A 10-year-old boy has fever, leukocytosis, and a painful diaphyseal tibial mass. X-ray shows a permeative lytic lesion with an 'onion-skin' periosteal reaction. Biopsy shows sheets of small round blue cells with scanty cytoplasm. Flow cytometry shows positivity for CD99. Which chromosomal translocation is characteristically associated with this tumor?

• A t(9;22)(q34;q11)
• B t(8;14)(q24;q32)
• C t(14;18)(q32;q21)
• D t(11;22)(q24;q12) ✓

Explanation

Ewing sarcoma is a small round blue cell tumor of bone arising in the diaphysis of long bones in children and adolescents. The lamellated 'onion-skin' periosteal reaction and CD99 surface expression are characteristic. The pathognomonic chromosomal translocation t(11;22)(q24;q12) fuses the EWSR1 gene on chromosome 22 with the FLI1 gene on chromosome 11, creating an aberrant transcription factor. t(9;22) is the Philadelphia chromosome of CML; t(8;14) occurs in Burkitt lymphoma.

Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.