Risk stratification for acute myeloid leukemia (AML) uses molecular and cytogenetic abnormalities identified at diagnosis. Response to therapy informs risk, and morphology continues to be used more frequently than flow cytometry. Herein, the largest cohort of pediatric patients prospectively assessed for measurable residual disease (MRD) by flow cytometry (N = 784) is reported. The "difference from normal" (ΔN) technique was applied: 31% of all patients tested positive (AML range, 0.02% to 91%) after the first course of treatment on Children's Oncology Group study AAML0531. Detection of MRD following initial chemotherapy proved the strongest predicator of overall survival (OS) in univariable and multivariable analyses, and was predictive of relapse risk, disease-free survival, and treatment-related mortality. Clearance of MRD after a second round of chemotherapy did not improve survival. The morphologic definition of persistent disease (>15% AML) failed 27% of the time; those identified as MRD- had superior outcomes. Similarly, for patients not achieving morphologic remission (>5% blasts), 36% of patients were MRD- and had favorable outcomes compared with those who were MRD+ (P < .001); hence an increase in myeloid progenitor cells can be favorable when ΔN classifies them as phenotypically normal. Furthermore, ΔN reclassified 20% of patients in morphologic remission as having detectable MRD with comparable poor outcomes. Retrospective analysis using the relapse phenotype as a template demonstrated that 96% of MRD- patients had <0.02% of the relapse immunophenotype in their end of induction 1 marrow. Thus, the detection of abnormal myeloid progenitor cells by ΔN is both specific and sensitive, with a high predictive signal identifiable early in treatment. This trial was registered at www.clinicaltrials.gov as #NCT00372593.

<p><strong>BACKGROUND: </strong>High-risk pediatric acute myeloid leukemia confers a poor prognosis, and alternative strategies are needed to improve outcomes. We hypothesized that intensifying induction on the AAML1031 clinical trial would improve outcomes compared to the predecessor trial AAML0531.</p>

<p><strong>METHODS: </strong>Patients on AAML0531 received cytarabine (1600&nbsp;mg/m )/daunorubicin (150&nbsp;mg/m )/etoposide (ADE) for induction II and patients on AAML1031 received mitoxantrone (48&nbsp;mg/m )/cytarabine (8000&nbsp;mg/m ) (MA). Stem cell transplant (SCT) conditioning included busulfan/cyclophosphamide on AAML0531, whereas AAML1031 used busulfan/fludarabine and liberalized donor eligibility. Patients were included in this analysis if they met high-risk criteria common to the two trials by cytogenics or poor disease response after induction I ADE.</p>

<p><strong>RESULTS: </strong>MA provided no benefit over ADE at: induction II response (complete response [CR]: 64% vs. 62%, p&nbsp;=&nbsp;.87; measurable residual disease [MRD]+: 57% vs. 46%, p&nbsp;=&nbsp;.34); or intensification I response (CR: 79% vs. 94%, p&nbsp;=&nbsp;.27; MRD+: 27% vs. 20%, p&nbsp;=&nbsp;1.0). When considered with altered SCT approach, MA did not improve 5-year disease-free survival (24% ± 9% vs. 18% ± 15%, p&nbsp;=&nbsp;.63) or 5-year overall survival (35% ± 10% vs. 38% ± 18%, p&nbsp;=&nbsp;.66). MA was associated with slower neutrophil recovery (median 34 vs. 27&nbsp;days, p&nbsp;=&nbsp;.007) and platelet recovery (median 29 vs. 24.5&nbsp;days, p&nbsp;=&nbsp;.04) and longer hospital stay (32 vs. 28&nbsp;days, p&nbsp;=&nbsp;.01) during induction II.</p>

<p><strong>CONCLUSION: </strong>Intensification of induction II did not improve treatment response or survival, but did increase toxicity and resource utilization. Alternative strategies are urgently needed to improve outcomes for pediatric patients with high-risk acute myeloid leukemia (trials registered at clinicaltrials.gov NCT01371981, NCT00372593).</p>

<p><strong>BACKGROUND: </strong>The optimal number of chemotherapy courses for low-risk (LR) pediatric acute myeloid leukemia (AML) is not known.</p>

<p><strong>OBJECTIVE: </strong>To compare outcomes for four (21.6&nbsp;g/m cytarabine) versus five (45.6&nbsp;g/m cytarabine) chemotherapy courses for LR-AML using data from Children's Oncology Group (COG) AAML0531 and AAML1031.</p>

<p><strong>METHODS: </strong>We compared relapse risk (RR), disease-free survival (DFS), and overall survival (OS), and the differential impact in LR subgroups for patients receiving four versus five chemotherapy courses. Cox (OS and DFS) and risk (RR) regressions were used to estimate hazard ratios (HR) to compare outcomes.</p>

<p><strong>RESULTS: </strong>A total of 923 LR-AML patients were included; 21% received five courses. Overall, LR-AML patients who received four courses had higher RR (40.9% vs. 31.4%; HR&nbsp;=&nbsp;1.40, 95% confidence interval [CI]: 1.06-1.85), and worse DFS (56.0% vs. 67.0%; HR&nbsp;=&nbsp;1.45, 95% CI: 1.10-1.91). There was a similar decrement in OS though it was not statistically significant (77.0% vs. 83.5%; HR&nbsp;=&nbsp;1.45, 95% CI: 0.97-2.17). Stratified analyses revealed the detrimental effects of cytarabine dose de-escalation to be most pronounced in the LR-AML subgroup with uninformative cytogenetic/molecular features who were minimal residual disease (MRD) negative after the first induction course (EOI1). The absolute decrease in DFS with four courses for patients with favorable cytogenetic/molecular features and positive MRD was similar to that observed for patients with uninformative cytogenetic/molecular features and negative MRD at EOI1, though not statistically significant.</p>

<p><strong>CONCLUSIONS: </strong>Our results support de-escalation of cytarabine exposure through the elimination of a fifth chemotherapy course only for LR-AML patients who have both favorable cytogenetic/molecular features and negative MRD after the first induction cycle.</p>

<p><strong>PURPOSE: </strong>We investigated the impact of the CD33-targeted agent gemtuzumab ozogamicin (GO) on survival in pediatric patients with -rearranged (-r) acute myeloid leukemia (AML) enrolled in the Children's Oncology Group trial AAML0531 (NCT01407757).</p>

<p><strong>METHODS: </strong>Patients with -r AML were identified and clinical characteristics described. Five-year overall survival (OS), event-free survival (EFS), disease-free survival (DFS), and relapse risk (RR) were determined overall and for higher-risk versus not high-risk translocation partners. GO's impact on response was determined and outcomes based on consolidation approach (hematopoietic stem cell transplant [HSCT] chemotherapy) described.</p>

<p><strong>RESULTS: </strong>Two hundred fifteen (21%) of 1,022 patients enrolled had -r AML. Five-year EFS and OS from study entry were 38% and 58%, respectively. EFS was superior with GO treatment (EFS 48% with GO 29% without, = .003), although OS was comparable (63% 53%, = .054). For patients with -r AML who achieved complete remission, GO was associated with lower RR (40% GO 66% patients who did not receive GO [No-GO], = .001) and improved 5-year DFS (GO 57% No-GO 33%, = .002). GO benefit was observed in both higher-risk and not high-risk -r subsets. For patients who underwent HSCT, prior GO exposure was associated with decreased relapse (5-year RR: 28% GO and HSCT 73% No-GO and HSCT, = .006). In multivariable analysis, GO was independently associated with improved EFS, improved DFS, and reduced RR.</p>

<p><strong>CONCLUSION: </strong>GO added to conventional chemotherapy improved outcomes for -r AML; consolidation with HSCT may further enhance outcomes. Future clinical trials should study CD33-targeted agents in combination with HSCT for pediatric r AML.</p>