Minimal residual disease analysis in acute lymphoblastic leukemia of childhood after an induction therapy without asparaginase

The detection of minimal residual disease (MRD) is a major prognostic facto r for treatment in acute lymphoblastic leukemia (ALL) of childhood. Several groups showed the predictive value of MRD after 5 weeks of chemotherapy (a t the end of induction therapy). Patients with more than 1 leukemic cells i n 100 cells (greater than or equal to 10(-2)) at this timepoint have a sign ificantly higher relapse rate. The MRD measurement has been shown to be an independent prognostic factor at several time points in the BFM study (ALL- BFM 90) as well as in the EORTC study. The aim of our investigations was th e detection of MRD at the end of induction therapy within the COALL studies which is different from the above studies. In the COALL studies, therapy s tarts with a 1 week DNR prephase (24 h infusion on day one) and i.th. MTX. Induction therapy consisted of 3 drugs over a period of 4 weeks (Prednisolo ne, Vincristine and Daunorubicin), asparaginase is given later in consolida tion. At the end of induction therapy, bone marrow was obtained for cytomor phologic and molecular analysis. Patients and Methods: We investigated bone marrow samples from 76 patients. All patients were in morphologic remissio n at the end of induction therapy. For MRD analysis, DNA was isolated from bone marrow mononuclear cells. Clonal T-cell-receptor (TCR) or immunoglobul in gene (IgH) rearrangements were identified by PCR. Monoclonal products we re either sequenced directly (TCR) or after excision from high resolution a garose gels. Subsequently patient-specific oligonucleotides for allele-spec ific PCR were generated. PCR analysis was performed with 1 mu g DNA for eac h reaction within a semiquantitative matter. This method reached sensitivit ies down to 10(-5). Results: Eighty-four percent of the analysed samples we re MRD positive at the end of induction therapy. 20 out of 76 patient sampl es (26%) were highly positive (greater than or equal to 10(-2)), 28 patient s had levels of about 10(-3) (37%), 16 had levels around 10(-4) (21%) and 1 2 patients had no detectable residual cells (16%). All analysed 15 T-ALL pa tients had detectable residual disease at this timepoint. Until now, 5/20 p atients with very high MRD level at the end of induction therapy suffered a relapse. Discussion: Patients with very high MRD level at the end of induc tion therapy showed an elevated risk of relapse, but the predictive value i s much poorer than for example in the BFM 90 MRD-study. We suggest, that a high MRD level at this timepoint results from a different induction therapy compared to the BFM 90 study. In the COALL studies asparaginase is given o nly after induction therapy to decrease the risk of thrombosis. We would li ke to conclude that this differences were compensated later during therapy as the event free survival of both studies is similar. In conclusion, an optimal information from MRD studies is strongly associat ed with the given therapy. Therefore we initiated an additional MRD time-po int after the first chemotherapy block in consolidation.