Prognostic significance of, and gene and microRNA expression signatures associated with, CEBPA mutations in cytogenetically normal acute myeloid leukemia with high-risk molecular features: a Cancer and Leukemia Group B Study

Abstract

Purpose: To evaluate the prognostic significance of CEBPA mutations in the context of established molecular markers in cytogenetically normal (CN) acute myeloid leukemia (AML) and gain biologic insights into leukemogenesis of the CN-AML molecular high-risk subset (FLT3 internal tandem duplication [ITD] positive and/or NPM1 wild type) that has a significantly higher incidence of CEBPA mutations than the molecular low-risk subset (FLT3-ITD negative and NPM1 mutated).

Patients and methods: One hundred seventy-five adults age less than 60 years with untreated primary CN-AML were screened before treatment for CEBPA, FLT3, MLL, WT1, and NPM1 mutations and BAALC and ERG expression levels. Gene and microRNA (miRNA) expression profiles were obtained for the CN-AML molecular high-risk patients.

Results: CEBPA mutations predicted better event-free (P = .007), disease-free (P = .014), and overall survival (P < .001) independently of other molecular and clinical prognosticators. Among patients with CEBPA mutations, 91% were in the CN-AML molecular high-risk group. Within this group, CEBPA mutations predicted better event-free (P < .001), disease-free (P = .004), and overall survival (P = .009) independently of other molecular and clinical characteristics and were associated with unique gene and miRNA expression profiles. The major features of these profiles were upregulation of genes (eg, GATA1, ZFPM1, EPOR, and GFI1B) and miRNAs (ie, the miR-181 family) involved in erythroid differentiation and downregulation of homeobox genes.

Conclusion: Pretreatment testing for CEBPA mutations identifies CN-AML patients with different outcomes, particularly in the molecular high-risk group, thus improving molecular risk-based classification of this large cytogenetic subset of AML. The gene and miRNA expression profiling provided insights into leukemogenesis of the CN-AML molecular high-risk group, indicating that CEBPA mutations are associated with partial erythroid differentiation.

Fig A1.

Frequencies and distribution of mutations in the FLT3 (internal tandem duplication [ITD] and tyrosine kinase domain [TKD]), NPM1, MLL (partial tandem duplication [PTD]), and WT1 genes, as well as expression (high v low) of the BAALC and ERG genes among cytogenetically normal acute myeloid leukemia patients in the molecular high-risk group (ie, patients with FLT3-ITD and/or wild-type NPM1) according to CEBPA mutation status. The percentages provided on the right side of the image indicate overall proportions of patients with a given mutation or, in the case of BAALC and ERG expression, proportions of patients classified as high expressers. Only those patients for whom data on all genes were available are included.

Fig 1.

Outcome of cytogenetically normal acute myeloid leukemia (CN-AML) according to CEBPA mutational status. (A) Event-free survival of all patients with CN-AML. (B) Event-free survival of patients with molecular high-risk CN-AML (ie, patients with FLT3 internal tandem duplication and/or wild-type NPM1). (C) Disease-free survival of patients with molecular high-risk CN-AML. (D) Overall survival of patients with molecular high-risk CN-AML. CEBPA^mut, patients with CEBPA mutations; CEBPA^wt, patients with wild-type CEBPA.

Fig 2.

Heat map of selected genes involved in hematopoiesis (ie, erythroid and myeloid lineage and HOX genes) from the gene expression signature associated with CEBPA mutational status in cytogenetically normal acute myeloid leukemia patients in the molecular high-risk group (ie, patients with FLT3 internal tandem duplication and/or wild-type NPM1). Expression values of the probe sets are represented by color, with green indicating expression less than and red indicating expression greater than the median value for the given probe set. For display purposes, the expression values of the probe sets were centered so that each probe set has the same median expression value. Rows represent probe sets, and columns represent patients. Patients are grouped by CEBPA mutational status. Within each CEBPA subgroup, patients are ordered according to a summary measure of the expression of the probe sets displayed in the heat map. The summary measure was a linear combination of the expression values of the probe sets, using the base 2 logarithm of the average fold change in expression (CEBPA mutations/CEBPA wild type) as the coefficient for each expression value.

Fig 3.

Heat map of the microRNA (miRNA) expression signature associated with CEBPA mutational status in cytogenetically normal acute myeloid leukemia patients in the molecular high-risk group (ie, patients with FLT3 internal tandem duplication and/or wild-type NPM1). Expression values of the 17 miRNA probes are represented by color, with green indicating expression less than and red indicating expression greater than the median value for the given probe set. For display purposes, the expression values of the probe sets were centered so that each probe set has the same median expression value. Rows represent probe sets, and columns represent patients. Patients are grouped by the CEBPA mutational status.