Single-cell multiomics reveals increased plasticity, resistant populations, and stem-cell-like blasts in KMT2A-rearranged leukemia.

KMT2A-rearranged (KMT2A-r) infant acute lymphoblastic leukemia (ALL) is a devastating malignancy with a dismal outcome, and younger age at diagnosis is associated with increased risk of relapse. To discover age-specific differences and critical drivers that mediate poor outcome in KMT2A-r ALL, we subjected KMT2A-r leukemias and normal hematopoietic cells from patients of different ages to single-cell multiomics analyses. We uncovered the following critical new insights: leukemia cells from patients <6 months have significantly increased lineage plasticity. Steroid response pathways are downregulated in the most immature blasts from younger patients. We identify a hematopoietic stem and progenitor-like (HSPC-like) population in the blood of younger patients that contains leukemic blasts and form an immunosuppressive signaling circuit with cytotoxic lymphocytes. These observations offer a compelling explanation for the ability of leukemias in young patients to evade chemotherapy and immune-mediated control. Our analysis also revealed preexisting lymphomyeloid primed progenitors and myeloid blasts at initial diagnosis of B-ALL. Tracking of leukemic clones in 2 patients whose leukemia underwent a lineage switch documented the evolution of such clones into frank acute myeloid leukemia (AML). These findings provide critical insights into KMT2A-r ALL and have clinical implications for molecularly targeted and immunotherapy approaches. Beyond infant ALL, our study demonstrates the power of single-cell multiomics to detect tumor intrinsic and extrinsic factors affecting rare but critical subpopulations within a malignant population that ultimately determines patient outcome.

Azacitidine as epigenetic priming for chemotherapy is safe and well-tolerated in infants with newly diagnosed KMT2A-rearranged acute lymphoblastic leukemia: Children's Oncology Group trial AALL15P1.

Infants less than 1 year old diagnosed with KMT2A-rearranged (KMT2A-r) acute lymphoblastic leukemia (ALL) are at high risk of remission failure, relapse, and death due to leukemia, despite intensive therapies. Infant KMT2A-r ALL blasts are characterized by DNA hypermethylation. Epigenetic priming with DNA methyltransferase inhibitors increases the cytotoxicity of chemotherapy in preclinical studies. The Children's Oncology Group trial AALL15P1 tested the safety and tolerability of five days of azacitidine immediately prior to the start of chemotherapy on day six, in four post-induction chemotherapy courses for infants with newly diagnosed KMT2A-r ALL. The treatment was welltolerated, with only two of 31 evaluable patients (6.5%) experiencing dose-limiting toxicity. Whole genome bisulfite sequencing of peripheral blood mononuclear cells (PBMCs) demonstrated decreased DNA methylation in 87% of samples tested following five days of azacitidine. Event-free survival was similar to prior studies of newly diagnosed infant ALL. Azacitidine is safe and results in decreased DNA methylation of PBMCs in infants with KMT2A-r ALL, but the incorporation of azacitidine to enhance cytotoxicity did not impact survival. Clinicaltrials.gov identifier: NCT02828358.

Minimal residual disease predicts outcomes in KMT2A-rearranged but not KMT2A-germline infant acute lymphoblastic leukemia: Report from Children's Oncology Group study AALL0631.

We measured minimal residual disease (MRD) by multiparameter flow cytometry at three time points (TP) in 117 infants with KMT2A (lysine [K]-specific methyltransferase 2A)-rearranged and 58 with KMT2A-germline acute lymphoblastic leukemia (ALL) on Children's Oncology Group AALL0631 study. For KMT2A-rearranged patients, 3-year event-free survival (EFS) by MRD-positive (≥0.01%) versus MRD-negative (<0.01%) was: TP1: 25% (±6%) versus 49% (±7%; p = .0009); TP2: 21% (±8%) versus 47% (±7%; p < .0001); and TP3: 22% (±14%) versus 51% (±6%; p = .0178). For KMT2A-germline patients, 3-year EFS was: TP1: 88% (±12%) versus 87% (±5%; p = .73); TP2: 100% versus 88% (±5%; p = .24); and TP3: 100% versus 87% (±5%; p = .53). MRD was a strong independent outcome predictor in KMT2A-rearranged, but not KMT2A-germline infant ALL.

Anaplastic Lymphoma Kinase Inhibitor in Treatment of Inflammatory Myofibroblastic Tumor of the Tongue in Infancy.

Inflammatory myofibroblastic tumors (IMTs) are rare in neonates. IMTs of the tongue are also very rare in infancy, with only 1 case reported in this age group. The mainstay of therapy has traditionally been surgery, which can be devastating to surrounding structures and negatively impact prognosis. Approximately 50% of IMTs harbor a translocation involving the anaplastic lymphoma kinase gene. We describe a case of IMT of the tongue in a neonate treated with debulking and an anaplastic lymphoma kinase inhibitor. The patient achieved complete response and remains disease-free 1.5 year following completion of therapy.

Treatment of children with relapsed and refractory acute lymphoblastic leukemia with mitoxantrone, vincristine, pegaspargase, dexamethasone, and bortezomib.

BACKGROUND: The treatment of relapsed or refractory acute lymphoblastic leukemia (ALL) in children is challenging and new treatment options are needed. Bortezomib is a proteasome inhibitor with activity in pediatric acute lymphoblastic leukemia. Adding bortezomib to standard reinduction chemotherapy in relapsed and refractory pediatric ALL has produced very good response rates in prior studies. METHODS: We evaluated bortezomib in combination with reinduction therapy (ALL R3) in 10 children with relapsed or refractory ALL. Bortezomib (1.3 mg/m2 /dose) was administered to patients on days 1, 4, 8, and 11. In addition, patients received mitoxantrone, dexamethasone, pegaspargase, vincristine, and intrathecal methotrexate over 4 weeks. RESULTS: Of the 10 patients, eight (80%) achieved a complete remission (CR) or complete remission with incomplete recovery (CRi). Of the patients in CR, two had undetectable minimal residual disease by flow cytometry (<0.01%). Five patients were subsequently treated with a stem cell transplant. All eight patients that achieved CR or CRi eventually relapsed. One patient remains alive following treatment with tisagenlecleucel after relapse. Grade 3 or higher infections occurred in four out of 10 patients, and other toxicities commonly associated with bortezomib were not seen. CONCLUSIONS: In children with relapsed or refractory ALL, the addition of bortezomib to reinduction chemotherapy that includes mitoxantrone produces a complete response in the majority of cases and does not lead to excessive toxicity.

Desensitization to pegaspargase in children with acute lymphoblastic leukemia and lymphoblastic lymphoma.

Hypersensitivity to pegaspargase is associated with inferior survival in pediatric patients with acute lymphoblastic leukemia and lymphoblastic lymphoma. In the past year, drug-supply shortages have led to the lack of an available alternative to pegaspargase. Rather than omit asparaginase from the treatment of acute lymphoblastic leukemia or lymphoblastic lymphoma patients with hypersensitivity to pegaspargase, we continued pegaspargase treatments for nine pediatric patients, utilizing a rapid desensitization protocol. There were no adverse events related to the pegaspargase during desensitization, and all patients who were checked had asparaginase serum levels above the threshold of 0.1 IU/mL at 7 to 14 days after pegaspargase therapy.

Combined heparin/acid citrate dextrose solution A anticoagulation in the Optia continuous mononuclear cell protocol for pediatric lymphocyte apheresis.

Collecting a sufficient number of T-cells is a critical first step in the production of chimeric antigen receptor (CAR)-T cells. Herein, we report a successful implementation of anticoagulation with combined heparin and acid citrate dextrose solution A (ACD-A) for the continuous mononuclear cell (CMNC) protocol on the Spectra Optia in a 20-month-old, 7.5 kg patient with refractory acute lymphoblastic leukemia for manufacture of tisagenlecleucel, a CAR-T cell therapy. Combined heparin/ACD-A was used following clotting issues when ACD-A was used alone during initial CMNC collections. To our knowledge, this is the first reported case in pediatrics of combined heparin/ACD-A anticoagulation with the Spectra Optia CMNC protocol.

Updates in the biology and therapy for infant acute lymphoblastic leukemia.

PURPOSE OF REVIEW: The prognosis for infants less than 12 months of age who are diagnosed with acute lymphoblastic leukemia (ALL) remains poor despite overall advances in the treatment of childhood ALL. In this review, we highlight the recent advances in the understanding of the pathogenesis of infant ALL and discuss opportunities for translating these findings into clinical trials. RECENT FINDINGS: Infant ALL can be divided into two major disease types, defined by the presence or absence of KMT2A (MLL) rearrangement (KMT2A-R). Recent molecular profiling studies have found that infant ALL with KMT2A-R is an epigenomic disease that lacks other somatic driver mutations. Strategies to intensify therapy have not improved survival for infants with KMT2A-R ALL. In contrast, infant ALL without KMT2A-R is more similar to ALL of older children and survival has improved modestly with intensification of chemotherapy. Discovery of clonal molecular markers that predict chemoresistance will allow further risk classification and development of novel treatment strategies. Modern clinical trials are integrating molecularly targeted therapies into the treatment of infant ALL. SUMMARY: Advances in molecular profiling and integration of targeted therapy have the potential to reduce toxicity and improve survival for infants with ALL.

Parental Perceptions of Obesity and Obesity Risk Associated With Childhood Acute Lymphoblastic Leukemia.

The prevalence of obesity and related comorbidities in survivors of childhood acute lymphoblastic leukemia (ALL) is well established and ranges anywhere from 29% to 69% depending on the study. We sought to explore the awareness of parents of survivors of childhood ALL regarding the increased risk of obesity and their perceptions regarding the overall health of their child. One hundred twenty-one parents of 99 survivors of pediatric ALL completed surveys regarding perceptions of obesity risk in survivors. Eighty percent of parents of overweight and obese survivors correctly identified their child as "a little overweight" or "overweight." Few parents recalled discussing weight gain (21%) or obesity risk (36%) with their practitioner. Parents that did recall having these discussions and/or reported a decreased level of posttherapy activity in their child were more likely to be concerned about their child's weight status. Improved awareness and education regarding the risk of obesity and associated comorbid conditions may provide an avenue for future prevention of obesity in survivors of pediatric ALL. Discussion and education regarding a healthy lifestyle, including proper diet and exercise, should be incorporated early in routine patient visits.

Evaluation of Hi-C sequencing for the detection of gene fusions in hematologic and solid pediatric cancer samples.

HiC sequencing is a DNA-based next-generation sequencing method that preserves the 3D conformation of the genome and has shown promise in detecting genomic rearrangements in translational research studies. To evaluate HiC as a potential clinical diagnostic platform, analytical concordance with routine laboratory testing was assessed using primary pediatric leukemia and sarcoma specimens previously positive for clinically significant genomic rearrangements. Archived specimen types tested included viable and nonviable frozen leukemic cells, as well as formalin-fixed paraffin-embedded (FFPE) tumor tissues. Initially, pediatric acute myeloid leukemia (AML) and alveolar rhabdomyosarcoma (A-RMS) specimens with known genomic rearrangements were subjected to HiC analysis to assess analytical concordance. Subsequently, a discovery cohort consisting of AML and acute lymphoblastic leukemia (ALL) cases with no known genomic rearrangements based on prior clinical diagnostic testing were evaluated to determine whether HiC could detect rearrangements. Using a standard sequencing depth of 50 million raw read-pairs per sample, or approximately 5X raw genomic coverage, 100% concordance was observed between HiC and previous clinical cytogenetic and molecular testing. In the discovery cohort, a clinically relevant gene fusion was detected in 45% of leukemia cases (5/11). This study demonstrates the value of HiC sequencing to medical diagnostic testing as it identified several clinically significant rearrangements, including those that might have been missed by current clinical testing workflows. Key points: HiC sequencing is a DNA-based next-generation sequencing method that preserves the 3D conformation of the genome, facilitating detection of genomic rearrangements.HiC was 100% concordant with clinical diagnostic testing workflows for detecting clinically significant genomic rearrangements in pediatric leukemia and rhabdomyosarcoma specimens.HiC detected clinically significant genomic rearrangements not previously detected by prior clinical cytogenetic and molecular testing.HiC performed well with archived non-viable and viable frozen leukemic cell samples, as well as archived formalin-fixed paraffin-embedded tumor tissue specimens.

Evaluation of Hi-C Sequencing for Detection of Gene Fusions in Hematologic and Solid Tumor Pediatric Cancer Samples.

Hi-C sequencing is a DNA-based next-generation sequencing method that preserves the 3D genome conformation and has shown promise in detecting genomic rearrangements in translational research studies. To evaluate Hi-C as a potential clinical diagnostic platform, analytical concordance with routine laboratory testing was assessed using primary pediatric leukemia and sarcoma specimens. Archived viable and non-viable frozen leukemic cells and formalin-fixed paraffin-embedded (FFPE) tumor specimens were analyzed. Pediatric acute myeloid leukemia (AML) and alveolar rhabdomyosarcoma (A-RMS) specimens with known genomic rearrangements were subjected to Hi-C to assess analytical concordance. Subsequently, a discovery cohort consisting of AML and acute lymphoblastic leukemia (ALL) cases without known genomic rearrangements based on prior clinical diagnostic testing was evaluated to determine whether Hi-C could detect rearrangements. Using a standard sequencing depth of 50 million raw read-pairs per sample, or approximately 5X raw genomic coverage, we observed 100% concordance between Hi-C and previous clinical cytogenetic and molecular testing. In the discovery cohort, a clinically relevant gene fusion was detected in 45% of leukemia cases (5/11). This study provides an institutional proof of principle evaluation of Hi-C sequencing to medical diagnostic testing as it identified several clinically relevant rearrangements, including those that were missed by current clinical testing workflows.

Optimized cytogenetic risk-group stratification of KMT2A-rearranged pediatric acute myeloid leukemia.

ABSTRACT: A comprehensive international consensus on the cytogenetic risk-group stratification of KMT2A-rearranged (KMT2A-r) pediatric acute myeloid leukemia (AML) is lacking. This retrospective (2005-2016) International Berlin-Frankfurt-Münster Study Group study on 1256 children with KMT2A-r AML aims to validate the prognostic value of established recurring KMT2A fusions and additional cytogenetic aberrations (ACAs) and to define additional, recurring KMT2A fusions and ACAs, evaluating their prognostic relevance. Compared with our previous study, 3 additional, recurring KMT2A-r groups were defined: Xq24/KMT2A::SEPT6, 1p32/KMT2A::EPS15, and 17q12/t(11;17)(q23;q12). Across 13 KMT2A-r groups, 5-year event-free survival probabilities varied significantly (21.8%-76.2%; P < .01). ACAs occurred in 46.8% of 1200 patients with complete karyotypes, correlating with inferior overall survival (56.8% vs 67.9%; P < .01). Multivariable analyses confirmed independent associations of 4q21/KMT2A::AFF1, 6q27/KMT2A::AFDN, 10p12/KMT2A::MLLT10, 10p11.2/KMT2A::ABI1, and 19p13.3/KMT2A::MLLT1 with adverse outcomes, but not those of 1q21/KMT2A::MLLT11 and trisomy 19 with favorable and adverse outcomes, respectively. Newly identified ACAs with independent adverse prognoses were monosomy 10, trisomies 1, 6, 16, and X, add(12p), and del(9q). Among patients with 9p22/KMT2A::MLLT3, the independent association of French-American-British-type M5 with favorable outcomes was confirmed, and those of trisomy 6 and measurable residual disease at end of induction with adverse outcomes were identified. We provide evidence to incorporate 5 adverse-risk KMT2A fusions into the cytogenetic risk-group stratification of KMT2A-r pediatric AML, to revise the favorable-risk classification of 1q21/KMT2A::MLLT11 to intermediate risk, and to refine the risk-stratification of 9p22/KMT2A::MLLT3 AML. Future studies should validate the associations between the newly identified ACAs and outcomes and unravel the underlying biological pathogenesis of KMT2A fusions and ACAs.

Severus: accurate detection and characterization of somatic structural variation in tumor genomes using long reads.

Most current studies rely on short-read sequencing to detect somatic structural variation (SV) in cancer genomes. Long-read sequencing offers the advantage of better mappability and long-range phasing, which results in substantial improvements in germline SV detection. However, current long-read SV detection methods do not generalize well to the analysis of somatic SVs in tumor genomes with complex rearrangements, heterogeneity, and aneuploidy. Here, we present Severus: a method for the accurate detection of different types of somatic SVs using a phased breakpoint graph approach. To benchmark various short- and long-read SV detection methods, we sequenced five tumor/normal cell line pairs with Illumina, Nanopore, and PacBio sequencing platforms; on this benchmark Severus showed the highest F1 scores (harmonic mean of the precision and recall) as compared to long-read and short-read methods. We then applied Severus to three clinical cases of pediatric cancer, demonstrating concordance with known genetic findings as well as revealing clinically relevant cryptic rearrangements missed by standard genomic panels.

Menin inhibitors in pediatric acute leukemia: a comprehensive review and recommendations to accelerate progress in collaboration with adult leukemia and the international community.

Aberrant expression of HOX and MEIS1 family genes, as seen in KMT2A-rearranged, NUP98-rearranged, or NPM1-mutated leukemias leads to arrested differentiation and leukemia development. HOX family genes are essential gatekeepers of physiologic hematopoiesis, and their expression is regulated by the interaction between KMT2A and menin. Menin inhibitors block this interaction, downregulate the abnormal expression of MEIS1 and other transcription factors and thereby release the differentiation block. Menin inhibitors show significant clinical efficacy against KMT2A-rearranged and NPM1-mutated acute leukemias, with promising potential to address unmet needs in various pediatric leukemia subtypes. In this collaborative initiative, pediatric and adult hematologists/oncologists, and stem cell transplant physicians have united their expertise to explore the potential of menin inhibitors in pediatric leukemia treatment internationally. Our efforts aim to provide a comprehensive clinical overview of menin inhibitors, integrating preclinical evidence and insights from ongoing global clinical trials. Additionally, we propose future international, inclusive, and efficient clinical trial designs, integrating pediatric populations in adult trials, to ensure broad access to this promising therapy for all children and adolescents with menin-dependent leukemias.

Preclinical efficacy of azacitidine and venetoclax for infant KMT2A-rearranged acute lymphoblastic leukemia reveals a new therapeutic strategy.

Infants with KMT2A-rearranged B-cell acute lymphoblastic leukemia (ALL) have a dismal prognosis. Survival outcomes have remained static in recent decades despite treatment intensification and novel therapies are urgently required. KMT2A-rearranged infant ALL cells are characterized by an abundance of promoter hypermethylation and exhibit high BCL-2 expression, highlighting potential for therapeutic targeting. Here, we show that hypomethylating agents exhibit in vitro additivity when combined with most conventional chemotherapeutic agents. However, in a subset of samples an antagonistic effect was seen between several agents. This was most evident when hypomethylating agents were combined with methotrexate, with upregulation of ATP-binding cassette transporters identified as a potential mechanism. Single agent treatment with azacitidine and decitabine significantly prolonged in vivo survival in KMT2A-rearranged infant ALL xenografts. Treatment of KMT2A-rearranged infant ALL cell lines with azacitidine and decitabine led to differential genome-wide DNA methylation, changes in gene expression and thermal proteome profiling revealed the target protein-binding landscape of these agents. The selective BCL-2 inhibitor, venetoclax, exhibited in vitro additivity in combination with hypomethylating or conventional chemotherapeutic agents. The addition of venetoclax to azacitidine resulted in a significant in vivo survival advantage indicating the therapeutic potential of this combination to improve outcome for infants with KMT2A-rearranged ALL.

Racial and ethnic disparities in childhood and young adult acute lymphocytic leukaemia: secondary analyses of eight Children's Oncology Group cohort trials.

BACKGROUND: Previous studies have identified racial and ethnic disparities in childhood acute lymphocytic leukaemia survival. We aimed to establish whether disparities persist in contemporaneous cohorts and, if present, are attributable to differences in leukaemia biology or insurance status. METHODS: Patients with newly diagnosed acute lymphocytic leukaemia in inpatient and outpatient centres in the USA, Canada, Australia, and New Zealand, aged 0-30 years, who had race or ethnicity data available, enrolled on eight completed Children's Oncology Group trials (NCT00103285, NCT00075725, NCT00408005, NCT01190930, NCT02883049, NCT02112916, NCT02828358, and NCT00557193) were included in this secondary analysis. Race and ethnicity were categorised as non-Hispanic White, Hispanic, non-Hispanic Black, non-Hispanic Asian, and non-Hispanic other. Event-free survival and overall survival were compared across race and ethnicity groups. The relative contribution of clinical and biological disease prognosticators and insurance status was examined through multivariable regression models, both among the entire cohort and among those with B-cell lineage versus T-cell lineage disease. FINDINGS: Between Jan 1, 2004, and Dec 31, 2019, 24 979 eligible children, adolescents, and young adults with acute lymphocytic leukaemia were enrolled, of which 21 152 had race or ethnicity data available. 11 849 (56·0%) were male and 9303 (44·0%) were female. Non-Hispanic White patients comprised the largest racial or ethnic group (13 872 [65·6%]), followed by Hispanic patients (4354 [20·6%]), non-Hispanic Black patients (1517 [7·2%]), non-Hispanic Asian (n=1071 [5·1%]), and non-Hispanic other (n=338 [1·6%]). 5-year event-free survival was 87·4% (95% CI 86·7-88·0%) among non-Hispanic White patients compared with 82·8% (81·4-84·1%; hazard ratio [HR] 1·37, 95% CI 1·26-1·49; p<0·0001) among Hispanic patients and 81·8% (79·3-84·0; HR 1·45, 1·28-1·65; p<0·0001) among non-Hispanic Black patients. Non-hispanic Asian patients had a 5-year event-free survival of 88·1% (95% CI 85·5-90·3%) and non-Hispanic other patients had a survival of 82·8% (76·4-87·6%). Inferior event-free survival among Hispanic patients was substantially attenuated by disease prognosticators and insurance status (HR decreased from 1·37 [1·26-1·49; p<0·0001] to 1·11 [1·00-1·22; p=0·045]). The increased risk among non-Hispanic Black patients was minimally attenuated (HR 1·45 [1·28-1·65; p<0·0001] to 1·32 [1·14-1·52; p<0·0001]). 5-year overall survival was 93·6% (91·5-95·1%) in non-Hispanic Asian patients, 93·3% (92·8-93·7%) in non-Hispanic White patients, 89·9% (88·7-90·9%) in Hispanic, 89·7% (87·6-91·4%) in non-Hispanic Black patients, 88·9% (83·2-92·7%) in non-Hispanic other patients. Disparities in overall survival were wider than event-free survival (eg, among non-Hispanic other patients, the HR for event-free survival was 1·43 [1·10-1·85] compared with 1·74 [1·27-2·40] for overall survival). Disparities were restricted to patients with B-cell acute lymphocytic leukaemia, no differences in event-free survival or overall survival were seen in the T-cell acute lymphocytic leukaemia group. INTERPRETATION: Substantial disparities in outcome for B-cell acute lymphocytic leukaemia persist by race and ethnicity, but are not observed in T-cell acute lymphocytic leukaemia. Future studies of relapsed patients, access to and quality of care, and other potential aspects of structural racism are warranted to inform interventions aimed at dismantling racial and ethnic disparities. FUNDING: National Cancer Institute and St Baldrick's Foundation.

Measurable Residual Disease and Fusion Partner Independently Predict Survival and Relapse Risk in Childhood KMT2A-Rearranged Acute Myeloid Leukemia: A Study by the International Berlin-Frankfurt-Münster Study Group.

PURPOSE: A previous study by the International Berlin-Frankfurt-Münster Study Group (I-BFM-SG) on childhood KMT2A-rearranged (KMT2A-r) AML demonstrated the prognostic value of the fusion partner. This I-BFM-SG study investigated the value of flow cytometry-based measurable residual disease (flow-MRD) and evaluated the benefit of allogeneic stem-cell transplantation (allo-SCT) in first complete remission (CR1) in this disease. METHODS: A total of 1,130 children with KMT2A-r AML, diagnosed between January 2005 and December 2016, were assigned to high-risk (n = 402; 35.6%) or non-high-risk (n = 728; 64.4%) fusion partner-based groups. Flow-MRD levels at both end of induction 1 (EOI1) and 2 (EOI2) were available for 456 patients and were considered negative (<0.1%) or positive (≥0.1%). End points were 5-year event-free survival (EFS), cumulative incidence of relapse (CIR), and overall survival (OS). RESULTS: The high-risk group had inferior EFS (30.3% high risk v 54.0% non-high risk; P < .0001), CIR (59.7% v 35.2%; P < .0001), and OS (49.2% v 70.5%; P < .0001). EOI2 MRD negativity was associated with superior EFS (n = 413; 47.6% MRD negativity v n = 43; 16.3% MRD positivity; P < .0001) and OS (n = 413; 66.0% v n = 43; 27.9%; P < .0001), and showed a trend toward lower CIR (n = 392; 46.1% v n = 26; 65.4%; P = .016). Similar results were obtained for patients with EOI2 MRD negativity within both risk groups, except that within the non-high-risk group, CIR was comparable with that of patients with EOI2 MRD positivity. Allo-SCT in CR1 only reduced CIR (hazard ratio, 0.5 [95% CI, 0.4 to 0.8]; P = .00096) within the high-risk group but did not improve OS. In multivariable analyses, EOI2 MRD positivity and high-risk group were independently associated with inferior EFS, CIR, and OS. CONCLUSION: EOI2 flow-MRD is an independent prognostic factor and should be included as risk stratification factor in childhood KMT2A-r AML. Treatment approaches other than allo-SCT in CR1 are needed to improve prognosis.

MicroRNA Content of Ewing Sarcoma Derived Extracellular Vesicles Leads to Biomarker Potential and Identification of a Previously Undocumented EWS-FLI1 Translocation.

Objective: Ewing Sarcoma Family of Tumors (ESFT) are a highly aggressive pediatric bone and soft tissue malignancy with poor outcomes in the refractory and recurrent setting. Over 90% of Ewing Sarcoma (ES) tumors are driven by the pathognomonic EWS-ETS chimeric transcripts and their corresponding oncoproteins. It has been suggested that the EWS-ETS oncogenic action can mediate microRNA (miRNA) processing. Importantly, small extracellular vesicles (sEVs), including those frequently referred to as exosomes have been shown to be highly enriched with tumor-derived small RNAs such as miRNAs. We hypothesized that ESFT-specific sEVs are enriched with certain miRNAs which could be utilized toward an exo-miRNA biomarker signature specific to this disease. Methods: We performed miRNAseq to compare both the exo-derived and cell-derived miRNA content from 8 ESFT, 2 osteosarcoma, 2 non-cancerous cell lines, and pediatric plasma samples. Results: We found that sEVs derived from ESFT cells contained nearly 2-fold more number of unique individual miRNAs as compared to non-ESFT samples. Quantitative analysis of the differential enrichment of sEV miRNAs resulted in the identification of 62 sEV-miRNAs (exo-miRNAs) with significant (P < .05) enrichment variation between ESFT and non-ESFT sEV samples. To determine if we could utilize this miRNA signature to diagnose ESFT patients via a liquid biopsy, we analyzed the RNA content of total circulating sEVs isolated from 500 µL plasma from 5 pediatric ESFT patients, 2 pediatric osteosarcoma patients, 2 pediatric rhabdomyosarcoma patients, and 4 non-cancer pediatric controls. Pearson's clustering of 60 of the 62 candidate exo-miRNAs correctly identified 80% (4 of 5) of pathology confirmed ESFT patients. Importantly, RNAseq analysis of tumor tissue from the 1 outlier, revealed a previously uncharacterized EWS-FLI1 translocation.Conclusions: Taken together, these findings support the development and validation of an exo-miRNA-based liquid biopsy to aid in the diagnosis and monitoring of ESFT.