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FLT3 internal tandem duplication (FLT3

Aberrant transcriptional programs are cardinal features of Acute Myeloid Leukemia (AML). Recently, it has been shown that specific distal cis-regulatory elements called enhancers communicate with promoters through 3-D DNA looping to regulate tissue-specific gene expression. Recurrent mutations in epigenetic regulators that modify enhancers, transcription factors that bind enhancers and the structural proteins that promote DNA looping, such as the Cohesin complex and its major binding partner CTCF have been demonstrated in AML. However, how these mutations regulate chromatin and alter 3D-DNA topology and communication between enhancers and promoters to generate leukemia-specific transcriptional programs remains poorly understood. In addition, many AML cases lack mutations in epigenetic regulators, transcription factors or DNA structural proteins, yet still demonstrate aberrant transcription, suggesting indirect effects of other mutations on enhancer function and the epigenetic landscape. To address these questions, we have utilized an allelic series of mice carrying the most common mutations in AML, namely Flt3-ITD and Npm1c (co-mutated in ~15% of all AMLs). These model different "transition states" (normal: wild type (WT), Pre-Malignant: single mutant (SM) with either Flt3-ITD or Npm1c mutations and Malignant: double mutant (DM)) during AML induction. Moreover, our design allows analysis of the SM mice to deconvolute the contribution of individual mutations to altered chromatin regulation. We have analyzed hematopoietic stem and progenitor cells (HSPCs) from WT and mutant mice for gene expression (RNA-seq), chromatin activation states (ChIP-seq for H3K4me1, H3K4me3, H3K27ac and H3K27me3), chromatin accessibility (ATAC-seq), and promoter-anchored 3-D chromatin interaction (promoter capture HiC, pCHiC)(Figure 1) and have integrated these analyses to determine the transcriptional, epigenetic and DNA-topological evolution of AML. Through pairwise comparisons between mutant and WT HSPCs, our data demonstrated that SM cells, with either Flt3-ITDor Npm1c mutations, alter gene expression only very modestly. However, when both mutations are present in DM cells, much larger gene programs that drive leukemia are both up- and downregulated. To examine the epigenetic regulation of these programs, we next built an enhancer compendium across all 4 allelic states using the H3K4me1 mark. Layering on H3K27ac activation, our data demonstrated that, in contrast to gene expression, significant alterations in enhancer specification and activation occur in advance of gene expression changes, to "prime" critical genes in Flt3-ITD, but not in Npm1c HSPCs. By contrast, Flt3-ITD and Npm1c mutations both altered global chromatin accessibility, with losses and gains evident at multiple critical genes. Similarly, our pCHiC data demonstrated significant alterations in DNA topology in mutant HSPCs that culminate in alterations in DNA "compartments" in DM HSPC. Moreover, they identified "hardwired" and "rewired" interactions between promoters and enhancers important for expression of critical leukemia programs. Analyses of all of these separate layers demonstrated a uniform pattern; progressive alterations in the transition from SM to DM HSPCs. Integrating these layers of analysis clearly demonstrated synergy between the mutations and a correlation between gene expression changes and chromatin dynamics in mutant cells. Furthermore, performing de novo motif analysis suggested a signal-specific transcription factor (TF) network downstream of Flt3-ITD that was amplified in the DM HSPC and that was corroborated by GSEA analysis. Our data had identified long-range regulatory control regions at the Spi1/PU.1 and Hoxa cluster loci amongst many others, and motif analysis had suggested Hox and Pu.1 to be important TFs in our malignant networks. Using these as examplars, we then perturbed the genes and regulatory elements at these loci by shRNA knockdown and CRISPR-mediated excision and could abrogate leukemic growth, validating the importance of our proposed networks. Taken together, these integrated analyses demonstrate a highly dynamic and coordinated process, where the effects of individual mutations synergize to remodel the chromatin landscape and 3D-DNA topology to generate networks that initiate and maintain AML transcriptional programs. Figure Disclosures Vassiliou: Kymab Ltd: Consultancy, Other: Minor Stockholder; Oxstem Ltd: Consultancy; Celgene: Research Funding.

Introduction: For more than a decade, bortezomib (V) has become an integral part of initial treatment of AL amyloidosis It is cytotoxic to plasma cells. We report published literature on efficacy and safety of bortezomib based regimens in patients (pts) with newly diagnosed amyloidosis (ND-AL). Methods: Following PRISMA guidelines, we performed a comprehensive literature search for articles published after 2007 using Pubmed, Embase, Clinical Trials.gov, Cochrane Library and Web of Science. Initially, 649 articles were identified and after a thorough screening, we finalized 9 studies involving 213 ND-AL patients. Prospective (n=91) and retrospective (n=122) studies were included. MeSH terms and keywords were bortezomib and newly diagnosed AL amyloidosis. Results: Chemotherapy followed by HDCT versus frontline HDCT / ASCT: In a retrospective study involving 31 pts by Scott et al., with induction chemotherapy with V-based regimens (n=12), with non-V-based regimens (n=6) and frontline (n=13) high dose melphalan (HDM) therapy followed by autologous stem cell transplant (ASCT). Overall hematological response (OHR) and organ response (OR) rates in the entire cohort after ASCT were 77% and 58% respectively. OHR and OR were 92% & 75% in V-pretreated group and 69% & 54% in pts who received no treatment. The trend was similar for other responses (Table 1). In a clinical trial by Huang, X., et al., induction therapy with Vd (V in combination with dexamethasone) prior to HDM/SCT was compared with frontline HDM/SCT in 58 patients. The OHR, and complete response (CR) between Vd+HDM/SCT (20 evaluable pts) and frontline HDM/SCT (23 evaluable pts) groups were 85.7% versus 53.5% and 67.9% versus 35.7% respectively. All organs showed better response in Vd+HDM/SCT group (Table 1). Vd/CyBorD (Cyclophosphamide, bortezomib, dexamethasone) prior to ASCT: In a prospective clinical trial by Sanchorawala et al., 35 pts were given induction with Vd before HDM and ASCT. Among 27 evaluable pts, OHR was 100% with CR in 76.9% and very good partial response (VGPR) in 23% pts. In a study by Hong et al., 20 patients received induction with Vd or CyBorD prior to ASCT. OHR was 89% with CR in 55%, partial response (PR) in 10% and VGPR in 33%. 5-year overall survival (OS) was 80% and 5-year progression free survival (PFS) was 69%. Vd/CyBorD without ASCT: In a retrospective study by Zhao et al., 23 pts received Vd. OHR was 100% with CR in 44% and PR in 38.9% pts. Median overall survival (mOS) was 38 months and 3-year OS was 41-72%. OR was 25% with kidney being the organ showing response in maximum pts (84%). Kikukawa et al., reported 8 pts who received CyBorD, OHR was 100% with CR in 50%, PR in 25% and VGPR in 25% pts. 63% pts showed OR in heart and/or kidney. In a study by Huang, B., et al., Vd was given to 12 renal ND-AL pts and among 10 evaluable pts, OHR was 80% with CR in 50% and PR in 10%. mOS was 8.2 months and OR was 50%. Other Regimens: In a study by Lee et al., involving 19 pts, VMP (bortezomib, melphalan, prednisone) was given as induction therapy. OHR was 84% with CR in 37%, PR in 26% and VGPR in 21% pts. OS was 39% at 2 years and PFS was 8 months. OR was 53% with heart (50%) and kidney (40%). In a retrospective review by Chari et al., 9 pts were treated with a triplet regimen (V, cyclophosphamide or lenalidomide/thalidomide and d). OHR was 88% with CR in 22% and PR in 66% pts. OR was 77% with heart and kidney both at 44%. Conclusion: In ND-AL pts, V-based combination regimens are very effective and well tolerated as induction therapy, or when used as therapy prior to HDM/ASCT and this approach resulted in better outcomes when compared to frontline HDM/ASCT. Three drug combination therapy with V is effective. Kidney and heart were the major organs to show improvement with therapy. Novel combinations need to be studied in randomized prospective clinical trials. Disclosures Anwer: In-Cyte: Speakers Bureau; Seattle Genetics: Membership on an entity's Board of Directors or advisory committees.

BACKGROUND: Patients with relapsed and/or refractory non-Hodgkin's lymphoma (NHL), especially those with aggressive lymphomas, have overall poor prognosis. Novel targets and therapies are under investigation. Molibresib (GSK525762) is a potent and specific inhibitor of the bromodomain and extraterminal domain (BET) family of proteins, the inhibition of which prevents transcriptional complex assembly and the subsequent expression of oncogenic drivers. Molibresib inhibits growth in NHL cell lines, both in vitro and in vivo. Study BET116183 was designed to evaluate the safety, tolerability, and preliminary efficacy of molibresib in relapsed and refractory hematologic malignancies. Here we report the results from the NHL dose escalation cohort. METHODS: Eligible subjects were adults with relapsed or refractory NHL. An accelerated dose titration was employed with one subject per dose level until the occurrence of a ≥Grade 2 drug-related toxicity; thereafter, subjects were enrolled in a standard 3+3 design. A Neuenschwander continual reassessment method (N-CRM) model was used to provide guidance for the next dose level. Dose escalation continued until the maximum tolerated dose (MTD) was identified. All data, including safety, tolerability, pharmacokinetics (PK), and efficacy, were used to identify the recommended part 2 dose (RP2D). RESULTS: From 14 May 2014 to the data cutoff date of 24 June 2018, 27 NHL subjects were enrolled and received at least one dose of study drug. Of these, 19 (70%) had B-cell lymphomas (diffuse large B-cell lymphoma [DLBCL], mantle cell lymphoma, marginal zone lymphoma, follicular lymphoma , and Burkitt's lymphoma); eight subjects (30%) had T-cell lymphomas (cutaneous T-cell lymphoma [CTCL], anaplastic T-cell lymphoma [ATCL], peripheral T-cell lymphoma, and adult T-cell leukemia/lymphoma). The median age was 64 years (range 24 to 76); 20 subjects (76%) were male and 7 subjects (24%) were female. The median number of prior treatments was 3 (range 1 to > 4). From the starting dose of 10 mg molibresib orally once daily (QD), the dose was escalated to 80 mg QD. The median time on study was 1.4 months (range 0.2 to 20 months). Two dose-limiting toxicities (DLTs) were identified in subjects treated at 60 mg QD, though one was subsequently determined not to be a DLT. One subject experienced Grade 4 thrombocytopenia related to study drug. A second subject experienced a Grade 2 mechanical fall; this event was later revised to unrelated to study drug. Across all dose levels, all subjects experienced an adverse event (AE); 25 subjects (93%) experienced at least one AE that was deemed to be related to molibresib treatment. The most common related AEs across all dose levels were thrombocytopenia (n = 21 [78%]), fatigue (n = 6 [22%]), nausea (n = 6 [22%]), diarrhea (n = 4 [15%]), and rash (n = 4 [15%]). Blood bilirubin was increased in 3 subjects (11%), and prothrombin time and activated partial thromboplastin time were prolonged in 2 subjects each (7%). Common Grade 3 and Grade 4 related events included thrombocytopenia (n = 19 [70%]), as well as anemia, asthenia, and increased blood bilirubin (n = 2 [7%] each). No Grade 5 related AEs were reported. Among all subjects, 11 (41%) required dose reduction for toxicity: 7 subjects at the 60 mg dose level (39% treated at that dose) and 4 at the 80 mg dose level (57% treated at that dose). PK analyses showed dose-proportionality after single and repeat dosing, with large variability between subjects. One subject with DLBCL achieved a complete remission that was durable through week 54 on study. Four additional subjects (one DLBCL and 3 CTCL) achieved partial remission, for an objective response rate (ORR) of 5/27 (18.5%). Five more subjects had stable disease as best response. Of six CTCL/ATCL subjects enrolled, three subjects had partial response for an ORR of 50% in this sub-population. CONCLUSIONS: This is the first study evaluating the safety and efficacy of the BET inhibitor molibresib in NHL subjects. Overall, thrombocytopenia and other AEs were monitorable, manageable and reversible. The RP2D was identified as 60 mg QD. Single-agent activity was observed across multiple NHL subtypes at both 60 mg and 80 mg doses; most notable was a 50% response rate in subjects with CTCL. Because of the promising data, Part 2 of the BET116183 study is currently open and enrolling subjects with CTCL to better define the clinical activity of BET bromodomain inhibition in this histology. Disclosures Dickinson: GSK: Consultancy. Kamdar:Genentech: Consultancy; Seattle Genetics: Speakers Bureau. Mateos:Janssen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; GSK: Consultancy, Membership on an entity's Board of Directors or advisory committees; Amgen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; GSK: Consultancy, Membership on an entity's Board of Directors or advisory committees; Amgen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Takeda: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Abbvie: Consultancy, Membership on an entity's Board of Directors or advisory committees. Alegre:Janssen: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees; Takeda: Membership on an entity's Board of Directors or advisory committees; Amgen: Membership on an entity's Board of Directors or advisory committees. Kim:Roche: Research Funding; Mundipharma: Research Funding; J&J: Research Funding; Novartis: Research Funding; Kyowa-Kirin: Research Funding; Celltrion: Research Funding; Takeda: Research Funding. Martín:Janssen: Honoraria, Other: Travel expenses; Celgene: Consultancy, Honoraria, Other: Travel expenses; Roche: Consultancy, Honoraria, Other: Travel expenses; Servier: Honoraria, Other: Travel expenses. Horner:GSK: Employment. Winnberg:GSK: Employment. Mathew:GSK: Employment. Botbyl:GSK: Employment. Karpinich:GSK: Employment. Kremer:GSK: Employment. Dhar:GSK: Employment. Karadimitris:GSK: Research Funding; Gilead: Honoraria; Celgene: Research Funding.

Background: The γc-family of cytokines (IL-2, IL-4, IL-7, IL-9, IL-15, IL-21) control major immune responses and lymphocyte development. However, aberrant γc cytokine activity contributes to or pathologically drives human diseases including T-cell malignancies, graft-versus-host disease, and numerous autoimmune diseases (e.g., alopecia areata), where IL-2, IL-9, and IL-15 have been specifically implicated. Importantly, these multi-cytokine diseases are not effectively and safely treated by the currently available anti-cytokine approaches. Methods: BNZ-1 is the first of a novel class of rationally-designed, multi-cytokine inhibitors that selectively inhibits IL-2 and IL-15, and to a lesser degree, IL-9 signaling through the γc receptor, without affecting IL-4, IL-7, or IL-21. Preclinical proof-of-concept has been demonstrated in several animal models of T-cell malignancies (Nata et al., 2015 J Biol Chem), including Large Granular Lymphocyte Leukemia (LGL) and Adult T-cell Leukemia. In this open-label, single-dose, dose-escalation, first-in-human study conducted at a single center in the United States (NCT03046459), 18 healthy adults (n=3/cohort) received a single intravenous dose of 0.2, 0.4, 0.8, 1.6, 3.2 or 6.4 mg/kg infused over ≤5 minutes on Day 1 and were followed for safety and sample collection for 30 days. Results: All subjects completed the study. BNZ-1 was considered well-tolerated with a good safety profile with no serious or severe adverse events (AEs), no dose-limiting toxicities, and no clinically-significant changes on clinical labs (serum biochemistry, hematology, liver enzymes), vital signs or electrocardiograms. Headache was the only AE reported in ≥1 subject (n=3). BNZ-1 exposure was generally dose proportional with an elimination half-life of ~5 days across the range of doses tested, which is consistent with other PEGylated peptides and supports weekly or every other week dosing. The pharmacodynamic activity of BNZ-1 was characterized by flow cytometry of PBMCs obtained on Days 4, 15 and 31 and used to calculate the maximum change from baseline (Emax) for regulatory T-cells (Tregs; IL-2 effect), NK cells (IL-15 effect) and CD8+ central memory T-cells (Tcm; IL-2 & IL-15 effect). For Tregs, a ~50-60% decrease was observed on Day 4 after doses of 0.4 to 1.6mg/kg, while doses of 3.2 and 6.4mg/kg produced an 80-93% decrease from baseline that peaked on Day 15. NK cells were decreased from baseline on Day 4 by 20%, 40% and 60% at 0.2, 0.4 and 0.8mg/kg, respectively, and plateaued at 70 to 80% decrease at doses ≥1.6 mg/kg. Tcm were decreased at Day 4 for the three highest dose cohorts that continued to decline to Day 15 when all doses, except 0.2 mg/kg, showed a mean decrease ranging from 10 to 81% that generally trended with dose. Tregs, NK cells, and Tcm returned to/toward baseline by 30 days post dose. Post-dose counts of CD4+ and CD8+ T-cells, B-cells, and monocytes were unchanged at all time points studied. Conclusions: These preliminary clinical data suggest that BNZ-1 is a highly-active, selective immunomodulator that safely decreases Tregs, NK cells and Tcm, while leaving the major leukocyte populations unaffected. These data support the planned Phase 1/2 dose-ranging study in LGL and Cutaneous T-cell Lymphoma. Disclosures Frohna: Bioniz Therapeutics: Employment. Tagaya: Bioniz Therapeutics: Equity Ownership. Ratnayake: Bioniz Therapeutics: Consultancy. Doerr: Bioniz Therapeutics: Employment. Basheer: Bioniz Therapeutics: Employment. Al-Mawsawi: Bioniz Therapeutics: Employment. Kim: Bioniz Therapeutics: Employment. Azimi: Bioniz Therapeutics: Employment.

Background Massive transfusion (MT) has been defined as transfusion of ≥10 red blood cell units in 24 hours or half the blood volume (≥5 units) in 4 hours. Launceston General Hospital is a 330 bed hospital in regional Australia and we developed critical bleeding - massive transfusion protocol in accordance with the National Blood Authority (Australia) patient blood management guidelines. In 2012 we developed a system by which blood samples on all the MT patients are flagged as 'super-urgent', and our lab staff will perform assays for full blood counts, coagulation profile, crossmatch and biochemistry immediately and communicate to the clinicians, providing a rapid turnaround time. We sourced a dedicated blue specimen bag for MT for easy identification of blood specimens (both hand delivered and via Lamson tube) by the lab staff. We postulate that this system is both practical and achievable in hospitals dealing with MT and has the potential to improve patient outcomes and reduce wastage of blood components, when compared to empirical use. Methods We performed a retrospective analysis on the data collected for patients who underwent MT for 4 years between January 2012 and December 2015. All the patients who had critical blood loss requiring ≥10 units of packed red cells within a 24 hour period or ≥5 units within a 4 hour period were included in our study. The clinical and lab parameters were collected from the MT data entry sheets. Full blood counts (FBC) were performed by Sysmex XE-5000 and coagulation assays on the plasma (PT, aPTT and fibrinogen) by Sysmex CS2100i analyser. The turnaround time (TAT) from specimen reception at the lab to authorization of results for each of the super-urgent episodes sent in blue specimen bags (FBC and coagulation assays) were extracted from the laboratory information system. Clotted and hemolysed specimens were excluded. Data on blood components transfused and clinical outcomes across different clinical settings were reviewed. Statistical analyses were performed with Graph-Pad Prism software (Version 6.01, San Diego, CA). Results A total number of 127 MT episodes in 125 patients were included in the study. The median age was 63 years (range: 20-89) with 73 males (58%) and 52 females (42%). Table1 presents the details of blood component management. For the 127 MT episodes, there were a total of 265 super-urgent FBC and 285 super-urgent coagulation assays. We observed that median TAT for super-urgent tests were significantly lower than the median of average TAT calculated for urgent tests performed in the lab on the same days of MT for both FBC (10 minutes [IQR: 6-16] vs 31 minutes [IQR: 27-36], P Conclusion Many current MT protocols are based on empirical therapy to maintain the ratio of packed red cells to FFP and packed red cells to platelets. Short TAT and rapid communication of lab results to the clinicians during MT episodes will provide real-time estimation of the coagulation system and aid in more appropriate usage of blood components when compared to empirical administration. In our cohort of MT patients, we were able to achieve shorter TAT for super-urgent than urgent FBC and coagulation assays. Point-of-care (POC) hemostasis testing devices are currently used in MT settings; however their main limitations are accuracy, testing performed by non-lab-trained personnel and quality assurance. Hence lab FBC and coagulation tests with rapid TAT can provide better directed information for management of MT. We also observed that mortality rates in our cohort were lower than seen in comparable studies. Based on our retrospective analysis, we postulate that rapid TAT of lab results contributed to the low mortality rates by assisting our clinicians in the rational management of blood components and avoidance of under-treatment or over-treatment. This is a pilot study which will form the basis for prospective randomised studies to fully evaluate the true utility of the system. We believe this pragmatic solution will contribute to improved patient outcomes and optimise the appropriate use of precious resources in the setting of critical bleeding massive transfusion. Disclosures No relevant conflicts of interest to declare.

Loss-of-function mutations of the cyclic-AMP response element binding protein, binding protein (CREBBP) gene have recently been described at high frequencies across a spectrum of lymphoid malignancies, particularly follicular lymphoma (FL) and diffuse large B-cell lymphoma (DLBCL). The multiple effects of this epigenetic regulator on developmental and homeostatic processes have been extensively studied, however, exactly how CREBBP functions as a tumor suppressor and the reasons for its particular predilection for suppression of lymphoid tumors remains unclear. In addition, for many mature lymphoid malignancies, the existence of cancer stem cells is unproven and their provenance and the initial target cell for transformation a source of ongoing debate. Here we use multiple mouse strains to model loss of Crebbp in different lymphoid compartments to address these questions. We demonstrate that early loss of Crebbp in hematopoietic stem and progenitor cells (HSPC), through disruption by the Mx1-Cre recombinase, leads to increased development of hematological malignancies, particularly of the B-lymphoid lineage that mimic features of human lymphomas. Theses B-cell malignancies are of long latency and are preceded by significant alterations in the proliferation, self-renewal and differentiation of lymphoid progenitors, allowing hyperproliferative lymphoid progenitors whose differentiation is blocked to accumulate. Using an aberrant surface phenotype that resembles the eventual tumor, we identify a pre-malignant population in the peripheral blood of animals that is often evident many months before any disease characteristics. We demonstrate pre-malignant stem cell characteristics for this population in functional experiments, where it generates high level reconstitution of peripheral blood in transplant recipients, but only gives rise to disease in these animals after a long latency. We also utilize this unique cellular population in longitudinal genome scale analyses (clonality, RNA-Seq, ChIP-Seq and exome sequencing) to document the mechanisms of malignant evolution. Linking the increased rate of mutation we describe to Crebbp loss, we also demonstrate increased DNA damage and an altered DNA-damage response in premalignant lymphoid progenitors. Importantly, using a Cd19-Cre recombinase that excises only within committed lymphoid cells, we are able to demonstrate that when Crebbp is lost at a later stage of lymphoid development, the marked cellular abnormalities described above are completely lost and the development of tumors is no different from normal (Figure, below). Taken together, these findings define the developmental stage-specific tumor suppressor functions of Crebbp and shed light on the cellular origins and subsequent evolution of lymphoid malignancies. In addition, the altered response to DNA damage that we demonstrate upon loss of Crebbp, allied to the increased exposure to physiological DNA-damage during lymphoid ontogeny offers an explanation for the high incidence of CREBBP mutations in mature lymphoid malignancies. Figure Left panel, Kaplan Meier graph for Mx1-Cre Crebbp mice with loss of Crebbp in the HSPC compartment demonstrates significantly shorter survival vs WT littermates with intact expression of Crebbp. In contrast, when Crebbp is excised in a later lymphoid compartment through Cd19-Cre mediated recombination, right panel, no difference in survival is noted from WT littermate controls. Figure. Left panel, Kaplan Meier graph for Mx1-Cre Crebbp mice with loss of Crebbp in the HSPC compartment demonstrates significantly shorter survival vs WT littermates with intact expression of Crebbp. In contrast, when Crebbp is excised in a later lymphoid compartment through Cd19-Cre mediated recombination, right panel, no difference in survival is noted from WT littermate controls. Disclosures Huntly: Novartis: Speakers Bureau; BMS: Speakers Bureau; Ariad: Speakers Bureau; Pfizer: Speakers Bureau.

Background Remarkable improvements in the treatment of childhood acute lymphoblastic leukemia (ALL) have been achieved primarily because of the work of cooperative groups such as the Children’s Oncology Group. The objective of the present study was to compare survival outcomes among children with standard-risk (SR) B-precursor acute lymphoblastic leukemia (ALL) treated at Princess Norah Oncology Center, Jeddah, Saudi Arabia, with survival outcomes of the Children’s Cancer Group-1991 (CCG-1991). Methods A retrospective study of newly diagnosed SR B-precursor ALL children during the period January 2000 to December 2007 and treated on CCG-1991 protocol following the oral methotrexate/double delayed intensification arm (regimen OD). Medical records of patients were reviewed. Data collected include: age, sex, WBC, date of: diagnosis, remission, induction, relapse, death, last follow-up; cytogenetics, phenotype at diagnosis, CNS status, toxicity, and outcome. Statistical Analysis Overall survival (OS) was calculated from the time of diagnosis to the time of death from any cause or until the last follow-up for surviving patients. Event-free survival (EFS) was measured from the date of diagnosis until the occurrence of first event (failure to achieve remission, relapse, death from any cause, or until the last follow-up). Kaplan-Meier method was used to estimate survival rates. Results A total of 123 SR B-precursor ALL patients were treated following CCG-1991 (regimen OD). The median duration of follow up was 7 (range: 0.03 – 11.7) years. Median age was 3.9 (range: 1.5 – 9.6) years and the median WBC count was 5.6 (range: 0.9 – 16.7) x 109/L. There were 67 male patients accounting for 54.5% compared to 56 (45.5%) females. The 5-year EFS and OS for SR B-precursor ALL patients were 79.4%±3.7% and 86%±3.2%, respectively. In total, 19 (15.4%) patients had relapse as first event. Death as first event occurred in 6 (4.9%) patients. Of this, 3 (2.4%) occurred during induction, and 3 (2.4%) occurred while in remission. Comparison of treatment outcomes revealed that our patients had inferior 5-year EFS and OS compared to those reported in the CCG-1991 study (EFS and OS rates of 90.7%±0.9% and 96.2%±0.6%; respectively). The difference is significant and may have been due to treatment regimen, as all our patients were treated with regimen OD. However, when comparison was limited to patients treated with regimen OD in the CCG-1991 study (EFS and OS rates of 88.7%±1.4% and 96%±0.9%; respectively), the difference in survival outcome remained significant. Conclusion We postulate that clinical and biological factors may have contributed for the outcome to vary between the present and the CCG-1991 study. The high incidence of death as first event in our patient population may be related to these factors and deserves further exploration. The fact that our patients were not on clinical trial and were treated following a standard protocol may have contributed to this variation. This underscores the need to further refine risk stratification. Disclosures: No relevant conflicts of interest to declare.

Abstract 4957 Multiple myeloma (MM), a disease usually observed in elderly patients, is extremely rare below 30 years of age. We present a case of a MM in a 10-year-old boy who has been admitted in September 2007 to the paediatric unit from the university hospital in Montpellier, with a fracture of his left femoral bone after a rugby match. In his history, he was known to present a juvenile myelomonocytic leukaemia (JMML) when he was 4-month-old in December 1998. For this diagnosis, he has been treated with aracytine and hydroxyurea for 4 years and he got a complete response (CR) since July 2005. At admission, surprisingly the radiography showed two lytic bone lesions. At MRI, it was found proximal and distal medullar metadiaphyseal spreading associated to a fracture, with no clinical symptom. The histology of the two tissue biopsies showed large dystrophic plasma cells, MI 15 positive with no clear evidence of a monoclonality by using light chain immunostaining. The bone marrow biopsy showed an interstitial infiltrate of dystrophic plasma cells, with only lambda light chain expression. Five percent of dystrophic plasma cells were observed on bone marrow smears. The monoclonal component IgG Lamda was 3.56 G/dL. Free kappa and lambda light chain dosages were respectively 5.65 mg/L and 766 mg/L, with a kappa lambda ratio under 0.01. Proteinuria was 0.64 g/day, haemoglobin was 106 G/L, and Beta2 microglobulin was 2.6mg/L. There was no hypercalcaemia and serum albumin and creatinin clearance were normal. Plasma cell labelling index (PCLI) was 1.16 % in the bone marrow and 6.6 circulating plasma cells/μL were counted in peripheral blood. Unfortunately, gene expression profiling analysis failed due to the low number of cells. PET scan found multiple uptakes in femoral, vertebral costal and sternal bones. So, this boy presented a multiple myeloma with stage IIIA according to Durie Salmon staging and ISS (International staging system) I. He underwent nine cycles of bortezomib (1.3 mg/m2 D1, D4, D8, D11) and dexamethazone (40mg/D, D1 to D4) to reach a complete response. A myeloablative allogenic stem cell transplantation was performed from his sister the 11th of September 2008, with a regimen based on cyclophosphamide (60mg/Kg, D1, D2) and TBI 12Gy. The immunosuppressive regimen associated methotrexate (D1, D3, D6) and cyclosporine. The graft contained 4.14 ×108 MNC/kg, 4.19 106 CD34/Kg and 6.16 107 CD3/Kg. At Day 120, a full donor chimerism was obtained, with no GVHd, but the monoclonal component reappeared. He received only a single cycle of bortezomib and dexamethazone because of severe peripheral neuropathy and gastro-intestinal intolerance. A second CR has been obtained in June 2009. Minimal residual disease by flow cytometry will be soon performed in order to discuss donor lymphocyte infusions. We report a case of MM during the childhood that is extremely rare. Very few cases have been reported in the literature. In this particular case, the patient has been also treated for a JMML that may have a relationship with the MM. Unfortunately, no cytogenetic or DNA profiling has been performed. To our knowledge, it is the first time that such feature is reported. The overall survival (OS) reported by the Mayo clinic in a series of 10 children was 87 months that may suggests a better OS as compared to adults (Blade J, Kyle RA, Greipp PR. Multiple myeloma in patients younger than 30 years - Report of 10 cases and review of the literature. Arch Intern Med. 1996;156:1463-8). Disclosures No relevant conflicts of interest to declare.

FLT3 internal tandem duplication (FLT3ITD) mutations are common in acute myeloid leukemia (AML) associated with poor patient prognosis. Although new-generation FLT3 tyrosine kinase inhibitors (TKI) have shown promising results, the outcome of FLT3ITD AML patients remains poor and demands the identification of novel, specific, and validated therapeutic targets for this highly aggressive AML subtype. Utilizing an unbiased genome-wide clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 screen, we identify GLS, the first enzyme in glutamine metabolism, as synthetically lethal with FLT3-TKI treatment. Using complementary metabolomic and gene-expression analysis, we demonstrate that glutamine metabolism, through its ability to support both mitochondrial function and cellular redox metabolism, becomes a metabolic dependency of FLT3ITD AML, specifically unmasked by FLT3-TKI treatment. We extend these findings to AML subtypes driven by other tyrosine kinase (TK) activating mutations and validate the role of GLS as a clinically actionable therapeutic target in both primary AML and in vivo models. Our work highlights the role of metabolic adaptations as a resistance mechanism to several TKI and suggests glutaminolysis as a therapeutically targetable vulnerability when combined with specific TKI in FLT3ITD and other TK activating mutation-driven leukemias.