[Ewing sarcoma osseous and extraosseous : a clinicopathologic study of 29 cases].

Background: Ewing's sarcoma (ES) is a rare tumour accounting for 10% of primary malignant bone tumours in children and 3% of all childhood malignancies. ES belongs to a group of small round cell tumours.

Aim: In this review, we will describe the main clinicopathological features of this rare tumour and discuss its prognosis.

Methods: We report a retrospective study of 29 cases of ES, of which 4 were extraosseous, diagnosed over a period 11 years (January 1989 - December 1999). Clinicopathological data were described. Hematoxylin-eosin staining and immunohistochemical study were reviewed.

Results: 12 patients were male and 17 were female (ratio: 0,8) with a median age of 16 years. 62,5% of tumours were located in flat bone and 33,3% in long bone. The medium size of the tumor was 10,6 cm (range:3-25cm). 27,5% of patients presented with metastatic disease at time of diagnosis. Microscopically, tumour tissue was composed of round, small, blue cells with fine granular chromatin. Tumour cells strongly coexpressed CD99 and vimentin (100%). Systemic treatment consisted of adjuvant chemotherapy (84,2%). Local control was based on and surgery (57,9%) or radiation therapy (36,8%). A good response to chemotherapy was obtained in 37.5%; 13,7% of patients were alive without disease (medium follow up: 169 mois); 34,5% of patients developed metastases (medium follow up : 23 months) and 10,3% developed recurrences (medium follow up :13 months).

Conclusion: Our study emphasizes two points : the great size of the tumor and the frequent location in flat bone which may explain the poor prognosis of Ewing sarcoma in our series despite the multidisciplinary treatment.