Ewing's tumour is the second most frequent primary tumour of bone. It is 
associated in 85% of cases with a specific and recurrent chromosome 
translocation, a t(11; 22)(q24; q12) which generates a fusion gene between the 
5' part of EWS and the 3' part of FLI-1, a member of the ETS family. Less 
frequently, this gene fusion involves EWS and another member of the ETS family 
which can be: ERG, ETV1, E1AF or FEV depending on the cases. The EWS-ETS fusion 
is causative in the development of Ewing's tumour. Its mechanism of action 
mainly relies on the abnormal transcription regulation of key target genes which 
are involved in the regulation of cell cycle, signal transduction, migration. 
The cellular context within which EWS-FLI-1 exerts its oncogenic action is a 
long standing matter of debate. Recent data converge to suggest that the Ewing 
cell origin is a mesenchymal stem cell.