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Of 1003 children with acute lymphoblastic leukaemia (ALL), 147 (14.7%) presented without peripheral blood blasts (PBB). While absence of PBB was not independently associated with survival outcomes when compared to those with PBB, patients without PBB had distinct genetic and clinical characteristics. Notably, we identified a novel genotype-phenotype relationship, in that the patients without PBB had a significantly higher incidence of hyperdiploid B-ALL, accounting for almost half of all patients without PBB (46.9% vs. 22.7%, p 0.001). Further, absence of PBB was associated with decreased rates of leukaemia involvement of the central nervous system (p 0.001).

The prognostic significance of bone marrow minimal residual disease (MRD) in pediatric patients with acute myeloid leukemia (AML) is well-characterized, but the impact of blood MRD is not known. We therefore used flow-cytometric assessment of leukemia-specific immunophenotypes to measure levels of MRD in both blood and bone marrow of patients treated on the AML08 (NCT00703820) clinical trial. Blood samples were obtained at days 8 and 22 of therapy, whereas bone marrow samples were obtained at day 22. Among patients who were MRD-negative in the bone marrow at day 22, neither day 8 nor day 22 blood MRD was significantly associated with outcome. However, day 8 blood MRD was highly predictive of outcome among patients who were bone marrow MRD-positive at day 22. Although the measurement of blood MRD at day 8 cannot be used to detect day 22 bone marrow MRD-negative patients who are likely to relapse, our findings suggest that day 8 blood MRD can identify bone marrow MRD-positive patients who have a dismal prognosis and who may be candidates for the early use of experimental therapy.

The genetics of relapsed pediatric acute myeloid leukemia (AML) has yet to be comprehensively defined. Here, we present the spectrum of genomic alterations in 136 relapsed pediatric AMLs. We identified recurrent exon 13 tandem duplications (TD) in upstream binding transcription factor (UBTF) in 9% of relapsed AML cases. UBTF-TD AMLs commonly have normal karyotype or trisomy 8 with cooccurring WT1 mutations or FLT3-ITD but not other known oncogenic fusions. These UBTF-TD events are stable during disease progression and are present in the founding clone. In addition, we observed that UBTF-TD AMLs account for approximately 4% of all de novo pediatric AMLs, are less common in adults, and are associated with poor outcomes and MRD positivity. Expression of UBTF-TD in primary hematopoietic cells is sufficient to enhance serial clonogenic activity and to drive a similar transcriptional program to UBTF-TD AMLs. Collectively, these clinical, genomic, and functional data establish UBTF-TD as a new recurrent mutation in AML. Significance: We defined the spectrum of mutations in relapsed pediatric AML and identified UBTF-TDs as a new recurrent genetic alteration. These duplications are more common in children and define a group of AMLs with intermediate-risk cytogenetic abnormalities, FLT3-ITD and WT1 alterations, and are associated with poor outcomes. See related commentary by Hasserjian and Nardi, p. 173. This article is highlighted in the In This Issue feature, p. 171.

Key Points CPX-351 treatment is well tolerated and results in morphologic remission in newly diagnosed pediatric secondary myeloid malignancies.Favorable outcomes are achieved despite the presence of high-risk genetic lesions and previous therapies., Visual Abstract, Secondary myelodysplastic syndromes and acute myeloid leukemia (sMDS/AML) are rare in children and adolescents and have a dismal prognosis. The mainstay therapy is hematopoietic cell transplantation (HCT), but there has been no innovation in cytoreductive regimens. CP X-351, a fixed 5:1 molar ratio of liposomal cytarabine to daunorubicin, has shown favorable safety and efficacy in elderly individuals with secondary AML and children with relapsed de novo AML. We report the outcomes of 7 young patients (6 with newly diagnosed sMDS/AML and 1 with primary MDS/AML) uniformly treated with CP X-351. Five patients had previously received chemotherapy for osteosarcoma, Ewing sarcoma, neuroblastoma, or T-cell acute lymphoblastic leukemia; 1 had predisposing genomic instability disorder (Cornelia de Lange syndrome) and 1 had MDS-related AML and multiorgan failure. The median age at diagnosis of myeloid malignancy was 17 years (range, 13-23 years). Patients received 1 to 3 cycles of CP X-351 (cytarabine 100 mg/m2 plus daunorubicin 44 mg/m2) on days 1, 3, and 5, resulting in complete morphologic remission without overt toxicity or treatment-related mortality. This approach allowed for adding an FLT3 inhibitor as individualized therapy in 1 patient. Six patients were alive and leukemia-free at 0.5 to 3.3 years after HCT. One patient died as a result of disease progression before HCT. To summarize, CP X-351 is an effective and well-tolerated regimen for cytoreduction in pediatric sMDS/AML that warrants prospective studies.

Cytarabine arabinoside (Ara-C) has been the cornerstone of AML chemotherapy for decades. Following cellular uptake, it is phosphorylated into its active triphosphate form (Ara-CTP), which primarily exerts its cytotoxic effects by inhibiting DNA synthesis in proliferating cells. Interpatient variation in the enzymes involved in the Ara-C metabolic pathway have been shown to impact intracellular abundance of Ara-CTP and thus its therapeutic benefit. Recently, SAMHD1 (SAM and HD domain containing deoxynucleoside triphosphate triphosphohydrolase 1) has emerged to play a role in Ara-CTP inactivation, development of drug resistance and consequently, clinical response in AML. Despite this the impact of genetic variations in SAMHD1 on outcome in AML has not been investigated in depth. In this study, we evaluated 25 single nucleotide polymorphisms (SNPs) within SAMHD1 gene for association with clinical outcome in 400 newly diagnosed pediatric AML patients from two clinical trials- AML02 and AML08. Three SNPs, rs1291128, rs1291141, and rs7265241 located in the 3' region of SAMHD1 were significantly associated with at least one clinical outcome endpoint: minimal residual disease (MRD) after induction I, event free survival (EFS), or overall survival (OS) in the two cohorts. In an independent cohort of patients from COG-AAML1031 trial (n=854), rs7265241 A>G remained significantly associated with EFS and OS. In multivariable analysis, adjusting for other prognostic factors such as race, age, risk group, and white blood cell count, all the SNPs remained independent predictors of clinical outcome endpoints. These results highlight the relevance of the SAMHD1 pharmacogenomics in context of response to Ara-C in AML and warrants the need for further validation in expanded patient cohorts.

Chemotherapy dosages are often compromised, but most reports lack data on dosages that are actually delivered. In two consecutive acute lymphoblastic leukemia trials that differed in their asparaginase formulation, native E. coli L-asparaginase in St. Jude Total 15 (T15, n=365) and pegaspargase in Total 16 (T16, n=524), we tallied the dose intensities for all drugs on the low-risk or standard-risk arms, analyzing 504,039 dosing records. The median dose intensity for each drug ranged from 61-100%. Dose intensities for several drugs were more than 10% higher on T15 than on T16: cyclophosphamide (P

Cumulative burden of chronic health conditions and neurocognitive and physical function were examined among survivors of childhood acute myeloid leukemia (AML) treated with hematopoietic cell transplant (HCT; n = 66) or conventional therapy (CT; n = 67). Survivors and controls underwent a comprehensive clinical assessment, and health conditions were graded using a modified version of the Common Terminology Criteria for Adverse Events. By age 40 years, HCT and CT survivors had an average 17.4 (95% confidence interval [CI] 14.6-20.1) and 9.3 (7.7-11.1) grade 1-4 conditions versus 3.8 (3.3-4.2) in community controls. Compared to controls, HCT survivors had a higher prevalence of hypertriglyceridemia (45.5% vs. 18.3%), hypercholesterolemia (47.0% vs. 30.9%), hypothyroidism (27.3% vs. 4.0%), and primary hypogonadism (p < 0.001). CT survivors had a higher prevalence of cardiomyopathy (11.9% vs. 2.7%) and hypertension (53.7% vs. 44.3%). Neurocognitive impairment was elevated across all domains compared to controls but did not differ by treatment modality. Compared to controls, a higher proportion of HCT survivors had impairments in strength and endurance; whereas flexibility and mobility impairments were noted among CT survivors. Despite successful advances in childhood AML therapy, many therapeutic exposures remain unchanged. These findings support ongoing investigations of novel therapies and strategies to ameliorate the risk of late morbidities.

Recently, mRNA-expression signature enriched in LSCs was used to create a 17-gene leukemic stem cell (LSC17) score predictive of prognosis in adult AML. By fitting a Cox-LASSO regression model to the clinical outcome and gene-expression levels of LSC enriched genes in 163 pediatric participants of the AML02 multi-center clinical trial (NCT00136084), we developed a six-gene LSC score of prognostic value in pediatric AML (pLSC6). In the AML02 cohort, the 5-year event-free survival (EFS) of patients within low-pLSC6 group (n = 97) was 78.3 (95% CI = 70.5–86.9%) as compared with 34.5(95% CI = 24.7–48.2 %) in patients within high-pLSC6 group (n = 66 subjects), p

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.

Acute myeloid leukemia (AML) is a heterogeneous disease characterized in part by genetic and epigenetic alterations. Cytarabine arabinoside (Ara-C) has been the cornerstone of chemotherapy treatment for patients diagnosed with AML for decades. Following cellular uptake, ara-C is phosphorylated into its active metabolite, ara-CTP, which primarily exerts its cytotoxic effects by inhibiting DNA synthesis in proliferating cells. Interpatient variation in the enzymes involved in ara-C activation/inactivation pathway (Fig 1A), can impact intracellular abundance of ara-CTP and thus its therapeutic benefit. Recently, deoxynucleoside triphosphate (dNTP) triphosphohydrolase SAM domain and HD domain 1 (SAMHD1) was shown to limit the efficacy of ara-C by intracellularly hydrolyzing its active metabolite (PMID: 27991919). Other nucleoside analogs, such as clofarabine, fludarabine, and gemcitabine have also been shown to be substrates of SAMHD1 (PMID:30305425). Among adult AML patients, higher SAMHD1 expression in the leukemic cells has been found to correlate with poor outcome (PMID: 30341277). However, whether genetic variation in SAMHD1 has any impact on the clinical outcomes in pediatric AML patients has not been evaluated in depth. In this study, we looked into 25 single nucleotide polymorphisms (SNPs) within SAMHD1 gene for their association with clinical outcome of newly diagnosed pediatric AML patients in 2 cohorts (multi-site AML02 [NCT00136084, n=167] and AML08 [NCT00703820, n=231] clinical trials). Briefly, genotypes for the 25 SNPs within SAMHD1 genes were obtained from Illumina 2.5 Omni data of AML patients. Association analysis was conducted using logistic regression models comparing minimal residual disease (MRD) positivity after treatment with chemotherapy using an unadjusted model and an adjusted model stratified by initial risk assignment of the patient determined at diagnosis (i.e. low, standard, and high). MRD positivity was defined as one or more leukemic cell per 1000 mononuclear bone-marrow cells. Cox proportional hazard models were used to examine the association of the SNPs with EFS and OS and considered three modes of inheritance. Cox regression models were performed with or without adjusting for provisional risk group assignment at time of diagnosis. Significance levels for association of SNP with clinical outcome were set at p < 0.05. Three top SNPs significantly associated with clinical outcomes were all localized in the 3'UTR region of SAMHD1(Fig 1B). Presence of the variant allele of rs7265241 was associated with a lower EFS and OS in both AML02 and AML08 cohorts. Figure 1C shows the results for OS in AML02 (HR = 2.24, 95% CI (1.05-3.55), p=0.02) and AML08 (HR = 1.52, 95% CI (1.04-1.99), p=0.01). Another 3'UTR SNP, rs1291128 was associated with poor OS in AML02 and in the clofarabine plus ara-C treatment arm in AML08 trial. For rs1291141, T allele was associated with higher MRD positivity (OR: 2.12, p=0.01) in AML02 and poor OS (HR = 1.55, 95% CI (1.12-2.14), p=0.008) in AML08(Fig 1D). Consistent with the clinical outcome results, rs1291141 T allele was also associated with higher SAMHD1 expression in the whole blood (p=8.1e-14) and several other tissues in the GTEx database. https://gtexportal.org/home/ Our results suggest that genetic variation in SAMHD1 is associated with clinical outcomes in pediatric AML patients. Future studies are aimed at looking at haplotypes and SNP-SNP combinations to establish the impact SAMHD1 pharmacogenomics on its expression within leukemic cells and subsequent response to nucleoside analogs in AML patients. SAMHD1 has also been implicated as a tumor suppressor; thus, future studies will evaluate its role both as a proliferation regulator and in drug resistance. Acknowledgements: NIH-R01-CA132946 (Lamba and Pounds), University of Florida Opportunity Seed Grant (Lamba), American Lebanese Syrian Associated Charities (ALSAC), and American Society of Hematology Bridge funding (Lamba) funded the study. We thank Drs. Campana, Coustan-Smith, and Raimondi for MRD and cytogenetic data. Figure 1 Figure 1. Disclosures No relevant conflicts of interest to declare.

Rearrangements in KMT2A (KMT2Ar) are associated with pediatric, adult and therapy-induced acute leukemias. Infants with KMT2Ar acute lymphoblastic leukemia (ALL) have a poor prognosis, with an event-free-survival (EFS) of 33.6-36.9%. In the context of the remarkable improvements in the treatment of childhood ALL, the dismal outcome of infantile KMT2Ar ALL and the lack of any significant progress for more than two decades are striking . The St. Jude Total Therapy 16 study (the most recently reported study of a program for childhood ALL that begun in 1962) yielded a 5-year EFS of 88.2% overall. Total 16 enrolled all subtypes of newly diagnosed pediatric ALL patients including infants, with intensity of treatment adapted to presenting clinical and genomic features, and early treatment response as determined by minimal/measurable residual disease (MRD). KMT2Ar infants were treated on an intensified high-risk arm and received clofarabine in combination with cyclophosphamide and etoposide (CCE) at two points during treatment: Induction days 22-25 and Reinduction I. Infants who lacked KMT2Ar and KMT2Ar patients who were one year of age or older received the same risk-directed treatment plan given to all other patients enrolled on study. A total of 28 patients with KMT2Ar were enrolled on Total 16; the 19 patients > 1 year of age received standard-risk therapy, and the 9 patients < 1 year of age received high-risk therapy on the infant arm with CCE. The probabilities of 5-year EFS and overall survival in KMT2Ar patients > 1 year of age and those < 1 year of age were 73.3% vs. 44.4% (p=0.071) and 84.2% vs. 55.6% (p=0.060), respectively. Six of the nine infants were MRD-positive on Induction day 15 prior to CCE (MRD-positive range, 0.012% to 13.7%; median, 2.13%) with MRD negative status ( 1 year of age and 12.5% for those < 1 year of age (p=0.454). Five infants remain alive (four in CR1, one in CR2), while four expired in CR1. Three deaths were secondary to infection, including a multi-drug resistant soft tissue bacterial infection during Induction days 1-21, a respiratory syncytial virus pneumonia during Reinduction II, and a chronic parainfluenza 3 infection during Continuation weeks 70-101 that led to chronic pneumonitis and interstitial fibrosis. The fourth patient developed grade 5 pulmonary hypertension following induction, a complication potentially compounded by their presenting WBC count of 905 x 10 9/L and pulmonary leukostasis. A comparison of 3-year cumulative risk of selected major toxic effects of treatment revealed that high-risk infants had a lower incidence of asparaginase allergic reactions, osteonecrosis, hyperglycemia, and pancreatitis; in contrast, the incidence of fever and neutropenia, hepatic toxicity and seizures, was similar in high-risk patients regardless of age. Infants had a higher risk of thrombosis (46.7% vs. 23.1%, p 1 year of age that received one or more clofarabine-containing Reintensification chemotherapy cycles prior to hematopoietic stem cell transplant in first remission (CR1). This revealed a higher frequency of infections in infants, suggesting a greater susceptibility to this complication independent from clofarabine exposure (mean number of episodes, 2.39 vs. 1, p Disclosures Gruber: Kura Oncology: Consultancy. Coustan-Smith: Juno Therapeutics: Patents & Royalties; Nkarta Therapeutics: Current holder of individual stocks in a privately-held company; Medisix Therapeutics: Current holder of individual stocks in a privately-held company. Campana: Nkarta Therapeutics: Current holder of stock options in a privately-held company; Medisix Therapeutics: Current holder of stock options in a privately-held company; Juno: Other: patent licensing payments; Juno Therapeutics (a Bristol-Myers Squibb company),: Other: patents on methods for minimal residual disease detection.. Evans: St. Jude Children's Research Hospital, Emeritus Member (began Jan 2021): Ended employment in the past 24 months; BioSkryb, Inc.: Membership on an entity's Board of Directors or advisory committees; Princess Máxima Center for Pediatric Oncology, Scientific Advisory Board, Chair: Membership on an entity's Board of Directors or advisory committees. Pui: Adaptive Biotechnologies: Membership on an entity's Board of Directors or advisory committees; Novartis: Other: Data Monitoring Committee.

Secondary myelodysplastic syndromes and acute myeloid leukemia (sMDS/AML) are rare myeloid neoplasms in children/adolescents and have a dismal prognosis. The mainstay therapy is hematopoietic cell transplantation (HCT) but there has been little therapeutic innovation for decades and outcomes remain poor. CPX-351, a fixed 5:1 molar ratio of liposomal cytarabine/daunorubicin, has shown favorable safety and efficacy in elderly individuals with sAML and children with relapsed de novo AML, which led the FDA to recently expand the label of CPX-351 to include pediatric patients with secondary AML, however, no data has been reported in this patient group. We report the outcomes of seven young patients with newly diagnosed sMDS/AML uniformly treated with CPX-351. Five patients had previously received chemotherapy for osteosarcoma, Ewing sarcoma, neuroblastoma, or T-ALL; one had predisposing genomic instability disorder (Cornelia de Lange syndrome); and one presented with MDS-related AML and multi-organ failure. The median age at diagnosis of myeloid malignancy was 17 (13-23) years. We identified somatic mutations and copy-number changes across 16 leukemia driver genes in six cases (including TP53 in two), abnormal karyotypes in six cases and rearrangements involving MECOM or NIM1K-TERT in two patients. Additional genomic studies identified pathogenic germline mutations in CHEK2 and SMC3 each in a single patient . Patients received 1-3 cycles of CPX-351 (100 units/m 2 on days 1, 3, and 5) resulting in complete morphologic remission without overt toxicity or treatment-related mortality. This approach allowed for adding FLT3 inhibitor as individualized therapy in one patient. Six patients were alive and leukemia-free at 0.51-3.25 years after HCT. One patient died from disease progression before HCT. Concluding, CPX-351 is an effective and well-tolerated regimen for cytoreduction in pediatric secondary myeloid malignancies warranting further investigation Figure 1 Figure 1. Disclosures Triplett: Miltenyi: Other: Travel, meeting registration.

Introduction KMT2A-rearranged (KMT2A-r) acute myeloid leukemia (AML) is a heterogeneous genetic subgroup with a frequency of about 25% in children with AML. At the 62 nd ASH annual meeting last year, we reported on the differences in outcome of various KMT2A subgroups based on translocation partner and the significance of minimal residual disease (MRD) status during and after induction as a follow-up study of Balgobind et al., Blood 2009. The impact of allogeneic hematopoietic stem cell transplantation (allo-HSCT) in first complete remission (CR1) and the presence of additional cytogenetic aberrations (ACAs) on prognosis have not yet been described for our cohort. Methods Data on allo-HSCT in CR1 and the presence of ACAs of 1256 KMT2A-r de novo pediatric AML patients from 15 AML study groups affiliated with the I-BFM Study Group, diagnosed between 2005 and 2016, were retrospectively collected and studied. Karyotypes were reviewed and classified by two of the authors (RW&CH). Based on translocation partners, patients were classified to the KMT2A high-risk subgroup (6q27, 10p11.2, 10p12, 4q21, and 19p13.3) or non-high-risk subgroup (9p22, 19p13, 19p13.1, 1q21, Xq24, 17q21, 1p32, and 17q12). These two categories have been used to estimate a Cox model. Patients with unknown translocation partners were excluded from these analyses (n=126). Flow cytometry MRD levels at the end of induction course 1 (EOI1) and 2 (EOI2) Results Of 1256 pediatric patients with KMT2A-r AML, data on HSCT in CR1 and ACAs were available for 1186 (94.4%) and 1204 patients (95.9%), respectively; 211 (17.8%) patients received HSCT in CR1 and ACAs were present in 601 (49.9%) patients. Compared with the KMT2A non-high-risk subgroup, patients in the KMT2A high-risk subgroup underwent HSCT in CR1 more often (23.8% vs 15.0%; P < .001). ACAs were borderline significantly more common in the KMT2A high-risk subgroup (54.1% vs 46.4%; P = .015). Univariate analysis of the probability of DFS (Table 1) showed that the KMT2A high-risk subgroup (HR 2.1; 95% CI, 1.7-2.5), age ≥10 years (HR 1.4; 95% CI, 1.2-1.7), and MRD ≥0.1 at EOI1 (HR 1.5; 95% CI, 1.1-1.9) were associated with DFS. HSCT in CR1 was a borderline significant prognostic factor (HR 0.7; 95% CI, 0.6-0.9). In a multivariate analysis for DFS (n=515) (Table 1), the KMT2A high-risk subgroup (HR 2.0; 95% CI, 1.6-2.6), MRD ≥0.1 at EOI1 (HR 1.7; 95% CI, 1.2-2.3), and HSCT in CR1 (HR 0.6; 95% CI, 0.4-0.9) were associated with DFS. Univariate analysis of the probability of OS (Table 1) showed that the KMT2A high-risk subgroup (HR 1.8; 95% CI, 1.5-2.2), age ≥10 years (HR 1.6; 95% CI 1.3-2.0), WBC ≥100 x10 9/L (HR 1.4; 95% CI, 1.1-1.7), the presence of ACAs (HR 1.4; 95% CI, 1.2-1.7), and MRD ≥0.1 at EOI1 (HR 2.1; 95% CI, 1.6-2.7) were associated with OS. HSCT in CR1 was not associated with OS. The effect of HSCT in CR1 was not significantly different between the KMT2A high-risk and non-high-risk subgroups. In a multivariate analysis for OS (n=557) (Table 1), the KMT2A high-risk subgroup (HR 1.9; 95% CI, 1.4-2.5), age ≥10 years (HR 1.5; 95% CI, 1.1-1.9), the presence of ACAs (HR 1.6; 95% CI, 1.2-2.1), and MRD positivity at EOI1 (HR 1.9; 95% CI, 1.4-2.5) were associated with OS. Conclusions In this cohort of KMT2A-r pediatric AML patients, the presence of ACAs at diagnosis was independently associated with inferior OS, but not with DFS. This may be due to the exclusion of refractory patients in DFS analysis, who were significantly more common in the group of patients with ACAs. Analysis has yet to be performed to distinguish karyotype complexity. In addition, allo-HSCT in CR1 was an independent predictor of improved DFS, but was not a prognostic factor for OS. Figure 1 Figure 1. Disclosures Abrahamsson: wedish Children´s Cancer Foundation. Research grants and 50% senior research position for clinical research on pediatric leukemia: Research Funding. Locatelli: Amgen: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Novartis: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Miltenyi: Speakers Bureau; Medac: Speakers Bureau; Jazz Pharamceutical: Speakers Bureau; Takeda: Speakers Bureau.

Background Hyperleukocytosis is observed in 5% to 20% of patients with newly diagnosed acute myeloid leukemia (AML) and is associated with an increased risk of early complications and mortality. While being used frequently in patients with AML and hyperleukocytosis, the clinical utility of leukapheresis has not been conclusive. Low-dose chemotherapy has also been used recently as a cytoreduction method in these patients, but the data are limited. Objectives: To describe and compare the clinical and laboratory characteristics, early adverse events, and outcomes of children with newly diagnosed AML and hyperleukocytosis according to cytoreductive methods; leukapheresis, low dose chemotherapy (cytarabine), or no intervention. Methods: We studied patients with newly diagnosed AML treated on three multi-institutional St. Jude protocols, AML97, AML02, and AML08, between 1997 and 2017. Hyperleukocytosis was defined as white blood cell (WBC) counts of 100 x 10 9/L or higher at diagnosis. The decision of cytoreductive treatment was made as the discretion of the treating physician. Leukoreduction was used in the AML97 and AML02 studies, and cytarabine (100mg/m 2/dose every 12 hours) was the first choice for AML08 study. We reviewed baseline clinical characteristics and laboratory data (complete blood cell counts [CBC], chemistries, coagulation) and adverse effects (grade 3 or higher on neurologic, renal, respiratory, and hemorrhagic complications based on Common Terminology Criteria for Adverse Events) from diagnosis to day 14 of protocol-based chemotherapy. Cairo-Bishop criteria was used for laboratory/clinical tumor lysis syndrome. The time from the first CBC to administration of protocol-based chemotherapy was calculated. Results: A total of 49 patients were identified: 8 patients in AML97, 19 in AML02, and 22 in AML08) (Table). The age at diagnosis was 10.8 years with a median initial WBC count of 157.6 x 10 9/L; CNS (CNS 2, 3 or traumatic lumbar puncture with blasts) was seen in 29 (59.2%) cases. FAB M4 or M5 subtype was found in 30 patients (61.2%), 11q23 abnormalities in 15 (30.6%) and inv(16) in 8 (16.3%). In regards to leukoreduction method, 16 patients received leukapheresis (14 patients in AML97/02 and 2 in AML08), 18 cytarabine (all in AML08) and 1 hydroxyurea (in AML08); 14 did not receive leukoreduction (13 patients in AML97/02 and 1 in AML08). Leukapheresis was used more often in patients with higher diagnostic WBC counts (218.7 x 10 9/L) than those treated with cytarabine (152.9 x 10 9/L) or without intervention (127.3 x 10 9/L) (P Conclusion: Low-dose cytarabine treatment appears to be a safe and effective mean of cytoreduction for patients with AML and hyperleukocytosis. Further studies are needed to determine if this approach is preferable among patients treated with contemporary treatment. Figure 1 Figure 1. Disclosures Pui: Adaptive Biotechnologies: Membership on an entity's Board of Directors or advisory committees; Novartis: Other: Data Monitoring Committee.

Context: The genomic characterization of acute myeloid leukemia (AML) in adults, both at diagnosis and relapse, has been extensively reported. Previous work has shown a clear difference between AML in adults and children, yet the genetic changes associated with relapsed disease in children have yet to be fully described. Objective: To elucidate the genetic background of pediatric AML at relapse and identify gene alterations related to poor prognosis. Design: Transcriptomic and genetic analyses were performed on relapsed AML from multiple clinical studies held in St. Jude Children’s Research Hospital from 2002 to 2020. No blinding was performed in this study. Patients or Other Participants: RNA sequencing was performed from 136 patients (median age of 9.2 years) with relapsed pediatric AML. Ninety-one of these samples were also studied by tumor–normal-paired whole-genome sequencing. Additional transcriptomic data from pediatric AML at diagnosis (n=417) were also obtained from previous reports to define the molecular alterations common in relapsed pediatric AML. The clinical outcome of each molecular category is confirmed using clinical data of the diagnosis cohort of the TARGET pediatric AML study. Results: Genomic profiling of relapsed pediatric AML demonstrated an increase in KMT2A (n=36, 26.5%) and NUP98 rearrangements (n=18, 13.2%) when compared to de novo pediatric AML, as well as an increase in WT1 mutations (n=33, 24.3%). Comprehensive characterization of pediatric AML with extension RNA transcriptome data revealed 18 molecular categories with unique expression patterns and mutually exclusive gene alteration patterns. These molecular categories included rare categories with structural variants involving oncogenes of MECOM (n=3, 2.2%) or BCL11B (n=2, 1.5%), which led to the upregulation and allele-specific expression (ASE) of each gene. The entire molecular categories showed unique distribution in the relapse cohort compared to the TARGET cohort (p Conclusions: Integrated genomic profiling of pediatric AML identified unique molecular categories associated with relapsed disease and poor outcome.

Oncogenic addiction to the Fms-like tyrosine kinase 3 (FLT3) is a hallmark of acute myeloid leukemia (AML) that harbors the FLT3-internal tandem duplication (FLT3-ITD) mutation. While FLT3 inhibitors like sorafenib show initial therapeutic efficacy, resistance rapidly develops through mechanisms that are incompletely understood. Here, we used RNA-Seq-based analysis of patient leukemic cells and found that upregulation of the Tec family kinase BMX occurs during sorafenib resistance. This upregulation was recapitulated in an in vivo murine FLT3-ITD-positive (FLT3-ITD+) model of sorafenib resistance. Mechanistically, the antiangiogenic effects of sorafenib led to increased bone marrow hypoxia, which contributed to HIF-dependent BMX upregulation. In in vitro experiments, hypoxia-dependent BMX upregulation was observed in both AML and non-AML cell lines. Functional studies in human FLT3-ITD+ cell lines showed that BMX is part of a compensatory signaling mechanism that promotes AML cell survival during FLT3 inhibition. Taken together, our results demonstrate that hypoxia-dependent upregulation of BMX contributes to therapeutic resistance through a compensatory prosurvival signaling mechanism. These results also reveal the role of off-target drug effects on tumor microenvironment and development of acquired drug resistance. We propose that the bone marrow niche can be altered by anticancer therapeutics, resulting in drug resistance through cell-nonautonomous microenvironment-dependent effects.

Comprehensive studies on neutropenia and infection-related complications in patients with acute lymphoblastic leukemia (ALL) are lacking.We evaluated infection-related complications that were grade ≥3 on National Cancer Institute's Common Terminology Criteria for Adverse Events (version 3.0) and their risk factors in 409 children with newly diagnosed ALL throughout the treatment period.Of the 2420 infection episodes, febrile neutropenia and clinically or microbiologically documented infection were seen in 1107 and 1313 episodes, respectively. Among documented infection episodes, upper respiratory tract was the most common site (n = 389), followed by ear (n = 151), bloodstream (n = 147), and gastrointestinal tract (n = 145) infections. These episodes were more common during intensified therapy phases such as remission induction and reinduction, but respiratory and ear infections, presumably viral in origin, also occurred during continuation phases. The 3-year cumulative incidence of infection-related death was low (1.0±0.9%, n = 4), including 2 from Bacillus cereus bacteremia. There was no fungal infection-related mortality. Age 1-9.9 years at diagnosis was associated with febrile neutropenia (P = 0.002) during induction and febrile neutropenia and documented infection (both P 0.001) during later continuation. White race was associated with documented infection (P = 0.034) during induction. Compared with low-risk patients, standard- and high-risk patients received more intensive therapy during early continuation and had higher incidences of febrile neutropenia (P 0.001) and documented infections (P = 0.043). Furthermore, poor neutrophil surge after dexamethasone pulses during continuation, which can reflect the poor bone marrow reserve, was associated with infections (P 0.001).The incidence of infection-related death was low. However, young age, white race, intensive chemotherapy, and lack of neutrophil surge after dexamethasone treatment were associated with infection-related complications. Close monitoring for prompt administration of antibiotics and modification of chemotherapy should be considered in these patients.

Background: Improved therapeutic strategies for patients with relapsed/refractory (R/R) acute lymphoblastic leukemia (ALL) and lymphoblastic lymphoma (LL) remain an unmet need. Venetoclax (Ven), a potent, highly selective, oral B-cell lymphoma 2 (BCL-2) inhibitor, and navitoclax (Nav), an oral BCL-2, BCL-XL, and BCL-W inhibitor, directly bind their BCL-2 family member targets to promote apoptosis. Ven and Nav have shown synergistic antileukemic effects in ALL preclinical models, suggesting dependence on BCL-2 family members. The addition of Ven to low-dose Nav may potentiate efficacy without the dose-limiting thrombocytopenia associated with Nav monotherapy (J Clin Oncol. 2012;30:488). Ven in combination with Nav and chemotherapy are under investigation in a Phase 1, multicenter, open-label, dose-escalation study in patients with R/R ALL and LL (NCT03181126). The results of a previous report on the overall study population (adult and pediatric patients) showed the triplet combination was well tolerated, with promising response rates observed (Jabbour, et al. EHA 2020. Abstract 2389). For the first time, reported here are safety, tolerability, pharmacokinetics, and antitumor activity of Ven with Nav and chemotherapy among the pediatric patients treated in that Phase 1 study. Methods: Eligible pediatric patients (aged ≥4- Results: As of June 23, 2020, 18 pediatric patients (pts) have enrolled (12 in dose-escalation; 6 in safety expansion); 13, 3, and 2 pts had B-ALL, T-ALL, and LL, respectively. Among pts in the dose-escalation phase, 6 received 25 mg Nav and 6 received 50 mg. Median age was 10 years (range, 6-16 years), 56% of pts were male, and the median number of prior therapies was 2 (range, 1-6). Median time on study was 10.4 months. All pediatric pts experienced treatment-emergent adverse events (TEAEs), and the most common were febrile neutropenia (50%), vomiting (44%), hyperglycemia (39%), and hypokalemia (39%). Grade 3/4 TEAEs occurred in 89% of pediatric pts, and the most common were febrile neutropenia (50%), neutropenia (33%), thrombocytopenia (33%), and anemia (28%). The only Grade 3/4 nonhematologic TEAEs related to Ven or Nav that occurred in >1 pediatric pt were alanine aminotransferase increased (n=2) and vomiting (n=2). Of 8 dose-limiting toxicities (DLTs), 2 occurred in pediatric pts. The 2 DLTs included delayed count recovery (25 mg Nav) and sepsis (50 mg Nav, occurred after database lock). No pediatric pts experienced tumor lysis syndrome. No Grade 5 TEAEs occurred in pediatric pts; 8 pediatric pts (44%) died from disease progression. Ten pediatric pts (56%) achieved complete response (CR)/CR incomplete recovery (CRi)/CR without platelet recovery (CRp); 7 pts (39%) achieved undetectable MRD. Median overall survival was 11.4 months (95% CI, 2.9 months-not estimable). Eight pts (44%) proceeded to transplantation (n=5) or CAR T-cell therapy (n=3; cells harvested before start of study; Figure). Weight-based dosing of Ven and Nav achieved comparable exposures in pediatric pts. Exploratory correlative biomarker analyses, including BH3 profiling and genomic analyses, are underway and will be presented. Conclusion: In this Phase 1 study, Ven with Nav and chemotherapy was well tolerated and had promising efficacy in heavily pretreated pediatric patients with ALL and LL. Given that there were four DLTs with 100 mg Nav without evidence of increased efficacy, the recommended Phase 2 dose for adult and pediatric patients is 400 mg Ven with 50 mg Nav for patients weighing ≥45 kg and 25 mg Nav for patients weighing Figure Disclosures Rubnitz: AbbVie Inc.: Research Funding. Alexander:Abbvie, Inc.: Other: Travel Support. Laetsch:Bayer: Consultancy, Research Funding; Cellectis: Consultancy; Novartis: Consultancy, Research Funding; Pfizer: Research Funding. Khaw:Amgen: Other: Travel Support, Research Funding; Novartis: Other: Travel Support; AbbVie, Inc.: Research Funding; Bristol-Myers Squibb: Research Funding; Jazz Pharmaceuticals: Research Funding; Walter and Eliza Hall Institute of Medical Research: Patents & Royalties: recipient of a share in royalty payments . Pullarkat:Servier: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Jazz Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Pfizer: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Dova: Consultancy, Honoraria; Amgen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Genetech: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; AbbVie, Inc.: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Opferman:St. Jude Children's Research Hospital: Current Employment; AbbVie, Inc.: Research Funding; National Institutes of Health: Research Funding. Rosenwinkel:AbbVie, Inc.: Current Employment, Other: may hold stock or other options. Tong:AbbVie, Inc.: Current Employment, Other: may hold stock or other options. Pesko:AbbVie, Inc.: Current Employment, Other: may hold stock or other options. Badawi:AbbVie, Inc.: Current Employment, Other: may hold stock or other options. Vishwamitra:AbbVie, Inc.: Current Employment, Other: may hold stock or other options. Kim:AbbVie, Inc.: Current Employment, Current equity holder in publicly-traded company, Divested equity in a private or publicly-traded company in the past 24 months, Other: may hold stock or other options. Mullighan:Illumina: Consultancy, Honoraria, Speakers Bureau; AbbVie, Inc.: Research Funding; Pfizer: Honoraria, Research Funding, Speakers Bureau. OffLabel Disclosure: Yes, venetoclax is a BCL-2 inhibitor that is FDA approved for some indications. Venetoclax for treatment of acute lymphoblastic leukemia is not an approved indication.

Introduction Outcome of KMT2A-rearranged (KMT2A-r) pediatric AML (pAML) is in general poor with a 5-year probability of event-free survival (5y-pEFS) and overall survival (5y-pOS) of 44% and 56%, respectively (Balgobind et al., 2009). However, over the past decades, the heterogeneity of KMT2A-r pAML has emerged, showing differences in outcome between subgroups based on translocation partners. The predictive value of MRD in KMT2A-r pAML is undefined. This retrospective study aimed to confirm the outcome of pediatric KMT2A subgroups (Balgobind et al., 2009) in a more recent era and to study the significance of MRD status during and after induction. Methods Outcome and MRD data of 1257 KMT2A-rde novo pAML patients from 15 AML groups affiliated with the I-BFM-AML study group, diagnosed between 2005 and 2016 were retrospectively collected. Patients were assigned to KMT2A subgroups, or to the KMT2A-other group in case of unknown translocation partner. Flow cytometry MRD levels Results The 1257 patients were assigned to 13 KMT2A subgroups, or the KMT2A-other group. Two novel subgroups were identified: t(X;11)(q24;q23) (n=21, 2%) and t(1;11)(p32;q23) (n=12, 1%). The median age was 2.5 years (range, 0-18.9). The median WBC was 21.4 x 109/L (range, 0.2-727). Overall complete remission rate was 91%. The 5y-pEFS was 46% [SE, 2%] and the 5y-pOS was 62% [SE, 2%]. Differences across subgroups in 5y-pEFS (Figure 1) ranged from 24% [SE, 5%] to 76% [SE, 9%], and in 5y-pOS from 25% [SE, 13%] to 92% [SE, 8%] (both p The subgroups t(10;11)(p12;q23) (HR 1.7, p100 x 10^9/L (HR 1.3, p=.006), and age >10y (HR 1.3, p=.005) were revealed as independent predictors of poor EFS. These factors also predicted OS. MRD data after induction course one were available for n=635 (MRD-positivity (range, 0.1-94) n=126, 20%) and after course two for n=527 (MRD-positivity (range, 0.1-88) n=51, 10%). In the four KMT2A poor-risk subgroups, MRD-positivity was not significantly more common after induction course one (p=.0232) or two (p=.066), compared with the other subgroups. MRD-positivity was associated with inferior 5y-pDFS after both induction course one (36% [SE, 4%] vs 48% [SE, 2%]; p=.002) and course two (28% [SE, 6%] vs 49% [SE, 2%]; p10y (HR 1.5, p=.002) were revealed as independent predictors of poor DFS. Within the group of patients with MRD-negativity after induction course two, the subgroups t(10;11)(p12;q23) and t(10;11)(p11.2;q23) were independent predictors of poor EFS (5y-pEFS 35%, HR 1.7, p=.003 and 5y-pEFS 18%, HR 2.7, p=.004, respectively). Conclusion Outcome for KMT2A-r pAML patients has improved slightly, but similar subgroups were identified as poor risk (Balgobind et al., 2009), including t(10;11)(p12;q23), t(10;11)(p11.2;q23) and t(6;11)(q27;q23). In our study, t(4;11)(q21;q23) was poor risk as well. These subgroups should be considered for high-risk pAML therapy protocols. The favorable risk of t(1;11)(q21;q23) could not be confirmed in our cohort. MRD status is highly predictive of outcome within KMT2A subgroups. In MRD-negative patients after induction course two, both t(10;11) KMT2A subgroups were associated with poor outcome. Disclosures Guest: Syndax Pharmaceuticals: Consultancy. Locatelli:Medac: Speakers Bureau; Miltenyi: Speakers Bureau; Bellicum Pharmaceutical: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Amgen: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Jazz Pharmaceeutical: Speakers Bureau. Rubnitz:AbbVie Inc.: Research Funding. Kaspers: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; AbbVie: Ended employment in the past 24 months.

Background: FLT3-mutant pediatric AML represents a biological and clinically diverse disease and is associated with a poor outcome. Sorafenib has limited activity against tyrosine kinase domain mutations. Crenolanib is a pan-FLT3 inhibitor, which, at the time of this compassionate use program, had already been safely administered to over 55 children (age 2-18) with diffuse intrinsic pontine glioma as well as high grade gliomas. Crenolanib at a dose of 66mg/m2 TID has been well tolerated in pediatric patients. Methods: We here report our experience with five consecutive children (ages 4-12y) who received crenolanib for FLT3 mutant AML on a compassionate basis between April 2017 to October 2019. All patients treated had IRB/local ethics approval prior to treatment and all patients' guardians signed informed consent forms. Results: Patient Characteristics: Of the five patients, three were refractory to induction therapy and required salvage therapy to get into remission. All five patients were then able to undergo HSCT, but all subsequently relapsed. Two patients were successfully salvaged and underwent a second HSCT. Only two pts received sorafenib. By the time of the compassionate use request, all children had exhausted all standard and experimental therapies (3-9 prior therapies, Table 1). Two patients had FLT3-ITDs and three had FLT3 kinase domain mutations (A848P in one, D835H in another and both D835H and D835E in trans in third). Co-occurring events included KMT2A fusion/mutations in three pts as follows: i) one pt with KMT2A-rearranged infant AML, ii) one with treatment-related AML with KMT2A fusion and t(9;11) and iii) a third patient with KMT2A fusion along with p53 mutation. Another patient with biphenotypic AML had a co-occurring NOTCH1 mutation with 9;14 translocation. Three patients had complex karyotypes and a number of translocations were identified including t(9;11), t(3;5), t(1;16), and t(9;14) (Table 1). In addition to bone-marrow disease and circulating blasts, all patients had extramedullary AML. Three patients had CNS leukemia. Three patients had non-CNS extramedullary AML (submandibular, testicular, liver and spleen). Treatment: Crenolanib was given with curative intent to three patients, one in combination with Vyxeos (liposomal cytarabine/daunorubicin), one with high-dose cytarabine, and one as maintenance therapy after her second HSCT. Two patients received crenolanib as palliation for rapidly progressing AML. Tolerability: All children tolerated crenolanib well. Reasons for crenolanib discontinuation were bridge to HSCT in two patients and completion of 12 months of maintenance in another. One patient stopped crenolanib early as he developed fungal pneumonia and one patient stopped due to lack of benefit. Only one patient required dose reduction due to grade 2 transaminitis. There were no cardiac toxicities, pericardial effusion, fluid retention or weight gain. Response: Four of five patients reported clinical benefit with crenolanib. Interestingly, the child with KMT2A-rearranged infant AML achieved a molecular CR after salvage therapy with Vyxeos plus crenolanib. This child was successfully bridged to a second HSCT and remains in remission one year after the start of his compassionate use crenolanib. Another patient with KMT2A fusion, p53 mutation and CNS AML achieved a CR with crenolanib + sorafenib, was successfully bridged to 2nd HSCT and received one year of post-transplant crenolanib maintenance. She remains in remission 3.5 years after initiation of crenolanib. The third patient with KMT2A fusion was successfully bridged to allo HSCT but relapsed 4 months after HSCT (she did not receive maintenance). The patient with bi-phenotypic AML (and D835H mutation) had a quick reduction in circulating blasts (within 24 h) but died of fungal sepsis. The fifth patient received reduced doses of crenolanib due to transaminitis and did not have a clinical benefit. Conclusion: This series of five children with multiply relapsed FLT3-mutant AML shows that treatment with full doses of crenolanib can be safely combined with salvage chemotherapy. Rapid remissions could be obtained even in patients with co-occurring KMT2A, 3q, and p53 mutations. Crenolanib, which is novel type-I pan FLT3 inhibitor, was able to inhibit variant FLT3 mutations (D835H, D835E and D848P). Crenolanib can be safely combined with ITT (2 of these children remain alive 1-3.5 years). Figure Disclosures Rubnitz: AbbVie Inc.: Research Funding. Karol:AbbVie Inc.: Other: Unrelated to this study, St. Jude has received a charitable contribution from AbbVie, Inc. The charitable contribution is not being used for clinical or research activities, including any activities related to this study. . Pathan:Arog Pharmaceuticals: Current Employment. Messahel:AROG Pharmaceuticals: Current Employment.

To determine the clinical significance of minimal residual disease (MRD) in patients with prognostically relevant subtypes of childhood acute lymphoblastic leukemia (ALL), we analyzed data from 488 patients treated in St Jude Total Therapy Study XV with treatment intensity based mainly on MRD levels measured during remission induction. MRD levels on day 19 predicted treatment outcome for patients with hyperdiploid >50 ALL, National Cancer Institute (NCI) standard-risk B-ALL or T-cell ALL, while MRD levels on day 46 were prognostic for patients with NCI standard-risk or high-risk B-ALL. Patients with t(12;21)/(ETV6-RUNX1) or hyperdiploidy >50 ALL had the best prognosis; those with a negative MRD on day 19 had a particularly low risk of relapse: 1.9% and 3.8%, respectively. Patients with NCI high-risk B-ALL or T-cell ALL had an inferior outcome; even with undetectable MRD on day 46, cumulative risk of relapse was 12.7% and 15.5%, respectively. Among patients with NCI standard-risk B-ALL, the outcome was intermediate overall but was poor if MRD was ⩾1% on day 19 or MRD was detectable at any level on day 46. Our results indicate that the clinical impact of MRD on treatment outcome in childhood ALL varies considerably according to leukemia subtype and time of measurement.

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...

Background Hyperleukocytosis in children with acute lymphoblastic leukemia (ALL) has been associated with early morbidity and mortality. The use of leukapheresis in these children treated with contemporary therapy remains controversial. Procedure We analyzed clinical data from patients enrolled onto frontline protocols for ALL (Total Therapy XV and XVI) between 2003 and 2014. We documented adverse events within the first 14 days in patients with a white blood cell (WBC) count ≥200 × 109/l and reviewed their management. Results Fifty-three (7.8%) of 678 consecutive pediatric patients with newly diagnosed ALL presented with hyperleukocytosis (median WBC count 393 × 109/l; range 200–1,014). Two deaths in patients without initial hyperleukocytosis occurred within the first 2 weeks from diagnosis secondary to bacterial sepsis. A total of 21 (40%) patients with ALL and hyperleukocytosis developed grade 3 or 4 adverse events regardless of the use of leukapheresis (P > 0.99 and P = 0.19). Sixteen of 53 (30%) patients with ALL received low-dose chemotherapy for leukocytoreduction initially. One-third of patients received urate oxidase, and none of the patients with hyperleukocytosis required hemodialysis. Conclusions The early morbidity and mortality commonly associated with hyperleukocytosis in children with newly diagnosed ALL can be avoided with contemporary supportive care and conservative management possibly obviating the need for costly and potentially dangerous leukapheresis.

Background Optimal management of acute myeloid leukemia (AML) requires monitoring of treatment response, but minimal residual disease (MRD) may escape detection. We sought to identify distinctive features of AML cells for universal MRD monitoring. Methods We compared genome-wide gene expression of AML cells from 157 patients with that of normal myeloblasts. Markers encoded by aberrantly expressed genes, including some previously associated with leukemia stem cells, were studied by flow cytometry in 240 patients with AML and in nonleukemic myeloblasts from 63 bone marrow samples. Results Twenty-two (CD9, CD18, CD25, CD32, CD44, CD47, CD52, CD54, CD59, CD64, CD68, CD86, CD93, CD96, CD97, CD99, CD123, CD200, CD300a/c, CD366, CD371, and CX3CR1) markers were aberrantly expressed in AML. Leukemia-associated profiles defined by these markers extended to immature CD34+CD38- AML cells; expression remained stable during treatment. The markers yielded MRD measurements matching those of standard methods in 208 samples from 52 patients undergoing chemotherapy and revealed otherwise undetectable MRD. They allowed MRD monitoring in 129 consecutive patients, yielding prognostically significant results. Using a machine-learning algorithm to reduce high-dimensional data sets to 2-dimensional data, the markers allowed a clear visualization of MRD and could detect 1 leukemic cell among more than 100,000 normal cells. Conclusion The markers uncovered in this study allow universal and sensitive monitoring of MRD in AML. In combination with contemporary analytical tools, the markers improve the discrimination between leukemic and normal cells, thus facilitating data interpretation and, hence, the reliability of MRD results. Funding National Cancer Institute (CA60419 and CA21765); American Lebanese Syrian Associated Charities; National Medical Research Council of Singapore (1299/2011); Viva Foundation for Children with Cancer, Children's Cancer Foundation, Tote Board & Turf Club, and Lee Foundation of Singapore.

Despite initial remission, approximately 60-70% of adult and 30% of pediatric patients experience relapse or refractory AML. Studies so far have identified base line gene expression profiles of pathogenic and prognostic significance in AML, however extent of change in gene expression post-initiation of treatment has not been investigated. Exposure of leukemic cells to chemotherapeutic agents such as cytarabine, a mainstay of AML chemotherapy can trigger adaptive response by influencing leukemic cell transcriptome and hence development of resistance or refractory disease. It is however challenging to perform such a study due to lack of availability of specimens post-drug treatment. In this study our primary objective was to identify in vivo cytarabine induced changes in leukemia cell transcriptome and to evaluate their impact on clinical outcome. Our results highlight genes relevant to cytarabine resistance and support the concept of targeting cytarabine-induced genes as a means of improving response.

Correction to: Leukemia (2016); 30(5), 1184–1187; doi:10.1038/leu.2015.246 Following the publication of this article the authors noted that the labels in Figures 1b and d have been switched. The correct labels in Figure 1b are; mixed lineage leukemia rearranged (MLL rearranged; dotted line) and unknown (thin solid line).

Background Novel therapies are needed for children with relapsed or refractory leukemia. We therefore tested the safety and feasibility of haploidentical natural killer cell therapy in this patient population.

Minimal residual disease (MRD) is a strong prognostic factor in children and adolescents with acute myeloid leukaemia (AML) but nearly one-quarter of patients who achieve MRD-negative status still relapse. The adverse prognostic factors among MRD-negative patients remain unknown. We analysed the AML02 study cohort to identify demographic and genetic prognostic factors. Among the presenting features, certain 11q23 abnormalities, such as t(6;11) and t(10;11), acute megakaryoblastic leukaemia without the t(1;22), and age ≥10 years were associated with inferior outcome in patients who had MRD-negative status after either remission induction I or II. By contrast, those with rearrangement of CBF genes had superior outcome. Our study identifies patient populations for whom close post-remission MRD monitoring to detect and treat emerging relapse and adjustment in treatment intensity might be indicated.

With improved contemporary therapy, we re-assess long-term outcome in patients completing treatment for childhood acute lymphoblastic leukemia to determine when cure can be declared with a high degree of confidence. In 6 successive clinical trials between 1984 and 2007, 1291(84.5%) patients completed all therapy in continuous complete remission. The post-therapy cumulative risk of relapse or development of a second neoplasm and the event-free survival rate and overall survival were analyzed according to the presenting features and the three treatment periods defined by relative outcome. Over the three treatment periods, there has been progressive increase in the rate of event-free survival (65.2% vs. 74.8% vs. 85.1% [P

Introduction: Venetoclax (VEN) is a potent and selective inhibitor of BCL-2. It has demonstrated activity in adults with acute myeloid leukemia (AML) in combination with low-dose cytarabine ( Methods: VEN was given daily for 28 days and chemotherapy was started on day 8, or earlier in cases of disease progression. Dosages of VEN and chemotherapy were escalated separately using a rolling-six design. Response to the VEN window was determined using total peripheral blood blast count or, in a subset of patients, bone marrow blast percentage as determined by flow-cytometry based minimal residual disease (MRD). Pharmacokinetics of VEN both as a single agent and in combination with chemotherapy were measured in a subset of patients treated at the maximum tolerated combination dose of VEN. Response to therapy was determined using bone marrow evaluation between days 29-50 of therapy. All patients received antimicrobial prophylaxis, typically with levofloxacin and micafungin. Azoles were prohibited during VEN administration. Results: Thirty-six patients aged 2-22 years were enrolled. All dose levels were tolerated. The recommended phase 2 dose of VEN in combination with high-dose cytarabine with or without idarubicin was 360 mg/m2 daily (max 600mg). One patient (treated with 240mg/m2 of VEN and intermediate-dose cytarabine) experienced a dose-limiting toxicity due to delayed count recovery and one patient died of recurrent colitis (at dose level 3) which first occurred during prior therapy and was deemed unrelated to VEN. Patients experienced a mean of 2.4 non-hematologic grade 3+ toxicities, with infections including culture-negative febrile neutropenia, sepsis, and colitis the most common toxicities. Patient-reported quality of life was similar at study entry and at the completion of cycle 1 and was within normal limits in most patients. Among 22 patients receiving VEN with high-dose cytarabine ± idarubicin, 14 (64%) achieved a complete response (CR) or complete response with incomplete count recovery (CRi). Response to the VEN window was associated with end of cycle 1 response; 13/15 (87%) patients with a greater than 80% reduction in peripheral blasts achieved a partial response (PR; 3) or CR/CRi (10). In contrast, only 8/15 (53%) patients with less than an 80% reduction in blasts responded to combination therapy (7 CR, 1 PR). Window response to VEN was associated with BH3 dependence as determined by cytochrome c release from leukemia cells in a flow-cytometry based assay. 5 of the 6 (83%) patients with primary BCL-2 dependence had a >80% reduction in blasts; the single patient with a poor response had a change to BCL-XL dependence at the end of cycle 1. In contrast, 4 of the 6 (66%) patients with primary BCL-XL dependence had a 90% reduction had secondary BCL-2 dependence. None of the 4 patients with FLT3-ITD or point mutations responded as determined by end of cycle 1 marrow. VEN levels were consistent across weights and ages and similar to levels seen in adults. The levels were similar between patients who did and did not receive idarubicin (mean AUC24 38.3 ± 32.7 vs. 47.3 ± 22.9 μg•h/mL). Conclusion: VEN combined with high-dose cytarabine or high-dose cytarabine and idarubicin was well tolerated and effective in children and young adults with relapsed or refractory AML. Enrollment continues to refine estimates of response rate. VEN window response is associated with BH3 dependence and end of cycle 1 response rates. Targeting BCL-XL or FLT3 may improve response to combination therapy. Table Disclosures Karol: Abbvie: Other: Unrelated to this study, St. Jude has received a charitable contribution from AbbVie, Inc. The charitable contribution is not being used for clinical or research activities, including any activities related to this study.. Alexander:AbbVie: Other: travel funding. Salem:AbbVie: Employment, Other: Stock/stock options. Palenski:Abbvie: Employment, Other: Stock/ stock options. Opferman:AbbVie: Research Funding. Rubnitz:AbbVie: Research Funding.

Background: There remains an unmet need for novel therapeutic strategies for relapsed or refractory (R/R) acute lymphoblastic leukemia (ALL) and lymphoblastic lymphoma (LLy). Venetoclax (Ven) is a highly selective BCL-2 inhibitor with established efficacy in adults with hematologic malignancies. Navitoclax (Nav) is a BCL-2/BCL-XL/BCL-W inhibitor with promising effects, but prolonged thrombocytopenia limits its continuous use at higher doses (J Clin Oncol. 2012;30:488). In a previous report of 32 patients (pts) with ALL, Ven+Nav was well tolerated without unexpected toxicity and with promising preliminary efficacy (EHA 2019. Abstr #PS940). Here we report updated outcomes for 36 pts with ALL or LLy treated with Ven+Nav and chemotherapy. Methods: This phase 1, multicenter, open-label, dose escalation study enrolled pts aged ≥4 years with R/R ALL or LLy (NCT03181126). Pts received the weight-adjusted equivalent of 200 mg Ven on day 1 and 400 mg equivalent daily thereafter. From day 3 onward, oral daily Nav was administered at 25, 50, or 100 mg for pts weighing ≥45 kg or at 25 or 50 mg for pts weighing 20 to Results: As of May 6, 2019, 36 pts have been enrolled with B-cell ALL (B-ALL, n=18), T-cell ALL (T-ALL, n=16), or LLy (n=2). The median age was 29 years (range, 6-72 years), including 7 pediatric pts (Table), and pts had a median of 4 prior therapies (range, 1-10) including 5 (14%) with prior stem cell transplant (SCT) and 6 (17%) with prior CAR-T therapy. Median time on study was 2.1 months (range, 1.3 - 8.3 months). The most common treatment-emergent adverse events (AEs) were nausea (47%), vomiting (42%), diarrhea (42%), hypokalemia (42%), abdominal pain (36%), febrile neutropenia (33%), alanine aminotransferase increase (31%), and neutropenia (31%). The only grade 3/4 non-hematologic AE related to Ven occurring in more than 1 pt was vomiting (3 [8%]); only hematologic events related to Nav occurred in >1 pt. Dose-limiting toxicities included ischemic bowel and delayed count recovery (n=1 each, 100 mg Nav, ≥45 kg); drug-induced hepatitis (n=1, 50 mg Nav, ≥45 kg); and delayed count recovery (n=1, 25 mg, Conclusions:Ven+Nav in combination with chemotherapy is well tolerated, with few discontinuations or dose reductions from AEs in pts with R/R ALL or LLy. The preliminary efficacy of Ven+Nav was promising in this heavily pretreated population of pts including those with prior SCT or CAR-T, with high rates of CR/CRi/CRp, and 10/18 (56%) with undetectable MRD. Additional correlative biomarker analyses are ongoing and will be presented. Disclosures Stock: Kite, a Gilead Company: Membership on an entity's Board of Directors or advisory committees; Pfizer: Membership on an entity's Board of Directors or advisory committees; Daiichi: Membership on an entity's Board of Directors or advisory committees; Astellas: Membership on an entity's Board of Directors or advisory committees; Agios: Membership on an entity's Board of Directors or advisory committees; UpToDate: Honoraria; Research to Practice: Honoraria. Jabbour:Adaptive: Consultancy, Research Funding; Amgen: Consultancy, Research Funding; AbbVie: Consultancy, Research Funding; Pfizer: Consultancy, Research Funding; Cyclacel LTD: Research Funding; Takeda: Consultancy, Research Funding; BMS: Consultancy, Research Funding. Bajel:AbbVie: Membership on an entity's Board of Directors or advisory committees, Other: travel funding. Rubnitz:AbbVie: Research Funding. Leonard:Amgen: Research Funding. Mullighan:Illumina: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: sponsored travel; Pfizer: Honoraria, Other: speaker, sponsored travel, Research Funding; AbbVie: Research Funding; Loxo Oncology: Research Funding; Amgen: Honoraria, Other: speaker, sponsored travel. Khaw:Amgen: Other: travel accommodations, Research Funding; Bristol Myers Squibb: Research Funding; Jazz Pharmaceuticals: Research Funding; AbbVie: Research Funding; Novartis: Other: travel accommodations. Opferman:AbbVie: Research Funding. Salem:AbbVie: Employment, Other: Stock/stock options. Schmidt:AbbVie: Employment, Other: stock or options. Tong:AbbVie: Employment, Other: stock or options. Zhou:AbbVie: Employment, Other: Stock or options. Ross:AbbVie: Employment, Other: Stock/stock options. Bensman:AbbVie: Employment, Other: stock or options. Jacobson:AbbVie: Employment, Other: Stock or options. Alexander:AbbVie: Other: travel funding.

Introduction: Cytarabine, daunorubicin and etoposide (ADE) are commonly used for remission and intensification of pediatric acute myeloid leukemia (AML). However, development of drug resistance is a major cause of treatment failure. In this study, we performed a comprehensive evaluation of expression levels of genes of pharmacological significance (pharmacokinetic /pharmacodynamic) to ADE and derived a drug response score predictive of treatment outcomes in pediatric AML patients. Methods: This study included 163 cases (median age=8.79 year, range= (0.013-21.1)) with AML enrolled in the multicenter AML02 clinical trial (ClinicalTrials.gov Identifier: NCT00136084) with Affymetrix U133A microarray gene expression and clinical data available. We used a penalized LASSO regression algorithm (glmnet R-package) to fit a cox regression model on diagnostic leukemic cell gene expression levels of 66 genes of pharmacological significance to ADE. We performed 1000 bootstraps of LASSO regression with event free survival (EFS) as the outcome variable and the five genes represented in at least 95% of the models were included to build an ADE-Response Score (ADE-RS) equation. Patients were classified into low or high score groups using recursive portioning implemented in Rpart-R package and evaluated for association with minimal residual disease after induction I (MRD1), EFS and overall survival (OS). ADE response score equation was further validated using RNA-Seq gene-expression data obtained from diagnostic samples of 432 pediatric AML patients enrolled in Children's Oncology Group (COG) AAML0531 and AAML03P1 treatment protocols. Results: After applying LASSO regression, we defined the equation: ADE-RS = (0.128 x DCTD) - (0.0993 x TOP2A) + (0.212 x ABCC1) - (0.113 x MPO) - (0.126 x CBR1) to develop ADE-response score (ADE-RS), followed by classifying patients into low (60%; 98 patients) or high (40%; 65 patients) score groups. Patients in the high ADE-RS group had significantly worse EFS (HR=4.07(2.43-6.84), P < 0.0001; Figure 1A) and OS (HR= 4.54(2.42-8.49), P In a multivariable cox-regression models that included pLSC6-ADE response score groups, MRD1 status, risk groups, WBC at diagnosis and age in AML02 cohort, high pLSC6-ADE score group was found significantly associated with poor EFS (HR=6.02(2.71-13.2), P Discussion: In this study, we defined a pharmacological response score focused on key genes of PK/PD significance to ADE. We further integrated LSC score with the ADE response score to improve our ability to predict treatment outcome in AML patients across different clinical trials. ADE-RS was composed of five genes: DCTD, which is a deaminase, involved in ara-C inactivation; CBR1, a carbonyl reductase involved in inactivation of daunorubicin (DNR); MPO, myeloperoxidase, an etoposide activator; ABCC1, an efflux transporter of DNR and etoposide; and TOP2A, DNA topoisomerase II alpha, which is a target for DNR and etoposide. Integrated pLSC6 and ADE-RS has a potential to predict treatment outcomes using diagnostic gene expression levels and accordingly develop treatment strategies to improve treatment outcome. Figure 1 Disclosures Gruber: Bristol-Myers Squibb: Consultancy. Rubnitz:AbbVie: Research Funding.