A critical review of the perioperative fluid therapy and hemodynamic monitoring recommendations of the Enhanced Recovery of the Adult Pathway (RICA): A position statement of the fluid therapy and hemodynamic monitoring Subcommittee of the Hemostasis, Transfusion Medicine and Fluid Therapy Section (SHTF) of the Spanish Society of Anesthesiology and Critical Care (SEDAR).

In an effort to standardize perioperative management and improve postoperative outcomes of adult patients undergoing surgery, the Ministry of Health, through the Spanish Multimodal Rehabilitation Group (GERM), and the Aragonese Institute of Health Sciences, in collaboration with multiple Spanish scientific societies and based on the available evidence, published in 2021 the Spanish Intensified Adult Recovery (RICA) guideline. This document includes 12 perioperative measures related to fluid therapy and hemodynamic monitoring. Fluid administration and hemodynamic monitoring are not straightforward but are directly related to postoperative patient outcomes. The Fluid Therapy and Hemodynamic Monitoring Subcommittee of the Hemostasis, Transfusion Medicine and Fluid Therapy Section (SHTF) of the Spanish Society of Anesthesiology and Critical Care (SEDAR) has reviewed these recommendations and concluded that they should be revised as they do not follow an adequate methodology.

Fluid challenges in operating room: A planned sub study of the Fluid Day observational study.

BACKGROUND: Intraoperative fluid administration is a ubiquitous intervention in surgical patients. But inadequate fluid administration may lead to poor postoperative outcomes. Fluid challenges (FCs), in or outside the so-called goal-directed fluid therapy, allows testing the cardiovascular system and the need for further fluid administration. Our primary aim was to evaluate how anesthesiologists conduct FCs in the operating room in terms of type, volume, variables used to trigger a FC and to compare the proportion of patients receiving further fluid administration based on the response to the FC. METHODS: This was a planned substudy of an observational study conducted in 131 centres in Spain in patients undergoing surgery. RESULTS: A total of 396 patients were enrolled and analysed in the study. The median [interquartile range] amount of fluid given during a FC was 250ml (200-400). The main indication for FC was a decrease in systolic arterial pressure in 246 cases (62.2%). The second was a decrease in mean arterial pressure (54.4%). Cardiac output was used in 30 patients (7.58%), while stroke volume variation in 29 of 385 cases (7.32%). The response to the initial FC did not have an impact when prescribing further fluid administration. CONCLUSIONS: The current indication and evaluation of FC in surgical patients is highly variable. Prediction of fluid responsiveness is not routinely used, and inappropriate variables are frequently evaluated for assessing the hemodynamic response to FC, which may result in deleterious effects.

Research priorities in perioperative fluid therapy and hemodynamic monitoring: A Delphi Consensus Survey from the Fluid Therapy and Hemodynamic Monitoring Subcommittee of the Hemostasis, Transfusion Medicine and Fluid Therapy Section (SHTF) of the Spanish Society of Anesthesiology and Critical Care (SEDAR).

BACKGROUND: Research in fluid therapy and perioperative hemodynamic monitoring is difficult and expensive. The objectives of this study were to summarize these topics and to prioritize these topics in order of research importance. METHODS: Electronic structured Delphi questionnaire over three rounds among 30 experts in fluid therapy and hemodynamic monitoring identified through the Fluid Therapy and Hemodynamic Monitoring Subcommittee of the Hemostasis, Transfusion Medicine and Fluid Therapy Section of the Spanish Society of Anesthesiology and Critical Care. RESULTS: 77 topics were identified and ranked in order of prioritization. Topics were categorized into themes of crystalloids, colloids, hemodynamic monitoring and others. 31 topics were ranked as essential research priority. To determine whether intraoperative hemodynamic optimization algorithms based on the invasive or noninvasive Hypotension Prediction Index versus other management strategies could decrease the incidence of postoperative complications. As well as whether the use of renal stress biomarkers together with a goal-directed fluid therapy protocol could reduce hospital stay and the incidence of acute kidney injury in adult patients undergoing non-cardiac surgery, reached the highest consensus. CONCLUSIONS: The Fluid Therapy and Hemodynamic Monitoring Subcommittee of the Hemostasis, Transfusion Medicine and Fluid Therapy Section of the Spanish Society of Anesthesiology and Critical Care will use these results to carry out the research.

The KMT2A recombinome of acute leukemias in 2023.

Chromosomal rearrangements of the human KMT2A/MLL gene are associated with de novo as well as therapy-induced infant, pediatric, and adult acute leukemias. Here, we present the data obtained from 3401 acute leukemia patients that have been analyzed between 2003 and 2022. Genomic breakpoints within the KMT2A gene and the involved translocation partner genes (TPGs) and KMT2A-partial tandem duplications (PTDs) were determined. Including the published data from the literature, a total of 107 in-frame KMT2A gene fusions have been identified so far. Further 16 rearrangements were out-of-frame fusions, 18 patients had no partner gene fused to 5'-KMT2A, two patients had a 5'-KMT2A deletion, and one ETV6::RUNX1 patient had an KMT2A insertion at the breakpoint. The seven most frequent TPGs and PTDs account for more than 90% of all recombinations of the KMT2A, 37 occur recurrently and 63 were identified so far only once. This study provides a comprehensive analysis of the KMT2A recombinome in acute leukemia patients. Besides the scientific gain of information, genomic breakpoint sequences of these patients were used to monitor minimal residual disease (MRD). Thus, this work may be directly translated from the bench to the bedside of patients and meet the clinical needs to improve patient survival.

In vivo CRISPR/Cas9 targeting of fusion oncogenes for selective elimination of cancer cells.

Fusion oncogenes (FOs) are common in many cancer types and are powerful drivers of tumor development. Because their expression is exclusive to cancer cells and their elimination induces cell apoptosis in FO-driven cancers, FOs are attractive therapeutic targets. However, specifically targeting the resulting chimeric products is challenging. Based on CRISPR/Cas9 technology, here we devise a simple, efficient and non-patient-specific gene-editing strategy through targeting of two introns of the genes involved in the rearrangement, allowing for robust disruption of the FO specifically in cancer cells. As a proof-of-concept of its potential, we demonstrate the efficacy of intron-based targeting of transcription factors or tyrosine kinase FOs in reducing tumor burden/mortality in in vivo models. The FO targeting approach presented here might open new horizons for the selective elimination of cancer cells.

Correction: NG2 antigen is involved in leukemia invasiveness and central nervous system infiltration in MLL-rearranged infant B-ALL.

The original version of this Article contained an error in the spelling of the author Juan Carlos Rodriguez-Manzaneque, which was incorrectly given as J Carlos Rodríguez-Manzaneque. This has now been corrected in both the PDF and HTML versions of the Article.

NG2 antigen is involved in leukemia invasiveness and central nervous system infiltration in MLL-rearranged infant B-ALL.

Mixed-lineage leukemia (MLL)-rearranged (MLLr) infant B-cell acute lymphoblastic leukemia (iMLLr-B-ALL) has a dismal prognosis and is associated with a pro-B/mixed phenotype, therapy refractoriness and frequent central nervous system (CNS) disease/relapse. Neuron-glial antigen 2 (NG2) is specifically expressed in MLLr leukemias and is used in leukemia immunophenotyping because of its predictive value for MLLr acute leukemias. NG2 is involved in melanoma metastasis and brain development; however, its role in MLL-mediated leukemogenesis remains elusive. Here we evaluated whether NG2 distinguishes leukemia-initiating/propagating cells (L-ICs) and/or CNS-infiltrating cells (CNS-ICs) in iMLLr-B-ALL. Clinical data from the Interfant cohort of iMLLr-B-ALL demonstrated that high NG2 expression associates with lower event-free survival, higher number of circulating blasts and more frequent CNS disease/relapse. Serial xenotransplantation of primary MLL-AF4+ leukemias indicated that NG2 is a malleable marker that does not enrich for L-IC or CNS-IC in iMLLr-B-All. However, NG2 expression was highly upregulated in blasts infiltrating extramedullar hematopoietic sites and CNS, and specific blockage of NG2 resulted in almost complete loss of engraftment. Indeed, gene expression profiling of primary blasts and primografts revealed a migratory signature of NG2+ blasts. This study provides new insights on the biology of NG2 in iMLLr-B-ALL and suggests NG2 as a potential therapeutic target to reduce the risk of CNS disease/relapse and to provide safer CNS-directed therapies for iMLLr-B-ALL.

The MLL recombinome of acute leukemias in 2017.

Chromosomal rearrangements of the human MLL/KMT2A gene are associated with infant, pediatric, adult and therapy-induced acute leukemias. Here we present the data obtained from 2345 acute leukemia patients. Genomic breakpoints within the MLL gene and the involved translocation partner genes (TPGs) were determined and 11 novel TPGs were identified. Thus, a total of 135 different MLL rearrangements have been identified so far, of which 94 TPGs are now characterized at the molecular level. In all, 35 out of these 94 TPGs occur recurrently, but only 9 specific gene fusions account for more than 90% of all illegitimate recombinations of the MLL gene. We observed an age-dependent breakpoint shift with breakpoints localizing within MLL intron 11 associated with acute lymphoblastic leukemia and younger patients, while breakpoints in MLL intron 9 predominate in AML or older patients. The molecular characterization of MLL breakpoints suggests different etiologies in the different age groups and allows the correlation of functional domains of the MLL gene with clinical outcome. This study provides a comprehensive analysis of the MLL recombinome in acute leukemia and demonstrates that the establishment of patient-specific chromosomal fusion sites allows the design of specific PCR primers for minimal residual disease analyses for all patients.

Reprogramming human B cells into induced pluripotent stem cells and its enhancement by C/EBPα.

B cells have been shown to be refractory to reprogramming and B-cell-derived induced pluripotent stem cells (iPSC) have only been generated from murine B cells engineered to carry doxycycline-inducible Oct4, Sox2, Klf4 and Myc (OSKM) cassette in every tissue and from EBV/SV40LT-immortalized lymphoblastoid cell lines. Here, we show for the first time that freshly isolated non-cultured human cord blood (CB)- and peripheral blood (PB)-derived CD19+CD20+ B cells can be reprogrammed to iPSCs carrying complete VDJH immunoglobulin (Ig) gene monoclonal rearrangements using non-integrative tetracistronic, but not monocistronic, OSKM-expressing Sendai Virus. Co-expression of C/EBPα with OSKM facilitates iPSC generation from both CB- and PB-derived B cells. We also demonstrate that myeloid cells are much easier to reprogram than B and T lymphocytes. Differentiation potential back into the cell type of their origin of B-cell-, T-cell-, myeloid- and fibroblast-iPSCs is not skewed, suggesting that their differentiation does not seem influenced by 'epigenetic memory'. Our data reflect the actual cell-autonomous reprogramming capacity of human primary B cells because biased reprogramming was avoided by using freshly isolated primary cells, not exposed to cytokine cocktails favoring proliferation, differentiation or survival. The ability to reprogram CB/PB-derived primary human B cells offers an unprecedented opportunity for studying developmental B lymphopoiesis and modeling B-cell malignancies.

The Notch ligand DLL4 specifically marks human hematoendothelial progenitors and regulates their hematopoietic fate.

Notch signaling is essential for definitive hematopoiesis, but its role in human embryonic hematopoiesis is largely unknown. We show that in hESCs the expression of the Notch ligand DLL4 is induced during hematopoietic differentiation. We found that DLL4 is only expressed in a sub-population of bipotent hematoendothelial progenitors (HEPs) and segregates their hematopoietic versus endothelial potential. We demonstrate at the clonal level and through transcriptome analyses that DLL4(high) HEPs are enriched in endothelial potential, whereas DLL4(low/-) HEPs are committed to the hematopoietic lineage, albeit both populations still contain bipotent cells. Moreover, DLL4 stimulation enhances hematopoietic differentiation of HEPs and increases the amount of clonogenic hematopoietic progenitors. Confocal microscopy analysis of whole differentiating embryoid bodies revealed that DLL4(high) HEPs are located close to DLL4(low/-) HEPs, and at the base of clusters of CD45+ cells, resembling intra-aortic hematopoietic clusters found in mouse embryos. We propose a model for human embryonic hematopoiesis in which DLL4(low/-) cells within hemogenic endothelium receive Notch-activating signals from DLL4(high) cells, resulting in an endothelial-to-hematopoietic transition and their differentiation into CD45+ hematopoietic cells.

Transmissible cytotoxicity of multiple myeloma cells by cord blood-derived NK cells is mediated by vesicle trafficking.

Natural killer cells (NK) are important effectors of anti-tumor immunity, activated either by the downregulation of HLA-I molecules on tumor cells and/or the interaction of NK-activating receptors with ligands that are overexpressed on target cells upon tumor transformation (including NKG2D and NKP30). NK kill target cells by the vesicular delivery of cytolytic molecules such as Granzyme-B and Granulysin activating different cell death pathways, which can be Caspase-3 dependent or Caspase-3 independent. Multiple myeloma (MM) remains an incurable neoplastic plasma-cell disorder. However, we previously reported the encouraging observation that cord blood-derived NK (CB-NK), a new source of NK, showed anti-tumor activity in an in vivo murine model of MM and confirmed a correlation between high levels of NKG2D expression by MM cells and increased efficacy of CB-NK in reducing tumor burden. We aimed to characterize the mechanism of CB-NK-mediated cytotoxicity against MM cells. We show a Caspase-3- and Granzyme-B-independent cell death, and we reveal a mechanism of transmissible cell death between cells, which involves lipid-protein vesicle transfer from CB-NK to MM cells. These vesicles are secondarily transferred from recipient MM cells to neighboring MM cells amplifying the initial CB-NK cytotoxicity achieved. This indirect cytotoxicity involves the transfer of NKG2D and NKP30 and leads to lysosomal cell death and decreased levels of reactive oxygen species in MM cells. These findings suggest a novel and unique mechanism of CB-NK cytotoxicity against MM cells and highlight the importance of lipids and lipid transfer in this process. Further, these data provide a rationale for the development of CB-NK-based cellular therapies in the treatment of MM.

[Paravertebral and intra-abdominal abscess due to oxygen-ozone therapy for lower back pain]. / Absceso paravertebral e intraabdominal secundario a ozonoterapia por lumbalgia.

Complications secondary to oxygen-ozone therapy are rare, but they have been described in medical literature. There are only two cases of infectious complications after oxygen-ozone therapy. Our aim is to describe a rare case of purulent complication that was secondary to oxygen-ozone therapy for the treatment of lower back pain. We report the clinical improvement with conservative treatment for a local complication after percutaneous oxygen-ozone treatment. According to the clinical improvement of our patient, conservative treatment should be considered before any aggressive surgery.

Ligand-independent FLT3 activation does not cooperate with MLL-AF4 to immortalize/transform cord blood CD34+ cells.

MLL-AF4 fusion is hallmark in high-risk infant pro-B-acute lymphoblastic leukemia (pro-B-ALL). Our limited understanding of MLL-AF4-mediated transformation reflects the absence of human models reproducing this leukemia. Hematopoietic stem/progenitor cells (HSPCs) constitute likely targets for transformation. We previously reported that MLL-AF4 enhanced hematopoietic engraftment and clonogenic potential in cord blood (CB)-derived CD34+ HSPCs but was not sufficient for leukemogenesis, suggesting that additional oncogenic lesions are required for MLL-AF4-mediated transformation. MLL-AF4+ pro-B-ALL display enormous levels of FLT3, and occasionally FLT3-activating mutations, thus representing a candidate cooperating event in MLL-AF4+ pro-B-ALL. We have explored whether FLT3.TKD (tyrosine kinase domain) mutation or increased expression of FLT3.WT (wild type) cooperates with MLL-AF4 to immortalize/transform CB-CD34+ HSPCs. In vivo, FLT3.TKD/FLT3.WT alone, or in combination with MLL-AF4, enhances hematopoietic repopulating function of CB-CD34+ HSPCs without impairing migration or hematopoietic differentiation. None of the animals transplanted with MLL-AF4+FLT3.TKD/WT-CD34+ HSPCs showed any sign of disease after 16 weeks. In vitro, enforced expression of FLT3.TKD/FLT3.WT conveys a transient overexpansion of MLL-AF4-expressing CD34+ HSPCs associated to higher proportion of cycling cells coupled to lower apoptotic levels, but does not augment clonogenic potential nor confer stable replating. Together, FLT3 activation does not suffice to immortalize/transform MLL-AF4-expressing CB-CD34+ HSPCs, suggesting the need of alternative (epi)-genetic cooperating oncogenic lesions.

[Serum microRNA-21 usefulness in inflammatory pathology of the colon]. / Utilidad de la determinación sérica de microRNA-21 en la enfermedad inflamatoria del colon.

BACKGROUND: MicroRNAs are 20-22 nucleotide molecular structures with post-transcriptional activity that are involved in the immune response, as well as in the inflammatory pathways of different cells and tissues. AIMS: We present herein a prospective study in which serum microRNA-21 expression was determined in patients diagnosed with acute appendicitis as a model of bowel inflammation. MATERIAL AND METHODS: A prospective cohort study of patients diagnosed with acute appendicitis was conducted. Serum microRNA-21 was analyzed through the PCR of blood samples taken from the patients prior to surgery. MicroRNA-21 values were compared with the analytic variables (leukocytes, hemoglobin, hematocrit, platelets, prothrombin activity, glucose, urea, and creatinine) and the anatomopathologic variables (normal appendix, phlegmonous, gangrenous, and perforated acute appendicitis). RESULTS: A total of 60 patients with acute appendicitis diagnosis were consecutively included in the study from June to October 2009. Sixty-six percent of the patients were men (40 men and 20 women), with a mean age of 26.2±14.8 years. The mean absolute level of microRNA-21 was 24.8±0.93, whereas the mean microRNA-21 gene expression was 1.04±0.28. No correlation between the analytic and anatomopathologic parameters evaluated was observed (P=.47). CONCLUSIONS: It is necessary to continue to search for the most appropriate microRNAs, so that their determination in serum can lead to greater precision in establishing the diagnosis and outcome of inflammatory disorders of the bowel.

The MLL recombinome of acute leukemias in 2013.

Chromosomal rearrangements of the human MLL (mixed lineage leukemia) gene are associated with high-risk infant, pediatric, adult and therapy-induced acute leukemias. We used long-distance inverse-polymerase chain reaction to characterize the chromosomal rearrangement of individual acute leukemia patients. We present data of the molecular characterization of 1590 MLL-rearranged biopsy samples obtained from acute leukemia patients. The precise localization of genomic breakpoints within the MLL gene and the involved translocation partner genes (TPGs) were determined and novel TPGs identified. All patients were classified according to their gender (852 females and 745 males), age at diagnosis (558 infant, 416 pediatric and 616 adult leukemia patients) and other clinical criteria. Combined data of our study and recently published data revealed a total of 121 different MLL rearrangements, of which 79 TPGs are now characterized at the molecular level. However, only seven rearrangements seem to be predominantly associated with illegitimate recombinations of the MLL gene (≈ 90%): AFF1/AF4, MLLT3/AF9, MLLT1/ENL, MLLT10/AF10, ELL, partial tandem duplications (MLL PTDs) and MLLT4/AF6, respectively. The MLL breakpoint distributions for all clinical relevant subtypes (gender, disease type, age at diagnosis, reciprocal, complex and therapy-induced translocations) are presented. Finally, we present the extending network of reciprocal MLL fusions deriving from complex rearrangements.

The differentiation stage of p53-Rb-deficient bone marrow mesenchymal stem cells imposes the phenotype of in vivo sarcoma development.

Increasing evidence suggests that mesenchymal stem/stromal cells (MSCs) carrying specific mutations are at the origin of some sarcomas. We have reported that the deficiency of p53 alone or in combination with Rb (Rb(-/-) p53(-/-)) in adipose-derived MSCs (ASCs) promotes leiomyosarcoma-like tumors in vivo. Here, we hypothesized that the source of MSCs and/or the cell differentiation stage could determine the phenotype of sarcoma development. To investigate whether there is a link between the source of MSCs and sarcoma phenotype, we generated p53(-/-) and Rb(-/-)p53(-/-) MSCs from bone marrow (BM-MSCs). Both genotypes of BM-MSCs initiated leiomyosarcoma formation similar to p53(-/-) and Rb(-/-)p53(-/-) ASCs. In addition, gene expression profiling revealed transcriptome similarities between p53- or Rb-p53-deficient BM-MSCs/ASCs and muscle-associated sarcomagenesis. These data suggest that the tissue source of MSC does not seem to determine the development of a particular sarcoma phenotype. To analyze whether the differentiation stage defines the sarcoma phenotype, BM-MSCs and ASCs were induced to differentiate toward the osteogenic lineage, and both p53 and Rb were excised using Cre-expressing adenovectors at different stages along osteogenic differentiation. Regardless the level of osteogenic commitment, the inactivation of Rb and p53 in BM-MSC-derived, but not in ASC-derived, osteogenic progenitors gave rise to osteosarcoma-like tumors, which could be serially transplanted. This indicates that the osteogenic differentiation stage of BM-MSCs imposes the phenotype of in vivo sarcoma development, and that BM-MSC-derived osteogenic progenitors rather than undifferentiated BM-MSCs, undifferentiated ASCs or ASC-derived osteogenic progenitors, represent the cell of origin for osteosarcoma development.

Only in patients with hormone-dependent breast infiltrating ductal carcinomas, CA15.3 serum levels are inversely correlated with the immunohistochemical expression of Bcl2.

OBJECTIVE: To study possible association between serum CA15.3 levels and immunohistochemical expression of Bcl2 in women affected by infiltrating ductal breast carcinomas. MATERIALS AND METHODS: Two hundred and fifty consecutives women with breast infiltrating ductal carcinomas, aged between 37 and 83 years were included in this study. Serum CA15.3 was determined by electro-chemoluminescence assay (ECLIA-Elecsys 170 Roche). Immunohistochemical staining on tissue sections of 4-5 microns was done by the EnVision method with a heat-induced antigen retrieval step. Antibody used for Bcl2 was (124, Dako, dilution 1/150). Bcl2 expression was assessed as negative (-), weak positive (+) or strong positive (++). RESULTS: In the study group, serum CA15.3 concentrations ranged between 1 and 1743 U/ml, with 25, 50 and 75 percentiles of 12.7, 17.6 and 24.3 U/ml respectively. Serum CA15.3 concentrations were higher in Bcl2 negative cases than in Bcl2 + and Bcl2 ++. We found statistically significant differences between subgroups Bcl2 negative and Bcl2 ++ (p=0.044), between Bcl2 + Bcl2 ++ (p=0.039) and between Bcl2 ++ and Bcl2 -/+ (p=0.013). When we considered 25 U/mL as the threshold of positivity, antigen values>25 U/ml were more frequent in tumors Bcl2- than in Bcl2 ++ (20/52 vs 29/170, p=0.001). The same behavior was observed when comparing the subgroups -/+ with ++ (p=0.001). A very important aspect of our work was that this CA15.3 behavior in relation to the immunohistochemical expression of Bcl2 was maintained in hormone-dependent tumors (ER+), but not in hormone-independent ones. CONCLUSIONS: The results led us to the following consideration: In women affected by infiltrating ductal breast carcinomas, serum levels of CA15.3 associated inversely, both qualitatively and quantitatively, with the immunohistochemical expression of Bcl2, but this fact exists only in hormone-dependent tumors.

Prognostic significance of FLT3 mutational status and expression levels in MLL-AF4+ and MLL-germline acute lymphoblastic leukemia.

There is barely any information about the prognostic significance of FLT3 expression and mutational status in cytogenetically distinct subgroups of acute lymphoblastic leukemia (ALL). We analyzed the presence of FLT3-tyrosine kinase domain (TKD) and FLT3-internal tandem duplication (ITD) mutations as well as FLT3 expression levels in 54 newly diagnosed patients with B-ALL (n=49) or T-ALL (n=5). All B/T-ALL samples tested negative for the presence of FLT3-TKD or FLT3-ITD. None of the T-ALL and E2A-PBX1+ B-ALL overexpressed FLT3. In contrast, mainly MLL-AF4+ B-ALL but also ETV6-RUNX1+, BCR-ABL+ or B-ALL displaying normal cytogenetics exhibited significantly higher FLT3 expression levels than normal bone marrow, supporting that aberrantly increased transcription of FLT3, rather than activating FLT3 mutations, contributes to the pathogenesis of these B-ALL. Using the median FLT3 expression as cut-off value we found that high-level FLT3 expression is associated with an extremely poor 1-year overall survival (OS; 0 vs 71%; P=0.002) and disease-free survival (DFS; 0 vs 43%; P=0.03) in MLL-AF4+ B-ALL but not in MLL-germline B-ALL. Cox regression analysis with OS/DFS as end points showed that age>14 years and high-level FLT3 expression were independent prognostic factors when all ALL patients were analyzed together. Importantly, when the MLL-AF4+ B-ALL subgroup was analyzed separately, high-level FLT3 expression was the only independent prognostic factor for OS and treatment outcome. These findings indicate that high FLT3 expression identifies MLL-AF4+ ALL patients at very high risk of treatment failure and poor survival, emphasizing the value of ongoing/future clinical trials for FLT3 inhibitors.