Page 259 - Haematologica Vol. 110 - January 2025

LETTER TO THE EDITOR
Adverse prognostic impact of KIT exon 17 mutations despite negative flow cytometric measurable residual disease in pediatric acute myeloid leukemia with RUNX1::RUNX1T1
Pediatric patients with acute myeloid leukemia (AML) with t(8;21)(q22;q22)/RUNX1::RUNX1T1 are classified as a fa- vorable risk with an excellent 3-year event-free survival (EFS) of approximately 70-80%, while some of them have refractory diseases after relapse.1,2 Prognostic factors in RUNX1::RUNX1T1-positive AML include secondary genetic abnormalities3-5 and treatment responses.1,6,7 KIT mutations are observed almost exclusively in core-binding factor AML8 and many pediatric and adult studies have revealed that KIT mutations, particularly in exon 17, are associated with poor prognosis in AML with RUNX1::RUNX1T1.9-11 Also, flow cytometry-based measurable residual disease (flow-MRD) has emerged as a robust prognostic predictor for pediatric AML.1,6,7,12,13 However, the combined prognostic impact of KIT mutations and flow-MRD remains to be examined. Herein, we investigated how KIT exon 17 mutations and flow-MRD status coordinately affected the prognosis of children with RUNX1::RUNX1T1-positive AML who were enrolled in the Ja- pan Children’s Cancer Group (JCCG) trial, JPLSG-AML-12, and revealed that KIT exon 17 mutations were associated with a significantly poor prognosis even among patients with negative MRD.
Patients were recruited to the AML-12 trial from March 2014 to February 2018. The AML-12 trial randomly assigned patients to receive initial induction therapy, including stan- dard-dose cytarabine (ECM) or high-dose cytarabine (HD- ECM).12 Flow-MRD was centrally monitored at the end of inductions 1 (EOI1) and 2 but did not guide toward subsequent therapies. Gemtuzumab ozogamicin (GO) was not involved in the treatment plan. Targeted capture sequencing with a custom gene panel for mutation profiling of pediatric AML was used to analyze DNA extracted from leukemic sam- ples. The institutional review board of each participating institution approved the treatment methods and data and sample collection protocols in the clinical trial, and written informed consent was obtained from all patients or their parents/guardians. This study was approved by the Insti- tutional Review Board of Yokohama City University Hospital and the Ethical Review Board of the JCCG, and conducted under the Declaration of Helsinki.
The AML-12 trial included 101 pediatric patients with AML with RUNX1::RUNX1T1 who were 0-17 years old. Six patients who were treated in the non-selected phase II institutions were excluded.12 Hence, 95 patients were included in the analysis with a median of 9.7 (range, 2.2-17.9) years and 45
(47.4%) female patients (Online Supplementary Table S1). In the targeted capture sequencing analysis, KIT was the most affected gene detected in 37 (38.9%) patients, with 29 and ten patients with exon 17 and 8 mutations, respectively. The 29 (30.5%) patients with KIT exon 17 mutations had a lower frequency of CD19 expression (P=0.006) and a higher frequency of CD56 expression (P=0.026) in the flow cytometry analysis for diagnostic samples than those without the mutations. The 5-year EFS and OS (95% confidence interval [CI]) from registration were 67.4% (95% confidence interval: 57.0- 75.8) and 82.6% (95% CI: 73.1-89.0) in the entire cohort (Online Supplementary Figure S1A). The 5-year EFS and OS of patients with KIT exon 17 mutations (44.8% [95% CI: 26.5-61.6] and 61.7% [95% CI: 41.6-76.7], respectively) were significantly inferior to those without (77.3% [95% CI: 65.2- 85.6] and 92.0% [95% CI: 81.8-96.6], respectively; both, P<0.001) (Online Supplementary Figure S1B, C). KIT exon 8 mutations did not show a significant prognostic impact (Online Supplementary Figure S1D, E). As well as in the entire cohort of the AML-12 trial,12 HD-ECM induction treatment did not show a prognostic superiority over ECM induction treatment in the entire RUNX1::RUNX1T1 cohort (5-year EFS of 73.1% [95% CI: 58.8-83.1] and 60.5% [95% CI: 44.3-73.3] in the ECM and HD-ECM group, respectively; P=0.206; and 5-year OS of 90.3% [95% CI: 78.1-95.8] and 72.5% [95% CI: 55.4-83.9] in the ECM and HD-ECM group, respectively; P=0.027) and in the patients with or without KIT exon 17 mutations (Online Supplementary Figure S1F, G). Multivari- able Cox regression analyses adjusted by treatment arms and previously investigated prognostic factors12 revealed that KIT exon 17 mutations remained significantly associ- ated with inferior EFS and OS from registration (Table 1). Next, we analyzed EFS and OS from EOI1 in 82 patients whose flow-MRD data at EOI1 were available to evaluate the association of both KIT exon 17 mutations and flow-MRD status with prognosis. KIT exon 17 mutations still demon- strated an adverse effect on EFS and OS from EOI1 (Figure 1A, B). Also, the 5-year EFS and OS of patients achieving negative MRD with a cutoff at 0.1% (71.6% [95% CI: 59.9- 80.5] and 85.9% [95% CI: 75.2-92.2], respectively) were significantly better than those with positive MRD (12.5% [95% CI: 0.7-42.3] and 37.5% [95% CI: 8.7-67.4], respectively) (both P<0.001; Figure 1C, D). In the combined analysis of KIT exon 17 status and flow-MRD levels (Figure 1E, F), pa- tients with both unmutated KIT exon 17 and negative MRD
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