Case of the Month: October 2025
Clinical history
An otherwise healthy 10-year-old boy presents to the emergency department with ongoing difficulty walking after injuring his leg one week ago playing soccer. Review of systems is significant for intermittent fevers over the prior week. On examination, a tender area is identified over the distal femur.
No bony fracture is identified by plain radiograph. However, bone destruction and a periosteal reaction is seen over the distal femoral metadiaphysis. MRI confirms bone destruction with an adjacent soft tissue proliferation. A biopsy is performed.
Questions:
- What is your differential diagnosis and favoured diagnosis?
- What additional studies could be performed by the pathologist in this case and why?
- What are the favourable and unfavourable prognostic factors for this entity?
How to participate
Take a look at the images.
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If you are a medical student at the University of Toronto, you can also:
H&E stained section of soft tissue biopsy, low-power magnification.
H&E stained section of soft tissue biopsy, high-power magnification.
Discover the answer to October's case of the month
Key Points
- Small round blue cell tumours are common in paediatric patients and carry a wide histologic differential diagnosis that includes leukaemia and lymphoma, blastomas, and sarcomas.
- Distinguishing between these entities requires correlation clinical, radiological and pathological correlation in addition to ancillary testing such as immunohistochemistry and molecular studies.
- Ewing sarcoma is a prototypical small round blue cell tumour presenting in bone or soft tissue and characterized by its unique molecular signature, a gene fusion between a FET gene family member and an ETS transcription factor (most commonly EWSR1::FLI1).
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