[Pathology of Ewing sarcoma].

Ewing's sarcoma is a very rare tumor which has, however, attracted much oncological interest since the dramatic improvement of its prognosis under chemotherapy. Its histogenesis has been discussed controversially for a long time, including a possible origin in immature reticulum, myogenous, endothelial and undifferentiated mesenchymal cells. Repeated reports have also suggested a possible neuroectodermal genesis. Convincing arguments, however, have only been brought forward during recent years, since it was found that Ewing's sarcoma and malignant peripheral neuroectodermal tumor share a common chromosome translocation 11;22. In the meantime this hypothesis has been strengthened by numerous cell biological analyses. There seems to be no clear border between Ewing's sarcoma and malignant peripheral neuroectodermal tumors with definite neural differentiation. Histological differential diagnosis of Ewing's sarcoma has been improved by immunohistological methods. In most cases, they can be distinguished from lymphoma (leucocyte common antigen, B and T markers) and embryonal rhabdomyosarcoma (muscle specific actin, desmin) without problems. Apart from that, it is possible nowadays to obtain antibodies against the MIC 2-protein, which is preferably expressed in Ewing sarcoma. The diagnostics of Ewing's sarcoma and the malignant peripheral neuroectodermal tumor have considerably been enriched by the fact that the specific chromosome translocation t(11;22) can be proved molecular biologically. In contrast to the cytogenetic evidence, it is not necessary to establish cell cultures.