The Significance of BAALC Expression and CEBPa Mutations as New Prognostic Factors in Pediatric Acute Myeloid Leukemia with Normal Karyotype.

Approximately half of children with acute myeloid leukemia (AML) have no chromosomal or genetic abnormalities that can predict outcome. To improve the prognostic stratification on this heterogeneous group of patients, novel markers need to be investigated. Recently, CEBPa (CCAAT/enhancer binding protein alpha) mutations have been described as a favorable prognostic factor and the high expression level of BAALC (brain and acute leukemia, cytoplasmic) was found to be a poor prognostic marker, in adult AML with normal karyotype. To explore their significance in childhood, we studied the prognostic impact of the high expression level of BAALC and CEBPa mutations in pediatric AML with normal karyotype. Samples were available from pediatric patients 3 months to 15 years of age, treated on Japanese Childhood AML Cooperative Study Group Protocol, AML99. BAALC expression was determined by comparative real-time RT-PCR assay in 29 patients. The relative BAALC expression was determined using the comparative cycle threshold method. The median value of healthy volunteers was used as cutoff. The mutational analysis of CEBPa was performed in 49 patients with RT-PCR followed by direct sequencing. For samples carrying mutations, additional subcloning analysis were carried out. 72.4% (21 of 29) of patients had high BAALC expression and 27.6% (8 of 29) had low. High BAALC expression was associated with the FAB subtypes M0, M1, and M2, whereas low BAALC expression correlated with M4 and M5. Overall survival and event-free survival was 52.3%; 49.5% (high BAALC expression group) and 75.0%; 62.5% (low BAALC expression group), respectively. CEBPa mutations were detected in four patients (8.2 %, 4 of 49; two each in M1 and M2). N-terminal frameshift mutations and inframe insertions in the basic-leucine zipper (bZIP) domain were detected. Novel mutations (212 insertion (ins) C, 214–224 deletion CCCCGCACGCG, 720 ins CGCACC, 1074 ins AGA, 1092 ins CAC) were identified. One patient had mutations occurred in both N-terminal part and bZIP domain. Moreover, above patients with CEBPa mutations had not cooperating mutations with FLT3-ITD (fms-like tyrosine kinase 3 internal tandem duplication) and maintain in complete remission for at least 21 months duration. In conclusion, BAALC expression and CEBPa mutations may be prognostic factors in pediatric AML with normal karyotype.