 2). Discuss your approach to local control."
Scenario 3: Metastatic Disease Management (~3 min)
"A 17-year-old presents with Ewing sarcoma of the proximal humerus. Staging workup reveals 4 pulmonary nodules (5-12mm) on CT chest and bone marrow involvement (5% tumor cells on bilateral iliac crest biopsy). How would you manage this patient?"
MCQ Practice Points
Pathognomonic Translocation Question
Q: What is the most common chromosomal translocation in Ewing sarcoma? A: t(11;22)(q24;q12) creating the EWS-FLI1 fusion oncogene, present in 85% of cases. The remaining 15% have variant translocations (e.g., EWS-ERG). This fusion is detected by FISH or RT-PCR and is diagnostic for Ewing sarcoma, distinguishing it from other small round cell tumors.
Histopathology Question
Q: What immunohistochemical marker is most sensitive for Ewing sarcoma? A: CD99 (MIC2) with strong diffuse membrane staining, positive in 95% of Ewing sarcomas. However, CD99 is not entirely specific (can be positive in lymphoblastic lymphoma, synovial sarcoma). The combination of CD99 positivity, PAS-positive glycogen, and EWS-FLI1 fusion confirms the diagnosis.
Treatment Sequencing Question
Q: What is the correct sequence of treatment for localized Ewing sarcoma? A: Neoadjuvant chemotherapy → Local control (surgery or radiation) → Adjuvant chemotherapy. Total treatment duration is approximately 48 weeks. Operating before chemotherapy is a critical error that worsens outcomes by failing to treat micrometastases and assess chemotherapy response.
Prognostic Factor Question
Q: What is the most important modifiable prognostic factor in Ewing sarcoma? A: Percent tumor necrosis after neoadjuvant chemotherapy. Patients with over 90% necrosis have 75% 5-year survival vs 50% for under 90% necrosis. This finding guides adjuvant therapy intensity. However, surgical margins are more important than necrosis for local control.
Differential Diagnosis Question
Q: How do you differentiate Ewing sarcoma from osteomyelitis clinically? A: Key features: Ewing has longer symptom duration (months vs weeks), diaphyseal location (osteomyelitis favors metaphysis), large soft tissue mass, and no response to antibiotics. Always biopsy a suspected infection that does not improve within 48-72 hours of antibiotics, especially with lytic diaphyseal lesion and soft tissue mass.
Metastatic Disease Question
Q: What percentage of Ewing sarcoma patients present with metastatic disease, and what are the most common sites? A: 25% present with metastases. Most common sites: Lungs (15%), bone (10%), and bone marrow (5%). Metastatic disease at presentation reduces 5-year survival from 70% to 25-30%. Complete staging includes CT chest, PET-CT or bone scan, and bilateral bone marrow biopsy.
Guidelines, Registries & Global Practice
Global Epidemiology
Ewing sarcoma is the second most common primary bone malignancy in children and adolescents, with an annual incidence of approximately 1 to 3 per million in populations of European ancestry. It is markedly less common in populations of African and East Asian ancestry, a disparity now attributed in part to germline variation at the EGR2 locus and ancestry-related differences in regulatory microsatellites. Population-based registry data (SEER) confirm a male predominance and a peak in the second decade, and identify pelvic/axial site, tumour size over 8cm, older age and metastatic extent as the principal adverse-risk factors (Shi 2020).
International Guidance: Localised Ewing Sarcoma
| Body / Region | Local control | Systemic therapy | Evidence level |
|---|---|---|---|
| NCCN (North America) | Wide surgical excision preferred; definitive RT for unresectable axial sites; post-op RT for close/positive margins or poor response | Neoadjuvant VDC-IE, interval-compressed (q2-weekly) for localised disease | Category 1 / 2A (RCT-backed) |
| ESMO-EURACAN-GENTURIS-ERN PaedCan (Europe) | Surgery where adequate margins achievable; RT for inoperable sites or as adjuvant; combined surgery+RT for marginal margins/poor response | VIDE / VDC-IE backbone; busulfan-melphalan high-dose consolidation for selected high-risk (EE2008/R2 evidence) | Grade A/B |
| BSG / NICE-aligned (UK) | Management exclusively in designated supraregional bone-sarcoma centres; MDT decision on surgery vs RT | Euro Ewing protocol chemotherapy within national trials | Expert consensus + RCT |
| ANZSA (Australia / NZ) | Treatment at tertiary paediatric/sarcoma centres; surgery preferred, RT for axial sites | PBS-subsidised VDC-IE agents within international protocols | Consensus / adopted RCT |
Registry & Trial Evidence Underpinning Practice
| Source | Contribution | Key result |
|---|---|---|
| INT-0091 (Grier, NEJM 2003) | Established VDC-IE backbone for localised disease | 5-yr EFS 69% vs 54% with addition of ifosfamide/etoposide |
| AEWS0031 (Womer, JCO 2012) | Established interval compression (q2-weekly) | 5-yr EFS 73% vs 65%; durable at 10 years |
| CESS/EICESS (Schuck, 2003) | Defined local-control hierarchy | Local failure 7.5% surgery vs 26.3% definitive RT |
| SEER (Shi, 2020) | Population-level risk stratification | Pelvic site OR 2.49 and size over 8cm OR 1.91 for metastasis |
Practice Variation
The principal axis of international variation is high-dose chemotherapy with autologous stem-cell rescue: European protocols (EE2008/R2) incorporate busulfan-melphalan consolidation for selected high-risk localised patients, whereas North American practice has not adopted routine high-dose consolidation. Interval-compressed chemotherapy is standard in paediatric North American practice but is applied more selectively in adults. Relapsed/refractory disease is increasingly managed within the international rEECur platform, which is establishing the most active salvage regimen. Across all systems, care is mandated within designated bone-sarcoma reference centres with a specialist multidisciplinary team (orthopaedic oncologist, paediatric/medical oncologist, radiation oncologist, radiologist, pathologist).
Australian / NZ Context
- ANZSA (Australian and New Zealand Sarcoma Association) coordinates national guidance
- Care centralised at tertiary paediatric/sarcoma centres (e.g. Royal Children's Hospital Melbourne, Children's Hospital at Westmead)
- PBS subsidises the cytotoxic agents (vincristine, doxorubicin, cyclophosphamide, ifosfamide, etoposide)
- eTG guides surgical antibiotic prophylaxis
Universal MDT Principles
- Histological + molecular confirmation (EWSR1 rearrangement) before starting therapy
- Neoadjuvant chemotherapy before any local treatment
- Biopsy planned by the resecting surgeon (tract excised en bloc)
- Fertility preservation discussed before alkylating chemotherapy
Medicolegal Considerations
Key documentation requirements:
- Informed consent for chemotherapy (cardiotoxicity, hemorrhagic cystitis, infertility, secondary malignancy risks)
- Informed consent for surgery (infection, local recurrence, limb length discrepancy, neurovascular injury)
- Tumor board documentation of treatment plan
- Pathology confirmation of EWS-FLI1 fusion before starting chemotherapy
- Discussion of fertility preservation (sperm banking for males, oocyte preservation for females) before starting chemotherapy - alkylating agents cause infertility
- Long-term surveillance plan documented (cardiac monitoring, secondary malignancy screening)
Common litigation issues:
- Delayed diagnosis (misdiagnosed as osteomyelitis or sports injury)
- Operating before chemotherapy (incorrect sequencing)
- Inadequate surgical margins leading to local recurrence
- Failure to discuss fertility preservation before chemotherapy
EWING SARCOMA
Clinical summary
Key Pathology
- •EWS-FLI1 fusion t(11;22) in 85% - diagnostic hallmark
- •Small round blue cells, PAS-positive glycogen
- •CD99 strong diffuse membrane staining (95%)
- •High-grade malignancy, early hematogenous spread
Clinical Presentation
- •Age 10-20 years, diaphysis of long bones (90%)
- •Painful swelling, fever (30%), elevated ESR - mimics infection
- •Femur and pelvis most common (60% of cases)
- •25% present with metastases (lung, bone, marrow)
Staging Workup
- •MRI local site - assess extent, soft tissue involvement
- •CT chest - detect lung metastases (15% at diagnosis)
- •PET-CT or bone scan - skeletal metastases (10% at diagnosis)
- •Bilateral bone marrow biopsy - marrow involvement (5%)
Treatment Algorithm
- •Neoadjuvant chemo FIRST (VDC-IE protocol, 10-14 weeks)
- •Local control: Wide excision (preferred) or radiation (55.8 Gy)
- •Adjuvant chemo to complete 48 weeks total (14-17 cycles)
- •Assess percent necrosis: over 90% = good prognosis
Surgical Pearls
- •Limb salvage in 85-90% of extremity tumors
- •Wide margins (2cm healthy tissue) more important than necrosis
- •Excise biopsy tract en bloc with tumor
- •Expandable prosthesis for skeletally immature patients
Prognostic Factors
- •Metastases at diagnosis: 70% vs 25-30% survival (localized vs metastatic)
- •Over 90% necrosis post-chemo: 75% vs 50% survival
- •Tumor volume under 200ml: Better prognosis
- •Pelvic tumors: Worse prognosis (large, difficult resection)