ID1 Expression Correlates with CEBPA Mutational Status and Is Not An Independent Risk Factor in Cytogenetically Normal AML,

Acute myeloid leukemia with normal karyotype (CN-AML) is a heterogenous disease. During the last years, mutations in several genes (e.g. NPM1, FLT3, CEBPA, WT1, IDH1, IDH2) have been identified which are involved in the pathogenesis of AML and affect the prognosis of these patients. Moreover, deregulated expression of genes such as MN1, BAALC, ERG and WT1 was demonstrated to be predictive of outcome in CN-AML. Recently, high expression of the ID1 gene was described as a negative prognostic factor in AML (Tang et al. Blood 2009, 114:2993–3000).

We have shown that C/EBPα, a transcription factor encoded by the CEBPA gene, binds to a regulatory element in the promoter region of the ID1 gene and regulates ID1 expression in leukemic cells (Wagner et al. Proc Natl Acad Sci USA 2006, 103:6338–6343). Therefore, we wanted to analyze the prognostic impact of ID1 expression in CN-AML in the context of other molecular markers, in particular CEBPA mutations.

ID1 expression was quantified normalized to ABL by real time RT-PCR in 269 patients (age 16–60 years) with CN-AML treated with intensive double induction and consolidation therapy within the AMLSG 295 and 0199 trials (NCT00209833). The patients were also analyzed for mutations in the genes NPM1, FLT3, CEBPA, WT1, IDH1 and IDH2. Median follow up was 79 months.

Expression of ID1 varied over a 3-log range. High expression of ID1 (ID1^high, defined as > median expression level) was significantly associated with the presence of a FLT3 -ITD or an IDH2 mutation and WT1 wildtype. Moreover, ID1 expression was closely associated with CEBPA mutational status. Altogether, 41 patients (15%) harboured a CEBPA mutation (24 monoallelic and 17 biallelic mutations). ID1 expression in the CEBPA wildtype patients was significantly higher than in patients with monoallelic CEBPA mutations and these patients had a significantly higher ID1 expression compared to patients with biallelic CEBPA mutations (p = 0.001). ID1^high patients had a trend to a lower complete remission (CR) rate (74% vs. 84%; p = 0.07), but in multivariate analysis only blast clearance on day 15 after induction 1, age and WT1 SNP rs16754 were independent predictors for the achievement of CR. In univariate analysis, ID1^high patients had an inferior overall survival (OS) compared to patients with low expression (median OS 29 vs. 78 months, 5 year OS 39% vs. 53%, p = 0.026). ID1^high status was an independent negative prognostic factor in multivariate analysis when analyzed together with NPM1, FLT3 -ITD, WT1, IDH1, IDH2, extramedullary disease and platelet counts (HR 1.51; 95% CI 1.06–2.19). However, when also CEBPA mutational status was entered into the model, ID1 expression lost its prognostic impact and the only independent prognostic factors were age, platelets, CEBPA mutations, NPM1 /FLT3 -ITD risk group and WT1 SNP rs16754. Likewise, ID1^high patients had a trend to an inferior relapse-free survival (RFS; HR 1.36, 95% CI 0.96–1.93, p = 0.086) in univariate analysis. However, in multivariate analysis including CEBPA mutational status, ID1 expression had no impact on RFS and the only prognostic factors for RFS were NPM1 and CEBPA mutations and WT1 SNP rs16754. In CEBPA wildtype patients, ID1 expression had no impact on CR-rate, OS or RFS in univariate or multivariate analysis.

CEBPA mutations seem to deregulate ID1 expression in CN-AML. Therefore, ID1 expression is not an independent prognostic factor in CN-AML.

No relevant conflicts of interest to declare.