Insertion and Deletions Mutations of the CEBPA Gene Affecting the bZIP Region Are Strong Predictors for Achieving Complete Remission and Improved Overall Survival in Adult Patients with AML - An Analysis in 1536 Patients Treated in the AML96 Protocol of the DSIL.

Mutations of the CEBPA gene coding for the key myeloid transcription factor CCAAT/enhancer binding protein alpha have been reported in up to 20% of patients with AML and normal karyotype. In addition CEBPA mutations appear to be associated with an improved outcome after chemotherapy. However, so far most studies investigated selected patient populations or relatively small cohorts. To gain further insight and to study this abnormality in an unselected cohort, including older patients and all karyotype abnormalities, we analyzed more than 1500 patients for the predominant type of CEBPA mutation, namely insertion/deletion mutations affecting the basic leucine zipper region (bZIP-mutations). Patients screened were treated in the AML96 protocol of the DSIL. Screening for CEBPA bZIP mutations was done on DNA isolated at the time of diagnosis using high resolution fragment analysis with fluorescent primers.

Results: CEBPA bZIP length mutations were identified in 56/1537 patients (3.6%). All mutations were confirmed by sequence analysis, 7 patients had deletions whereas 49 had insertions, median length was 3 bases (range 1–57 bases), 8 patients had clear evidence of allelic loss of the wt-CEBPA allele. The mutation rate was significantly higher in patients with normal karyotype (44/664; 6.2%) compared to patients with karyotype abnormalities (11/707; 1.5%; P<.001). CEBPA bZIP mutations were observed exclusively in FAB M1 (8.9%), M2 (4.9%) and M6 (6.1%) patients. The presence of a bZIP mutation was associated with an increased white blood cell count (25.7 vs. 16.8 GPT/l; P=.019), and a higher rate of CD34+ cells (60% vs. 28%; P<.001), but not with BM blasts, platelet counts or haemoglobin levels. Interestingly, CEBPA bZIP mutations were associated with a significantly lower median age at diagnosis (47 yrs) compared to bZIPwt patients (60 yrs.; P<.001). bZIP mutations were negatively associated with the presence of NPM1-mutations (P<.001), but there was no significant association with FLT3-ITD mutations. Patients with CEBPA bZIP mutations were found to have a significantly higher rate of complete remission (CR) after double induction chemotherapy (e.g. <60 yrs, norm. karyo: bZIPmut: 79.5% vs. bZIPwt: 59.2%; P=.015) and a significantly higher probability of overall survival (OS) (median all pts with norm karyotype; bZIP+: not reached vs. bZIPwt: 19.3 mo). This association was confirmed also in a multivariate analysis. In conclusion, although CEBPA bZIP mutations affect only a small subgroup of all patients with AML, they are found in a significant proportion of patients with normal karyotype. CEBPA bZIP mutations are strong independent predictors for the achievement of CR and favourable OS. Thus, the easy and rapid screening technique used here might be a useful diagnostic tool in the standard workup of patients with AML, especially in individuals with normal karyotype.