P552: measurable residual disease detected by wt1 is an independent predictor of survival in children with acute myeloid leukemia

Background: Molecular testing has an evolving role in monitoring of measurable residual disease (MRD) to refine risk stratification and to guide treatment strategies in pediatric patients with AML. Wilms tumor gene 1 (WT1) is frequently overexpressed in AML and has been proposed as a potential molecular marker for MRD. Aims: To assess the predictive value of WT1 as an MRD marker and its prognostic impact on the outcome. Methods: Quantification of WT1 level using the standardized European Leukemia network real time quantitative polymerase chain reaction assay (qRT-PCR) was done among 146 pediatric patients with AML and considered high if the level was >250 copies/104ABL on bone marrow sample. We evaluated the MRD response by WT1 post induction I and post intensification I and those with ≥2 log reduction (2×104 copies/104 ABL copies compared with the pretreatment level) were considered as good responders while patients who failed to achieve 2 log were poor responders. Results:WT1 overexpression was detected in 76.7% of patients (112/146) at diagnosis, and were significantly higher in patients with core binding fusion transcript (t(8:21),P=0.018; inv 16, P=0.016), M4- FAB subtype (P=0.018), and among low and intermediate-risk groups compared to high-risk group (P<0.001). After induction treatment, achieving ≥2 log reduction by WT1 MRD predicted reduced relapse risk (2-year cumulative incidence of relapse (CIR) 7.9% vs 33.2%, p=0.008). While poor responders by WT1 MRD after intensification I were associated with significant lower overall survival (OS) (51% vs 93.2%, p <0.001), event-free survival (RFS) (33.3% vs 82.6%, p value <0.001) and higher CIR (66.6% vs 10.6%, p value <0.001) at 24 months as compared to good responders, which also remained as an independent adverse prognostic factor when adjusted for other potential confounders (OS (Hazards Ratio (HR), 3; 95% confidence interval (CI), 0.9 to 10.6; p=0.04) and EFS (HR, 3.115; CI, 1.35—7.19, P=0.008). Combining flow cytometry (MFC) and WT1 based MRD results among LR and IR group showed that outcome of MFC MRD positive patients was not influenced by the amount of residual disease, but with WT1 MRD response. Post induction I, good responder patients by WT1 had lower incidence of relapse and significantly better relapse free survival (RFS) (2-year RFS, 90% vs 64.4%, p=0.024) despite of positive MRD by MFC. On the other hand after intensification I, failure to achieve 2 log reduction by WT1 predicted significantly worse outcome even with negative MRD by MFC (2- year RFS 38.9% vs 87.5%, p<0.001). High concordance rate was found between MRD response by WT1 and molecular MRD by RT-PCR within the LR group. Summary/Conclusion: MRD assessment by WT1 can be used as a sensitive tool for prediction of the clinical outcome in pediatric patients with AML. Incorporation of MRD results by both WT1 and MFC enhanced the reliability of MRD-based prognostic stratification especially in patients without specific markers to be followed and hence influence the treatment strategies. Keywords: Minimal residual disease (MRD), WT1, AML