Wilms' Tumor 1 Gene Expression Using a Standardized European LeukemiaNet-Certified Assay Compared to Other Methods for Detection of Minimal Residual Disease in Myelodysplastic Syndrome and Acute Myelogenous Leukemia after Allogeneic Blood Stem Cell Transplantation.

Overexpression of the Wilms' tumor 1 (WT1) gene is informative in many patients with acute myelogenous leukemia (AML) and myelodysplastic syndromes (MDS) and is measurable in peripheral blood (PB). Despite these advantages, WT1 has not broadly been established as a marker for minimal residual disease (MRD) monitoring after allogeneic hematopoietic stem cell transplantation (allo-HSCT) due to limited patient numbers, differing sample sources, and nonstandardized in-house methods. To estimate the value of WT1 as an MRD marker, we serially quantified PB WT1 expression using a standardized European LeukemiaNet-certified assay in 59 patients with AML and MDS after allo-HSCT. We compared its performance with routine methods such as chimerism, XY-fluorescence in situ hybridization (FISH), disease-specific cytogenetic, and molecular analyses, which were accessible in 100%, 34%, 68%, and 37%, respectively. Twenty-four patients (41%) relapsed within a median of 126 days after allo-HSCT, and 20 of them showed at least 1 elevated WT1 value above the validated cutoff. The other 35 patients (59%) remained in complete remission, and only 1 patient had a transient increase in WT1 expression. This reflects a sensitivity of 83% and a specificity of 97% for WT1 and appears to be favorable compared with the sensitivities and specificities observed for chimerism (33% and 91%), XY-FISH (67% and 73%), cytogenetic (33% and 77%), and molecular (78% and 85%) analyses. Further supporting its predictive impact, elevated WT1 expression prompted an earlier BM biopsy and consecutively the diagnosis of relapse in 62% of patients. The results of this real-life experience imply that PB WT1 expression is measurable by a standardized assay and predicts imminent relapse after allo-HSCT with high sensitivity and specificity in most patients with AML and MDS.