Characterization of Genomic Landscape and Risk Stratification of De Novo Cytogenetically Normal Acute Myeloid Leukaemia

Background. Acute myeloid leukaemia (AML) is a group of heterogeneous diseases with distinct clinicopathologic, cytogenetic and genetic features, sharing in common an abnormal increase in myeloblasts in blood or bone marrow (BM). Induction and consolidation chemotherapy as well as allogeneic haematopoietic stem cell transplantation (HSCT) are the mainstays of treatment. However, treatment outcome is unsatisfactory and only 30-40% patients achieve durable remission. Disease heterogeneity in AML may account for different treatment responses. In this study, we examined the mutation spectrum of cytogenetically normal AML (CN-AML) patients in Hong Kong, where AML treatment and indications for allogeneic HSCT are uniform, and evaluated their clinical outcome with respect to the specific gene mutations.

Patients. Young adult patients (18-60 years old) with AML diagnosed between August 2003 to September 2017 in 8 regional hospitals in Hong Kong were included. Their clinicopathologic and cytogenetic features as well as treatment outcome were examined.

Treatment and endpoints. Treatment comprised induction (daunorubicin 60-90 mg/m² for 3 days; cytarabine 100 mg/m² for 7 days) and consolidation (cytarabine 3 gram/m² for 4-6 doses) for 3-4 courses. BM examination was performed on day 28 or until white cell and platelet counts recovered. Non-remission or relapsed cases were treated with salvage chemotherapy comprising combinations of cytarabine with idarubicin/etoposide, fludarabine, mitoxantrone or clofarabine. Complete remission (CR) was defined as circulating and BM blasts of ≤5% with neutrophil (≥1x10⁹/L) and platelet count (≥100x10⁹/L) recovery. CR with incomplete haematological recovery (CRi) was defined as circulating and BM blasts of ≤5% without complete neutrophil or platelet recovery.

Mutation profiling. Next generation sequencing (NGS) for 36 recurrently mutated genes in AML was performed in diagnostic BM samples. Sequencing data were analyzed by in-house bioinformatics pipeline.

Statistical evaluation. Patient survivals were calculated by Kaplan-Meier analysis and compared by log-rank test. P-values of <0.05 were considered statistically significant.

Results. One hundred and seventy five patients were studied, with CR achieved in 150 cases after 1 (N=105, 70%), 2 (N=27, 18%) or ≥ 3 (N=18, 12%) courses of induction chemotherapy; and not achieved in 25 cases (primary refractory). Allogeneic HSCT was performed in 64 patients (at CR1,N=35; CR2, N=21; ≥ CR3, N=2; relapsed / persistent leukaemia, N=6). Relapse-free-survivals (RFS) at 1, 2 and 5 years were 41.3%, 27.3% and 9.3%; with median at 0.84 year. Overall survival (OS) at 1, 2 and 5 years were 69.1%, 38.3% and 15.4%, with median at 1.51 years. Mutations of ≥ 1 genes occurred in 169 cases (96%); involving with highest frequencies NPM1 (44%), FLT3-ITD (35.3%), DNMT3A (31%), IDH2 R140Q + R172K (14.3%) and CEBPA (bi-allelic, 13.7%). Individually these gene mutations had no impact on CR. However, FLT3-ITD + wildtype NPM1 and FLT3-ITD + mutated DNMT3A portended extremely poor RFS and OS. Bi-allelic CEBPA mutations portended significantly better OS but not RFS, suggesting that these cases were susceptible to relapse but were salvageable with re-induction and allogeneic HSCT. Co-existing mutations of NPM1, DNMT3A and FLT3 were common. Other mutations were mostly solitary, including bi-allelic CEBPA and IDH2 R172K mutations. NRAS and FLT3 mutations were mutually exclusive.

Conclusion. CN-AMLs were intrinsically heterogeneous. Mutational profile might be useful for personalized treatment. The cooperativity and mutual exclusivity of gene mutations may be of pathogenetic significance and can inform patient-specific therapeutic strategies.