9. Ewing sarcoma Flashcards
1
Q
Definition of Ewing sarcoma
A
Also known as Primitive Neuroectodermal Tumour (PNET); a highly malignant neoplasm composed of small round, rather uniform cells that do not form matrix
2
Q
Epidemiology of Ewing sarcoma
A
Usually whites aged 5-20 years
3
Q
Pathogenesis of Ewing sarcoma
A
Unique karyotypic abnormality (seen in 90%):
- t(11;22) (q24;q12)
- Results in expression of chimeric protein EWSR1-FLI-1
4
Q
Morphology of Ewing sarcoma
A
- Grossly:
- Sites affected:
i. Marrow of femur, tibia, humerus, fibula, pelvis, ribs, vertebra, mandible, clavicle
ii. May permeate cortex into soft tissue
- Soft white (fish flesh) mass of almost liquid consistency - Histologically:
- Sheets of small round uniform cells 10-15 microns (larger than lymphocytes) with scant clear cytoplasm & small nucleoli
- May have Homer-Wright rosettes (tumour cells arranged around a central fibrillary space) or pseudorosettes (cells arranged around vessels)
- Immunohistochemistry:
i. Positive membranous CD99 staining
ii. PAS positive, diastase sensitive
iii. NSE, Leu7, FLI1 protein, vimentin
iv. Variable low molecular weight keratin & synaptophysin
5
Q
Clinical features of Ewing sarcoma
A
- Xray findings:
- Destructive lytic tumour
- Onion-skin appearance (concentric layers of new bone formation incited by permeating of cortex by tumour) - Treatment:
- Preoperative chemotherapy
- Surgery
- Radiation therapy - Prognosis:
- 5-year survival rate: 75% (50% are cured)
- Metastases to lung, skull, pleura, CNS
- 10-25% have multiple lesions at presentation
- Poor prognostic factors: high stage, direct extension into soft tissue, aneuploidy, metastases, grossly viable tumour post-chemotherapy (poor response) - Differential diagnoses (other small blue round tumours):
- Sarcomas (neuroblastoma, desmoplastic small round cell tumour, rhabdomyosarcoma)
- Carcinomas (small cell carcinoma)
- Lymphomas
