Multiparameter flow cytometry versus droplet digital polymerase chain reaction for monitoring measurable residual disease in paediatric fusion gene-positive acute myeloid leukaemia.

Measurable residual disease (MRD) monitoring is crucial for prognostic stratification in paediatric acute myeloid leukaemia (AML). This study compared the performance of multiparameter flow cytometry (MFC) and droplet digital polymerase chain reaction (ddPCR) for MRD assessment in 116 paediatric AML patients at end of induction (EOI)-1, EOI-2 and end of consolidation (EOC)-1. Compared to MFC, ddPCR revealed a significantly slower rate of MRD negativity conversion, with moderate concordance between methods. Both MFC and ddPCR were significant predictors of 5-year event-free survival (EFS) at EOIs. For instance, MFC-MRD ≥1% at EOI-1 was associated with a 5-year EFS of 50.2 ± 19.8% vs. 79.4 ± 6.4% for patients with MRD <1% (p = 0.003), while corresponding ddPCR rates were 41.0 ± 23.8% vs. 91.7 ± 4.5% (p < 0.001). Notably, the prognostic power of MFC diminished at EOC-1, while ddPCR remained significant. Subgroup analysis by genetic alterations revealed that ddPCR provided significant prognostic stratification across all genetic subgroups while MFC did not. Combining both methods yielded improved risk discrimination. Patients with double positive MRD presented very low survival rates either at EOI-1, EOI-2 and EOC-1. In conclusion, ddPCR offers higher sensitivity and sustained prognostic performance, whereas MFC remains a practical front-line tool; integrating the two methods enables more precise risk stratification.