Favorable Prognostic Impact of WT1 SNP rs16754 in Cytogenetically Normal AML Independent of MN1, BAALC, and ERG Expression.

Abstract 1622

Poster Board I-648

We have previously shown that the minor allele of single nucleotide polymorphism (SNP) rs16754 located in the mutational hotspot of WT1 predicts a favorable prognosis in patients with cytogenetically normal acute myeloid leukemia (CN-AML) independent of mutations in NPM1, FLT3, CEBPA, or WT1. The minor allele of SNP rs16754 was found in 26% of CN-AML patients without any association to known mutations. In the present study we investigated the prognostic impact of WT1 SNP rs16754 in the context of three additional prognostic markers, MN1, BAALC and ERG, in 249 CN-AML patients. High MN1, BAALC, and ERG expression (defined as expression above the median expression level) has been associated with poor prognosis in CN-AML in previous studies. RNA was extracted from diagnostic bone marrow or peripheral blood cells, reversely transcribed, and amplified by quantitative RT-PCR. All patients were uniformly treated on the AML SHG 0295 or AML SHG 0199 treatment protocols. Statistical analyses were performed using SPSS. In univariate analysis the negative prognostic impact of MN1, BAALC, and ERG could be confirmed in our study population. The complete remission rate was significantly lower in patients with overexpression of MN1 (P=.012), BAALC (P=.001) or ERG (P=.041) compared to low expression of these genes. Furthermore, patients with high expression of MN1 or BAALC had significantly shorter relapse-free survival (RFS, P=.002 and P=.007, respectively), while high expression of ERG did not affect RFS (P=.21). Overall survival (OS) was significantly shorter in patients with high expression of MN1, BAALC, or ERG compared to low expressing patients (P=.005, P <.001, P=.034, respectively). Next we evaluated whether WT1 SNP rs16754 allele status was associated with expression levels of MN1, BAALC, and ERG. No correlation was found by chi-squared analysis (MN1 P=.69, BAALC P=.29 or ERG P=.82). The prognostic impact of WT1 SNP rs16754 was then investigated in the subgroup of patients with high MN1, BAALC, or ERG expression. Interestingly, patients with high MN1 expression (n=123) and at least one minor allele of WT1 SNP rs16754 had a significantly longer RFS (P=.008) and OS (P<.001) than patients with the two major alleles. Similarly, patients with high BAALC (n=122) or ERG expression (n=122) and at least one minor allele of WT1 SNP rs16754 had a longer RFS (P=.05 and P=.055, respectively) and OS (P=.013 and P=.005, respectively) compared to patients with the two major alleles. In multivariate analysis for OS, WT1 SNP rs16754 status independently predicted favorable prognosis (HR 0.47, 95% CI 0.28 to 0.77, P=.003) when considered together with NPM1/FLT3 mutation status, CEBPA mutation status, WT1 expression status, MN1 expression status, BAALC expression status, ERG expression status, age, WBC count, and platelet count. In multivariate analysis for RFS, WT1 SNP rs16754 status was an independent favorable prognostic factor (HR 0.49, 95% CI 0.3 to 0.82, P=.006) when considered together with NPM1/FLT3 mutation status, CEBPA mutation status, MN1 expression status, BAALC expression status, ERG expression status, WBC count, and platelet count. Thus, WT1 SNP allele status appears to be a very powerful prognostic marker that may refine currently available prognostic tools. In summary, we identified the minor allele of SNP rs16754 located in exon 7 of the WT1 gene as an independent favorable risk marker in CN-AML patients, enabling the identification of a significant proportion of patients with favorable prognosis that are neither identified by mutational analysis for NPM1, FLT3-ITD, CEBPA and WT1, nor by expression analysis for MN1, BAALC and ERG.