Prevalence and Prognostic Implications of CEBPα Mutations in Pediatric AML.
Authors: Ho Phoenix A. , Alonzo Todd A. , Gerbing Robert B. , Pollard Jessica , Stirewalt Derek L. , Heerema Nyla A. , Lange Beverly , Radich Jerald , Meshinchi Soheil 
Published: April 2020

Abstract
CCAAT/enhancer binding protein-α (C/EBPα) is a transcription factor that regulates granulocytic differentiation. Molecular alterations of the CEBPα gene which alter its function have been identified in AML; their presence may have prognostic implications in AML. We evaluated the prevalence and prognostic significance of CEBPα mutations in a cohort of 428 pediatric AML patients treated on pediatric AML trials CCG-2941 and CCG-2961. Initial screening of 100 samples by direct sequencing of the entire coding region of the CEBPα gene identified mutations in 8/100 (8%) of the patients tested. All 8 mutations were insertional or deletional mutations. A multiplex micro-capillary electrophoresis was devised to facilitate further screening of an additional 328 samples. Of the 428 samples analyzed, 65 mutations were identified in 57 patients (13%). 16/65 mutations (25%) were insertions or deletions in the N-terminal region, 14 of which would cause a frameshift resulting in a premature stop codon. 32/65 (49%) mutations involved the second transactivation domain (TAD2); except for one case, all were 6 bp insertions, and except for one case, all occurred at the same location. 17/65 (26%) mutations were in-frame insertions (N=16) or deletions (N=1) in the basic region leucine zipper (bZip) domain. This resulted in the insertion of one to twelve amino acids, or the deletion of six amino acids, which would be expected to disrupt the leucine zipper. 6/57 (11%) patients with mutations harbored more than one distinct mutation; all such instances of combined mutations included at least one mutation in the N-terminal region coupled with at least one mutation in the bZip domain. Presence of mutations was correlated with laboratory and clinical characteristics and clinical outcome. There were no differences in median age, sex, race, median diagnostic blast % or median diagnostic WBC between those with and without CEBPα mutations, although such mutations were less common in the younger patients between ages of 0–2 years (p=0.02). CEBPα mutations were more common in those with normal karyotype (38% vs. 21%, p=0.03) and less common in those with 11q23 abnormalities (8% vs. 26%, p=0.01). Of the 57 patients with CEBPα mutations, 15% and 10% had t(8;21) and inv(16), respectively, no different than those without mutations. Four of the 57 patients with CEBPα mutations had FLT3/ITD (7%) compared to 41/363 (11%) of the CEBPα-WT patients (p=0.46). Response to induction therapy was similar for those with and without mutations (91% vs. 86%, p=0.43). Actuarial overall survival (OS) from study entry was 63% for those with and 52% for those without CEBPα mutations (P=0.12). Of those who achieved an initial remission, cumulative incidence of relapse from remission was 25% vs. 39% for those with and without CEBPα mutations (p=0.069) with a corresponding OS at 5 years from remission of 67% vs. 58%, (p=0.27). CEBPα mutations are frequent events in pediatric AML and are highly associated with normal karyotype. Analysis of a larger cohort of patients may determine whether those with CEBPα mutations have a lower relapse rate and improved survival.