Mutation of the Wilms’ Tumor 1 Gene Is a Poor Prognostic Factor Associated with Chemoresistance in Normal Karyotype Acute Myeloid Leukemia.

The Wilms’ tumour 1 (WT1) gene is highly expressed in various types of leukemia, suggesting a role both as a target for immunotherapy and a means for monitoring minimal residual disease. More recently WT1 has been recognised as an important mutational target in normal karyotype (NK) acute myeloid leukemia (AML), with clustering of mutations to exons 7 and 9. In this study, we set out to determine the clinical relevance of these mutations. Diagnostic DNA samples were obtained from peripheral blood or bone marrow of 470 young adult AML patients entered into the UK Medical Research Council AML 10 and 12 trials. Mutation analysis was performed using standard PCR-based direct sequencing and/or high-resolution capillary electrophoresis of exons 7 and 9. Overall, 51 mutations were observed in 47 cases (10%). Of these, 42 cases had 46 frameshift mutations arising from insertions (n=41) or deletions (n=5) of between 1 and 28 bps that would result in disruption of the C-terminal DNA binding domain of the protein. Median mutant level was 45% (range 8–86%). The remaining 5 cases were non-synonymous amino acid substitutions in exon 9, D396N (n=3) which is implicated in Denys-Drash syndrome, and 1 each of H397Y and H397Q that are of unknown functional significance. There was a borderline inverse relationship between the presence of WT1 mutations and NPM1 exon 12 mutations (p=.05), and an increased proportion of FLT3-ITDs in WT1 mutant cases (p=.08). In order to determine the clinical relevance of WT1 mutations we compared patient characteristics between WT1 mutated and WT1 wild-type cases. There was no difference between the 2 groups in age, gender, presenting WBC, or type of AML (de novo/secondary). Patients with WT1 mutations had an inferior response to therapy compared to WT1 wild-type cases (complete remission [CR] 79% Vs 90% respectively, odds ratio [OR] 3.02, 95% confidence intervals [CI] 1.17–7.82, p=.02) which was due to a higher rate of resistant disease (RD) (15% Vs 4%, OR 9.33, CI 2.38–36.6, p=.001). In univariate analysis mutated cases also had a significantly reduced disease free survival (DFS), 22% Vs 44% at 5 years (OR 2.16, CI 1.32–3.55, p=.005) and overall survival (OS), 26% Vs 47%, OR 1.91, CI 1.23–2.95, p=.007). In multivariate analysis considering age, gender, type of leukemia, WBC, FLT3-ITD and NPM1 mutant status, a WT1 mutation remained an independent adverse prognostic factor for both response to therapy (CR: OR 3.19, CI 1.25–8.13, p=.01; RD: OR 4.93, CI 1.58–15.37, p=.006) and survival (DFS: OR 1.60, CI 1.07–2.38, p=.02; OS: OR 1.52, CI 1.05–2.18, p=.03). These results indicate that WT1 mutations are an additional prognostic marker in NK AML and may be suitable for targeted therapy.