[Contribution of immunology and molecular biology].

Recent technical advances in immunology and molecular genetics have allowed to better delineate Ewing sarcoma among other small round cell tumors of bone and soft tissues. Ewing cells present with a characteristic translocation t (11;22) (q23-24; q11-12) shared with neuroepithelioma. They express a series of cell-surface antigens associated with the neuroectodermal differentiation lineage. These data open new avenues for exploring the origin and the mechanism of transformation of these tumors and to conceive new therapeutical approaches.