High-dose AraC is Essential for the Treatment of ML-DS Independent of Post-Induction MRD: Results of COG AAML1531.

Myeloid leukemia in children with Down syndrome (ML-DS) is associated with young age and somatic GATA1 mutations. Due to high event-free survival (EFS) and hypersensitivity of the leukemic blasts to chemotherapy, the prior Children's Oncology Group protocol ML-DS protocol (AAML0431), reduced overall treatment intensity but lacking risk stratification, retained the high-dose cytarabine course (HD-AraC), which was highly associated with infectious morbidity. Despite high EFS of ML-DS, survival for those who relapse is rare. AAML1531 introduced therapeutic risk stratification based on the previously identified prognostic factor, measurable residual disease (MRD) at the end of the first induction course. Standard risk (SR) patients were identified by negative MRD using flow cytometry (<0.05%) and did not receive the historically administered HD-AraC course. Interim analysis of 114 SR patients revealed a 2-year EFS of 85.6% (95% confidence interval (CI), 75.7-95.5%), which was significantly lower than for MRD-negative patients treated with HD-AraC on AAML0431 (p=0.0002). Overall survival at 2 years was 91.0% (95% CI 83.8%-95.0%). Twelve SR patients relapsed, mostly within one year from study entry and had a 1-year OS of 16.7% (95% CI 2.7% - 41.3%). Complex karyotypes were more frequent in SR patients who relapsed compared to those who did not (36% vs. 9%; p=0.0248). MRD by error-corrected sequencing of GATA1 mutations was piloted in 18 SR patients and detectable in 60% who relapsed vs. 23% who did not (p=0.2682). Patients with SR ML-DS had worse outcomes without HD-AraC after risk classification based on flow cytometric MRD. ClinicalTrials.gov NCT02521493.