Patients
All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki. This study has been approved by the Ethic Committee of the Nanfang Hospital of Southern Medical University. Informed written consent was obtained from all of the children and/or parents before study inclusion. This retrospective cohort study enrolled 150 children newly diagnosed with AML (non-M3). Two patients were excluded due to loss to follow-up, and three patients did not complete induction chemotherapy. Ultimately, this research included 145 children treated in the Department of Pediatrics, Nanfang Hospital of Southern Medical University and Fujian Medical University Union Hospital, China from January 2015 to April 2021. The diagnostic criteria and AML subtype were based on the 2008 World Health Organization (WHO) AML criteria. Patients with a second tumor and myeloid blast crisis phase of chronic myeloid leukemia were excluded. Blood was extracted from bone marrow at the first diagnosis for the detection of CD56 expression and cytogenetic abnormalities. According to the characteristics of genetic abnormality and the response to induction chemotherapy, all patients were classified according to risk stratification based on the C-HUANAN-AML15 protocol (Supplement 1).
Flow cytometry
Flow cytometry was performed using bone marrow samples taken at diagnosis and analyzed in the specialized laboratory. Cells were stained with anti-CD45 (mAb), gated by CD45 expression and analyzed by flow cytometry. Plots were created based on the CD45 fluorescence intensity and side scattered (SSC) light. Cells were additionally stained with fluorescein-conjugated mAb against CD2, CD3, CD4, CD10, CD13, CD15, CD22, CD33, CD34, CD56, CD64, CD117, CD123, CD11b, CD19, CD20 and HLA-DR surface antigens. Antigen-negative subpopulations of cells were used as negative controls. The blast population was gated using scatter parameters, and antigen expression was rated positive when greater than 20% of AML cells expressed a specific antigen [11].
Cytogenetic abnormality screening
Real-time polymerase chain reaction (RT–PCR) technology and G-banding technology were used for cytogenetic abnormality detection and chromosome karyotype analysis by Guangzhou KingMed Center for Clinical Laboratory.
Chemotherapy treatment
All patients were treated according to the C-HUANAN-AML15 protocol. Based on the protocol, patients received induction and consolidation therapy. Induction therapy included two tandem courses of the FLAG-IDA regimen (course 1 and course 2): fludarabine (30 mg/m2/d IV on days 2 to 6), cytarabine (2 g/m2/d IV on days 2 to 6), idarubicin (8 mg/m2/d IV on days 4 to 6), and glycosylated G-CSF (5 μg/kg/d Ih on days 1 to 7). Consolidation therapy included the HAE and MidAC regimens. The HAE (course 3) regimen was administered as follows: homoharringtonine (HHT) (3 mg/m2/d IV on days 1 to 5), cytarabine (100 mg/m2 q12h IV on days 1 to 7), and etoposide (100 mg/m2/d, IV on days 1 to 5). The MidAC (course 4) regimen was administered as follows: mitoxantrone (10 mg/m2/d IV on days 1 to 5) and cytarabine (1 g/m2 q12h IV on days 1 to 3).
Evaluation timing and definition
For patients treated with chemotherapy, bone marrow examination was performed on days 18 ~ 21 after every treatment to evaluate the effectiveness. The measured outcomes included death, relapse, CR, CR with incomplete recovery (CRi), event-free survival (EFS) and overall survival (OS). The definitions used for response criteria are based on those provided by Cheson et al. [12]. Specifically, relapse was defined as bone marrow blasts> 5% or occurrence of extramedullary disease. CR was defined as bone marrow blasts< 5%, absence of blasts with Auer rods, absence of extramedullary disease, ANC > 1.0 × 109/L, PLT > 100 × 109/L, and red cell transfusion independence.
CRi was defined as all CR criteria except for ANC > 1.0 × 109/L and PLT > 100 × 109/L. Resistance was noted when CR or CRi was not reached after 2 courses of induction therapy. The outcome measures were defined according to a review [13]: OS was calculated from the start of chemotherapy until death or last follow-up. EFS was calculated from the date of entry into the study until the date of induction treatment failure, relapse from CR or CRi or death from any cause. If the status of patients was not known at the last follow-up, they were censored on the date they were last examined.
Statistical analysis
Statistical analyses were performed using SPSS software version 26.0. Groups were compared using Gray’s test. Statistical analyses were performed using Fisher’s exact test for categorical variables and the Mann–Whitney U test for continuous variables. Kaplan–Meier curves were used to describe changes in OS and EFS, and log-rank tests were used to compare the differences in the survival curves. Univariate and multivariate Cox regression analyses were used to correct for the effects of other confounding factors on survival. The hazard ratio was calculated for only the variables included in the Cox regression model, and the factors not included in the model had no corresponding hazard ratios. P < 0.05 was considered significant.