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VAF concordance

Supplementary Data file including supplementary methods and clinical case vignettes.

Reasons for not using recommended targeted therapy.

Patient sequencing data, by patient number and diagnosis.

Acute lymphoblastic leukemia (ALL) is the most common cancer diagnosed in childhood. Survival for patients following relapse remains poor, and achieving complete remission (CR) after relapse is the first critical step to cure. Carfilzomib is a proteasome inhibitor with an acceptable safety profile and clinical activity in adults with multiple myeloma but has not been assessed in children. The primary objective of this phase 1b study was to assess the safety and tolerability of carfilzomib combined with vincristine, dexamethasone, asparaginase, and daunorubicin (VXLD) in children with relapsed and/or refractory ALL.Patients aged 1-21 years (n = 24) received 4-week induction therapy with carfilzomib at dose levels of 27 mg/mFollowing dose escalation of carfilzomib, the recommended phase 2 carfilzomib dose was identified as 56 mg/mThese data support the use of carfilzomib in pediatric patients with relapsed and/or refractory ALL.

Plasmablastic lymphoma (PBL) is a rare subtype of aggressive large B-cell lymphoma, with a dismal prognosis despite aggressive therapies. New approaches are needed for those with refractory disease. PBL expresses antigens similar to multiple myeloma (MM), including B-cell maturation antigen (BCMA). Chimeric antigen receptor T-cell (CAR-T) therapy directed against BCMA has shown efficacy for the treatment of heavily pretreated MM with low rates of grades 3 and 4 cytokine release syndrome (CRS) and immune effector cell-associated neurotoxicity syndrome (ICANS) in a phase Ib/II trial (A Study of JNJ-68284528, a CAR-T Directed Against BCMA in Participants With Relapsed or Refractory Multiple Myeloma (CARTITUDE-1),NCT03548207). However, data for the use of BCMA CAR-T for treating PBL are lacking.We report a challenging case of multiple refractory PBL that emerged from B-cell acute lymphoblastic leukemia in an adolescent who failed to respond to an allogeneic hematopoietic cell transplant. The patient developed rapidly advancing disease despite withdrawal of immunosuppression, treatment with etoposide, ibrutinib, and daratumumab, prompting consideration of BCMA CAR-T (under emergency investigational new drug (eIND)). The patient achieved a complete remission (CR), without recurrent acute graft versus host disease (GVHD), CRS or ICANS after BCMA CAR-T therapy. BCMA CAR-T expansion was detected in vivo, peaking on day 15. The patient remains in CR for more than a year post CAR-T therapy, supporting consideration of immunotherapy for future patients with refractory PBL, a disease with few treatment options.

Relapse- and continuous complete remission (CCR)-associated pediatric acute myeloid leukemia (AML) patient bone marrows collected at the time of diagnosis (Dx), end of induction (EOI) and relapse were analyzed by single cell RNA sequencing. A novel AML blasts-associated 7-genes signature (CLEC11A, PRAME, AZU1, NREP, ARMH1, C1QBP, TRH) displayed a strong correlation with blast percentages and overall survival in the TARGET AML dataset (HR=2.3; P-value=.007). Distinct clusters of AML-blasts at Dx were observed for relapse- and CCR-associated samples with differential expression of genes associated with survival. Relapse-associated samples demonstrated enrichment of exhausted T cells and M2 macrophages as opposed to inflammatory M1 macrophages in CCR-associated samples at Dx. EOI treatment resistant blast cells overexpressed fatty acid oxidation, tumor growth and stemness genes. Also, a relapse-associated EOI samples T cells subset showed downregulation of MHC Class I and regulatory genes. Altogether, this study deeply characterizes pediatric AML relapse-/CCR-associated tumor microenvironment transcriptome landscape.

Relapse- and continuous complete remission (CCR)-associated pediatric acute myeloid leukemia (AML) patient bone marrows collected at the time of diagnosis (Dx), end of induction (EOI) and relapse were analyzed by single cell RNA sequencing. A novel AML blasts-associated 7-genes signature (CLEC11A, PRAME, AZU1, NREP, ARMH1, C1QBP, TRH) displayed a strong correlation with blast percentages and overall survival in the TARGET AML dataset (HR = 2.3; P-value = .007). Distinct clusters of AML-blasts at Dx were observed for relapse- and CCR-associated samples with differential expression of genes associated with survival. Relapse-associated samples demonstrated enrichment of exhausted T cells and M2 macrophages as opposed to inflammatory M1 macrophages in CCR-associated samples at Dx. EOI treatment resistant blast cells overexpressed fatty acid oxidation, tumor growth and stemness genes. Also, a relapse-associated EOI samples T cells subset showed downregulation of MHC Class I and regulatory genes. Altogether, this study deeply characterizes pediatric AML relapse-/CCR-associated tumor microenvironment transcriptome landscape.

Despite a remarkable increase in the genomic profiling of cancer, integration of genomic discoveries into clinical care has lagged behind. We report the feasibility of rapid identification of targetable mutations in 153 pediatric patients with relapsed/refractory or high-risk leukemias enrolled on a prospective clinical trial conducted by the LEAP Consortium. Eighteen percent of patients had a high confidence Tier 1 or 2 recommendation. We describe clinical responses in the 14% of patients with relapsed/refractory leukemia who received the matched targeted therapy. Further, in order to inform future targeted therapy for patients, we validated variants of uncertain significance, performed ex vivo drug-sensitivity testing in patient leukemia samples, and identified new combinations of targeted therapies in cell lines and patient-derived xenograft models. These data and our collaborative approach should inform the design of future precision medicine trials. Significance: Patients with relapsed/refractory leukemias face limited treatment options. Systematic integration of precision medicine efforts can inform therapy. We report the feasibility of identifying targetable mutations in children with leukemia and describe correlative biology studies validating therapeutic hypotheses and novel mutations. See related commentary by Bornhauser and Bourquin, p. 1322. This article is highlighted in the In This Issue feature, p. 1307

The relationship between the hematopoietic stem cell (HSC) population and its surrounding bone marrow microenvironment is a rapidly evolving area of research. Normal HSC processes rely heavily on a complex communication network involving various marrow niches. Although leukemogenesis largely results from abnormal genetic activity within the leukemia stem cell itself, mounting evidence indicates a significant contributory role played by marrow niche dysregulation. Furthermore, numerous instances of activating or inactivating germline mutations within marrow microenvironment cells have been shown to be sufficient for development of myelodysplastic syndrome, myeloproliferative neoplasm, and acute myeloid leukemia, even in the context of wild-type HSCs. Recent evidence suggests that targeting aberrant chemokine production from germline-mutated marrow stromal cells can potentially reverse the process of leukemogenesis. This elaborate interplay between the HSC population and the marrow microenvironment allows for a number of unique clinical possibilities in efforts to induce remission, enhance chemosensitivity, manage relapsed disease, and prevent leukemia development, both in de novo and germline mutation-associated leukemias, including the use of targeted cytokine/chemokine inhibitors, immune checkpoint blockade, CXCR4/CXCL12 axis antagonists, and combined allogeneic HSC and mesenchymal stem cell transplantation. In this review, we discuss the pathways underlying normal and abnormal bone marrow niche functioning, the relationship between germline mutations in the stem cell microenvironment and dysregulated hematopoiesis, and future clinical perspectives that may be particularly applicable to prevention and treatment of germline-associated leukemias.

Background Hyperleukocytosis is a serious, life-threatening complication of pediatric acute leukemia that can cause neurologic injury, pulmonary leukostasis, metabolic derangements, and coagulopathy. Acute leukemia has the highest risk of mortality and morbidity at presentation when associated with hyperleukocytosis. Infant leukemia presents unique challenges and treatment considerations due to the disease itself and size and overall health of the patient. While medical management of hyperleukocytosis in older patients with acute leukemia has been described, including cytoreductive procedures with automated leukapheresis (AL) or manual whole blood (WB) exchange transfusion, very little data exist for standardized management of hyperleukocytosis in infant leukemia patients. Case reports We describe four cases of infant acute leukemia presenting with hyperleukocytosis and leukostasis who each received manual WB exchange transfusions in conjunction with induction chemotherapy and review the existing literature on the use of procedural leukoreduction in infants with hyperleukocytosis. Special attention is given to challenges and technical aspects of leukapheresis in infants: when to perform manual WB exchange versus AL, optimal vascular access, blood product selection, exchange rates, and the monitoring for complications. Using published cases, we outline benefits versus risks of manual WB exchange and AL in infants less than 10 kg. Conclusion If providers perform procedural leukoreduction, the literature and our experience demonstrate manual WB exchange transfusion is favored over AL in infants less than 10 kg because of technical and complication risks associated with AL. Additional studies are needed to understand the impact of cytoreduction on long-term outcomes.

Salvage options for children with relapsed ALL remain sub-optimal, particularly for T-cell ALL, with disease refractoriness and further relapse remaining the leading cause of death. Achieving complete remission (CR) after relapse is the first critical step to cure. Combining the proteasome inhibitor (PI) bortezomib with chemotherapy showed promising CR rates in previous studies in pediatric ALL (Messinger 2012, Horton 2019, Bertaina 2017). We report a multicenter phase 1 pediatric trial for relapsed ALL (NCT02303821) investigating the second generation PI carfilzomib plus VXLD (vincristine, dexamethasone, PEG-asparaginase, daunorubicin) induction therapy. Carfilzomib plus UKALLR3 (dexamethasone, mitoxantrone, methotrexate, PEG-asparaginase, vincristine) was also evaluated but considered not tolerable (Burke 2019). Patients (pts) received 4 weeks of VXLD plus carfilzomib administered intravenously on days 1, 2, 8, 9, 15, and 16. Pts were recruited in cohorts of 3 dose-limiting-toxicity (DLT) evaluable pts, with carfilzomib dose escalation based on a Bayesian logistic regression model. Pts achieving ≥ stable disease post-induction, could receive a cycle of modified BFM consolidation therapy (mercaptopurine, cyclophosphamide, cytarabine, pegaspargase, vincristine) plus carfilzomib at the same dose level and schedule given during induction. Pts Of 16 DLT-evaluable pts, 2 DLTs were observed in the VXLD cohort among 8 DLT-evaluable pts at the 56 mg/m 2 dose level (pulmonary hemorrhage on day 1 [n=1] and G4 thrombocytopenia past day 45 of induction [n=1]). G3-4 hematological AEs occurred in 54% of pts. Non-hematological >G3 treatment emergent adverse events (TEAEs) of note are listed in Table 2. Serious TEAEs (SAEs) were reported in 58% of pts with the most common being bacteremia, acute pancreatitis, and posterior reversible encephalopathy syndrome (PRES; all n=2, 8%); both cases of PRES were considered carfilzomib related and occurred in pts given a prior allogeneic stem cell transplant. Three fatal TEAEs occurred within 30 days of the last dose, all in the 56 mg/m 2 cohort (multiorganism sepsis, pneumonia-unspecified, and leukemia). Both pts who died due to toxicity had refractory relapse 9 and 6 months after a stem cell transplant, respectively. The RP2D was identified as 56mg/m 2. PK assays demonstrated no significant age-related differences in area under the curve across age groups or between children and adults (Table 3). Pharmacodynamic assays indicated complete suppression of proteasome activity in peripheral blood at dose levels >27 mg/m 2. Among all pts (n=24), 21% (n=5) achieved CR; 29% (n=7) CRi or CRp; 8% (n=2) partial response (PR); 17% (n=4) stable disease (SD); 8% (n=2) progressive disease; 8% (n=2) were not evaluable (NE); 8% (n=2) died without response assessment. CR/CRp/CRi by dose are listed in Table 2. All pts with CRi or better recovered full or partial hematological function by day 45 without evidence of leukemia progression. Twelve pts proceeded to consolidation, including 2 NE, 1 with PR, and 1 with SD at the end of induction. Ten pts (83%) who received consolidation were in remission on day 29 post-consolidation (CR, n=5; CRi/CRp, n=5), 1 was NE, and 1 remained in SD. Carfilzomib in combination with VXLD chemotherapy was found to be tolerable with promising efficacy in pediatric pts with highly advanced ALL. The RP2D of carfilzomib in this combination chemotherapy regimen was identified as 56 mg/m 2. Further efficacy and additional safety data are currently being investigated in phase 2 of this trial. Figure 1 Figure 1. Disclosures Ziegler: Amgen: Membership on an entity's Board of Directors or advisory committees; Bayer: Membership on an entity's Board of Directors or advisory committees. Bautista: Bayer: Consultancy; Amgen: Consultancy; Roche/Genentech: Consultancy, Honoraria; Eusa Pharma: Consultancy; Sanofi: Membership on an entity's Board of Directors or advisory committees. Gore: Sanofi Paris: Current equity holder in publicly-traded company; Anchiano: Current equity holder in publicly-traded company; Blueprint Medicines: Current equity holder in publicly-traded company; Roche/Genentech: Consultancy, Honoraria; Mirati: Current equity holder in publicly-traded company; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees; Amgen: Consultancy, Current equity holder in publicly-traded company, Honoraria, Membership on an entity's Board of Directors or advisory committees; Clovis: Current equity holder in publicly-traded company; Celgene: Current equity holder in publicly-traded company, Membership on an entity's Board of Directors or advisory committees. Locatelli: Amgen: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Novartis: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Miltenyi: Speakers Bureau; Medac: Speakers Bureau; Jazz Pharamceutical: Speakers Bureau; Takeda: Speakers Bureau. O'Brien: Jazz: Honoraria; Pfizer: Honoraria, Research Funding. Obreja: Amgen: Current Employment, Current equity holder in publicly-traded company. Morris: Amgen: Current Employment, Current equity holder in publicly-traded company. OffLabel Disclosure: Carfilzomib is approved in the United States for the treatment of adult patients with relapsed or refractory multiple myeloma. It has not been approved for use in pediatric patients with ALL.

Background Infections represent a significant cause of morbidity and mortality in pediatric patients undergoing treatment for hematologic malignancies. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection has led to a worldwide pandemic of coronavirus disease 2019 (COVID-19) and pediatric patients with cancer appear to be at higher risk of severe disease than reported in the general pediatric population. Data are limited on the optimal management of children infected with SARS-CoV-2 and a new diagnosis of leukemia. The objective of this study was to describe our experience of six children who presented with a new diagnosis of acute leukemia and concurrent COVID-19. Methods The study was IRB approved and children were enrolled following informed consent and assent as appropriate for age. The clinical presentations, serologic responses, treatments, and outcomes of patients who presented with acute leukemia and concurrent SARS-CoV-2 infection were abstracted. Residual blood was tested by ELISA for quantitative IgG to the SARS-CoV-2 spike protein receptor binding domain (RBD). Results From March 1, 2020 to Dec 31, 2020, 6 patients were identified with a new diagnosis of acute leukemia and SARS-CoV-2 infection including 3 with acute myeloid leukemia (AML) and 3 with acute lymphoblastic leukemia (ALL). The median age of our cohort was 9 years old (range 1 to 19 years old), 5 of 6 were male, and 4 of 6 patients were Hispanic. All 6 patients presented with symptoms that could be attributed to COVID-19 or acute leukemia, with fever being the most common. All 3 of the AML patients presented with hyperleukocytosis (white blood cell count > 50 x 109/L) and required oxygen therapy and intensive care. At the time of presentation, all patients with specimens available (n=5) had IgG antibodies to SARS-CoV-2 RBD. All patients received COVID-19 directed therapy, with remdesivir (n=5) and convalescent plasma (n=5) being the most common. Chemotherapy was modified or delayed in 5 of the 6 patients. The patient who received standard AML chemotherapy without awaiting COVID-19 directed treatment had delayed serologic response, delayed viral clearance from the nasopharynx, protracted respiratory failure, and ultimately died. For patients with a 12-week follow-up (n=5), 2 patients with AML had died, and the ALL patients were in remission and continuing their leukemia treatment. Conclusion COVID-19 may present concurrently in children with new onset leukemia resulting in severe morbidity and mortality. Our experience adds to growing evidence that children with AML and SARS-CoV-2 infection are at risk for severe COVID-19. Screening for SARS-CoV-2 infection with subsequent delay in chemotherapy and administration of COVID-19 directed therapies should be considered for pediatric patients with newly diagnosed acute leukemia and COVID-19.

Summary Treatment with dose-adjusted EPOCH (etoposide, doxorubicin, cyclophosphamide, vincristine, prednisone) chemotherapy and rituximab (DA-EPOCH-R) has become the standard of care for primary mediastinal B-cell lymphoma (PMBCL) at many institutions despite limited data in the multi-centre setting. We report a large, multi-centre retrospective analysis of children and adults with PMBCL treated with DA-EPOCH-R to characterize outcomes and evaluate prognostic factors. We assessed 156 patients with PMBCL treated with DA-EPOCH-R across 24 academic centres, including 38 children and 118 adults. All patients received at least one cycle of DA-EPOCH-R. Radiation therapy was administered in 14·9% of patients. With median follow-up of 22·6 months, the estimated 3-year event-free survival (EFS) was 85·9% [95% confidence interval (CI) 80·3–91·5] and overall survival was 95·4% (95% CI 91·8–99·0). Outcomes were not statistically different between paediatric and adult patients. Thrombotic complications were reported in 28·2% of patients and were more common in paediatric patients (45·9% vs. 22·9%, P = 0·011). Seventy-five per cent of patients had a negative fluorodeoxyglucose positron emission tomography (FDG-PET) scan at the completion of DA-EPOCH-R, defined as Deauville score 1–3. Negative FDG-PET at end-of-therapy was associated with improved EFS (95·4% vs. 54·9%, P

Introduction: While advances in front-line conventional chemotherapy have increased the likelihood of attaining remission in pediatric AML, relapse rates remain high (25-35%), and novel therapies are needed (Zhang, Savage et al. 2019). The clinical and molecular heterogeneity of AML makes it complex to study and creates challenges for the development of novel therapies (Bolouri, Farrar et al. 2018). It is important to identify cells and pathways underlying relapse to facilitate development of novel therapies. Single-cell RNA Sequencing (scRNA-Seq) allows in-depth analysis of the heterogeneous AML landscape to provide a detailed view of the tumor microenvironment, revealing populations of blasts and immune cells which may be relevant to relapse or complete remission. Methods: We analyzed ~36,500 cells from 14 pediatric AML bone marrow samples in our institutional biorepository, spanning different AML subtypes and 3 healthy children to generate a comprehensive scRNA-Seq landscape of immature AML-associated blasts and microenvironment cells. Samples collected at the time of diagnosis (Dx), end of induction (EOI), and relapse (Rel) were used to generate scRNA-Seq data using a droplet-based barcoding technique (Panigrahy, Gartung et al. 2019). After normalization of scRNA-Seq data, the cell clusters were identified using principal component analysis and Uniform Manifold Approximation and Projection (UMAP) approach (Becht et al, 2018). Differential expression, pathways and systems biology analysis between relapsed and remission patients reveal differences for specific cell clusters (Panigrahy, Gartung et al. 2019). To determine the clinical outcome association of our AML blast specific markers, survival analysis was performed on AML TARGET data (https://ocg.cancer.gov/programs/target) using cox proportional hazard survival approach. To characterize AML blast cells with high accuracy, we used support vector machine (SVM), an Artificial Intelligence based feature extraction and model development approach (Bhasin, Ndebele et al. 2016). Results:ScRNA-Seq analysis of paired Dx and EOI samples using UMAP identified three blast cell clusters with significant gene expression differences among different patients, indicating heterogeneity of AML blast cells (Fig 1a, b). Comparative analysis of the three Dx enriched blast cell clusters with other cells identified a "core blast cell signature" with overexpression of genes like AZU1, CLEC11A, FLT3, and NREP (Fig 1c). These core AML-blast genes were linked to significant activation of the Wnt/Ca2+, Phospholipase C, and integrin signaling pathways (Z score >2 and P-value The scRNA-Seq of AML specific blast cells from relapsed and remission samples exhibited a different clustering pattern indicating different transcriptome landscapes. Relapse-associated AML cell clusters expressed high levels of AZU1, S100A4, LGALS1, and GRK2 genes (Fig 2a). Analysis of the non-AML tumor microenvironment demonstrated enrichment of T/NK in relapsed samples, with differential expression of T cell regulatory/activation genes (Fig 2b, c). ScRNA-Seq showed enrichment of monocyte/macrophage cell clusters in remission samples with distinct relapse- and remission-specific clusters. Remission associated macrophage/monocyte clusters showed overexpression of S100A10, FTH1, CST3 and IFITM2 genes (Fig 2d). Similarly, enrichment of T cell and monocyte/macrophage clusters was observed in relapse and remission samples respectively during EOI. Conclusions: Using single cell transcriptomics we developed a novel potential gene signature to characterize heterogenous AML blast populations with high sensitivity. These genes and the pathways they regulate implicate potential therapeutic targets in pediatric AML. Single cell transcriptome analysis also enabled identification of cell clusters with modulated gene expression at both Dx and EOI that may be useful in predicting relapse/remission. Disclosures Bhasin: Canomiiks Inc: Current equity holder in private company, Other: Co-Founder.

Germline activating mutations of the protein tyrosine phosphatase SHP2 (encoded by PTPN11), a positive regulator of the RAS signalling pathway, are found in 50% of patients with Noonan syndrome. These patients have an increased risk of developing leukaemia, especially juvenile myelomonocytic leukaemia (JMML), a childhood myeloproliferative neoplasm (MPN). Previous studies have demonstrated that mutations in Ptpn11 induce a JMML-like MPN through cell-autonomous mechanisms that are dependent on Shp2 catalytic activity. However, the effect of these mutations in the bone marrow microenvironment remains unclear. Here we report that Ptpn11 activating mutations in the mouse bone marrow microenvironment promote the development and progression of MPN through profound detrimental effects on haematopoietic stem cells (HSCs). Ptpn11 mutations in mesenchymal stem/progenitor cells and osteoprogenitors, but not in differentiated osteoblasts or endothelial cells, cause excessive production of the CC chemokine CCL3 (also known as MIP-1α), which recruits monocytes to the area in which HSCs also reside. Consequently, HSCs are hyperactivated by interleukin-1β and possibly other proinflammatory cytokines produced by monocytes, leading to exacerbated MPN and to donor-cell-derived MPN following stem cell transplantation. Remarkably, administration of CCL3 receptor antagonists effectively reverses MPN development induced by the Ptpn11-mutated bone marrow microenvironment. This study reveals the critical contribution of Ptpn11 mutations in the bone marrow microenvironment to leukaemogenesis and identifies CCL3 as a potential therapeutic target for controlling leukaemic progression in Noonan syndrome and for improving stem cell transplantation therapy in Noonan-syndrome-associated leukaemias.

Objective: SARS-CoV-2 infection has led to a worldwide pandemic of COVID-19 (coronavirus disease 2019), placing individuals with pre-existing medical conditions at a higher risk for morbidity and mortality. Limited data in pediatric patients with malignancies suggest that severe COVID-19 illness is rare. The objective of this study was to describe our experience of two adolescents who presented with new diagnoses of acute myeloid leukemia (AML) and concurrent COVID-19. Methods: The clinical presentation, treatment, and serology of two patients who presented with AML and concurrent SARS-CoV-2 infection were abstracted. Residual blood was tested for serial quantitative IgG by ELISA to the SARS-CoV-2 spike protein receptor binding domain, which has high sensitivity and specificity to SARS-CoV-2. The study was approved by Children’s Healthcare of Atlanta and Emory University IRBs. Results: Patient 1 was a 16-year-old Caucasian male with previously treated classical Hodgkin’s lymphoma who presented with fever, cough, hyperleukocytosis, and pulmonary infiltrates and was diagnosed with therapy-related AML (TR-AML). SARS-CoV-2 was detected by nasopharyngeal (NP) RT-PCR testing on admission. He received remdesivir for treatment of COVID-19 and modified induction therapy with cytarabine alone starting on hospital day (HD) 3. He demonstrated high SARS-CoV-2 IgG titer (1:1327.3) on HD 4 and cleared SARS-CoV-2 with a negative NP RT-PCR on HD 14. He went on to receive additional myelosuppressive AML therapy on HD 26 with azacitidine and gemtuzamab ozogamicin. On HD 34, his IgG titer remains elevated (1:5621.4) and he is currently awaiting count recovery. Patient 2 was a 19-year-old Hispanic, previously healthy male who presented with fever, cough, dyspnea, and hyperleukocytosis and was diagnosed with de novo AML (D-AML). He also tested positive for SARS-CoV-2 via NP RT-PCR on admission. He began standard induction therapy with cytarabine, etoposide, and daunorubicin on HD 2. He developed hypoxemic respiratory failure on HD 4 and received COVID-19 directed therapies of convalescent plasma, remdesivir, and tocilizumab. His serologic testing showed low SARS-CoV-2 IgG titer (1:619.3) on HD 4 despite administration of convalescent plasma. His titers waned over the subsequent two weeks and he continued to test positive for SARS-CoV-2 via NP RT-PCR on HD 21. He remains critically ill in multiorgan failure with signs of neutrophil recovery on HD 25. Conclusion: COVID-19 can be severe in children with AML and make treatment decisions challenging. Clinical presentation, curative modalities (hematopoietic stem cell transplantation for TR-AML versus potentially chemotherapy alone for D-AML), and concurrent COVID-19 were considered in determining induction therapy. While difficult to draw definite conclusions from two patients, the differential serologic response in these patients seems to correlate with the intensity of therapy they received and may have contributed to the overall severity of their COVID-19. Citation Format: Pratik A. Patel, Christina A. Rostad, Stacey A. Lapp, Claire L. Stokes, Melinda G. Pauly, Evan J. Anderson, Himalee S. Sabnis. Clinical features and antibody response of two pediatric patients presenting with new-onset acute myeloid leukemia and concomitant severe COVID-19 [abstract]. In: Proceedings of the AACR Virtual Meeting: COVID-19 and Cancer; 2020 Jul 20-22. Philadelphia (PA): AACR; Clin Cancer Res 2020;26(18_Suppl):Abstract nr PO-012.

Salvage options for children with relapsed ALL remain sub-optimal, particularly for T-cell ALL patients, and relapse remains the leading cause of death. Achieving complete remission (CR) after relapse is the first critical step to cure. Combining the proteasome inhibitor (PI) bortezomib with chemotherapy has previously shown promising results in achieving CR in pediatric phase 2 studies in ALL (Messinger 2012, Horton 2013, Bertaina 2017). In this ongoing dose-escalation phase 1 study, the second generation PI carfilzomib was combined with chemotherapy in children with relapsed ALL. Subjects received one 4-week cycle of induction chemotherapy with either UKALLR3 (dexamethasone, mitoxantrone, methotrexate, PEG-asparaginase, vincristine) or VXLD (vincristine, dexamethasone, PEG-asparaginase, daunorubicin) plus carfilzomib administered intravenously on days 1, 2, 8, 9, 15, and 16. The primary endpoint was dose limiting toxicities (DLTs) occurring during induction (grade 4 neutropenia or thrombocytopenia extending past day 45 or grade 4 non-hematological toxicity). Efficacy endpoints included CR (with or without hematological recovery) based on bone marrow (BM) and LP on day 29 of induction and consolidation. Subjects < 21 years of age and diagnosed with first early BM relapse ( Ten subjects with B (n=9) or T- (n=1) cell ALL were treated with UKALLR3 at 2 carfilzomib dose levels (20 or 27 mg/m2, 5 subjects each). Among DLT-evaluable subjects, 3 DLTs (meningoencephalitis, hemolytic uremic syndrome and neutropenia) were observed, 2 at 27 and 1 at 20 mg/m2 dose levels with an MTD of 27 mg/m2. The UKALLR3 regimen was considered too toxic by the protocol steering committee and was replaced with VXLD in January 2016. The VXLD cohort started at 27 mg/m2 and is currently in the 56 mg/m2 dose level. Fifteen subjects (7 B-cell and 8 T-cell) were treated with VXLD at carfilzomib dose levels of 27 (n=3), 36 (n=7), 45 (n=4), and 56 (n=1) mg/m2. One DLT of posterior reversible encephalopathy syndrome (PRES) occurred in the 36 mg/m2 cohort, with no further DLTs identified after expansion to 7 subjects. Table 2 lists the patient characteristics of the 15 subjects in the VXLD cohort. Grade 3-4 hematological AEs were nearly universal for both UKALLR3 and VXLD. Non-hematological > Grade 3 AE's of note are listed in Table 1. PRES occurred in 2 subjects in the VXLD cohort (both with prior allogeneic SCT) and rapidly reversed in both cases. Re-challenge with carfilzomib in one case was tolerated without PRES recurrence. Serious AE's (SAE) were reported in 50% and 56% of subjects receiving carfilzomib in combination with UKALLR3 or VXLD, respectively, with the most common SAE's among all subjects being sepsis (16%), pancreatitis and PRES (8% each). In the UKALLR3 cohort, 60% of subjects (n=6) achieved a remission, however only 30% proceeded to consolidation. In the VXLD cohort, 53% of evaluable subjects (n=8) achieved remission and 13% were non-evaluable due to hypocellular BM at day 29 of induction. All responding subjects recovered hematological counts by day 42 without evidence of progression. Eight subjects (53%) proceeded to consolidation, including 2 subjects with non-evaluable BM results and 1 with 8% BM blasts after induction. All subjects entering consolidation were in remission on day 29 post-consolidation. The overall remission rate with VXLD-carfilzomib was 67% at the end of consolidation. Detailed response data are listed in Table 3. Carfilzomib in combination with VXLD chemotherapy was tolerable in a predominantly T-cell ALL population, very early or post stem cell transplant relapse. Efficacy is promising in this small cohort of patients with carfilzomib dose escalation continuing. Disclosures Burke: Amgen, Inc.: Consultancy, Speakers Bureau. Bautista Sirvent:EusaPharma: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other: Support for attending symposia; Takeda: Other: Support for attending symposia; Bayer: Consultancy, Membership on an entity's Board of Directors or advisory committees; Jazz Pharmaceuticals: Honoraria, Other: Support for attending symposia; Amgen, Inc.: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees. Gore:Amgen: Consultancy, Equity Ownership, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: travel expenses; Novartis: Consultancy, Other: Service on Data Safety Monitoring Committee; travel, accommodations, expenses; Roche/Genentech: Consultancy, Honoraria, Other: travel expenses; Anchiano: Equity Ownership, Other: spouse employment and company leadership; Blueprint Medicines: Equity Ownership; Celgene: Equity Ownership, Other: DSMC member; Clovis: Equity Ownership; Mirati: Equity Ownership; Sanofi Paris: Equity Ownership. Locatelli:Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Miltenyi: Honoraria; bluebird bio: Consultancy; Bellicum: Consultancy, Membership on an entity's Board of Directors or advisory committees; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees. O'Brien:BMS: Research Funding; Celgene: Research Funding; Pfizer: Research Funding; AbbVie: Research Funding; Amgen: Research Funding; BTG: Research Funding. Obreja:Amgen, Inc.: Employment, Equity Ownership. Morris:Amgen, Inc.: Employment, Equity Ownership. Baruchel:Novartis: Consultancy, Honoraria; Servier: Consultancy, Honoraria; Bellicum: Consultancy; Celgene: Consultancy, Honoraria. OffLabel Disclosure: Kyprolis is a proteasomal inhibitor indicated in combination with dexamethasone or with lenalidomide plus dexamethasone for the treatment of patients with relapsed or refractory multiple myeloma who have received one to three lines of therapy. It is also indicated as a single agent for the treatment of patients with relapsed or refractory multiple myeloma who have received one or more lines of therapy.

Introduction: Pediatric and young adult patients (pts) with relapsed/refractory (R/R) acute leukemia have a poor prognosis. Selinexor is a first-in-class antagonist of exportin (XPO1) with single agent activity in adults with acute myelogenous leukemia (AML). Dose-defining non-hematologic toxicities in adult studies included nausea, weight loss and anorexia. Methods: DFCI Protocol 13-563 was a Phase I dose-escalation trial conducted at nine institutions to test the safety, tolerability and pharmacokinetic (PK) characteristics of selinexor administered to pediatric and young adult pts with R/R acute leukemias. Selinexor was orally administered twice weekly during 4-week cycles. Three dose levels (DLs) were tested (30 mg/m2, 40 mg/m2 and 56 mg/m2) with dose-escalation decisions based on standard 3+3 Phase I design rules. Required supportive care medications included antiemetics and bacterial prophylaxis. All grade ≥2 non-hematologic adverse events (AEs) were recorded with the exception of non-clinically significant grade 2 laboratory abnormalities. Grades 1-4 hematologic AEs were expected in a relapsed leukemia patient population and were not considered AEs. Results: Sixteen pts enrolled on study, including 5 with primary refractory disease and 7 with second or greater relapse; 6 pts had received prior hematopoietic stem cell transplant. Median age was 9.5 years (range 2.3-21.8). Twelve pts had AML and 4 had acute lymphoblastic leukemia (ALL). Median number of completed cycles was 1 (range 0-3). Thirteen pts (81%) were evaluable for dose limiting toxicity (DLT) assessment, having received at least 7 doses of selinexor during the first cycle. Of 9 pts enrolled at DL1 (30 mg/m2), 6 were DLT-evaluable; 1 pt experienced a DLT of grade 5 pancreatitis (possibly related to study treatment). Three pts enrolled at DL1 were not DLT-evaluable; 2 pts were removed from study due to disease progression and 1 pt died from complications of a pulmonary infection. Six pts enrolled at DL2 (40 mg/m2) and none experienced a DLT. One pt was treated at DL3 (56 mg/m2) and developed a DLT of cognitive impairment (grade 3). Further enrollment onto DL3 was suspended secondary to an amendment capping dose escalation at 40 mg/m2 (equivalent to recommended single-agent dose in adult AML). During Cycle 1, the most common selinexor treatment-related AE's were hyponatremia (31%), elevated alanine aminotransferase (25%), nausea (25%), hyperkalemia (25%), elevated aspartate aminotransferase (19%) and diarrhea (19%). The most common grade ≥ 3 selinexor treatment-related AE's were hyponatremia (31%), elevated alanine aminotransferase (19%), hyperglycemia (13%) and hyperkalemia (13%). In contrast to adults treated with selinexor, there were no cases of grade ≥ 3 weight loss or nausea and only one case of grade 3 anorexia. One AML pt, after 2 cycles, achieved a complete remission with incomplete recovery of platelet count and one ALL pt, after 1 cycle, achieved a partial response, resulting in a protocol-defined overall response rate of 12.5%. Two of 4 pts with ALL (one each in DLs 1 and 2) developed clinically significant (grade 4) TLS. These included the pt who achieved a PR and another pt with early T-cell precursor ALL. Overall, 9 pts (56%), including 6 AML and 3 ALL, experienced an objective response and/or an investigator-defined clinical benefit (e.g., reduction in transfusions, clearance of peripheral blasts, decreased pain) from therapy. Conclusions: Selinexor, at a doses of 30 or 40 mg/m2 given twice weekly, was well tolerated in pediatric and young adult pts with R/R acute leukemia, demonstrating single agent clinical activity and less GI toxicity than had been seen in adults. The high frequency of TLS in ALL pts is particularly notable as treatment of ALL with selinexor has not been previously reported. Analysis of pharmacokinetic and correlative biology studies are underway. Based on the results of this Phase I study, the recommended Phase II dose of single-agent selinexor in children with R/R acute leukemia is 40 mg/m2 administered twice weekly. These results also support the continued investigation of selinexor in combination with multiagent chemotherapy. Disclosures Burke: AMGEN: Speakers Bureau; JAZZ: Speakers Bureau; Shire: Speakers Bureau.

Despite the remarkable pace of characterizing the genomics of pediatric acute leukemias, the integration of real-time sequencing results into clinical practice has lagged. With increased availability of molecularly-targeted therapies, the promise of matching genetic lesions in patients' leukemia cells to treatment has not yet been fully realized. We established the first pediatric leukemia clinical genomics consortium in the United States, known as the Leukemia Precision-based Therapy (LEAP) Consortium, which includes 13 major pediatric cancer institutions. We hypothesized that it is feasible to identify and match, in real-time, actionable alterations with a targeted therapy for pediatric patients with relapsed, refractory or high-risk leukemias or myelodysplastic syndrome (MDS). Using a combination of a DNA-based next-generation sequencing panel and RNA-based gene fusion testing, followed by data review by our multidisciplinary molecular tumor board, we are conducting a clinical trial to test this hypothesis. To date, we have enrolled and reviewed data from 143 patients stratified by disease status: Cohort 1, patients with relapsed or refractory leukemias (n=93), and Cohort 2, patients with de novo high-risk leukemias or MDS (n=50). A matched targeted therapy (MTT) recommendation has been made for 72% (n=103) of patients, tiered based on the level of evidence linking the mutation to potential activity of targeted therapy in the context of each patient's disease (Tier 1: 11%, Tier 2: 4%, Tier 3: 41%, Tier 4: 6%, Tier 5: 10%). Of the 44 patients in Cohort 1 with clinical follow-up data, 5 (11%) had alterations in therapy made based upon sequencing results and MTT recommendation. These include the use of the MEK inhibitor trametinib for RAS mutant acute myeloid leukemia (AML) and acute lymphoblastic leukemia (ALL) (n=2), dasatinib for B-ALL and T-ALL with NUP214-ABL1 translocations (n=2) and ponatinib for B-ALL with an ABL1 T315I mutation (n=1). In addition, this genomic data refined diagnosis and supported additional germline assessment in a subset of patients. In parallel to the genomic sequencing, we are conducting high-throughput drug sensitivity (HTS) assays to study in vitro anti-leukemia effects of a panel of up to 120 targeted inhibitors in the context of leukemia-associated genetic alterations. Of the initial 106 accrued patients, 40 (38%) had adequate amounts of blood or bone marrow for in vitro drug testing. All samples were tested in the inhibitor panel assay, and 65% of the samples yielded interpretable results. Inhibitor screening data was compiled for all 12 patients with genetic alterations resulting in Tier 1, 2 or 3 MTT recommendations. This subset of patients had leukemias with two distinct molecular profiles: 1) oncogenic RAS signaling pathway mutations or 2) oncogenic tyrosine kinase alterations. Our molecular tumor board recommended trametinib for the first group of patients and tyrosine kinase inhibitors (TKIs), specific to the mutation, for the second group of patients. In vitro HTS data analysis demonstrated dose-response sensitivity of leukemia cells with RAS pathway mutations to trametinib, many of which had half-maximal inhibitory concentration (IC50) less than 50 nM. Similarly, leukemia cells from patients with FLT3, ABL1 or KIT mutations generally showed dose-responses to relevant TKIs with low IC50s. Overall, HTS data were concordant with MTT recommendations informed by the sequencing results. This first in the US multi-institutional prospective leukemia genomics trial brings state-of-the-art clinical genetic testing, assessment of prognostic biomarkers, selection of patients for germline testing, and targeted therapeutic treatment recommendations to children and young adults with high-risk, relapsed or refractory leukemias or MDS. Our collaboration provides a unique opportunity to perform sophisticated patient-specific in vitro drug testing assays to impact MTT discovery efforts, which we plan to validate in vivo using patient-derived xenograft models where feasible. We believe that a model like the LEAP Consortium has the potential to transform precision medicine approaches for children with high-risk leukemias and to inform future genomics-guided therapeutic trials and drug discovery efforts. Disclosures Tasian: Aleta Biopharmaceuticals: Membership on an entity's Board of Directors or advisory committees; Gilead Sciences: Research Funding; Incyte Corporation: Research Funding. Burke:JAZZ: Speakers Bureau; Shire: Speakers Bureau; AMGEN: Speakers Bureau. Tyner:AstraZeneca: Research Funding; Vivid Biosciences: Membership on an entity's Board of Directors or advisory committees; Takeda: Research Funding; Janssen: Research Funding; Array: Research Funding; Constellation: Research Funding; Gilead: Research Funding; Aptose: Research Funding; Incyte: Research Funding; Genentech: Research Funding.

Introduction: MLL-rearranged (MLL-r) acute leukemia in children is characterized by young age at presentation and a poor overall prognosis despite multi-agent chemotherapy. Aberrant fusion proteins involving the MLL histone methyltransferase (HMT) recruit another HMT, DOT1L, to a multi-protein complex leading to aberrant methylation of histone H3 lysine 79 (H3K79) at MLL target genes. This results in enhanced expression of critical genes for hematopoietic differentiation, including HOXA9 and MEIS1, and has been established as a key mechanism for leukemogenesis in MLL-r leukemias (Krivstov, 2007). Pinometostat is a small molecule inhibitor of DOT1L with sub-nanomolar affinity and >37,000 fold selectivity against non-MLL HMTs. Treatment of MLL-rearranged cells and xenograft models with pinometostat led to reduced histone 3, lysine 79 (H3K79) methylation, decreased MLL target gene expression and selective leukemia cell kill (Daigle, 2013). We report the preliminary safety, pharmacokinetics (PK), pharmacodynamics (PD) and target inhibition in leukemia cells of pinometostat in a phase 1 trial in children with relapsed/refractory (R/R) MLL-r acute leukemia. Methods: An open label dose escalation study of pinometostat was performed in patients (pts) aged 3 months to 18 years (yr) with R/R MLL-r leukemia (NCT02141828). Pinometostat was administered via continuous intravenous infusion until disease progression or unacceptable toxicity. Pts were assigned to one of two aged-based dose escalation schemas developed from simulations of pediatric exposures using a previously reported physiologically-based PK (PBPK) model (Waters, 2014). All patients underwent serial collection of PK and peripheral blood mononuclear cells (PBMC) for PD. Leukemic blasts were isolated from PBMCs using flow cytometry and quantified for di-methylation of H3K79 (H3K79-me2) by ChIP-Seq. Results: As of 28-June-2015, 11 pts have enrolled in the dose escalation of the study consisting of 10 pts (6 pts at 70 mg/m2/day, 4 pts at 90 mg/m2/day) in the older age cohort (1 to 18 yr) and 1 pt (45 mg/m2/day) in the younger age cohort ( Table 1. Patient Characteristics n (%) Median age, yrs (range) 4 (0.33 - 15) Sex (M / F) 6/5 Diagnosis AML 5 (45) ALL 4 (36) MLL 2 (18) # of prior therapeutic regimens 1 - 2 4 (36) 3 - 7 6 (54) 8 - 10 0 >10 1 (9) Prior allogeneic hematopoietic cell transplant 6 (54) Adverse events (AEs) reported in >3 pts regardless of attribution were: anemia, febrile neutropenia, abdominal pain, diarrhea, nausea, vomiting, pain, grade 1 prolonged QTcF, lymphopenia, thrombocytopenia, leukopenia, hypocalcemia, hypokalemia, hypophosphatemia, pleural effusion, respiratory failure, dry skin, rash and hypertension. Grade ≥3 related non-hematologic toxicities include: apnea (n=1 and the only protocol defined dose limiting toxicity), organizing pneumonia (n=1), anorexia (n=1), and febrile neutropenia (n=1). The median duration of treatment was 26 days (range 7- 53 days). Updated response data will be provided. Steady-state plasma concentrations (Css) of pinometostat in children >1 yr at 70 and 90 mg/m2 doses were comparable to that observed in adult patients at equivalent doses and were in the range of 800 - 1600 ng/mL, corroborating earlier PBPK modeling results (projected Css range of 1000-1600 ng/mL at 90 mg/m2/d in ≥1 yr). Steady-state CSF concentrations of pinometostat were low ( Conclusions: Pinometostat in children with R/R leukemia has an acceptable safety profile. Exposures of pinometostat in children were consistent with PBPK modeling based on adult exposure data, suggesting that dose/exposure relationships are similar between adults and children > 1 yr. Analysis of H3K79-me2 ChIP-Seq data demonstrated PD reductions in methylation of MLL-r target genes expected from DOT1L inhibition. Enrollment and dose escalation continue. Disclosures O'Brien: Seattle Genetics, Inc.: Research Funding. Pauly:Seattle Genetics, Inc.: Research Funding. Whitlock:Amgen: Honoraria. Thomson:Epizyme, Inc: Employment. Blakemore:Epizyme: Employment. Daigle:Epizyme, Inc: Employment. Pimentel:Epizyme, Inc: Employment. Waters:Epizyme, Inc: Employment. Armstrong:Epizyme, Inc: Consultancy. Ho:Epizyme, Inc: Employment.

Introduction: Treatment of relapsed childhood acute lymphoblastic leukemia (ALL) remains a significant clinical challenge with a need for novel, more effective therapies. Pre-clinical studies have demonstrated that mTOR inhibitors have single agent activity in ALL and are synergistic with other chemotherapy agents typically used to treat ALL, including vincristine, corticosteroids, doxorubicin and L-asparaginase. Methods: Dana-Farber Cancer Institute Protocol 11-237 tested the combination of everolimus (given orally on days 1-32) with a standard reinduction regimen of prednisone (40 mg/m2/daily orally on days 4-32), weekly vincristine (1.5 mg/m2/dose, max 2 mg, on days 4,11,18 and 25), PEG-asparaginase (2,500 U/m2/dose IV on days 5 and 18) and doxorubicin (30 mg/m2/dose on days 4 and 5) with dexrazoxane pretreatment (300 mg/m2/dose on days 4 and 5). Intrathecal cytarabine was administered on day 1 and intrathecal methotrexate, cytarabine and hydrocortisone (IT-MAH) was administered on days 18 and 32; patients (pts) with cerebrospinal fluid blasts at study entry received additional IT-MAH on days 11 and 25. Pts with first bone marrow relapse ALL occurring greater than 18 months after continuous remission were eligible for participation. The primary aim was to identify a maximum tolerated dose of everolimus in combination with this backbone utilizing a classic "3 + 3" dose escalation design. Three dose levels (DL) of everolimus were tested (2-, 3-, and 5-mg/m2/day). 5 mg/m2/day (DL3) was the highest dose tested because it was the recommended phase 2 dose (RP2D) of single-agent everolimus in children with solid tumors. Secondary aims included assessment of second complete remission (CR2) rate and levels of end-reinduction minimal residual disease (MRD) assessed by allele-specific oligonucleotide PCR. On-target activity of everolimus was assessed 6 hours after the first dose of everolimus by examining phosphorylated S6 (pS6) levels in peripheral blood blasts by flow cytometry. Results: Thirteen pts with first relapse B-ALL were enrolled. (Table 1) Median age at enrollment was 10 yrs (range: 2-22 yrs). Median duration of first CR was 3.7 yrs (range 1.5-7.7 yrs). One pt treated at DL 3 stopped study drug early due to Grade 4 infection (meningitis due to Rothia mucilaginosa ) and was inevaluable for dose limiting toxicity (DLT) assessment. Table 2 displays the most common Grade 2 or higher adverse events (AE's) attributable to everolimus. There were no Grade 5 events and no episodes of interstitial pneumonitis. No DLTs were observed at DL1 or DL2. One of 6 evaluable pts treated at DL3 experienced a DLT (Grade 4 hyperbilirubinemia). 12 of the 13 pts achieved CR (92%). Of the 12 pts who achieved CR, 9 (75%) had low end-reinduction MRD (²0.001). (Table 1) Of the 7 pts with evaluable samples (2 at DL1, 1 at DL2 and 4 at DL3), 6 (86%) had decrease in pS6 in peripheral blasts (>20% decrease in mean fluorescence intensity), consistent with on-target mTOR inhibition. Only 1 pt (treated at DL1) did not have evidence of pS6 inhibition; this pt achieved CR2 with low MRD. Discussion: Everolimus given in combination with a standard 4-drug reinduction was well tolerated at all dose levels tested in pediatric pts with first relapse ALL. CR2 rates were comparable to published re-induction regimens, with a promising proportion of pts with low end-reinduction MRD. An expansion cohort is currently enrolling to further assess toxicity of this combination, particularly infectious risks, in order to define the RP2D. | Pt # | Dose Level | Age (yrs) | Duration of CR1 (yrs) | DLT? | CR? | MRD | | ---- | ---------- | --------- | --------------------- | ---- | --- | ---- | | 001 | 1 | 10 | 7.7 | No | Yes | High | | 002 | 1 | 20 | 3.5 | No | Yes | Low | | 003 | 1 | 8 | 3.1 | No | Yes | Low | | 004 | 2 | 2 | 1.5 | No | Yes | High | | 005 | 2 | 22 | 5.1 | No | No | N/A | | 006 | 2 | 5 | 3.7 | No | Yes | Low | | 007 | 3 | 12 | 5.7 | No | Yes | Low | | 008 | 3 | 10 | 3.0 | N/A | Yes | Low | | 009 | 3 | 11 | 4.3 | No | Yes | Low | | 010 | 3 | 21 | 4.8 | Yes | Yes | High | | 011 | 3 | 7 | 3.4 | No | Yes | Low | | 012 | 3 | 13 | 5.0 | No | Yes | Low | | 013 | 3 | 17 | 3.0 | No | Yes | Low | Table 1. Patients and Response to Therapy | Toxicity | Grade 2 | Grade 3 | Grade 4 | Grade 5 | | ----------------------- | ------- | ------- | ------- | ------- | | Bacteremia | | 3 | | | | Bacterial meningitis | | | 1 | | | Invasive fungal disease | | 1 | | | | Febrile Neutropenia | | 7 | | | | Mucositis | 2 | 2 | | | | Anorexia | 3 | 1 | | | | AST increase | 1 | 5 | 2 | | | ALT increase | 1 | 5 | 2 | | | Bilirubin increase | | 2 | 1 | | | Hypophosphatemia | 2 | 5 | 1 | | Table 2. Grade 2 or higher Adverse Events Attributable to Everolimus (Possible, Probable, Definite) at all dose levels; N=13 patients Disclosures Pauly: Seattle Genetics, Inc.: Research Funding. Stegmaier: Novartis Pharmaceuticals: Consultancy.

Background Denintuzumab mafodotin (SGN-CD19A) is an antibody-drug conjugate (ADC) composed of a humanized anti-CD19 monoclonal antibody conjugated to the microtubule-disrupting agent monomethyl auristatin F (MMAF) via a maleimidocaproyl linker. CD19 is a B cell-specific marker that is expressed in nearly all patients (pts) with B-lineage acute leukemia or lymphoma. Methods A phase 1 dose-escalation study is ongoing to evaluate the safety, tolerability, pharmacokinetics, and antitumor activity of denintuzumab mafodotin in pts with relapsed or refractory (R/R) B-ALL, B-cell lymphoma (B-LBL), or Burkitt leukemia/lymphoma (NCT 01786096). Eligible pts are ≥1 year of age and are R/R to ≥1 prior systemic regimen; patients with Philadelphia chromosome-positive (Ph+) disease must have failed a 2nd-generation TKI. A modified continual reassessment method was used for dose allocation and maximum tolerated dose (MTD) estimation. The study evaluated 2 dosing schedules: first weekly (Days 1 and 8 of 21-day cycles) and then once every 3 weeks (q3wk). This report presents data from the adult subset of pts in the study (≥18 years). Results To date, 71 adult pts with R/R B-ALL (n=59), B-LBL (n=6) or Burkitt leukemia/lymphoma (n=6) have been treated; median age is 45 years (range 18−77). Pts received a median of 2 prior therapies (range 1−8); 20 pts (28%) had prior allogeneic stem cell transplant. On the weekly schedule (0.3−3 mg/kg), 40 pts received a median of 2 cycles (range 1−27); 2 pts remain on treatment. On the q3wk schedule (4−6 mg/kg), 31 pts received a median of 3 cycles (range 1−6); 4 pts remain on treatment. An MTD was identified at 5 mg/kg q3wk and was not reached with weekly dosing. Best clinical responses to date for pts with B-ALL are summarized below: Table 1.Response category per Cheson 2003Efficacy-evaluable adult pts with B-ALLweekly dosing, N=32 n (%)q3wk dosing, N=23 n (%)Complete remission (CR)6 (19)3 (13)CR with incomplete platelet recovery (CRp)−3 (13)CR with incomplete blood recovery (CRi)−2 (9)Partial remission (PR)1 (3)−Resistant disease with clinical benefit15 (47)12 (52)Resistant disease without clinical benefit2 (6)-Progression8 (25)3 (13)CRc (CR+CRi+CRp), % (95% CI)19% (95% CI 7, 36)35% (95% CI 16, 57) In the q3wk schedule, the CRc rate was similar at 4, 5, and 6 mg/kg. The median duration of response across schedules is currently 27 weeks (95% CI 7, −). Of 12 pts with CRc and available minimal residual disease (MRD) assessment, 7 were MRD negative. 3 patients with MRD-negative CRs have been in remission for >1 year, 2 of whom have been on continuous treatment for 19 and 22 months. In the subset of pts with Ph+ B-ALL, 4 of 8 pts achieved CR and 1 pt a PR. In 6 pts with Burkitt leukemia/lymphoma, 1 achieved a CR. In 6 pts with B-LBL, objective responses were 1 CR and 2 PR. The adverse event (AE) profiles were similar across both dosing schedules; the most frequently reported AEs were pyrexia (54%), nausea (52%), fatigue (51%), headache (44%), chills (38%), vomiting (37%), blurred vision (35%), and anemia (34%). Ocular symptoms and corneal exam findings consistent with superficial microcystic keratopathy were observed in 40 pts (56%); symptoms were less severe than the associated corneal exam findings. Keratopathy was managed with topical steroids and dose modifications, and improved/resolved within a median of ~3 wks (range 1-17) in pts with sufficient follow-up. ADC exposures increased with dose, and in leukemia patients, target-mediated disposition was observed that diminished with higher doses in the q3wk schedule. Post treatment, flow cytometry data demonstrate that unbound CD19 on peripheral blasts inversely correlates with ADC concentration in circulation, and is present in the majority of evaluable patients at the end of the q3wk cycle. Conclusions Denintuzumab mafodotin is generally well tolerated and demonstrates activity in heavily pretreated adult pts with B-ALL and B-lineage highly aggressive lymphomas, including durable MRD-negative responses. The results of this trial indicate that the q3wk schedule, with a CRc rate of 35% in B-ALL, warrants further clinical investigation. Based on the encouraging responses observed to date in Ph+ B-ALL (CRs in 4 of 8 pts), an expansion cohort of these pts is currently enrolling on the q3wk schedule. Disclosures Fathi: Exelexis: Research Funding; Agios: Membership on an entity's Board of Directors or advisory committees; Merck: Membership on an entity's Board of Directors or advisory committees; Seattle Genetics: Membership on an entity's Board of Directors or advisory committees, Research Funding; Ariad: Consultancy; Takeda Pharmaceuticals International Co.: Research Funding. Off Label Use: SGN-CD19A is an investigational agent being studied in patients with B-cell malignancies. SGN-CD19A is not approved for use.. Borate:Seattle Genetics: Research Funding; Genoptix: Consultancy; Alexion: Speakers Bureau; Gilead: Speakers Bureau; Novartis: Speakers Bureau; Amgen: Speakers Bureau. DeAngelo:Agios: Consultancy; Incyte: Consultancy; Celgene: Consultancy; Amgen: Consultancy; Pfizer: Consultancy; Bristol Myers Squibb: Consultancy; Ariad: Consultancy; Novartis: Consultancy. O'Brien:Seattle Genetics, Inc.: Research Funding. Trippett:OSI Pharmaceuticals: Research Funding; Seattle Genetics, Inc.: Research Funding. Shah:NCCN: Consultancy; SWOG: Consultancy; Seattle Genetics: Research Funding; Acetylon Pharmaceuticals, INC: Membership on an entity's Board of Directors or advisory committees; Pharmacyclics: Speakers Bureau; Bayer: Honoraria; Celgene: Consultancy, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Janssen: Speakers Bureau; DeBartolo Institute for Personlaized Medicine: Research Funding; Rosetta Genomics: Research Funding; Plexus Communications: Honoraria; Spectrum: Speakers Bureau. Hale:Seattle Genetics, Inc.: Research Funding; Hyundai: Research Funding; V Foundation: Research Funding. Silverman:Seattle Genetics, Inc.: Research Funding. Pauly:Seattle Genetics, Inc.: Research Funding. Kim:Bayer: Consultancy; Seattle Genetics, Inc.: Consultancy, Research Funding; Eli Lilly: Consultancy. Kostic:Seattle Genetics, Inc.: Employment, Equity Ownership. Huang:Seattle Genetics, Inc.: Employment, Equity Ownership. Pan:Seattle Genetics, Inc.: Employment, Equity Ownership. Chen:Genentech: Consultancy, Speakers Bureau; Seattle Genetics, Inc.: Consultancy, Other: Travel expenses, Research Funding, Speakers Bureau; Millennium: Consultancy, Research Funding, Speakers Bureau.