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Extramedullary infiltration (EMI) is a rare condition defined by the accumulation of myeloid tumor cells beyond the bone marrow. The clinical significance is still controversial. This study was aimed to evaluate the incidence, characteristics, and prognostic significance of EMI on complete magnetic resonance imaging (MRI) investigation in newly diagnosed pediatric acute myeloid leukemia (AML) patients who are asymptomatic without clinical evidence to suspect EMI.Retrospective clinical and radiologic review of 121 patients with MRI examination at the time of initial diagnosis of AML without any clinical evidence suggestive of EMI was performed. Patients were divided into 2 groups according to the presence or absence of EMI, and the relationship between EMI and established risk factors was analyzed. Initial white blood cell count, the occurrence of an event (including relapse, death, and primary refractory disease), survival status, and detailed information on cytogenetic/molecular status was performed by a thorough review of electronic medical records system. All patients underwent full imaging evaluation with the contrast-enhanced whole body and some regional MRI at the time of initial diagnosis.The median age at diagnosis was 10.77 years (range, 0.37 to 18.83 y). Based on the risk stratification system of AML, 36, 45, and 40 patients are classified as low-risk, intermediate-risk, and high-risk groups, respectively. MRI at the time of the initial diagnosis of AML revealed 35 of 121 patients (28.9%) with EMI. The most common site of EMI was a skull, followed by the lower extremity bone and meninges of the brain. The median age at diagnosis was significantly younger in patients with EMI (7.87 vs. 11.08 y, P=0.0212). Low incidence of FLT3/ITD mutation, low incidence of AML-ETO gene rearrangement, and the larger extent and more severe degree of bone marrow involvement was related with EMI. However, there was no significant prognostic difference in event-free survival and overall survival regardless of the presence of EMI in the overall patient population and each risk group. The location of EMI occurrence was also not related to prognosis.Even if EMI symptoms are not evident, surveillance MRI scans at the initial diagnosis of pediatric AML patients are very helpful in detecting a significant number of EMIs. Younger age, some molecular features, and more severe bone marrow involvement of AML patients were related with EMI. However, there was no significant prognostic difference between patients with or without EMI regardless of risk group. Further prospective investigation is necessary to validate the prognostic effect of EMI in a larger group of patients with different risk groups.

Here, we introduced the first case of acute myeloid leukemia (AML) with RARG-NUP98 in a pediatric patient. The young male presented with structural and functional abnormalities similar to hypergranular acute promyelocytic leukemia, but was resistant to all transretinoic acids and arsenic trioxide. Till date, only 12 adult AML cases involving RARG rearrangement have been reported. At present, there is no standardized or optimal treatment option for this AML subtype. Disease management may typically require a joint treatment strategy involving chemotherapy, immunotherapy, and support therapy. In this study, we report the clinical manifestations and experimental results of a 10-year-old male and review other cases of RARG gene rearrangement reported in the literature.

Children with acute myeloid leukemia (AML) commonly develop extramedullary disease (EMD), which comprises central nervous system (CNS) lesions and myeloid sarcoma (MS). In this retrospective analysis, we aimed to determine the effect of EMD on the outcomes of allogeneic hematopoietic cell transplantation (HCT) in 678 pediatric patients with de novo AML (median age, 7 years; range, 0.3-15 years) between 2006 and 2016. We compared the outcomes between patients with (EMD group, n = 158; CNS lesion, n = 47, CNS lesion + MS, n = 9, and MS, n = 102) and without EMD at diagnosis (non-EMD group, n = 520). Survivors were followed for a median of 4.5 years, and the 4-year overall survival (OS) rates were 60.6% and 56.4% in the EMD and non-EMD groups, respectively (P = 0.60). No significant differences in OS were observed with respect to the EMD site, except bone lesions, which were associated with poor OS after HCT in a non-remission status. A multivariate analysis revealed that EMD did not affect the outcomes of HCT. In conclusion, the study findings suggest that EMD should not be considered a poor prognostic factor in HCT for children with AML.

BACKGROUND: In addition to treatment response, cytogenetic and molecular aberrations are the most important prognostic factors in children with de novo acute myeloid leukemia (AML). However, little is known about cytogenetics at the time of relapse.METHODS: This international study analyzed the prognostic value of cytogenetic profiles and karyotypic changes in pediatric relapsed AML in relation to the probability of event-free (pEFS) and overall survival (pOS). For this purpose, cytogenetic reports from all patients registered on the Relapsed AML 2001/01 Study were reviewed and classified.RESULTS: Cytogenetic information at relapse was available for 403 (71%) of 569 registered patients. Frequently detected aberrations at relapse were t(8;21)(q22;q22) (n = 60) and inv(16)(p13.1q22)/t(16;16)(p13.1;q22) (n = 24), both associated with relatively good outcome (4-year pOS 59% and 71%, respectively). Monosomy 7/7q-, t(9;11)(p22;q23), t(10;11)(p12;q23), and complex karyotypes were associated with poor outcomes (4-year pOS 17%, 19%, 22%, and 22%, respectively). Of 261 (65%) patients for whom cytogenetic data were reliable at both diagnosis and relapse, pEFS was inferior for patients with karyotypic instability (n = 128, 49%), but pOS was similar. Unstable karyotypes with both gain and loss of aberrations were associated with inferior outcome. Early treatment response, time to relapse, and cytogenetic profile at time of relapse were the most important prognostic factors, both outweighing karytoypic instability per se.CONCLUSION: The cytogenetic subgroup at relapse is an independent risk factor for (event-free) survival. Cytogenetic assessment at the time of relapse is of high importance and may contribute to improved risk-adapted treatment for children with relapsed AML.

To evaluate the outcome and prognostic significance of CEBPA mutations among pediatric acute myeloid leukemia (AML) from TARGET dataset. A total of 1803 pediatric patients who were diagnosed with AML were classified into two groups based on the CEBPA status by using a retrospective cohort study method from September 1996 to December 2016. The incidence of CEBPA mutations was 18%. CEBPA mutations were significantly associated with elder age (p

Background The optimal number of chemotherapy courses for low-risk (LR) pediatric acute myeloid leukemia (AML) is not known. Objective To compare outcomes for four (21.6 g/m2 cytarabine) versus five (45.6 g/m2 cytarabine) chemotherapy courses for LR-AML using data from Children's Oncology Group (COG) AAML0531 and AAML1031. Methods We compared relapse risk (RR), disease-free survival (DFS), and overall survival (OS), and the differential impact in LR subgroups for patients receiving four versus five chemotherapy courses. Cox (OS and DFS) and risk (RR) regressions were used to estimate hazard ratios (HR) to compare outcomes. Results A total of 923 LR-AML patients were included; 21% received five courses. Overall, LR-AML patients who received four courses had higher RR (40.9% vs. 31.4%; HR = 1.40, 95% confidence interval [CI]: 1.06-1.85), and worse DFS (56.0% vs. 67.0%; HR = 1.45, 95% CI: 1.10-1.91). There was a similar decrement in OS though it was not statistically significant (77.0% vs. 83.5%; HR = 1.45, 95% CI: 0.97-2.17). Stratified analyses revealed the detrimental effects of cytarabine dose de-escalation to be most pronounced in the LR-AML subgroup with uninformative cytogenetic/molecular features who were minimal residual disease (MRD) negative after the first induction course (EOI1). The absolute decrease in DFS with four courses for patients with favorable cytogenetic/molecular features and positive MRD was similar to that observed for patients with uninformative cytogenetic/molecular features and negative MRD at EOI1, though not statistically significant. Conclusions Our results support de-escalation of cytarabine exposure through the elimination of a fifth chemotherapy course only for LR-AML patients who have both favorable cytogenetic/molecular features and negative MRD after the first induction cycle.

Infections are responsible for most treatment-related morbidity and mortality in pediatric acute myeloid leukemia (AML). Children's Oncology Group (COG) recommends hospitalization following chemotherapy until early absolute neutrophil count (ANC) recovery. No standard guidelines exist for antibiotic prophylaxis and discharge practices vary. Our objective was to report our institution's experience with outpatient supportive care management following early discharge. A retrospective chart review of pediatric AML patients treated at our institution from 2010 to 2019 was conducted. Data was collected on length of hospitalization, antibiotics administered, infections, and neutropenia duration. Seventeen patients underwent 60 chemotherapy cycles. All were discharged after completion of chemotherapy if clinically stable. Patients were re-admitted for fever and discharged on empiric antibiotics if afebrile with negative cultures. Prophylactic antibiotics were administered in 55 cycles. There were 12 infections in 11 patients and no deaths due to infection. Patients remained outpatient for a mean of 15.8 neutropenia days per cycle. Outpatient supportive care for children with AML may be feasible and safe. Further studies are needed to establish outpatient supportive care guidelines.

Genetic aberrations in the epigenome are rare in pediatric AML, hence expression data in epigenetic regulation and its downstream effect is lacking in childhood AML. Our pilot study screened epigenetic modifiers and its related oncogenic signal transduction pathways concerning clinical outcomes in a small cohort of pediatric AML in KSA. RNA from diagnostic BM biopsies (n = 35) was subjected to expression analysis employing the nCounter Pan-Cancer pathway panel. The patients were dichotomized into low ASXL1 (17/35; 49%) and high ASXL1 (18/35; 51%) groups based on ROC curve analysis. Age, gender, hematological data or molecular risk factors (FLT3 mutation/molecular fusion) exposed no significant differences across these two distinct ASXL1 expression groups (P 0.05). High ASXL1 expression showed linkage with high expression of other epigenetic modifiers (TET2/EZH2/IDH12). Our data showed that high ASXL1 mRNA is interrelated with increased BRCA1 associated protein-1 (BAP1) and its target gene E2F Transcription Factor 1 (E2F1) expression. High ASXL1 expression was associated with high mortality {10/18 (56%) vs. 1/17; (6%) P 0 .002}. Low ASXL1 expressers showed better OS {740 days vs. 579 days; log-rank P= 0.023; HR 7.54 (0.98-54.1)}. The association between high ASXL1 expression and epigenetic modifiers is interesting but unexplained and require further investigation. High ASXL1 expression is associated with BAP1 and its target genes. Patients with high ASXL1 expression showed poor OS without any association with a conventional molecular prognostic marker.

Objective Long non‐coding RNA microvascular invasion in hepatocellular carcinoma (lnc‐MVIH) is correlated with unfavorable prognosis in several malignancies, while limitedly studied in pediatric acute myeloid leukemia (AML). This study aimed to investigate the correlation of lnc‐MVIH with disease features, response to induction therapy, and survival in pediatric AML patients. Methods A total of 129 de novo pediatric AML patients who were retrospectively analyzed and 60 children with non‐malignant hematological diseases who underwent bone marrow examination were reviewed as controls. Bone marrow mononuclear cells (BMMCs) were isolated from all participants to detect lnc‐MVIH expression by reverse transcription‐quantitative polymerase chain reaction. The complete remission status after 1 course of induction therapy, event‐free survival, and overall survival of pediatric AML patients were recorded. Results Lnc‐MVIH was upregulated in pediatric AML patients compared with controls (p, Objective: Long non‐coding RNA microvascular invasion in hepatocellular carcinoma (lnc‐MVIH) is correlated with unfavorable prognosis in several malignancies, while limitedly studied in pediatric acute myeloid leukemia (AML). This study aimed to investigate the correlation of lnc‐MVIH with disease features, response to induction therapy and survival in pediatric AML patients. Methods: A total of 129 de novo pediatric AML patients were retrospectively analyzed and 60 children with non‐malignant hematologic diseases underwent bone marrow examination were reviewed as controls. Bone marrow mononuclear cells (BMMCs) were isolated from all participants to detect lnc‐MVIH expression by reverse transcription quantitative polymerase chain reaction. The complete remission status after 1 course of induction therapy, event‐free survival and overall survival of pediatric AML patients were recorded. Results: Lnc‐MVIH was upregulated in pediatric AML patients compared with controls (p

Acute myeloid leukemia (AML) accounts for 15% to 20% of childhood leukemias. Because of high-intensive therapy, up to 5% of patients suffer from treatment-related mortality (TRM). Abdominal complications are frequent, however, literature on this subject is sparse. We aimed to characterize severe abdominal pain (AP) and hyperbilirubinemia experienced by pediatric AML patients treated according to the Nordic Society of Pediatric Hematology and Oncology (NOPHO)-AML 2004 protocol (n=313). Patients were censored at hematopoietic stem cell transplantation and relapse. Toxicity information was collected prospectively. Additional information was requested retrospectively from the treating centers. Sixteen episodes of hyperbilirubinemia and 107 episodes of AP were reported. The treating centers deemed infection (30%) and typhlitis (18%) as the most frequent causes of AP. Six patients developed appendicitis (2%). Patients experiencing concurrent AP and sepsis had a high risk of TRM (36%, n=4). Eighty percent of episodes with hyperbilirubinemia fulfilled the European Society for Bone and Marrow Transplantation criteria for sinusoidal obstruction syndrome. In conclusion, abdominal complications were frequent with infection considered the predominate cause. Most patients with hyperbilirubinemia fulfilled the criteria for sinusoidal obstruction syndrome. AML treatment might be associated with appendicitis. Patients suffering from concurrent AP and sepsis had a high risk of TRM indicating that high awareness of abdominal complications is essential to reduce mortality, especially during sepsis.

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Pediatric acute myeloid leukemia (AML) is a heterogeneous disease that requires a multifaceted treatment approach. Although outcomes for low-risk AML have improved significantly over recent decades, high-risk AML continues to be associated with an adverse prognosis. Recent advances in molecular diagnostics, risk stratification, and supportive care have contributed to improvements in outcomes in pediatric AML. Targeted approaches, for example, the use of tyrosine kinase inhibitors to treat FLT3-ITD AML, offer promise and are currently undergoing clinical investigation in pediatric patients. New approaches to hematopoietic stem cell transplantation, including the use of haploidentical donors, are significantly expanding donor options for patients with high-risk AML. This review provides an overview of recent advances in the treatment of pediatric AML that are likely to have clinical impact and reshape the standard of care.

A 15-year-old male presented with fatigue and weight loss for 1 month, petechiae and bruising for 2 weeks. He was diagnosed with concurrent new acute myeloid leukemia and coronavirus disease 2019. He was febrile and chest computed tomography scan showed ground glass opacities. Fever resolved after 4 days. Polymerase chain reaction test for coronavirus disease 2019 became negative after 2 days. Induction chemotherapy was initiated on day 8 and was complicated by multisystem inflammatory syndrome in children. The multisystem inflammatory syndrome in children was managed with symptomatic treatment and continued chemotherapy. Patient recovered and end of induction bone marrow showed remission of the leukemia.

Normal karyotype acute myeloid leukemia (NK-AML) constitutes 20–25% of pediatric AML and detailed molecular analysis is essential to unravel the genetic background of this group. Using publicly available sequencing data from the TARGET-AML initiative, we investigated the mutational landscape of NK-AML in comparison with abnormal karyotype AML (AK-AML). In 164 (97.6%) of 168 independent NK-AML samples, at least one somatic protein-coding mutation was identified using whole-genome or targeted capture sequencing. We identified a unique mutational landscape of NK-AML characterized by a higher prevalence of mutated CEBPA, FLT3, GATA2, NPM1, PTPN11, TET2, and WT1 and a lower prevalence of mutated KIT, KRAS, and NRAS compared with AK-AML. Mutated CEBPA often co-occurred with mutated GATA2, whereas mutated FLT3 co-occurred with mutated WT1 and NPM1. In multivariate regression analysis, we identified younger age, WBC count ≥50 × 109/L, FLT3-internal tandem duplications, and mutated WT1 as independent predictors of adverse prognosis and mutated NPM1 and GATA2 as independent predictors of favorable prognosis in NK-AML. In conclusion, NK-AML in children is characterized by a unique mutational landscape which impacts the disease outcome.

This report describes the first case of NUP98-HHEX rearrangement observed in pediatric acute myeloid leukemia (AML). The oncogenic potential of NUP98 fusions was first documented in hematological m...

AIM The aim of this study was to evaluate the diagnostic and prognostic performance of miRNA-29a and miRNA-100 in pediatric acute myeloid leukemia (AML). PATIENTS AND METHODS In all, 73 children with diagnosed pediatric AML (based on standard morphologic, cytochemical, cytogenetic, immunologic, and molecular workup, and the French-American British classification) admitted to Children's Cancer Hospital Egypt (CCHE-57357), and 9 healthy age-matched and sex-matched controls were recruited for a case-control study. Gene expression levels of miRNA-29a and miRNA-100 were assessed using real-time quantitative RT-PCR. RESULTS When diagnosed, patients had a significantly higher expression of miRNA-100 as against controls (median [range]: 12.99 [0.92-851.38] vs. 0.26 [0.03-2.67], P

Acute myeloid leukemia (AML) is a heterogenous group of diseases affecting ~500 children in the United States annually. With current therapy, 90% of these children will obtain complete remission. However, 30% to 40% of these patients will relapse, most commonly within the first 3 years. Very late relapses, defined as relapse occurring >5 years after complete remission, are rare, accounting for 1% to 3% of relapses. We describe a patient with AML harboring an AFDN/KMT2A translocation who relapsed 12 years after matched sibling stem cell transplant, provide a brief review of the relevant literature, and describe proposed mechanisms to explain very late relapse AML.

Hyperleukocytosis (HL) is a laboratory abnormality commonly presented in patients with acute myeloid leukemia (AML). However, large cohort studies on the clinical significance of HL in pediatric AML are paucity. Moreover, the effect of stem cell transplantation in HL patients remains unknown. The clinical profiles of 885 pediatric patients with AML were downloaded from the TARGET dataset. HL was defined as an initial peripheral WBC count of ≥ 100 ×109/L. We analyzed the prevalence, clinical profile and prognosis of HL in these patients. The frequency of HL among all the pediatric AML was 22.6%. FMS-like tyrosine kinase 3/internal tandem duplication (FLT3/ITD) mutation and gene fusion of NUP98/NSD1 occurred with higher incidence in HL patients. Overall, HL was associated with a low induction complete remission rate, and high risk of induction death. Moreover, HL predicted a significantly inferior 5-year event-free survival (EFS) (P P = 0.059). However, compared with chemotherapy, stem cell transplantation had no significant effect on the survival of HL patients in terms of 5-year leukemia-free survival (P = 0.449) or OS (P = 0.447). Multivariate analysis revealed that HL was an independent prognosis factor for EFS (Hazard ratio:1.352, P = 0.013) but not for OS (Hazard ratio:1.225, P = 0.170) in pediatric AML. HL might predict inferior clinical outcome in pediatric AML. SCT is an effective therapy for AML, but it may have no better effect on the survival of patients with HL, compared to chemotherapy.

The treatment for pediatric acute myeloid leukemia (AML) has not changed significantly over the past 3 decades, yet outcomes have improved with cure rates increasing from 30% to over 60% of all newly diagnosed children over this period. This improvement in survival has been attributed to both treatment intensification and improved supportive care over the decades, although the precise impact of each remains unknown.We retrospectively analyzed a unique cohort of 276 patients with de novo AML diagnosed in childhood, all treated with the same chemotherapy protocol over a 25-year period from 1986 to 2012.The contemporary cohort (2000-2012), compared with the historical cohort (1986-1999) had significantly improved overall survival (75% vs. 50%; hazard ratio, 2.17; 95% confidence interval, 1.15-2.93), lower disease-related mortality (38% vs. 19%, P=0.02) and were significantly more likely to receive an allogeneic transplant after relapse (stem cell transplantation [SCT], 73% vs. 12%; P0.0001). Allogeneic transplant postrelapse was associated with a significantly improved survival across the entire cohort (overall survival 50% for allogeneic SCT vs. 12% for autologous or none, P0.0001). There was no significant difference between the contemporary and historical cohorts in treatment-related mortality (13% vs. 7%, P=0.42) or relapse rates after induction (50% in older cohort vs. 40% in recent era, P=0.25), suggesting consistency of induction treatment efficacy and toxicity across the 2 periods.This data suggests improved survival in pediatric AML in the modern era has predominantly resulted from changes in treatment after relapse, including increased use of allogeneic SCT.

Data on the production of neutrophil extracellular traps (NETs) in leukemia patients are scant. Phagocytosis, hydrogen peroxide, neutrophil elastase and myeloperoxidase enzymatic activity as well as NETs formation were studied in 10 pediatric acute lymphoblastic leukemia and 7 pediatric acute myeloid leukemia (AML) patients after induction chemotherapy. Median neutrophil elastase activity and NETs formation were lower in AML versus acute lymphoblastic leukemia (41% vs. 90%, P=0.005 and 51% vs. 94%, P=0.008, respectively). AML patients had more episodes of febrile neutropenia during the first 2 blocks of treatment (100% vs. 40%, P=0.011) and a trend for more invasive bacterial and fungal infections.

Pediatric patients with acute myeloid leukemia (AML) are at high risk of invasive fungal infection (IFI). In adult patients, the D-index, which reflects the duration and intensity of neutropenia, was reported as a predictive factor of IFI after induction therapy for AML. The aim of this study was to assess whether the D-index is a predictive factor for IFI in pediatric AML. We define the D-index as the area over the neutrophil curve during neutropenia. Ninety-two courses of chemotherapy performed for 24 consecutive patients with AML undergoing chemotherapy at Sapporo Hokuyu Hospital between April 2007 and March 2017 were analyzed. We also evaluated the utility of the cumulative D-index (c-D-index) from the start of neutropenia until the clinical manifestation of IFI in these patients. The D-index and c-D-index were compared between courses with and without IFI episodes. The median D-index and c-D-index in 6 courses with IFI episodes were 12,816 (range 9500-27,412) and 7250 (range 3987-16,273), respectively, which was not statistically higher than the median D-index [10,127 (range 3788-20,897)] in 86 courses without IFI episodes (P = 0.081 and P = 0.108, respectively). Unlike in adult cases, neither the D-index nor c-D-index reflected the risk of IFI in pediatric AML.

Children with acute myeloid leukemia (AML) have a dismal prognosis due to a high relapse rate; however, the molecular basis leading to relapsed pediatric AML has not yet been fully characterized. To define the spectrum of alterations common at relapse, we performed integrated profiling of 136 relapsed pediatric AML cases with RNA sequencing (RNA-seq), whole-genome sequencing, and target-capture sequencing. In addition to well-characterized fusion oncoproteins, such as those involving KMT2A (n=36, 26.5%) or NUP98 (n=18, 13.2%), we also identified somatic mutations in UBTF (upstream binding transcription factor) in 12 of 136 cases (8.8%) of this relapsed cohort. Somatic alterations of the UBTF gene, which encodes a nucleolar protein that is a component of the RNA Pol I pre-initiation complex to ribosomal DNA promoters, have rarely been observed in AML. In our cohort, all alterations can be described as heterozygous in-frame exon 13 tandem duplications (UBTF-TD), either at the 3' end of exon 13 of UBTF or of the entire exon 13 (Fig. A). As we noticed limited detection in our pipeline as a result of complex secondary indels alongside the duplications, we established a soft-clipped read-based screening method to detect UBTF-TD more efficiently. Applying the screening to RNA-seq data of 417 additional pediatric AMLs from previous studies and our clinical service, we identified 15 additional UBTF-TDs, many of which have not been previously reported. At the amino acid level, UBTF-TDs caused amino acid insertions of variable sizes (15-181 amino acids), duplicating a portion of high mobility group domain 4 (HMG4), which includes short leucine-rich sequences. UBTF-TD AMLs commonly occurred in early adolescence (median age: 12.6, range: 2.4-19.6), and 19 of the total 27 cases had either normal karyotype (n=12) or trisomy 8 (n=7). UBTF-TD is mutually exclusive from other recurrent fusion oncoproteins, such as NUP98 and KMT2A rearrangements (Fig. B), but frequently occurred with FLT3-ITD (44.4%) or WT1 mutations (40.7%). The median variant allele fraction (VAF) of the UBTF-TD was 48.0% (range: 9.7-66.7%). In four cases with data at multiple disease time points, the identical UBTF-TDs were present at high allele fractions at all time points, suggesting that UBTF-TD is a clonal alteration. tSNE analysis of the transcriptome dataset showed that UBTF-TD AMLs share a similar expression pattern with NPM1 mutant and NUP98-NSD1 AML subtypes, including NKX2-3 and HOXB cluster genes (Fig. C) . Altogether, these findings suggest that UBTF-TD is a unique subtype of pediatric AML. To address the impact of UBTF-TD expression in primary hematopoietic cells, we introduced UBTF-TD and UBTF wildtype expression vectors into cord blood CD34+ cells via lentiviral transduction. UBTF-TD expression promotes colony-forming activity and cell growth, yielding cells with a persistent blast-like morphology (Fig. D). Further, transcriptional profiling of these cells demonstrated expression of HOXB genes and NKX2-3, similar to UBTF-TD AMLs in patients, indicating that UBTF-TD is sufficient to induce the leukemic phenotype. To investigate the prevalence of UBTF-TDs in larger de novo AML cohorts, we applied the above UBTF-TD screening method to the available de novo AML cohorts of TCGA (n=151, adult), BeatAML (n=220, pediatric and adult), and AAML1031 (n=1035, pediatric). We identified UBTF-TDs in 4.3% (45/1035) of the pediatric AAML1031 cohort, while the alteration is less common (0.9%: 3/329, p=0.002) in the adult AML cohorts (Fig. E). In the AAML1031 cohort, UBTF-TDs remain mutually exclusive with known molecular subtypes of AML and commonly occur with FLT3-ITD (66.7%) and WT1 (40.0%) mutations and either normal karyotype or trisomy 8. The presence of UBTF-TDs in the AAML1031 cohort is associated with a poor outcome (Fig. F, median overall survival, 2.3 years) and MRD positivity; multivariate analysis revealed that UBTF-TD and WT1 are independent risk factors for overall survival within FLT3-ITD+ AMLs. In conclusion, we demonstrate UBTF-TD defines a unique subtype of AMLs that previously lacked a clear oncogenic driver. While independent of subtype-defining oncogenic fusions, UBTF-TD AMLs are associated with FLT3-ITD and WT1 mutations, adolescent age, and poor outcomes. These alterations have been under-recognized by standard bioinformatic approaches yet will be critical for future risk-stratification of pediatric AML. Figure 1 Figure 1. Disclosures Iacobucci: Amgen: Honoraria; Mission Bio: Honoraria. Miller: Johnson & Johnson's Janssen: Current Employment. Mullighan: Pfizer: Research Funding; Illumina: Membership on an entity's Board of Directors or advisory committees; AbbVie: Research Funding; Amgen: Current equity holder in publicly-traded company.

Introduction: Relapse of pediatric acute myeloid leukemia (AML) remains a leading cause of childhood cancer mortality, and leukemias with activation of the Fms-like tyrosine kinase 3 (FLT3) are particularly susceptible to relapsed disease. Risk-directed therapy to prevent relapse is based both on genetic changes known to drive drug resistance, and measurable residual disease (MRD) at the end of induction therapy (EOI). In adult AML, resistance to type II FLT3-inhibitors, like sorafenib, is primarily driven by on-target FLT3 kinase domain (KD) mutations. However, the resistance mechanisms for pediatric leukemias, which are treated on combination therapies, have not been fully elucidated. MRD is considered the among the most predictive markers of future relapsed disease. It has been assumed that the major clone at the time of MRD assessment will predict the majority clone at relapse. However, this assumption has not been proven. The definition of the most specific genetic and MRD markers of relapse are essential to prognosticate and personalize therapy to prevent relapsed disease. Methods: We performed single cell sequencing (SCS) with a high-throughput DNA sequencing platform, Mission Bio Tapestri, on bone marrow or peripheral blood samples from 24 samples from 8 pediatric patients treated on COG AAML1031 with serial samples from diagnosis, EOI, and relapse. Results: We analyzed a total of 94,833 cells from 8 pediatric patients (median cells per patient 12,428) all treated on AAML1031. SCS revealed a sensitive and specific description of clonal evolution on the combination of sorafenib with cytotoxic chemotherapy. The FLT3 internal tandem duplication (ITD) was controlled by the therapy in only half of the patients. In five of the patients, the FLT3-ITD was present in multiple clones. The FLT3-ITD co-mutated with additional mutations (NRAS, SH2B3, WT1, TET2, or NPM1) in half of the patients. However, the presence of a co-mutation did not necessarily correlate with whether or not the ITD-containing clone persisted at the time of relapse. Of the leukemias whose relapse was not driven by FLT3, the most likely mutational driver of resistance was NRAS. Notably, however, despite the fact that FLT3 KD mutations make up the bulk of mutational resistance to type II FLT3i such as sorafenib in adult patients, there were no on-target FLT3 mutations found in any of these pediatric patients. Further, SCS allows for an unprecedented depth of analysis of the genetic complexity of pediatric AML. Phylogenic analysis revealed that the same mutations may arise independently in different cells (NPM1 W288fs, NRAS G60E). Additionally, the same gene may be mutated twice within the same cell (WT1, TET2). These data, consistent with our prior work, suggest that some leukemias may have a predilection to mutations within specific loci. Finally, although there is a standing assumption that the dominant MRD population will proliferate into relapsed disease, in 3/8 patients, the dominant MRD clone did not predict the dominant relapse clone. Conclusions: SCS allows for direct measurement of clonal hierarchy and evolution, phylogeny, co-mutational status, and zygosity, which can only be inferred through traditional bulk NGS. The mutational mechanisms of resistance seen in adult leukemias treated with sorafenib monotherapy are not necessarily relevant to the pediatric population; rather than on-target FLT3 mutations, off target mutations including NRAS are found. This corroborates prior findings that off-target RAS pathway mutations may drive resistance to FLT3i. Non-RAS off-target mutations found in this cohort do not necessarily predict sorafenib resistance, so may be passenger mutations. The lack of consistent resistance mutations suggests that other mechanisms of resistance such as epigenetic modifications may also drive resistance to combination chemotherapy with FLT3i in pediatric leukemia. Further, SCS exposes more genetic complexity in pediatric AML than has previously been appreciated: the same mutation may independently arise in more than one cell or the same cell may have multiple mutations within the same gene. Finally, the sensitivity of SCS reveals that the major clone at the time of MRD assessment is not necessarily the major clone at relapse. This suggests a benefit of more frequent MRD monitoring to track clonal evolution in real time. Disclosures Smith: Daiichi Sankyo: Consultancy; Revolutions Medicine: Research Funding; AbbVie: Research Funding; Amgen: Honoraria; FUJIFILM: Research Funding; Astellas Pharma: Consultancy, Research Funding.

Pediatric acute myeloid leukemia (AML) is the deadliest malignancy in children. Despite maximally intensive therapy, inclusive of chemotherapy and hematopoietic stem cell transplant, approximately 20% of patients experience recurrent disease. These patients are also burdened with treatment-related toxicities. Significant improvements in survival in pediatric AML patients necessitate the incorporation of rational targeted therapies with reduced toxicity. Recent studies demonstrate that PRMT5 knockout or inhibition in syngeneic mouse models of KMT2A (MLL) rearranged leukemic cells increased disease latency (Serio et al., Oncogene, 37:450, 2018; Kaushik et al., Leukemia, 32:499, 2018), indicating that PRMT5 is a potential therapeutic target in pediatric AML. However, there are no reports testing the efficacy of PRMT5 in PDX models of pediatric AML. We evaluated the preclinical efficacy of C220, a potent and selective PRMT5 inhibitor (PRMT5i) (Pastore et al., Cancer Discovery, 10:1742, 2020) in three distinct patient-derived xenograft (PDX) models of KMT2A rearranged AML. Based on the model used for the study, 3-5 million AML cells were injected intravenously in NSG-B2m mice. Disease progression was monitored by evaluating the percentage of human cells in mouse peripheral blood at periodic intervals by flow cytometry. At 2-3 weeks post transplantation, when human cells were detectable in peripheral blood, mice were randomly assigned to control (n=4-5) or treatment (n=2) groups. C220 was administered daily p.o. at a dose of 15 mg/kg for seven days with a break of two days. Mice were dosed with 2-3 additional cycles (indicated in the figure by shaded areas) based on their health status. Mice were monitored daily for experimental endpoints that included body condition score and human cell percentages in peripheral blood. Kaplan-Meier survival plots were generated based on the time when mice were euthanized because they met experimental endpoints. Chronic dosing of C220 prolonged survival and delayed the rise in percentage of human AML cells in mouse peripheral blood in all 3 PDX models (Fig. 1B, D, F). In the NTPL-146 model (KMT2A-MLLT1 fusion), a 135-day improvement in median survival was observed with C220-treatment (Fig. 1A). In the DF-2 (KMT2A-MLLT10 fusion) and DF-5 (KMT2A-MLLT4 fusion) models, which showed a faster engraftment compared to NTPL-146, there was a 5.5-day and 18-day improvement in median survival respectively (Fig. 1C, E). The improvement in median survival was statistically significant in all models (*P Figure 1 Figure 1. Disclosures Gopalakrishnapillai: Geron: Research Funding. Zhang: Prelude Therapeutics: Current Employment. Ruggeri: Prelude Therapeutics: Current Employment, Current equity holder in publicly-traded company. Scherle: Prelude Therapeutics: Current Employment, Current equity holder in publicly-traded company. Barwe: Prelude Therapeutics: Research Funding.

Background Relapse free survival of pediatric AML remains only 60%. Current standard myelosuppressive therapy has been maximized, so novel therapies with minimal toxicities are needed to improve outcomes. Previously, we found atovaquone (AQ), an FDA-approved drug that treats pneumocystis jiroveci pneumonia (PJP), reduces AML burden - by suppressing oxidative phosphorylation (OXPHOS) - in xenograft mice. Clinically achievable concentrations of AQ for anti-PJP are 40-80µM, but the anti-leukemia effects are observed as low as 10µM (Stevens et al, Bld Adv, 2019). This makes AQ an ideal drug to incorporate into AML treatment. AQ is a daily administered oral medication, and plasma levels depend on patient compliance, absorption, and entero-hepatic recirculation, which can be compromised due to the patient population and adverse events (AE) of chemotherapy. Here we investigated the feasibility of incorporating AQ into standard pediatric AML treatment. Methods Patients with de novo AML were enrolled at two children's hospitals in the USA. Daily administration of AQ at established PJP prophylaxis dosing was combined with standard chemotherapy for AML, based on the Medical Research Council (MRC) backbone of cytarabine 100mg/m2 q12h x 10 days, and daunorubicin 50mg/m2/dose on days 1, 3, and 5. As it was unclear if our AQ dosing would provide adequate PJP prophylaxis, it was left to provider discretion to give additional PJP protection. AQ compliance, AEs (per NCI CTCAE v5), parent/caregiver ease of administration score (scale: 1-5, 1=very difficult, 5=very easy to administer) and peripheral blood/bone marrow pharmacokinetics (PK) were collected during Induction 1. Real time AQ plasma concentration results were not provided. To address feasibility of achieving adequate levels, all gastrointestinal (GI) AEs ≥ grade 2 were collected, in addition to grade 4 or greater AEs. Patients who took at least 85% of planned doses and missed less than 2 consecutive doses of AQ were eligible for analyses. Correlative biology studies assessed AQ induced apoptosis at 30uM, effects on OXPHOS and relevant signaling activities. Patient derived xenografts (PDX) were established and treated with AQ. This trial is registered with ClinicalTrials.gov (NCT03568994). Results A total of 26 pediatric AML patients enrolled (ages 8 months - 19.7 years, mean 10.7 years); 24 patients were evaluable for this study. Two patients had Grade ≥ 3 GI toxicities that prohibited enteral administration so they were excluded from AQ PK and ease of administration analyses. We found that 14/24 (58%) patients achieved plasma levels above the target anti-leukemia concentration (10µM) by day 11. At the end of induction, 19/24 (75%) patients achieved plasma levels above 10µM, but only 7/24 (29%) patients achieved adequate levels for PJP prophylaxis (40µM). Only 1 patient achieved levels above 40µM throughout the trial [FIG A]. Mean ease of administration score was 3.8. For the youngest patients (x ≤ 2.6years), the average score was 3.4 which was not significantly different from older patients (ANOVA, p > 0.05) [FIG B]. Ease of administration scores showed no association with plasma levels (Pearson's correlation, p > 0.05). Finally, correlative biology studies in patient samples demonstrated robust AQ-induced apoptosis, OXPHOS suppression, and prolonged survival in a PDX model receiving AQ [FIG C]. Conclusion Our data demonstrate the feasibility of combining AQ with traditional chemotherapy for pediatric AML. Patients of all ages were able to tolerate AQ and no AEs were attributable to AQ administration. The target anti-leukemic concentration of AQ in the plasma (> 10uM) was frequently achieved, but concentrations of > 40uM at standard dosing were rare. Low plasma levels of AQ did not correlate with the presence of GI related AEs or weight loss, so plasma levels should be monitored to ensure sufficient PJP prophylaxis. Our correlative biology results support suppression of OXPHOS as the primary mechanism of action by which AQ exerts its anti-leukemia effect, and AQ may be an active anti-leukemia agent for pediatric AML patients. Figure 1 Figure 1. Disclosures No relevant conflicts of interest to declare.

Introduction Together with considerable improvement in diagnostics and supportive care measures, treatment intensification has contributed to the improvement of pediatric acute myeloid leukemia (AML) survival outcomes. However, treatment-related toxicity is a consequence of intensified chemotherapy regimens, which has profound implications for both morbidity and mortality. Despite the known devastating impact of all types of toxicity on quality of life (QoL), studies presenting the different forms of non-infectious toxicity prevalent during the most recent Dutch pediatric AML protocols are lacking given that only prior protocols have been evaluated in this manner as of yet. Furthermore, the literature on non-infectious toxicity incidence in pediatric AML patients is relatively scarce. Therefore, the objectives of this study were to: 1) evaluate the cumulative incidence (C.I.) of severe, but non-lethal, non-infectious toxicity during AML treatment according to the last three consecutive protocols of the Dutch Childhood Oncology Group (DCOG), and 2) compare treatment-related toxicity frequencies between protocols. Methods A retrospective chart review was performed on 245 Dutch patients diagnosed with de novo AML (acute promyelocytic leukemia, myeloid leukemia of Down Syndrome, and secondary AML were excluded) and treated according to ANLL-97/AML-12 (1998-2005) n=118, AML-15 (2005-2010) n=60, or DB-AML-01 (2010-2013) n=67. Table 1 details protocol specifics, including drug dosages per course. Grade 3-4 toxicities, including hematological toxicity, cardiotoxicity, respiratory toxicity, mucositis, typhlitis, nephrotoxicity, hepatotoxicity, neurotoxicity, pain, allergic anaphylactic reaction, and elevation of alanineaminotransferase or bilirubin were defined according to Common Terminology Criteria for Adverse Event version 4.0, excluding infectious toxicity. Grade 5 toxicity (treatment-related mortality) was beyond the scope of this study. Intensive care unit (ICU) admission data was additionally assessed. Toxicity C.I.s were determined via competing events analyses. Relapse and death were considered competing events. Patients were censored at time of stem cell transplantation. Per-protocol comparisons were conducted via Chi-square test, due to lack of sufficient power required to calculate C.I.s. Results Median age at diagnosis was 6.0 years [interquartile range (IQR) 1.0-12.0], 58% were male. Mucositis was the most frequent form of non-hematological toxicity with a C.I. of 86.1% (standard error (S.E.) 3.5%), followed by hepatotoxicity (C.I. 27.4%, S.E. 2.9%), and respiratory toxicity (C.I. 24.6%, S.E. 3.0%) (Table 2). Eighty-three patients (C.I. 33.9%, S.E. 3.0%) were admitted to the ICU at least once, for a median of 6.0 days [IQR 2.0-15.0] (Table 2). Relatively more blood transfusions (both erythrocyte and thrombocyte) were administered to patients treated according to AML-15 (98.3%) and DB-AML-01 (97.0%) compared to AML-12 (86.4%) (p=0.01 and p=0.02, respectively). Relatively more patients suffered from severe mucositis during DB-AML-01 compared to AML-12 (43.4% vs. 25.4%, p=0.01). More patients treated according to AML-15 had bilirubin levels >3x upper limit of normal (ULN) compared to those treated according to AML-12 (13.3% vs. 3.4%, p=0.01). There were no differences in non-infectious toxicity frequency between AML-15 and DB-AML-01. Other forms of toxicity did not differ significantly between protocols. The percentage of patients admitted to the ICU at least once during treatment was 33.9% in AML-12, 26.7% in AML-15, and 40.3% in DB-AML-01. Conclusions The high incidence of severe short- and long-term toxicities during pediatric AML therapy poses substantial challenges for patients, families, and care providers. Mucositis was the most common form of non-hematological, non-infectious toxicity in the whole cohort and across all Dutch protocols. Toxicities were more prevalent during the more recent protocols (AML-15 and DB-AML-01) compared to AML-12. Therefore, our findings are important in that they substantiate the need to optimize pediatric AML care in a manner which decreases treatment-related toxicity and QoL impairment. High treatment-related morbidity rates stress the urge to improve supportive care and develop less toxic treatment, while maintaining efficacy. Figure 1 Figure 1. Disclosures Zwaan: Sanofi: Consultancy.

Acute myeloid leukemia (AML) is a genetically heterogeneous hematologic malignancy characterized by uncontrolled proliferation of myeloid progenitor cells accompanied by impaired terminal differentiation. Despite intensive treatment regimes, the clinical outcomes remain poor, underscoring the need to decipher the underlying pathology and implement therapeutic interventions. Emerging evidence suggest myeloblasts could evolve machineries to evade T cell patrol and hinder immunotherapies. Here, we present a new mechanism driving immune escape in the context of pediatric AML, based on our discoveries of CD9 in hematopoietic stem cells (HSC; Leung et al, Blood, 2011) and acute lymphoblastic leukemia (ALL; Leung et al, Leukemia, 2020). We first examined CD9 expression and its prognostic impact in patient cohorts of childhood leukemia. The expression of cell surface CD9 on blasts of pediatric AML patients (13.2%, n=81) was significantly lower than that of pediatric ALL patients (90.4%, n=181, P Enforced CD9 expression in MV4-11 cells significantly suppressed proliferation (P A marked decrease of H3K9/27Ac occupancy in the CD9 locus was observed in AML than in ALL cells (4.8-14.2-fold, P Mechanistically, global transcriptome profiling of pediatric AML (n=31) revealed decreased stemness (NES: -1.7, P=0.01) and increased monocyte (NES: 1.8, P=0.034) gene signatures in CD9+ patient samples. Moreover, single-cell transcriptomic analyses of total bone marrow cells from MV4-11-tranplanted mice detected a significant enrichment of differentially regulated genes functioning in the antigen processing and presentation pathway. Concordantly, we observed a profound up-regulation of CD9 (9.4-51.1-fold, P Taken together, our data provided molecular, cellular and clinical evidence showing the plausible function of CD9 as a key driver intertwining differentiation and immunosurveillance in pediatric AML, and inspired a new combinatorial epigenetic/immunotherapy for this rare but aggressive malignancy. Disclosures No relevant conflicts of interest to declare.

Acute myeloid leukemia (AML) remains a therapeutic challenge with high mortality rates despite intensive and myeloablative therapies. While immunotherapies targeting CD19 have yielded remarkable outcomes in acute lymphoblastic leukemia, identifying similar antigen therapeutic targets in AML remains a challenge due to inherent heterogeneity associated with AML and overlapping immunophenotypes with normal hematopoietic stem and myeloid cell populations. Transcriptional heterogeneity within pediatric AML has primarily been linked to underlying fusion. Therefore, we integrated large transcriptomics and proteomics datasets from AML and normal tissues to identify potential targets expressed in leukemias, but not in normal bone marrow or other normal tissue types. To identify candidate therapeutic targets in pediatric AML, we leveraged transcriptome sequencing data from bone marrow aspirates or peripheral blood collected from 1,481 children, adolescents, and young adults with AML at the time of diagnosis. Patients were enrolled on one of four Children's Oncology Group trials spanning the past three decades: CCG-2961, AAML03P1, AAML0531, and AAML1031. We also leveraged transcriptome sequencing from normal bone marrow (NBM) and normal CD34+ hematopoietic stem and progenitor cells (HSPCs) in order to exclude targets that are highly expressed during normal hematopoiesis. Finally, we performed additional filtering based on proteomic databases to exclude targets that lack membrane localization (Human Protein Atlas, UniProt, and Ensembl) or that are highly expressed on normal tissue types (Human Proteome Map, Human Protein Atlas, and Proteomics DB databases) (Figure 1A). First, we computed the log expression ratio between AMLs and NBM/HSCPs for all protein coding genes. We next selected genes expressed greater than a threshold of two standard deviations above the mean in 50% or more of AMLs (Figure 1B). Additionally, we further selected genes on the basis of differential gene expression and absolute expression thresholds. This analysis was repeated for our entire pediatric AML cohort and the following AML subtypes: RUNX1-RUNX1T1, CBFB-MYH11, KMT2A-MLLT3, KMT2A-MLLT10, KMT2A-MLLT4, KMT2A-ELL, KMT2A-MLLT1, KMT2A-MLLT11, NUP98-NSD1, NUP98-KDM5A, and CBFA2T3-GLIS2. Candidate therapeutic targets were filtered based on membrane localization and normal tissue expression using the aforementioned proteomics databases (Figure 1C and 1D). Based on this algorithm, we identified a nonzero number of candidate therapeutic targets for each of our pediatric AML subtypes (Figure 1D). Intriguingly, we found no overlap between targets identified in our pediatric, adolescent, and young adult cohort and a previous similar analysis performed in AMLs diagnosed in older patients (PMID 29017060). This study demonstrates that by combining our large transcriptomics dataset with pre-existing proteomics datasets, we are able to identify a collection of candidate therapeutic targets in pediatric AML. Importantly, zero targets were identified that were inclusive to all pediatric AMLs within our cohort, which underscores the transcriptional heterogeneity that our group and others have previously identified in pediatric AML. Future preclinical and clinical studies will need to account for this heterogeneity by prioritizing targets on the basis of underlying molecular alteration. Our study comprises a platform and dataset of candidate targets for further functional validation and/or immunotherapy targeting studies in pediatric AML. Figure 1 Figure 1. Disclosures Shaw: T-Cell and/or Gene Therapy for Cancer: Patents & Royalties.

Background/Aims: Despite advances in chemotherapy-based treatment protocols, the outcomes of children with acute myeloid leukemia (AML) remain suboptimal. Implementation of targeted therapy based solely on genomics is challenging due to the complex mutational patterns and scarcity of pharmacologic agents for most lesions. In addition, pediatric and adult AML are genetically and biologically distinct, which poses a major hurdle for extrapolation of new agents approved for adult AML to the pediatric population. This study aims to adopt a functional approach that directly measure the response of patient-derived leukemic cells to targeted agents, and to establish the drug sensitivity pattern and identify candidates of immediate clinical relevance for precision usage in high-risk pediatric AML. Methods: A high-throughput drug screening, comprising 39 targeted agents (2 in Phase I, 10 in Phase II, 5 in Phase III, 22 FDA-approved) and 6 conventional chemotherapeutics, was performed on 30 pediatric AML samples collected at diagnosis or relapse using a serum-free, cytokine-supported culture system. A counter-screen of active drugs on cord blood hematopoietic stem cells was accomplished to reveal leukemia-selective activities. The robustness of the drug testing platform for predicting in vivo activities was validated in xenograft models. Genomic profiling was complementarily performed to identify the genetic markers and underlying mechanisms of drug sensitivity. Patients with refractory AML were treated with targeted agents based on drug profiling results, and assessed for clinical responses. Results: Unsupervised clustering revealed 5 distinct clusters of drug response: highly active compounds (IC50 2000 nM, 10 drugs). Targeted agents, including Bcl-2, HDAC, proteasome, HSP and survivin inhibitors, had substantially higher potency and selectivity over standard chemotherapeutic agents. New agents approved for adult AML were essentially inactive in pediatric AML. Drug sensitivity ex vivo accurately predicted in vivo single-agent and combinatorial activities with cytarabine in cell line- and patient-derived xenografts. Targeted resequencing of a 141-gene panel revealed novel mutations of prognostic relevance, such as KMT2C, in pediatric AML and their vulnerability to targeted agents. Whole-genome RNA-sequencing identified distinct gene expression signatures shaping the response to individual drugs. Administration of venetoclax to a child with refractory AML resulted in rapid blast clearance and achieved long-term remission. Complementary genomic profiling on serial specimens dictated the dynamic drug responses during disease evolution. Conclusions: Our study establishes a reliable drug testing platform and a pediatric-specific drug response profile of AML, which enables an evidence-based selection of targeted agents for patients without treatment options and endows therapies increasingly precise and personalized. The study also generates a valuable gene-drug-clinical dataset that could be leveraged to address the fundamental and translational biology of pediatric AML. It will ultimately impact the future design of clinical trials and protocols for managing this life-threatening malignancy. Disclosures No relevant conflicts of interest to declare.

INTRODUCTION: Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is a potentially curative therapy for high-risk acute myeloid leukemia (AML).The preparative regimen consisting of busulfan and cyclophosphamide (BuCy) is considered as one of the classical myeloablative conditioning regimens (MAC); however, it is associated with significant early and long-term toxicities, leading to a high rate of transplant-related mortality (TRM). P urpose: To compare toxicities and outcomes of BuCy and FluBu12 conditioning in the pediatric population. Methods: We retrospectively analyzed 71 pediatric high-risk AML patients in CR1/2 (n=51, 71,8%) and R/R disease (n=20, 28,2%) received allo-HSCT from MSD (n=16, 22,5%), MUD (n=43, 60,6%) and Haplo donor (n=12, 16,9%). BuCy and FluBu conditioning regimens were used in 47 (66,2%) and 24 (33,8%) patients respectively. Median age was 6 years (0-17). GVHD prophylaxis was PTCy±CNI±m-TOR inhibitor in 32 (45%) or ATG±CNI in 39 (55%) patients. The primary end points were TRM, relapse-free survival (RFS), graft-versus-host disease (GVHD) free, relapse free survival (GRFS) and overall survival (OS). Secondary end points included neutrophil engraftment, sinusoidal obstruction syndrome (SOS), acute and chronic GVHD. Patient were censored at the time of death or last follow-up. Probabilities of OS, RFS and GRFS were estimated using Kaplan-Meier curves. TRM was defined as any death that occurred in the absence of disease relapse; relapse was a competing risk for this event. Results: Engraftment rate was 91% and 87,5% in patients received BuCy and FluBu, respectively (p=0,4). There was a trend to lower day 100 TRM after FluBu (4,1% vs 14,9% after BuCy, p=0,07). Overall survival at 2 years did not differ as well (BuCy 48,9%, FluBu 56%, p=0,5). BuCy showed borderline higher RFS at 2 years (70,2% vs 52%, p=0,06). The composite endpoint GRFS did not differ between two study cohorts being 31,8% and 29,2% at 2 years for BuCy and FluBu (p=0,7). We observed a tendency towards a higher incidence of III0-IV0 aGVHD and cGVHD following BuCy when compared with FluBu: 57,1% vs 41% (p=0,06) and 46,5% vs 28,5% respectively (p=0,2). No significant differences were found between the BuCy and FluBu groups in risk of SOS (6% and 8%, respectively). Conclusions: The optimal conditioning regimen for children with AML is still a matter of debate. Our results suggest that FluBu represents a valid myeloablative regimen, able to provide lower TRM, aGVHD and cGVHD. This conditioning might become an alternative approach in patients with a high risk of severe post-transplant complications. Disclosures No relevant conflicts of interest to declare.

Sensitive and specific detection of measurable residual disease (MRD) after treatment in pediatric acute myeloid leukemia (AML) is prognostic of relapse and is important for clinical decision making. Mutation-based methods are increasingly being used, but are hampered by the limited number of common driver gene mutations to target as clone markers. Additional targets would greatly increase MRD detection power. However, even in cases with many AML-defining mutations, it is the limited accuracy of current molecular methods which establishes the lower bounds of sensitivity. Here we describe an ultrasensitive approach for disease monitoring with personalized hybrid capture panels targeting hundreds of somatic mutations identified by whole genome sequencing (WGS), and using extremely accurate Duplex Sequencing (DS) in longitudinal samples. In a pilot cohort of 13 patients we demonstrate detection sensitivities several orders of magnitude beyond currently available single locus testing or less accurate sequencing. With multi-target panels, overall power for MRD detection is cumulative across sites. For example, if a patient has MRD at a true frequency of 1/30,000, sequencing a single mutant site to 10,000x molecular depth would be unlikely to detect MRD. However, sequencing 10 sites each to 10,000x would effectively total 100,000x informative site depth, increasing power to >95%. However, standard sequencing assays are insufficiently accurate to achieve this theoretical limit of detection (LOD). DS enables accurate detection of individual variants to Marrow aspirates were collected from 13 uniformly treated pediatric AML patients at time of diagnosis (TOD), during treatment (end of induction, EOI), in remission (end of therapy, EOT), and at relapse. 9/13 patients relapsed. DNA from TOD was analyzed by WGS. Germline variants were excluded and somatic single nucleotide variants (SNVs) were targeted by a custom probe panel designed for each patient. An average of 170 SNVs were targeted per patient (range 53-200). More than 90% of the SNVs were noncoding. Longitudinal samples were then analyzed with DS, which compares sequences from both strands of each DNA molecule to eliminate technical noise and reveal biological mutation signal with extreme accuracy and sensitivity. A median of 82% of WGS SNVs were validated by DS in the TOD DNA, and the vast majority of those were also present at relapse. Relapsers had more SNVs at diagnosis than non-relapsers. EOT samples were sequenced to an average Duplex molecular depth of 29,400x, with a maximum of 61,283x. The figure below shows time course plots tracking SNVs at diagnosis, EOT and relapse for 2 patients. Among mutations validated in TOD samples, a median of only 8 (5%) were detected per EOT sample (range 0-66 mutations). MRD was detected in 8/9 relapsers. Targeting 1 or even 10 SNVs would therefore have missed MRD in the majority of these patients. Among relapsers, median EOT SNV VAF was 0.069%. The lowest single VAF detected per EOT sample ranged from 0.036% to 0.002%. The presence of an SNV at diagnosis and relapse implies that it must truly be present at EOT, whether or not it is detected. Therefore, if a small minority of leukemic mutations are detected at EOT, the true overall MRD frequency is much lower than the LOD at any single site. In the only relapser where MRD was not detected, targeted SNVs were present at diagnosis and relapse, so additional sequencing depth at EOT would eventually reveal ultra-low frequency mutations. Among patients that did not relapse by the end of the study, median VAF at EOI (the latest time point DNA available) was 0.0258%. Therefore, non-relapsers have a lower median VAF at EOI than relapsers do even later at EOT, potentially indicating very early on that treatment is more successful. This study shows excellent performance of DS-based assays for detecting MRD with patient-specific panels. We have demonstrated that among large panels of validated somatic SNVs present at time of diagnosis, a median of 5% are identified at EOT in eventual relapsers. DS detected MRD in 8/9 patients, and at a median VAF well below the limit of detection of any other sequencing technology. Comprehensive personalized hybrid selection panels coupled with DS represents a powerful option for MRD monitoring in pediatric AML and potentially other cancers. Figure Disclosures Higgins: TwinStrand Biosciences: Current Employment. Lo:TwinStrand Biosciences: Current Employment. Hipp:TwinStrand Biosciences: Current Employment. Valentine:TwinStrand Biosciences: Current Employment. Williams:TwinStrand Biosciences: Current Employment. Radich:TwinStrand Biosciences: Research Funding. Salk:TwinStrand Biosciences: Current Employment.

Background Cytogenetic and molecular aberrations are important prognostic factors in pediatric acute myeloid leukemia (AML). NUP98 translocations with more than 30 different partner genes have been identified in pediatric AML. The 2 most common fusions, NUP98-NSD1 and NUP98-KDM5A, have been shown to have distinct characteristics and are both associated with adverse outcomes. Although NUP98 fusions with less common fusion partners have been identified, the biological and clinical implications of these variants are unknown. Methods To determine the biological and clinical implications of the less common "other" NUP98 translocations (NUP98-X), we evaluated the clinical characteristics and transcriptome and genome sequencing data from 2396 children and young adults with AML within 4 consecutive Children's Cancer Group (CCG) and Children's Oncology Group (COG) trials CCG-2961, AAML03P1, AAML0531 and AAML1031. All NUP98-X translocations were confirmed by RNA sequencing. Results Of the 2396 patients screened, 164 patients (6.8%) had a NUP98 translocation. We identified 20 patients with a NUP98-X fusion (0.83%) and compared them with those with NUP98-NSD1 (n=110, 4.5%), NUP98-KDM5A(n=34, 1.4%), and a reference cohort without NUP98 translocations (n=2232). Translocation partners identified in the NUP98-X group were HOXA9 (n=4), HOXD13 (n=3), PHF15 (n=2), PHF23 (n=2), and single cases of BPTF, BRWD3, DDX10, HMGB3, HOXA13, KAT7, PRRX1, SET and TOP1. Besides the distinct characteristics of NUP98-NSD1 and NUP98-KDM5A, the NUP98-X group showed high inter-patient variance in clinical characteristics compared to our reference cohort. NUP98-X patients showed a clear bimodal age distribution with half of the patients being in the older age category and a similar number in the category We evaluated the impact of NUP98-X translocations in response to the initial induction therapy. The morphological complete remission (CR) rate after course 1 was 65% in the NUP98-X cohort versus 76% in the reference cohort (p=0.266). NUP98-NSD1 patients had an inferior CR rate (36%, p Conclusion NUP98-X translocated pediatric AML patients represent a rare cohort with a high variability in both translocation partners and other clinical characteristics. Despite this heterogeneity, the OS of these patients is comparable to high-risk pediatric AML patients, which justifies a high-risk stratification of these patients and emphasizes the need for developing new treatment strategies. Further research within large patient cohorts is needed to investigate the biologic and clinical characteristics of these rare translocations and potential differences between the different NUP98-X fusion partners. Disclosures Kaspers: AbbVie: Ended employment in the past 24 months; Helsinn Healthcare: Ended employment in the past 24 months; Boehringer Ingelheim: Membership on an entity's Board of Directors or advisory committees; Janssen R&D: Ended employment in the past 24 months. Cooper:Celgene: Other: Spouse was an employee of Celgene (through August 2019).

Biologically, Acute myeloid leukemia (AML) is highly heterogenous. AML with cup-like blast morphology variant has been reported to have important role in risk group stratification and treatment implications. In pediatric age group, this morphology and its clinical implication is rarely discussed. Although this morphology variant is not stated in World Health Organization (WHO) classification of Tumours of Haematopoietic and Lymphoid Tissues, it is associated with poor outcome from the association with other features. A 10- year old girl diagnosed to have AML with this morphology variant is reported in this study. Her laboratory features were hyperleucocytosis, high D-dimer, and blasts morphology of cup-like cells and few mimic the bilobed features of acute promyelocytic leukemia (APML). Further investigation showed clinical and laboratory features similar to what had been reported before in adults, including the presence of adverse marker of Fms-like tyrosine kinase 3 (FLT3) mutation. She was treated with chemotherapy, following which the bone marrow examination documented marrow in remission. Unfortunately, she succumbed to the disease complication from sepsis and marrow failure after few months of diagnosis. Haemato-morphologists might consider this unique morphological recognition and correlate it with other findings, including molecular testing for proper clinical evaluation. The blast feature and haematological findings could predict the clinical behaviour of this type of AML and guide the patient management. This morphological variant serves an important role especially if molecular testing is not available in some parts of the world or at the time of presentation when the result is still pending.

Improvements in survival have been achieved for children and adolescents with acute myeloid leukemia (AML), with the 5-year survival rates increasing from less than 20% to more than 70%.[1] However...

// Lonneke J. Verboon 1 , Askar Obulkasim 1 , Jasmijn D.E. de Rooij 1 , Jenny E. Katsman-Kuipers 1 , Edwin Sonneveld 2 , Andre Baruchel 3 , Jan Trka 4 , Dirk Reinhardt 5 , Rob Pieters 6 , Jacqueline Cloos 7 , Gertjan J.L. Kaspers 7 , Jan-Henning Klusmann 8 , Christian Michel Zwaan 1 , Maarten Fornerod 1 , Marry M. van den Heuvel-Eibrink 1, 6 1 Department of Pediatric Oncology, Erasmus MC-Sophia Children’s Hospital Rotterdam, Rotterdam, The Netherlands 2 Dutch Childhood Oncology Group (DCOG), The Hague, The Netherlands 3 Department of Hematology, Hopital Saint- Louis, Paris, France 4 Department of Pediatric Hematology/Oncology, 2nd Medical School, Charles University, Prague, Czech Republic 5 Clinic for Pediatrics III, University Hospital Essen, Essen, Germany 6 Princess Maxima Center for Pediatric Oncology, Utrecht, The Netherlands 7 Paediatric Oncology/Haematology, VU University Medical Centre, Amsterdam, The Netherlands 8 Department of Pediatric Hematology and Oncology, Hannover Medical School, Hannover, Germany Correspondence to: Marry M. van den Heuvel-Eibrink, email: m.m.vandenheuvel-eibrink@prinsesmaximacentrum.nl Keywords: acute myeloid leukemia, MLL, relapse, miR-106b~25 Received: February 28, 2016 Accepted: June 08, 2016 Published: June 24, 2016 ABSTRACT The most important reason for therapy failure in pediatric acute myeloid leukemia (AML) is relapse. In order to identify miRNAs that contribute to the clonal evolution towards relapse in pediatric AML, miRNA expression profiling of 127 de novo pediatric AML cases were used. In the diagnostic phase, no miRNA signatures could be identified that were predictive for relapse occurrence, in a large pediatric cohort, nor in a nested mixed lineage leukemia ( MLL) -rearranged pediatric cohort. AML with MLL - rearrangements are found in 15-20% of all pediatric AML samples, and reveal a relapse rate up to 50% for certain translocation partner subgroups. Therefore, microRNA expression profiling of six paired initial diagnosis-relapse MLL -rearranged pediatric AML samples (test cohort) and additional eight paired initial diagnosis-relapse samples with MLL -rearrangements (validation cohort) was performed. A list of 53 differentially expressed miRNAs was identified of which the miR-106b~25 cluster, located in intron 13 of MCM7 , was the most prominent. These differentially expressed miRNAs however could not predict a relapse in de novo AML samples with MLL -rearrangements at diagnosis. Furthermore, higher mRNA expression of both MCM7 and its upstream regulator E2F1 was found in relapse samples with MLL -rearrangements. In conclusion, we identified the miR-106b~25 cluster to be upregulated in relapse pediatric AML with MLL -rearrangements.

Approximately 20% of the pediatric acute myeloid leukemia (AML) cases show normal karyotypes without any recognizable cytogenetic alteration on conventional cytogenetic analysis. Recent state-of-th...