PATHOLOGY OF EWINGS-SARCOMA

Ewing's sarcoma is a very rare tumor which has, however, attracted muc h oncological interest since the dramatic improvement of its prognosis under chemotherapy. Its histogenesis has been discussed controversial ly for a long time, including a possible origin in immature reticulum, myogenous, endothelial and undifferentiated mesenchymal cells. Repeat ed reports have also suggested a possible neuroectodermal genesis. Con vincing arguments, however, have only been brought forward during rece nt years, since it was found that Ewing's sarcoma and malignant periph eral 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 Ew ing's sarcoma and malignant peripheral neuroectodermal tumors with def inite neural differentiation. Histological differential diagnosis of E wing's sarcoma has been improved by immunohistological methods. In mos t cases, they can be distinguished from lymphoma (leucocyte common ant igen, B and T markers) and embryonal rhabdomyosarcoma (muscle specific actin, desmin) without problems. Apart from that, it is possible nowa days to obtain antibodies against the MIC 2-protein, which is preferab ly 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;2 2) can be proved molecular biologically. In contrast to the cytogeneti c evidence, it is not necessary to establish cell cultures.