Minimal residual disease levels in bone marrow and peripheral blood are comparable in children with T cell acute lymphoblastic leukemia (ALL), but not in precursor-B-ALL

Minimal residual disease detection after allogeneic stem cell transplantation is correlated to relapse in patients with acute lymphoblastic leukaemia

Minimal residual disease (MRD) assessments were performed retrospectively after allogeneic stem cell transplantation (SCT) in 32 patients (23 children and nine adults) with acute lymphoblastic leukaemia (ALL). Using immunoglobulin and T-cell receptor rearrangements as clonal markers, MRD was detected after SCT in nine patients, eight of whom have relapsed. The median time between first MRD detection and relapse was 5.5 (range 0.5-30) months. In 23 patients without MRD, six have relapsed to date: lower sensitivity, central nervous system relapse and clonal exchange of the leukaemic clone were factors that may explain the failure to detect MRD before relapse in these patients. In univariate analysis, factors associated with decreased risk of relapse were transplantation in first remission (P=0.02), the combination of acute and chronic graft-versus-host disease (P=0.03) and absence of MRD after SCT (P=0.005). In multivariate analysis, only MRD detection after SCT was significantly associated with increased risk of relapse (P=0.05). In conclusion, MRD detection after SCT is correlated with relapse and provides the opportunity for initiating immunotherapeutic intervention at an early stage when the tumour cell burden is still low.

Minimal residual disease detection in childhood precursor-B-cell acute lymphoblastic leukemia: relation to other risk factors. A Children's Oncology Group study

Minimal residual disease (MRD) can be detected in the marrows of children undergoing chemotherapy either by flow cytometry or polymerase chain reaction. In this study, we used four-color flow cytometry to detect MRD in 1016 children undergoing therapy on Children's Oncology Group therapeutic protocols for precursor-B-cell ALL. Compliance was excellent, with follow-up samples received at the end of induction on nearly 95% of cases; sensitivity of detection at this time point was at least 1/10,000 in more than 90% of cases. Overall, 28.6% of patients had detectable MRD at the end of induction. Patients with M3 marrows at day 8 were much more likely to be MRD positive (MRD+) than those with M2 or M1 marrows. Different genetically defined groups of patients varied in their prevalence of MRD. Specifically, almost all patients with BCR-ABL had high levels of end-of-induction MRD. Only 8.4% of patients with TEL-AML1 were MRD+>0.01% compared with 20.3% of patients with trisomies of chromosomes 4 and 10. Our results show that MRD correlates with conventional measures of slow early response. However, the high frequency of MRD positivity in favorable trisomy patients suggests that the clinical significance of MRD positivity at the end of induction may not be the same in all patient groups.

Newly diagnosed childhood acute lymphoblastic leukemia: update on prognostic factors and treatment

The development of effective therapy for children with acute lymphoblastic leukemia is one of the great successes of clinical hematology andoncology. Fifty years ago, childhood acute lymphoblastic leukemia was universally fatal, but current long-term event-free survival rates are nearly 80%. Despite this improved outcome, there are still many challenges facing investigators today. In some recent clinical trials, the outcome of "high-risk" patients has approached that of "lower risk" patients, suggesting that currently applied clinical factors, such as age and presenting leukocyte count, no longer identify the 20% of newly diagnosed patients who ultimately will relapse. Additionally, therapy remains nonspecific, toxic, and sometimes lethal. As more children with acute lymphoblastic leukemia survive into adolescence and adulthood, there is a need to address the late sequelae of current therapy and to develop more leukemia-specific treatments. Promising avenues of research, which may identify biologically distinctive subsets of acute lymphoblastic leukemia and potential targets for novel therapies, include studies of minimal residual disease, lymphoblast genetics (including genetic profiling studies), and host-related pharmacogenomics.