CEBPA mutations are found as either biallelic (biCEBPA) or monoallelic (moCEBPA). We set out to explore whether the kind of CEBPA mutation is of prognostic relevance in cytogenetically normal (CN) acute myeloid leukemia (AML).

Four hundred sixty-seven homogeneously treated patients with CN-AML were subdivided into moCEBPA, biCEBPA, and wild-type (wt) CEBPA patients. The subgroups were analyzed for clinical parameters and for additional mutations in the NPM1, FLT3, and MLL genes. Furthermore, we obtained gene expression profiles using oligonucleotide microarrays.

Only patients with biCEBPA had an improved median overall survival when compared with patients with wtCEBPA (not reached v 20.4 months, respectively; P = .018), whereas patients with moCEBPA (20.9 months) and wtCEBPA had a similar outcome (P = .506). Multivariable analysis confirmed biCEBPA, but not moCEBPA, mutations as an independent favorable prognostic factor. Interestingly, biCEBPA mutations, compared with wtCEBPA, were never associated with mutated NPM1 (0% v 43%, respectively; P < .001) and rarely associated with FLT3 internal tandem duplication (ITD; 5% v 23%, respectively; P = .059), whereas patients with moCEBPA had a similar frequency of mutated NPM1 and a significantly higher association with FLT3-ITD compared with patients with wtCEBPA (44% v 23%, respectively; P = .037). Furthermore, patients with biCEBPA showed a homogeneous gene expression profile that was characterized by downregulation of HOX genes, whereas patients with moCEBPA showed greater heterogeneity in their gene expression profiles.

Biallelic disruption of the N and C terminus of CEBPA is required for the favorable clinical outcome of CEBPA-mutated patients and represents a distinct molecular subtype of CN-AML with a different frequency of associated gene mutations. These findings are of great significance for risk-adapted therapeutic strategies in AML.