Clinical Impact of WT1 Mutations in the Context of Other Molecular Markers in Cytogenetically Normal Acute Myeloid Leukemia (AML): A Study of the German-Austrian AML Study Group (AMLSG).

Background: The Wilms’ tumor 1 gene (WT1) encodes a zinc finger protein that functions as a transcriptional regulator. Although its role in haematopoiesis is still not clarified yet, disruption of WT1 function is discussed to promote stem cell proliferation and to induce a block in differentiation, the hallmarks of the two complementation groups of gene mutations that have been postulated for the development of acute myeloid leukemia (AML). In two small studies WT1 mutations were detected in 11% of cytogenetically normal (CN) AML and were associated with a lower complete remission (CR) rate and a higher rate of resistant disease (RD).

Aims: To evaluate the incidence and clinical impact of WT1 mutations in the context of NPM1, FLT3-ITD (internal tandem duplication)/TKD (tyrosine kinase domain mutations at codon 835), CEBPA, MLL-PTD (partial tandem duplication), and NRAS mutation status in CN-AML.

Methods: Bone marrow or peripheral blood samples from 279 younger adult patients (pts) 16 to 60 years of age with CN-AML (n=242 de novo, n=32 secondary, n=5 therapy-related) were studied. Pts had been entered on three AMLSG treatment trials (AML HD93, AML HD98A, AMLSG 07–04). WT1 gene mutation screening was performed using standard PCR-based direct sequencing of exons 1 to 10; mutation analyses for the other genes were performed as previously described.

Results: WT1 mutations were identified in 37/279 (13%) CN-AMLs, predominantly clustering in exon 7 (25/37) and exon 9 (6/37), but also occurring in exons 1, 2, 3, and 8. Most of them were frameshift mutations resulting from insertions or deletions; 33 pts had heterozygous and 4 pts had homozygous mutations. Correlation of WT1 to the FLT3-ITD/TKD, NPM1, CEBPA, MLL-PTD, and NRAS mutation status revealed mutant (mut) WT1 to be significantly associated with FLT3-ITDpos (p=0.003) and CEBPAmut (p=0.02). In a multivariable logistic regression model on induction success, the genotype WT1mut was not significant (p=0.89); the only significant variable was the NPM1mut/FLT3-ITDneg genotype (p=0.003). In univariable analyses for overall (OS), event-free (EFS) and relapse-free (RFS) survival, there was no difference between the WT1wt and the WT1mut group. Multivariable Cox proportional hazard models for OS, EFS and RFS also revealed no significant impact of the genotype WT1mut (p=0.4, p=0.71, and p=0.81, respectively); significant variables were the genotypes NPM1mut/FLT3-ITDneg (p=0.007, p=0.0001, and p=0.01) and CEPBAmut (p=0.01, p=0.0003, and p=0.03); and in addition logarithm of white blood cell count for OS (p=0.02).

Conclusion: In our study on a large series of molecularly well characterized CN-AML, WT1 mutations occurred in 13% of the pts and were significantly associated with the genotypes FLT3-ITDpos and CEBPAmut. However, in both univariable and multivariable analyses WT1 mutations did not impact on the prognosis of pts with CN-AML. Additional pts have to be investigated to determine whether WT1 mutation status might have an impact within distinct genotypes.