Prognostic Impact of Wilms Tumor 1 Single Nucleotide Polymorphism rs16754 In Older Patients with Acute Myeloid Leukemia

Abstract 2701

The Wilms tumor 1 (WT1) gene, located at chromosome band 11p13, encodes a transcriptional regulator involved in normal hematopoietic development. The role of WT1 in acute myeloid leukemia (AML) has been underlined by the finding of WT1 overexpression in most AML cases and WT1 gene mutations in approximately 10% of AML patients. Recently, the minor allele of the silent Arg301 single nucleotide polymorphism (SNP) (rs16754), which is a 903A>G substitution in WT1 exon 7, was suggested to predict a favorable prognosis in adult patients with cytogenetically normal (CN) acute myeloid leukemia (AML). In contrast, no prognostic impact of this SNP was found in another study performed in pediatric AML. Our aim was to evaluate the frequency, the main associated features and the prognostic significance of WT1 SNP rs16754 in elderly patients with AML. Diagnostic bone marrow or peripheral blood samples were analyzed from 266 patients (age 50 to 70 years) with previously untreated de novo AML included in the French ALFA-9801 trial. WT1 SNP rs16754 and gene mutations of NPM1, CEBPA, FLT3 (internal tandem duplication, ITD), WT1 (exon 7 and 9), IDH1 and IDH2 (exon 4) were screened on genomic DNA by direct sequencing and fragment-length analysis for the detection of small insertion/deletion. The minor allele of WT1 SNP rs16754 was found in 85 (32%) out of 266 cases. Patients heterozygous or homozygous for minor allele (WT1^AG or WT1^GG) and patients homozygous for the major allele (WT1^AA) did not significantly differ in terms of age, gender, white blood cell (WBC) count, FAB subtypes, cytogenetic categories, and gene mutations when those mutations are considered separately. However, among CN-AML, the frequency of the favorable genotype defined by the presence of NPM1 mutation or CEBPA mutation without neither FLT3-ITD nor IDH1 mutation was significantly lower in patients with at least one minor allele than in patients with two major alleles (5% vs 23% of CN-AML, p=0.02). In univariate analysis, complete remission rate was found similar between patients with at least one minor allele and patients with two major alleles (76% vs 75%, p=0.88). Patients with at least one minor allele tended to have a shorter median delay to relapse (7 vs 12.2 months, p=0.06) and had a significantly shorter overall survival compared to patients with the two major alleles (5-year OS, 14% vs 26%, p=0.02). In the subset of CN-AML (n=113), the presence of at least one minor allele was also associated with a shorter median delay to relapse (6.9 vs 12.5 months, p=0.02) but only a trend regarding overall survival was observed (5-year OS, 17% vs 30%, p=0.1). In multivariate analysis considering age, WBC count, cytogenetics (favorable, intermediate and unfavorable categories) as covariates, WT1 SNP rs16754 status was found to be an independent prognostic factor for relapse risk (HR 1.56, 95% CI 1.06 to 2.30, p=0.03) and overall survival (HR 1.54, 95% CI 1.08 to 2.20, p=0.02). Thus, in our cohort of older AML patients, the minor allele of WT1 SNP rs16754 appears to confer a relatively poor prognosis, which is in contradiction to what has been reported so far. Overall, our data suggest that WT1 SNP rs16754 is an interesting marker that may contribute to refine prognosis in AML, at least in this age group of patients. Further investigations are needed to clarify the relationship between WT1 SNP rs16754 and treatment outcome in AML and elucidate the biological effects of this SNP.