Characterization of AML Patients with CEBPA Mutations in a South-East Asian Population

Introduction: CCAAT/enhancer-binding protein alpha (CEBPA) is a known transcription factor that regulates the balance of differentiation and proliferation of myeloid progenitors. The nature of CEBPA mutations and their prognostic impact in acute myeloid leukemia (AML) have been extensively studied in the Western population, but have not been as well studied in other ethnic populations. There is some evidence that the AML mutational spectrum differs among ethnic groups (Yin et al, Leukemia Research, 2015). This study aims to characterize the AML patients with CEBPA mutations in a South-East Asian population comprising mainly Chinese, Indian and Malay ethnic groups.

Methods: Sanger-based sequencing was used to detect the CEBPA mutations. DNA was isolated from bone marrow aspirate or peripheral blood. PCR amplification-direct sequencing with overlapping primers targeting the CEBPA intronless gene was carried out using an in-house validated protocol. The PCR products were purified and bi-directionally sequenced, and the sequences compared to the reference sequence for the CEBPA gene. Clinical data including patients' ethnicity were extracted.

Results: Between January 2011 to April 2015, CEBPA mutational analysis was performed on 210 cases at the Molecular Diagnosis Centre (MDC) laboratory, Singapore. The patients were of mixed ethnicity, with 113 (54%) Chinese, 25 (12%) Malay, 4 (2%) Indian and 68 Others (Figure 1). When referenced to the COSMIC database, a total of 32 novel mutations were found: 27 in- or out-of-frame deletions/insertions and 5 with single base mutation. Mutations were detected in 35/210 (17%) cases, with a higher frequency of double-mutation cases (26/35; 74%) compared to single-mutation cases (9/35; 26%). In our CEBPA mutation-positive cohort, 24/26 (92%) of those with double mutations had wildtype FLT-3 and NPM1; in contrast to only 4/9 (56%) of those with single mutation having wildtype FLT-3 and NPM1 (p=0.002). 3/3 (100%), 11/13 (84.6%), 12/18 (66.7%) and 0/1 (0%) of Malay, Other ethnicities, Chinese and Indian CEBPA mutation-positive AML respectively, had double mutations (p=0.16) (Figure 1). With regards to prognostic impact, our data suggest that patients with double CEBPA mutations are highly likely (11/12; 92%) to have complete remission.

Conclusions: Our observed CEBPA mutation-positive frequency of 17% is consistent with those (7 to 20%) reported elsewhere in other regions. In our study cohort, the majority (92%, p=0.002) of those with CEBPA double mutations had wildtype FLT-3 and NPM1, which is also consistent with findings reported elsewhere.  Our clinical data show that only one of twelve patients (8%) with double CEBPA mutations relapsed, while the remaining eleven (92%) achieved complete remission, thus suggesting that favorable prognostic impact of double CEBPA mutations in AML patients is evident. Further research is needed to understand the frequency and prognostic implications of CEBPA mutations across the different ethnic groups.

 

 

 

 

Figure 1: CEBPA mutational status across ethnic groups in a South-East Asian population (n=210)