A 20-year-old presents with a painful mid-diaphyseal femur lesion. X-ray shows a permeative lytic lesion with 'onion skin' periosteal reaction. Biopsy shows small round blue cells forming rosettes. The chromosomal translocation most characteristic of this tumor is:
- A t(X;18)(p11;q11) — SYT-SSX fusion
- B t(12;16)(q13;p11) — FUS-DDIT3 fusion
- C t(2;13)(q35;q14) — PAX3-FOXO1 fusion
- D t(11;22)(q24;q12) — EWS-FLI1 fusion ✓
Explanation
Ewing's sarcoma is characterized by the t(11;22)(q24;q12) translocation producing the EWS-FLI1 fusion oncogene in ~85% of cases. This fusion protein acts as an aberrant transcription factor driving tumorigenesis. The 'onion skin' periosteal reaction, permeative lysis, and small round blue cells (resembling rosettes, or Homer-Wright pseudorosettes) are classic pathological findings. Treatment is multimodal: neoadjuvant chemotherapy (VIDE/VAC-IE protocols), local control with surgery or radiotherapy, and adjuvant chemotherapy. t(X;18) is synovial sarcoma; t(12;16) is myxoid liposarcoma; t(2;13) is alveolar rhabdomyosarcoma.
Reference: Maheshwari Essential Orthopaedics, 6th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.