A 16-year-old boy presents with a 3-month history of progressive pain and swelling over the left femur. Plain radiographs show a mixed lytic-sclerotic lesion in the diaphysis with periosteal reaction and soft tissue mass. Laboratory investigations reveal elevated LDH (850 U/L) and normal alkaline phosphatase. A diagnosis of Ewing sarcoma is suspected. What is the most appropriate next step in management?

Explanation

## Histopathological Confirmation is the Most Appropriate Next Step **Key Point:** In any suspected malignancy, a tissue diagnosis (biopsy) must be obtained before initiating definitive treatment. Ewing sarcoma is a clinical and radiological suspicion — it cannot be treated without histopathological confirmation, as several other lesions (osteomyelitis, osteosarcoma, lymphoma of bone) can mimic it. ### Why Biopsy Comes First 1. **Diagnosis must be confirmed before treatment** — Initiating chemotherapy or surgery without a tissue diagnosis is a fundamental error in oncological management. The clinical and radiological picture is suggestive, not diagnostic. 2. **Needle biopsy (core needle biopsy)** — Is the standard first step; it provides tissue for histology (small round blue cells), immunohistochemistry (CD99/MIC2 positivity), and molecular studies (EWSR1-FLI1 translocation t(11;22)). 3. **Imaging is complementary, not a substitute** — MRI and chest CT are essential for staging but do not replace tissue diagnosis. Per standard oncological protocols (NCCAP, COG), biopsy is performed after or concurrently with baseline imaging, but the *immediate next step* in a suspected-but-unconfirmed diagnosis is tissue confirmation. ### Sequence of Management in Ewing Sarcoma | Step | Action | Rationale | |---|---|---| | 1 | **Needle biopsy** | Confirm diagnosis histologically | | 2 | MRI + Chest CT (± PET-CT) | Staging — local extent and metastases | | 3 | Neoadjuvant chemotherapy (VAC/IE) | Tumor shrinkage, treat micrometastases | | 4 | Surgery / Radiation | Definitive local control | | 5 | Adjuvant chemotherapy | Consolidation | ### Why Other Options Are Incorrect - **Option A (Wide surgical excision):** Premature without diagnosis or staging; neoadjuvant chemotherapy is required first. - **Option B (MRI + Chest CT):** Important for staging but cannot replace tissue diagnosis; imaging alone does not confirm Ewing sarcoma. - **Option C (Neoadjuvant chemotherapy):** Cannot be initiated without histopathological confirmation — treating an unconfirmed diagnosis risks harm if the lesion is, e.g., osteomyelitis or lymphoma. **Clinical Pearl (Harrison's Principles of Internal Medicine):** "Biopsy of bone tumors should be performed after imaging studies are complete, but before any definitive treatment. The biopsy must be planned carefully so that the biopsy tract can be excised at the time of definitive surgery." **High-Yield:** The EWSR1-FLI1 translocation t(11;22)(q24;q12) is found in ~85% of Ewing sarcoma cases and is a key molecular diagnostic marker obtained from biopsy tissue. CD99 (MIC2) positivity on immunohistochemistry is a hallmark finding.