[Minimal metastatic and minimal residual disease in patients with Ewing tumors]

At least 95% of Ewing tumors (ET) are characterized by an EWS-gene rearrangement with either FLI-1 or ERG and by extraordinary high MIC2/CD99 expression. Both features can be used for the specific identification of tumor cells, which might also be present in blood and bone marrow in minimal metastatic or minimal residual disease. We report the establishment of sensitive ET cell detection methods based on these characteristics. Preliminary results of 14 patients are given and two cases are reported in detail. 6/14 patients showed RT-PCR positivity in the bone marrow whereas in 8/14 patients ET cells could be detected by immunofluorescence. Only in 2 patients, one at diagnosis and one at relapse, tumor cells were detected in blood samples by RT-PCR. Peripheral blood stem cells of 5 patients showed no contamination with ET cells. The versatility of the immunocytochemical approach as compared to the RT-PCR analysis is discussed in order to explain the discrepancies between the results obtained with the two detection methods.