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.