Question:medium
A diaphyseal tumor, probably small round blue cells. Which test/translocation is useful for diagnosis?
A diaphyseal tumor, probably small round blue cells. Which test/translocation is useful for diagnosis?
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"Small round blue cell" tumor of the bone diaphysis in a young patient — think of the EWS-FLI1 fusion.
Updated On: Jun 22, 2026
- t(11;22)
- t(15;17)
- —
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The Correct Option is A
Solution and Explanation
Mechanism-first approach.
The two clues to decode are the location and the cytology. "Diaphyseal" means the lesion sits in the central shaft of a long bone, and "small round blue cells" is a specific histologic category of childhood/adolescent tumors.
Among the small round blue cell tumors (Ewing sarcoma, neuroblastoma, rhabdomyosarcoma, lymphoma, small cell osteosarcoma), the one that classically arises in the diaphysis of long bones in children and young adults is Ewing sarcoma.
Ewing sarcoma is driven by fusion of the EWSR1 gene with an ETS-family transcription factor. The single most common fusion, seen in roughly 85% of cases, results from the translocation $t(11;22)(q24;q12)$ creating the EWS-FLI1 chimeric protein. Demonstrating this rearrangement (FISH break-apart probe for EWSR1 or RT-PCR for the fusion transcript) clinches the diagnosis - hence option (a).
The alternative, $t(15;17)$, is the hallmark of acute promyelocytic leukaemia (PML-RARA), a leukaemia treated with all-trans retinoic acid; it is unrelated to bone sarcomas and is the wrong choice.
Correct option: a - t(11;22).
The two clues to decode are the location and the cytology. "Diaphyseal" means the lesion sits in the central shaft of a long bone, and "small round blue cells" is a specific histologic category of childhood/adolescent tumors.
Among the small round blue cell tumors (Ewing sarcoma, neuroblastoma, rhabdomyosarcoma, lymphoma, small cell osteosarcoma), the one that classically arises in the diaphysis of long bones in children and young adults is Ewing sarcoma.
Ewing sarcoma is driven by fusion of the EWSR1 gene with an ETS-family transcription factor. The single most common fusion, seen in roughly 85% of cases, results from the translocation $t(11;22)(q24;q12)$ creating the EWS-FLI1 chimeric protein. Demonstrating this rearrangement (FISH break-apart probe for EWSR1 or RT-PCR for the fusion transcript) clinches the diagnosis - hence option (a).
The alternative, $t(15;17)$, is the hallmark of acute promyelocytic leukaemia (PML-RARA), a leukaemia treated with all-trans retinoic acid; it is unrelated to bone sarcomas and is the wrong choice.
Correct option: a - t(11;22).
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