Clinical significance of flowcytometric minimal residual disease detection in pediatric acute myeloid leukemia patients treated according to the DCOG ANLL97/MRC AML12 protocol.

Analysis of minimal residual disease (MRD) in childhood acute myeloid leukemia (AML) may predict for clinical outcome. MRD levels were assessed by flowcytometric immunophenotyping in 94 children with AML enrolled into a single trial (United Kingdom Medical Research Council AML12 and similar Dutch Childhood Oncology Group ANLL97). An aberrant immunophenotype could be detected in 94% of patients. MRD levels after the first course of chemotherapy predicted for clinical outcome: 3-year relapse-free survival was 85%+/-8% (s.e.) for MRD-negative patients (MRD<0.1%), 64%+/-10% for MRD-low-positive patients (0.1%<or=MRD<0.5%) and only 14+/-9% for MRD-high-positive patients (MRD>or=0.5%; P<0.001), whereas overall survival was 95%+/-5%, 70%+/-10% and 40%+/-13%, respectively, (P<0.001). Multivariate analysis allowing for age, karyotype, FLT3-internal tandem duplications and white blood cell count at diagnosis showed that MRD after the first course of chemotherapy was an independent prognostic factor. Although comparison of paired diagnosis-relapse samples (n=23) showed immunophenotypic shifts in 91% of cases, this did not hamper MRD analysis. In conclusion, flowcytometric MRD detection is possible in children with AML. The level of MRD after the first course of chemotherapy provides prognostic information that may be used to guide therapy.