BAALC-Associated Mir-3151 Is An Independent Prognostic Factor In Younger Patients With Intermediate-Risk Cytogenetic Acute Myeloid Leukemia

Patients with intermediate-risk cytogenetic AML (IR-AML) have a heterogeneous prognosis, and are currently further stratified based on determined gene mutations. However, the optimal post-remission therapy, especially in younger patients, is unclear. Recently, miR-3151, a novel microRNA (miRNA) located in intron 1 of the BAALC gene, has been identified. High miR-3151 expression –either alone or in combination with high BAALClevels– independently correlates with poor prognosis in patients ≥ 60 years with normal cytogenetics AML (CN-AML) (Eisfeld AK, et al. Blood 2012). However, the prognostic value of miR-3151 in younger patients (≤60 years) with IR-AML has not been examined. We hypothesized that miR-3151 expression could also be a prognostic marker in younger patients.

To analyze whether miR-3151 expression – either alone or in combination with BAALC– improved prognostic assessment in younger patients (up to 60 years) with IR-AML and to characterize in this subset of patients the miRNA signature associated with high miR-3151 expression.

Samples were available from two separate cohorts of patients with IR-AML who had received intensive therapy: a training set of 76 patients from a single institution and a validation set of 108 patients from several centers who had been treated within the CETLAM AML-2003 protocol. Information on NPM1, FLT3-ITD and CEBPA was available for both patient cohorts. The expression levels of 670 miRNAs had previously been analyzed in the 76 patients in the training set. In the present study, the expression of miR-3151 and BAALC was analyzed using TaqMan® MicroRNA Assay and TaqMan® Gene Expression Assay (Applied Biosystems), respectively. Expression levels of miR-3151 and BAALC –both alone and in combination – were correlated with patient outcome. Statistical analyses were performed with SPSS v.15.0.1, R software v.2.9.0 and TIGR MultiExperiment Viewerv4.0.

In the training set, higher expression of miR-3151(dichotomized by its median value of normalized expression) correlated with a shorter 5-year overall survival (OS) (32%±17% vs. 61±17%, p=0.029) and 5-year leukemia-free survival (LFS) (29%±17% vs. 58±17%, p=0.036) in patients ≤ 60 yrs. When the analysis was restricted to patients with CN-AML, miR-3151 expression retained its prognostic significance (p= 0.016). In addition, increased BAALCexpression was associated with shorter OS (28%±20% vs. 58±14%, p=0.054) and LFS (17%±18% vs. 55±14%, p=0.039).

In the multivariate analysis for OS and LFS, including age, WBC, NPM1mut, FLT3-ITD, BAALC and miR-3151 expression levels as covariates, miR-3151 showed independent prognostic significance for OS (p=0.016; HR=2.52, 95% CI: 1.2-5.4),and a statistical trend for LFS (p=0.09).

Patients with low expression of both miR-3151 and BAALC had better prognosis (OS: 66%±18% vs. 34±16%, p=0.027; LFS: 67%±20% vs. 27±16%, p=0.009).Interestingly, the combination of both miR-3151 and BAALC retained a significant prognostic value for LFS within the favorable molecular subgroup/ ELN favorable subgroup (patients harboring NPM1mut without FLT3-ITD or biallelic CEBPAmut; LFS: 44%±30% vs. 100%, p=0.017) and showed a trend in the unfavorable molecular subgroup/ELN Intermediate I&II subgroups (patients lacking both NPM1 and CEBPA mutations and/or harboring FLT3-ITD; OS: p=0.064 and LFS: p=0.072).

In the validation set, miR-3151 overexpression confirmed its prognostic impact in patients in the univariate analysis for OS (45%±12% vs. 26±19%, p=0.039) and LFS (51%±14% vs. 30±24%, p=0.034) and in the multivariate analysis for OS (OS: p=0.038; HR 1.88, IC 95%: 1.06-3.34) and LFS (p= 0.014; HR 2.411 (1.198-4.855)

Finally, a supervised analysis revealed that samples exhibiting high levels of miR-3151 expression had a distinctive miRNA signature including miR-509, miR-135a, miR-100*, miR-186*, let-7a* and miR-501.

miR-3151 is an independent prognostic marker in patients with IR-AML. The study of miR-3151 refines the molecular prognostic stratification of these patients and hence could be of help to guide therapy.

Marina Díaz-Beyá is supported by Fundación Española de Hematologia y Hemoterapia. This research is supported by Sociedad Española de Hematologia y Hemoterapia and by grants from Fondo de Investigaciones Sanitarias FIS-PI080158.

No relevant conflicts of interest to declare.