DNMT3A Mutations in Acute Myeloid Leukemia-Stability During Disease Evolution and the Clinical Implication
Authors: Hou Hsin-An , Kuo Yuan-Yeh , Liu Chieh-Yu , Chou Wen-Chien , Lee Ming Cheng , Chen Chien-Yuan , Lin Liang-In , Tseng Mei-Hsuan , Huang Chi-Fei , Chiang Ying-Chieh , Lee Fen-Yu , Liu Ming-Chih , Liu Chia-Wen , Tang Jih-Luh , Yao Ming , Huang Shang-Yi , Ko Bor-Sheng , Hsu Szu-Chun , Wu Shang-Ju , Tsay Woei , Chen Yao-Chang , Tien Hwei-Fang 
Published: October 2019

Abstract
Abstract 409

Background:
DNMT3A mutations are associated with poor prognosis in acute myeloid leukemia (AML), but the stability of this mutation during the clinical course remains unclear.

Materials and Methods:
Mutation analysis of DNMT3A exons 2–23 was performed by polymerase chain reaction and direct sequencing in 506 de novo AML patients. Their interaction with clinical parameters, chromosomal abnormalities and genetic mutations were analysed.

Results:
DNMT3A mutations were identified in 14% of total patients and 22.9% of patients with normal karyotype (CN-AML). 30 different kinds of DNMT3A mutations were identified in 70 patients. Twelve were missense mutations, eight were nonsense mutations, nine were frame-shift mutations and one, in-frame mutation. The most common mutation was R882H (26 patients), followed by R882C (15 patients), R882S (3 patients), R736H (3 patients) and R320X (2 patients). DNMT3A mutations were closely associated with older age, higher white blood cell (WBC) and platelet counts at diagnosis, FAB M4/M5 subtype, intermediate-risk and normal cytogenetics.
Among the 70 patients with DNMT3A mutations, 68 (97.1%) showed additional molecular abnormalities at diagnosis. The most common associated molecular event was NPM1 mutation (38 cases), followed by FLT3-ITD (30 cases), IDH2 mutation (16 cases) and FLT3-TKD (9 cases). Patients with DNMT3A mutations had significantly higher incidences of NPM1 mutation, FLT3-ITD, IDH2 and PTPN11 mutations than those with DNMT3A-wild type (54.3% vs. 15.3%, P<0.0001; 42.9% vs. 19.3%, P<0.0001; 22.9% vs. 9.1%, P=0.0016; and 10% vs. 3.5%; P=0.007, respectively). On the contrary, CEBPA was rarely seen in patients with DNMT3A mutations (4.3% vs. 14.7%, P=0.0134). Totally, 40 patients (58.8%) had concurrent both Class I and Class II or NPM1 mutations at diagnosis.
With a median follow-up of 55 months (ranges, 1.0 to 160), patients with DNMT3A mutation had significantly poorer overall survival (OS) and relapse-free survival (RFS) than those without DNMT3A mutation (median, 14.5 months vs. 38 months, P =0.013, and medium, 7.5 months vs. 15 months, P=0.012, respectively). In the subgroup of 130 younger patients (less than 60 years) with CN-AML, the differences between patients with and without DNMT3A mutation in OS (median, 15.5 months vs. not reached, P= 0.018) and RFS (median, 6 months vs. 21 months, P=0.004) were still significant. Multivariate analysis demonstrated that DNMT3A mutation was an independent poor prognostic factor for OS and RFS among total patients (HR 2.218, 95% CI 1.333–3.692, P=0.002 and HR 2.898, 95% CI 1.673–5.022, P<0.001, respectively) and CN-AML group (HR 2.303, 95% CI 1.088–4.876, P=0.029 and HR 3.496, 95% CI 1.773–6.896, P<0.001, respectively). Further, a scoring system incorporating DNMT3A mutation and eight other prognostic factors, including age, WBC count, cytogenetics, and gene mutations (NPM1/FLT3-ITD, CEBPA, AML1/RUNX1, WT1, and IDH2 mutations), into survival analysis was proved to be very useful to stratify AML patients into different prognostic groups (P<0.001).
DNMT3A mutations were serially studied in 316 samples from 138 patients, including 35 patients with distinct DNMT3A mutations and 103 patients without mutation at diagnosis. Among the 34 patients with DNMT3A mutations who had ever obtained a CR and had available samples for study, 29 lost the original mutation at remission status, but five retained it; all these five patients relapsed finally within a median of 3.5 months and died of disease progression, suggesting presence of leukemic cells. In the 13 patients who had available samples for serial study at relapse, all patients regained the original mutations, including mutant clone was found by TA cloning in one patient. Among the 103 patients who had no DNMT3A mutation at diagnosis, none acquired DNMT3A mutation at relapse, while karyotypic evolution was noted at relapse in 39% of them.

Conclusion:
DNMT3A mutations are associated with distinct clinical and biological features and poor prognosis in de novo AML patients. Furthermore, the mutation may be a potential biomarker for monitoring of minimal residual disease.

Disclosures:
No relevant conflicts of interest to declare.