MINIMAL METASTATIC AND MINIMAL RESIDUAL D ISEASE IN PATIENTS WITH EWING TUMORS

At least 95% of Ewing tumors (ET) are characterized by an EWS-gene rea rrangement with either FLI-1 or ERG and by extraordinary high MIC2/CD9 9 expression. Both features can be used for the specific identificatio n of tumor cells, which might also be present in blood and bone marrow in minimal metastatic or minimal residual disease. We report the esta blishment of sensitive ET cell detection methods based on these charac teristics. 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 imm unofluorescence. Only in 2 patients, one at diagnosis and one at relap se, turner 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 bet ween the results obtained with the two detection methods.