Prognostic Impact of CEBPA bZIP Domain Mutation in Cytogenetically Normal Acute Myeloid Leukemia

Introduction CCAAT/enhancer-binding protein alpha (CEBPA) is recurrently mutated gene in acute myeloid leukemia (AML). Biallelic mutation of CEBPA (CEBPA-bm) is associated with a favorable prognosis. Recently, mutation in the c-terminus basic leucine zipper domain (bZIP) was shown to be strongly associated with favorable prognosis (Taube F et al. Blood 2022; Wakita S et al. Blood Advances 2022). We analyzed the clinical features and prognosis of AML with CEBPA mutation based on our regional prospective cohort.

Patients and Methods Hokkaido Leukemia Net (HLN) is prospective cohort study collecting acute leukemia samples from hospitals of North Japan Hematology Study Group (NJHSG) covering Hokkaido. CEBPA and NPM1 mutations were analyzed for cytogenetically normal (CN) AML by Sanger sequencing. We retrospectively analyzed the mutation pattern of CEBPA and prognosis in patients with CN-AML. This study was conducted in accordance with the Helsinki Declaration and was approved by the institutional review boards.

Results A total of 264 CN-AML cases registered in HLN from January 2009 to December 2021 were analyzed (age range, 18-93 years; median age, 65 years; 140 males and 124 females). The numbers of AML cases with CEBPA-bm, CEBPA single mutation (CEBPA-sm) and CEBPA wild type (CEBPA-wt) were 28, 40, and 196, respectively. CEBPA bZIP mutation was found in 24 (85.7%) of 28 CEBPA-bm cases and in 9 (22.5%) of the CEBPA-sm cases. All of the bZIP mutations found in CEBPA-bm cases were in-frame mutations, whereas only 4 of the 9 bZIP mutations in CEBPA-sm cases were in-frame mutations. First, these patients were classified as patients with CEBPA-bm, CEBPA-sm, and CEBPA-wt. Patients with CEBPA-bm were significantly younger at diagnosis than were patients in the other two groups (median age: 46 vs 69 vs 65 years, P<0.001) and had higher WBC counts at diagnosis (median: 33500 vs 10600 vs 8500, P=0.038). However, there were no differences among the three groups in other characteristics (gender, blast ratio in bone marrow, FLT3-ITD-positive ratio, intensity of induction chemotherapy, and number of patients who received allogeneic hematopoietic stem cell transplantation (allo-HSCT)) (Table). As reported previously, patients with CEBPA-bm had a significantly higher rate of complete remission (CR) (CEBPA-bm, 93% vs CEBPA-sm, 70% vs CEBPA-wt, 71%; P=0.015) as well as a higher 5-year survival rate (CEBPA-bm, 78.8%; 95% CI, 0.562-0.908 vs CEBPA-sm, 33.2%; 95% CI, 0.174-0.499 vs CEBPA-wt, 32.9%; 95% CI, 0.244-0.416; P=0.0063). Then we reclassified the patients with CEBPA bZIP in-frame mutations as "CEBPA-bZIP inf” and those with other mutations as "CEBPA-other". Patients with CEBPA-bZIP inf were significantly younger at diagnosis than were patients in the CEBPA-other and CEBPA-wt groups (median age: 48 vs 69 vs 65 years, P<0.001). However, there were no differences in other characteristics (gender, WBC counts at diagnosis, blast ratio in bone marrow, FLT3-ITD-positive ratio, intensity of induction chemotherapy, and number of patients received who allo-HSCT). Patients with CEBPA-bZIP inf had a significantly higher rate of CR (CEBPA-bZIP inf, 96.1% vs CEBPA-other, 70% vs CEBPA-wt, 71%; P=0.015) as well as a higher 5-year survival rate (CEBPA-bm, 83.3%; 95% CI, 0.609-0.935 vs CEBPA-sm, 31.9%; 95% CI, 0.167-0.483 vs CEBPA-wt, 32.9%; 95% CI, 0.244-0.416; P=0.0034) (Figure). Univariate analysis was carried out for age, sex, WBC counts, CEBPA, FLT3-ITD, intensity of induction chemotherapy, and allo-HSCT. FLT3-ITD positive were associated with poor OS (P<0.001, 0.0078; log-rank test). Age <65 years, female gender, intensive chemotherapy, allo-HSCT, and CEBPA-bZIP inf were associated with favorable OS (P<0.001, 0.0094, <0.001, <0.001, 0.003; log-rank test). Multivariate analysis showed that CEBPA-bZIP inf and age <65 years were independently associated with favorable OS (CEBPA-bZIP inf; HR, 0.25; 95% CI, 0.087 to 0.75, P=0.011, age <65 years; HR, 0.45; 95% CI, 0.32 to 0.65, P<0.001; cox regression).

Conclusion CEBPA-bZIP inf had a very good prognosis, while CEBPA mt other than bZIP-inf had a prognosis comparable to that of CEBPA-wt. CEBPA-bZIP inf is a better prognostic marker than CEBPA-bm. The successful simplification of the CEBPA mt prognostic criteria has a great impact on genetic risk stratification of AML and potentially contributes to elucidation of the functional mechanisms of tumorigenesis of AML.

Kondo:Chugai Pharmaceutical: Honoraria; Alexion Pharma: Honoraria; PharmaEssentia Japan: Honoraria. Teshima:NIPPON SHINYAKU: Research Funding; Fuji Pharma: Research Funding; Chugai: Research Funding; Astellas: Research Funding; TEIJIN PHARMA: Research Funding; Bristol-Myers Squibb: Honoraria; Novartis: Membership on an entity's Board of Directors or advisory committees, Other: Manuscript preparation, Research Funding; Pfizer: Honoraria; Takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen: Other: Manuscript preparation; Merck Sharp & Dohme: Honoraria, Membership on an entity's Board of Directors or advisory committees; Sanofi: Research Funding; Luca Science Inc.: Research Funding; Kyowa Kirin: Honoraria, Research Funding.