Prognostic value of minimal residual disease quantification before allogeneic stem-cell transplantation in relapsed childhood acute lymphoblastic leukemia: the ALL-REZ BFM Study Group.

PURPOSE: Minimal residual disease (MRD) before allogeneic stem-cell transplantation was shown to predict outcome in children with relapsed acute lymphoblastic leukemia (ALL) in retrospective analysis. To verify this, the Acute Lymphoblastic Leukemia Relapse Berlin-Frankfurt-Münster (ALL-REZ BFM) Study Group conducted a prospective trial. PATIENTS AND METHODS: Between March 1999 and July 2005, 91 children with relapsed ALL treated according to the ALL-REZ BFM 96 or 2002 protocols and receiving stem-cell transplantation in >or= second remission were enrolled. MRD quantification was performed by real-time polymerase chain reaction using T-cell receptor and immunoglobulin gene rearrangements. RESULTS: Probability of event-free survival (pEFS) and cumulative incidence of relapse (CIR) in 45 patients with MRD >or= 10(-4) leukemic cells was 0.27 and 0.57 compared with 0.60 and 0.13 in 46 patients with MRD less than 10(-4) leukemic cells (EFS, P = .004; CIR, P < .001). Intermediate-risk patients (strategic group S1) with MRD >or= 10(-4) leukemic cells (n = 14) had a pEFS of 0.20 and CIR of 0.73, whereas patients with MRD less than 10(-4) leukemic cells (n = 21) had a pEFS of 0.68 and CIR of 0.09 (EFS, P = .020; CIR, P < .001). High-risk patients (S3/4, third complete remission) who received transplantation with an MRD load of less than 10(-4) leukemic cells (n = 25) showed a pEFS and CRI of 0.53 and 0.18, respectively. In contrast, pEFS and CRI were 0.30 and 0.50 in patients who received transplantation with an MRD load of >or= 10(-4) leukemic cells. Multivariate Cox regression analysis revealed MRD as the only independent parameter predictive for EFS (P = .006). CONCLUSION: MRD is an important predictor for post-transplantation outcome. As a result, new strategies with modified stem-cell transplantation procedures will be evaluated in ALL-BFM trials.

Development of an allele-specific minimal residual disease assay for patients with juvenile myelomonocytic leukemia.

Juvenile myelomonocytic leukemia is an aggressive and frequently lethal myeloproliferative disorder of childhood. Somatic mutations in NRAS, KRAS, or PTPN11 occur in 60% of cases. Monitoring disease status is difficult because of the lack of characteristic leukemic blasts at diagnosis. We designed a fluorescently based, allele-specific polymerase chain reaction assay called TaqMAMA to detect the most common RAS or PTPN11 mutations. We analyzed peripheral blood and/or bone marrow of 25 patients for levels of mutant alleles over time. Analysis of pre-hematopoietic stem-cell transplantation, samples revealed a broad distribution of the quantity of the mutant alleles. After hematopoietic stem-cell transplantation, the level of the mutant allele rose rapidly in patients who relapsed and correlated well with falling donor chimerism. Simultaneously analyzed peripheral blood and bone marrow samples demonstrate that blood can be monitored for residual disease. Importantly, these assays provide a sensitive strategy to evaluate molecular responses to new therapeutic strategies.