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Deregulation of the hematopoietic stem cell (HSC) compartment represents a hallmark of acute myeloid leukemia (AML). Recently, in vivo screening for genes that are involved in the regulation of HSCs has led to the discovery of Musashi-2 (MSI2) as a key regulator of HSCs and as a suppressor of NUMB. In order to analyze the prognostic importance of MSI2 and NUMB expression in AML, MSI2 and NUMB transcript levels from 454 AML patients treated in multicenter trials AML SHG 0199 (ClinicalTrials Identifier NCT00209833) and 0295, and 38 healthy volunteers were analyzed by reverse transcriptase PCR in the context of other molecular markers (NPM1, FLT3, CEBPA, IDH1/IDH2, DNMT3A, NRAS, WT1, KIT, MN1, BAALC, ERG, and WT1). In AML, patients with high MSI2 expression were more likely to be FLT3-ITD positive (P

Gene mutations and epigenetic changes have been shown to play significant roles in the pathogenesis of myelodysplastic syndromes. Recently, mutations in DNMT3A were identified in 22.1% of patients with acute myeloid leukemia. In this study, we analyzed the frequency and clinical impact of DNMT3A mutations in a cohort of 193 patients with myelodysplastic syndromes. Mutations in DNMT3A were found in 2.6% of patients. The majority of mutations were heterozygous missense mutations affecting codon R882. Patients with DNMT3A mutations were found to have a higher rate of transformation to acute myeloid leukemia. When assessing the global methylation levels in patients with mutated versus unmutated DNMT3A and healthy controls no difference in global DNA methylation levels between the two groups was seen. Our data show that in patients with myelodysplastic syndromes, DNMT3A mutations occur at a low frequency and may be a risk factor for leukemia progression.

Abstract 1734 Musashi (MSI) represents an evolutionarily conserved family of RNA-binding proteins. MSI2 is the predominant form in hematopoetic stem cells (HSC). Recently, overexpression of MSI2 in a mouse model was found to increase cell cycle progression and to cooperate with BCR-ABL1 to induce aggressive leukemia. The aim of this study was to analyze the prognostic importance of MSI2 expression in myelodysplastic syndrome (MDS) and in acute myeloid leukemia (AML). Diagnostic bone marrow or peripheral blood samples were analyzed from 454 adult patients (aged 17–60 years) with de novo (n=406) or secondary AML (n=48) with French-American-British (FAB] classification M0-M2, or M4-M7, who were entered into the multicenter treatment trials AML SHG 0199 or AML SHG 0295. Additionally, we analyzed a cohort of 148 patients (aged 36–92 years) with MDS with low to high IPSS scores. Real-time reverse-transcriptase-polymerase chain reaction (RT-PCR) was performed using patient-derived cDNA and ABL as an endogenous control. MSI-2 expression levels were quantified using the TaqMan Gene Expression Assay (Applied Biosystems, Assay ID MSI2: Hs01592567_m1). To define the MSI2 expression status patient cohorts were divided into four quartiles (Q) according to levels of MSI2/ABL expression and subsequently dichotomized into two groups including the three lower Qs (Q1, Q2, and Q3) and the upper Q (Q4) of MSI2/ABL values. Patients of the quartile with highest MSI2 expression levels were classified as high MSI2 expressing patients. In MDS, MSI2 high versus low expression was independent of transfusions (P=.55), cytogenetic risk (P=.6), and ASXL1 mutations (P=.99), but was associated with a higher blast percentage (p=.034). In AML, higher MSI2 expression correlated with increased peripheral blood blasts (P=.036), and inversely correlated with the favourable cytogenetic risk group defined by inv(16) and t(8;21) according to Medical Research Council criteria (P Next, we evaluated the effect of MSI2 expression levels on patient outcome in MDS and AML. In MDS, high MSI2 expression predicted an increased likelihood of and more rapid progression to AML (HR 2.95, 95%CI 1.55–5.64, P=.001), but MSI2 expression levels did not affect overall survival (OS, HR 1.34, 95%CI 0.81–2.23, P=.25). In multivariate analysis when adjusting for karyotype, transfusion dependence, percentage of bone marrow blasts, ASXL1 frameshift mutation status and IDH1 mutation status, high MSI2 expression remained an independent prognostic factor for AML transformation in MDS (HR 2.33, 95%CI 1.16–4.67, P=.018). In AML, OS was shorter in AML patients with higher MSI2 expression as compared to low expression (HR 1.48, 95%CI 1.13–1.95, P=.005). However, relapse free survival (RFS) and complete remission (CR) rates were not influenced by high versus low MSI2 expression (RFS, HR 1.27, 95%CI.92–1.76, P=.15; CR, P=.39). In multivariate analysis, when considering MSI2 high versus low expression, DNMT3A mutations, age, platelet count, secondary versus de novo AML, cytogenetic risk group, NPM1/FLT3-ITD high vs. low risk group, and MLL5 expression levels, MSI2 expression did not remain an independent prognostic marker for OS (HR 1.31, 95%CI.98–1.76, P=.07). In patients with cytogenetically normal AML (CN-AML), MSI2 also presented a negative prognostic marker for OS (HR 1.59, 95%CI 1.08–2.33, P=.019) but did not influence RFS (HR 1.10, 95%CI 0.69–1.76, P=.68) and CR (P=.39). In multivariate analyses for CN-AML, when considering age, platelet count, DNMT3A mutations, NPM1FLT3-ITD high vs. low risk group, CEBPA mutation status and WT1 SNPrs16754, MSI2 did not independently predict OS (HR 144, 95%CI 0.94–2.19, P=.096). In summary, our data suggest that MSI2 expression might contribute to the transformation from MDS to AML. Whether MSI2 expression is dysregulated through other associated prognostic markers, or whether it is an independent event in AML pathogenesis remains to be determined. However, it may represent a valuable therapeutic target both in MDS and AML patients. Disclosures: Ottmann: Novartis Corporation: Consultancy; Bristol-Myers Squibb: Consultancy, Research Funding. Hofmann:Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees.