WT1 Measurable Residual Disease Assay in Patients With Acute Myeloid Leukemia Who Underwent Allogeneic Hematopoietic Stem Cell Transplantation: Optimal Time Points, Thresholds, and Candidates

The absence of relevant guidelines for Wilms tumor 1 (WT1) gene quantification as a measurable residual disease (MRD) assessment for patients with acute myeloid leukemia (AML) undergoing allogeneic hematopoietic stem cell transplantation (allo-HSCT) has limited the widespread use in practice. We investigated optimal time points, thresholds, and candidates for the bone marrow WT1 MRD assay in 425 consecutive patients with AML who underwent allo-HSCT. WT1 expression kinetics before allo-HSCT and at 1 or 3 months after allo-HSCT were determined by real-time PCR using the European LeukemiaNet (ELN) normalized method. Relapsed patients had significantly higher WT1 levels before allo-HSCT and at 3 months after allo-HSCT. The best time point for the WT1 MRD assay was before allo-HSCT by the receiver operating characteristic curve. Among various thresholds, 250 copies recommended from ELN researchers were mostly predictive of post-transplant relapse. In multivariate analysis, WT1 MRD positivity independently predicted relapse, resulting in inferior survival. In subgroup analyses, pretransplant WT1 MRD positivity was predictive of post-transplant relapse in the intermediate group, whereas WT1 MRD positivity occurred at 3 months after allo-HSCT in favorable and adverse risk groups. Among MRD-positive patients before allo-HSCT, all patients who were MRD positive at 3 months relapsed within 6 months. The WT1 MRD assay before allo-HSCT or 3 months after allo-HSCT is useful for predicting post-transplant relapse with a different significance in each risk group by time points, showing the benefit of multiple tests over time. Such monitoring is particularly available in patients with AML without specific molecular targets.