Double CEBPA Mutations Are Not Associated With Favorable Clinical Outcome In Pediatric AML: A Report From The Japanese Pediatric Leukemia/Lymphoma Study Group (JPLSG)

CCAAT/enhancer binding protein alpha (CEBPA) is a transcription factor that coordinates cellular differentiation. Mutations in the CEBPA genes are found in about 10% of patients with AML and are associated with favorable prognosis. However, recent data suggests that the favorable prognosis is restricted only to the patients with double CEBPA mutations and normal karyotype. These data have large implications for risk-stratified therapy and require confirmation. In this study, we investigated CEBPA mutation status and clinical outcome of the pediatric AML patients treated in the Japanese Pediatric Leukemia/Lymphoma Study Group (JPLSG) AML-05 study.

AML-05 study, registered at http://www.umin.ac.jp/ctr/as UMIN000000511, is a nation-wide multi-institutional study for children (age <18 years) with de novo AML enrolled from 11/1/2006 to 12/31/2010. Cases with acute promyelocytic leukemia or Down syndrome were excluded. Patients were stratified by the specific cytogenetic characters and morphological treatment response into 3 risk groups; CBF-AML patients to the low risk (LR) group, those with either unfavorable cytogenetics (-7, 5q-, t(16;21)(p11;q22), Ph1, FLT3-ITD) or poor induction responders to the high risk (HR) group, and the rest to the intermediate risk (IR) group. In this trial, morphology was prospectively diagnosed by a central review system. Cytogenetic tests were carried out in regional laboratories, but the reports were reviewed centrally. FLT3-internal tandem duplication (ITD) was examined for all patients. Using the surplus RNA from the AML-05 study, CEBPA gene mutation was analyzed by RT-PCR and direct sequencing.

Of the 317 evaluable patients, 73 patients (23.0%) had normal karyotype, 42 patients (13.2%) were FLT3-ITD positive, and 19 patients (6.0%) had both normal karyotype and FLT3-ITD. Among the 54 cases with normal karyotype and negative FLT3-ITD, 16 patients (29.6%) had a single CEBPA mutation and 17 patients (31.5%) had double or more (hereafter described as Double) CEBPA mutations. Between the CEBPA wild type (WT) and Double mutated patients, there were no statistically significant differences in relapse-free survival (RFS) (53.9% vs. 71.1%, P=0.27) nor overall survival (OS) (68.9% vs. 64.7%, P=0.57).

An in-frame insertion of 6bp (ACCCGC) in CEBPAtrans-activator (TAD2) domain, resulting in a His-Pro duplication (HP196-197 ins), was detected in 131 patients (41.3% of all patients) in the current study, a considerably high incidence. However, this insertion was previously reported as polymorphism in adult AML (Leukemia 2008). When categorizing this insertion cases as CEBPA WT, 24 patients were CEBPA mutated among the 54 cases with normal karyotype and negative FLT3-ITD; 11 patients (20.4%) with single CEBPA mutation and 13 patients (24.1%) with Double CEBPA mutations. Although not statistically significant, there was a tendency of higher RFS (83.3% vs. 55.5%, P=0.20) and OS (79.1% vs. 63.3%, P=0.39) in patients with Double CEBPA mutations versus WT patients.

The current study is the first Japanese nation-wide investigation of the clinical significance of CEBPA mutations in pediatric AML. Our results suggest that CEBPA mutations have no prognostic impact on children with AML.

No relevant conflicts of interest to declare.