Search

Acute promyelocytic leukemia (APL) is a distinct subtype of acute myeloid leukemia (AML) that is characterized by a balanced translocation between chromosomes 15 and 17 [t(15;17)], which results in the fusion of the promyelocytic leukemia (PML) and retinoic acid receptor α (RARA) genes. Historically, APL was a fatal disease because of the high relapse rates with cytotoxic chemotherapy alone and a significant bleeding risk secondary to disseminated intravascular coagulation (DIC). However, APL is now one of the most curable hematological malignancies because of molecularly targeted therapies. With the advent of all-trans retinoic acid (ATRA) containing chemotherapy regimens, rates of complete remission and long-term, disease-free survival have improved dramatically. More recently, regimens incorporating both ATRA and arsenic trioxide (ATO) have allowed a substantial number of patients to be treated with little or no additional cytotoxic chemotherapy.

Introduction: We evaluated the impact of baseline (BL) co-mutations and FLT3-ITD VAF on overall survival (OS) and response (composite complete remission [CRc]) to quizartinib and SC in the phase III QuANTUM-R trial. Methods: We analyzed 37 recurrently mutated genes in AML in BL samples from 304 patients (pts) (83% of ITT population) with R/R FLT3-ITD-positive AML using next-generation sequencing and a customized Archer® Core Myeloid panel. Positive mutation status was defined as ≥1 mutation detected in the gene region using a VAF cutoff of 2.7%. FLT3-ITD VAF was measured by the Navigate BioPharma FLT3 Mutation Assay (polymerase chain reaction-based, VAF cutoff of 3%). Low and high FLT3-ITD VAF were defined as ≤25% and >25%, respectively. Results: In addition to FLT3-ITD, the prevalence of key BL co-mutations were 59.9% for DNMT3Amut and 55.3% for NPM1mut. Pts with DNMT3Amut treated with quizartinib had significantly longer OS vs SC (6.3 and 5.4 mos, respectively; hazard ratio [HR], 0.652), p Conclusions: Key co-mutations identified here potentially affect treatment response and OS with quizartinib vs SC. Our results suggest that molecular subsets of R/R AML pts may particularly derive clinical benefit from quizartinib. TableCRc, %Median OS, monthsQuizartinibSCQuizartinibSCHR95% CIITT Population (N = 367)a48276.24.70.760.58-0.98Single Gene Analyses (n = 304)bDNMT3Amut (n = 182)52376.35.40.6520.44-0.97DNMT3Awt (n = 122)40246.04.60.8490.53-1.37NPM1mut (n = 168)48395.14.70.9540.63-1.44NPM1wt (n = 136)47218.55.10.4850.31-0.76TET2mut (n = 98)34326.22.90.6640.38-1.16TET2wt (n = 206)54306.35.40.7280.51-1.05CEBPAmut (n = 46)44428.58.71.9220.80-4.62CEBPAwt (n = 258)48296.24.50.6130.45-0.84IDH1/2mut (n = 49)32275.53.70.4270.20-0.92IDH1/2wt (n = 255)51316.55.10.750.54-1.04Double Gene Analyses (n = 304)NPM1wt/DNMT3Amut (n = 44)61279.04.50.2390.09-0.61NPM1mut/DNMT3Amut (n = 138)50405.45.40.8370.52-1.34FLT3-ITD VAF AnalysesFLT3-ITD high VAF50195.53.90.6890.51-0.93FLT3-ITD low VAF43467.96.10.8570.53-1.40FLT3-ITD VAF Analyses in Selected MutationsDNMT3Amut high VAF53215.82.70.6260.40-0.98DNMT3Amut low VAF526910.26.40.7370.36-1.51NPM1wt/DNMT3Amut high VAF6409.01.50.01790.002-0.16NPM1wt/DNMT3Amut low VAF555011.36.20.3720.11-1.23aN = 367; quizartinib, n = 245; SC, n = 122bBaseline bone marrow samples were available and viable from 304 of 367 pts in the ITT population Citation Format: Alexander E. Perl, Jorge E. Cortes, Siddhartha Ganguly, Samer K. Khaled, Alwin Krämer, Giovanni Martinelli, Nigel H. Russell, Ken C. Chang, Kazunobu Kato, Yuhu Yan, Li-An Xu, Sergey Korkhov, Tobias Günnel, Hiroyuki Sumi, Arnaud Lesegretain, Flora Berisha, Derek Mires, Aziz Benzohra, Takeshi Isoyama, Cedric Dos Santos, Mark J. Levis. Effect of co-mutations and FLT3-ITD variant allele frequency (VAF) on response to quizartinib or salvage chemotherapy (SC) in relapsed/refractory (R/R) acute myeloid leukemia (AML) [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 784.

7514 Background: The phase 3 ADMIRAL trial showed that gilteritinib was superior to salvage chemotherapy (SC; median overall survival [OS]: 9.3 vs 5.6 mo, respectively) in FLT3mut+ R/R AML patients (pts; Perl, et al. N Engl J Med. 2019). This follow up (FU) of the ADMIRAL trial assessed long-term (LT) survivors and gilteritinib safety beyond 1 year. Methods: A data cut was performed 1 year after the primary analysis. Response outcomes in LT survivors (OS ≥18 mo) in the gilteritinib arm, and safety during and after 12 mo of gilteritinib therapy were assessed. Results: At 1 year after the primary analysis, median FU for OS was 29.2 mo. Median OS remained longer with gilteritinib (9.3 mo) than with SC (5.6 mo; HR=0.679 [95% CI: 0.527, 0.875], nominal P=0.0026); 18-mo OS rates were 27% and 15%, respectively (Table). Of 49 censored pts in the gilteritinib arm, 20 continued treatment; 13 of these 20 pts underwent transplantation (HSCT) and received gilteritinib post-HSCT. Median gilteritinib exposure was 4.1 mo (IQR, 2.1-8.2) and median average dose was 120 mg/day (range, 43.8-192.3); 12% (n=30/246) of pts had ≥18 mo and 7% (n=17/246) had ≥24 mo of drug exposure. A total of 63 gilteritinib-treated pts had OS ≥18 mo (median exposure, 17.6 mo [IQR, 3.1-25.7 mo]). A high proportion of these LT survivors achieved remission pre-HSCT (Table); median durations of complete remission (CR) or CR with partial hematologic recovery (CRh) have not been reached. After a median of 3.5 mo, 35 of 63 (56%) LT survivors underwent HSCT; 25 of these 35 pts (71%) received post-HSCT gilteritinib therapy. Of 28 pts who did not undergo HSCT, 15 (54%) received gilteritinib for ≥18 mo. Most common grade ≥3 adverse events (AEs) during the first 12 mo of gilteritinib therapy were febrile neutropenia (45%), anemia (40%), and thrombocytopenia (23%); rates of these grade ≥3 AEs decreased to 8%, 10%, and 0, respectively, after 12 mo of treatment. Most common fatal AEs during the first 12 mo of gilteritinib therapy were AML (11%), infections (11%), and cardiac disorders (3%); after 12 mo of treatment, rates of these fatal AEs were 6%, 8%, and 2%, respectively. Conclusions: Results from this ADMIRAL trial FU suggest LT survival in pts receiving gilteritinib is related to ongoing remission, subsequent HSCT, or post-HSCT gilteritinib therapy. The safety profile of gilteritinib beyond 1 year was stable. Clinical trial information: NCT02421939 . [Table: see text]

Introduction In QuANTUM-R, the once-daily, oral, highly potent and selective FLT3 inhibitor Q improved clinical benefit vs SC (median overall survival [mOS], 6.2 vs 4.7 mo [HR, 0.76 (95% CI, 0.58-0.98); P = .02]) in R/R FLT3-ITD AML (NCT02039726). Before randomization, 25% (Q) and 23% (SC) of pts had 1 prior HSCT. Objective To describe post hoc analyses in pts who underwent subsequent HSCT during QuANTUM-R. Methods Pts with FLT3-ITD R/R AML received Q (60 mg [30-mg lead-in]) or SC. Pts in the Q arm could resume Q 30-100 d after HSCT. Decisions to proceed to HSCT and resume Q after HSCT were made per investigator discretion/institutional policy. Results Of 367 randomized pts, 85 in the Q arm underwent any subsequent HSCT (allogeneic HSCT [allo-HSCT], 84 [6 with and 78 w/o additional AML therapy]; autologous HSCT, 1), and 19 in the SC arm underwent any HSCT (5 with and 14 w/o additional AML therapy]). Q + SC pooled data showed a longer mOS (95% CI) in 104 pts with any HSCT vs 263 w/o (12.2 [10.0-24.1] vs 4.4 [4.1-4.9] mo; P Regardless of treatment, mOS was longer with any HSCT vs w/o (Q, 11.9 [10.2-25.1] vs 4.5 [4.1-5.4] mo; SC, 12.7 [6.1-NA] vs 4.0 [2.7-5.0] mo); respective 1-year OS rates were 50% vs 13% and 51% vs 12%. In the Q arm, mOS (95% CI) was longer in pts with a best response of CRc who resumed Q after allo-HSCT (27.1 [18.2-NA] mo) vs pts not resuming Q (5.4 [4.7-11.4] mo; Fig 2). In 48 pts (62%) in the Q arm resuming Q after allo-HSCT, median time from allo-HSCT to Q resumption was 65 d (range, 30-106 d). Four pts (5%) in the Q arm died Conclusion Independent of HSCT, Q improved survival vs SC in pts with FLT3-ITD R/R AML in QuANTUM-R. Q + SC pooled analyses showed longer survival in pts with HSCT vs pts w/o and in pts with CRc before allo-HSCT. Survival in transplanted pts was similar in both arms, indicating that HSCT-eligible pts received transplants appropriately, and the higher HSCT rate in the Q arm was beneficial. In pts preselected for low-intensity SC at study entry, 13 were able to undergo HSCT after Q treatment. Q resumption after HSCT was associated with better survival outcomes and was tolerable. These data illustrate the value of using Q to target the FLT3-ITD mutation as a part of the overall treatment sequence in pts with FLT3-ITD R/R AML.

Gilteritinib is a potent and selective FLT3 kinase inhibitor with single-agent clinical efficacy in relapsed/refractory FLT3-mutated acute myeloid leukemia (AML). In this context, however, gilteritinib is not curative, and response duration is limited by the development of secondary resistance. To evaluate resistance mechanisms, we analyzed baseline and progression samples from patients treated on clinical trials of gilteritinib. Targeted next-generation sequencing at the time of AML progression on gilteritinib identified treatment-emergent mutations that activate RAS/MAPK pathway signaling, most commonly in NRAS or KRAS. Less frequently, secondary FLT3-F691L gatekeeper mutations or BCR–ABL1 fusions were identified at progression. Single-cell targeted DNA sequencing revealed diverse patterns of clonal selection and evolution in response to FLT3 inhibition, including the emergence of RAS mutations in FLT3-mutated subclones, the expansion of alternative wild-type FLT3 subclones, or both patterns simultaneously. These data illustrate dynamic and complex changes in clonal architecture underlying response and resistance to mutation-selective tyrosine kinase inhibitor therapy in AML.Significance:Comprehensive serial genotyping of AML specimens from patients treated with the selective FLT3 inhibitor gilteritinib demonstrates that complex, heterogeneous patterns of clonal selection and evolution mediate clinical resistance to tyrosine kinase inhibition in FLT3-mutated AML. Our data support the development of combinatorial targeted therapeutic approaches for advanced AML.See related commentary by Wei and Roberts, p. 998.This article is highlighted in the In This Issue feature, p. 983

Activating mutations in Fms-like tyrosine kinase 3 (FLT3) occur in ∼30% of adult cases of acute myeloid leukemia (AML). Selective second- and third-generation FLT3 inhibitors have shown significant clinical activity in patients with relapsed FLT3-mutant AML. However, clearance of FLT3-mutant clones does not consistently occur, and disease will progress in most patients after an initial response. This scenario challenges the model of FLT3-mutant AML being oncogene addicted, and it suggests that redundant signaling pathways regulate AML cell survival after FLT3 inhibition. We show that primary FLT3-mutant AML cells escape apoptosis induced by FLT3 inhibition in vitro in the presence of cytokines produced normally in the bone marrow, particularly granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin-3 (IL-3). Despite reactivating canonical FLT3-signaling pathways, GM-CSF and IL-3 maintain cell survival without rescuing proliferation. Cytokine-mediated resistance through GM-CSF and IL-3 is dependent on JAK kinase, STAT5, and proviral integration site of Moloney murine leukemia virus (PIM) but not MAPK or mammalian target of rapamycin signaling. Cotreatment with FLT3 inhibitors and inhibitors of JAK or PIM kinases blocks GM-CSF and IL-3 rescue of cell survival in vitro and in vivo. Altogether, these data provide a strong rationale for combination therapy with FLT3 inhibitors to potentially improve clinical responses in AML.

Primary refractory acute myeloid leukemia (AML), or primary induction failure, represents a continued challenge in clinical management. This review presents an overview of primary refractory disease and a discussion of risk factors for induction failure, including current evidence regarding the impact of karyotype and molecular mutation status on responsiveness to chemotherapy. We review the evidence for various treatment options for refractory AML including salvage chemotherapy regimens, allogeneic hematopoietic stem cell transplantation, targeted agents, and non-intensive therapies such as hypomethylating agents. A therapeutic approach to this patient population is presented, and several new and emerging therapies are reviewed.

International audience; BACKGROUND: Old age and FMS-like tyrosine kinase 3 internal tandem duplication (FLT3-ITD) mutations in patients with acute myeloid leukaemia are associated with early relapse and poor survival. Quizartinib is an oral, highly potent, and selective next-generation FLT3 inhibitor with clinical antileukaemic activity in relapsed or refractory acute myeloid leukaemia. We aimed to assess the efficacy and safety of single-agent quizartinib in patients with relapsed or refractory acute myeloid leukaemia.METHODS: We did an open-label, multicentre, single-arm, phase 2 trial at 76 hospitals and cancer centres in the USA, Europe, and Canada. We enrolled patients with morphologically documented primary acute myeloid leukaemia or acute myeloid leukaemia secondary to myelodysplastic syndromes and an Eastern Cooperative Oncology Group (ECOG) performance status of 0-2 into two predefined, independent cohorts: patients who were aged 60 years or older with relapsed or refractory acute myeloid leukaemia within 1 year after first-line therapy (cohort 1), and those who were 18 years or older with relapsed or refractory disease following salvage chemotherapy or haemopoietic stem cell transplantation (cohort 2). Patients with an FLT3-ITD allelic frequency of more than 10% were considered as FLT3-ITD positive, whereas all other patients were considered as FLT3-ITD negative. Patients received quizartinib once daily as an oral solution; the initial 17 patients received 200 mg per day but the QTcF interval was prolonged for more than 60 ms above baseline in some of these patients. Subsequently, doses were amended for all patients to 135 mg per day for men and 90 mg per day for women. The co-primary endpoints were the proportion of patients who achieved a composite complete remission (defined as complete remission + complete remission with incomplete platelet recovery + complete remission with incomplete haematological recovery) and the proportion of patients who achieved a complete remission. Efficacy and safety analyses included all patients who received at least one dose of quizartinib (ie, the intention-to-treat population). Patients with a locally assessed post-treatment bone marrow aspirate or biopsy were included in efficacy analyses by response; all other patients were considered to have an unknown response. This study is registered with ClinicalTrials.gov, number NCT00989261, and with the European Clinical Trials Database, EudraCT 2009-013093-41, and is completed.FINDINGS: Between Nov 19, 2009, and Oct 31, 2011, a total of 333 patients were enrolled (157 in cohort 1 and 176 in cohort 2). In cohort 1, 63 (56%) of 112 FLT3-ITD-positive patients and 16 (36%) of 44 FLT3-ITD-negative patients achieved composite complete remission, with three (3%) FLT3-ITD-positive patients and two (5%) FLT3-ITD-negative patients achieving complete remission. In cohort 2, 62 (46%) of 136 FLT3-ITD-positive patients achieved composite complete remission with five (4%) achieving complete remission, whereas 12 (30%) of 40 FLT3-ITD-negative patients achieved composite complete remission with one (3%) achieving complete remission. Across both cohorts (ie, the intention-to-treat population of 333 patients), grade 3 or worse treatment-related treatment-emergent adverse events in 5% or more of patients were febrile neutropenia (76 [23%] of 333), anaemia (75 [23%]), thrombocytopenia (39 [12%]), QT interval corrected using Fridericia's formula (QTcF) prolongation (33 [10%]), neutropenia (31 [9%]), leucopenia (22 [7%]), decreased platelet count (20 [6%]), and pneumonia (17 [5%]). Serious adverse events occurring in 5% or more of patients were febrile neutropenia (126 [38%] of 333; 76 treatment related), acute myeloid leukaemia progression (73 [22%]), pneumonia (40 [12%]; 14 treatment related), QTcF prolongation (33 [10%]; 32 treatment related), sepsis (25 [8%]; eight treatment related), and pyrexia (18 [5%]; nine treatment related). Notable serious adverse events occurring in less than 5% of patients were torsades de pointes (one [INTERPRETATION: Single-agent quizartinib was shown to be highly active and generally well tolerated in patients with relapsed or refractory acute myeloid leukaemia, particularly those with FLT3-ITD mutations. These findings confirm that targeting the FLT3-ITD driver mutation with a highly potent and selective FLT3 inhibitor is a promising clinical strategy to help improve clinical outcomes in patients with very few options. Phase 3 studies (NCT02039726; NCT02668653) will examine quizartinib at lower starting doses.FUNDING: Ambit Biosciences/Daiichi Sankyo.

Recurrent internal tandem duplication (ITD) mutations are observed in various cancers including acute myeloid leukemia (AML). ITD mutations of Fms-like tyrosine kinase 3 (FLT3) receptor increase kinase activity, and are associated with poor prognostic outcomes. Currently, several small-moleculeFLT3inhibitors (FLT3i) are in clinical trials for targeted therapy of high-risk FLT3-ITD-positive AML. However, the variability of survival following FLT3i treatment suggests that the mere presence ofFLT3-ITD mutations in a patient might not guarantee effective clinical response to targeted inhibition ofFLT3kinase. Motivated by the heterogeneity ofFLT3-ITD mutations, we sought to investigate the effects ofFLT3-ITD structural features on response to treatment in AML patients. To this end, we developed HeatITup (HEAT diffusion for Internal Tandem dUPlication), an algorithm to efficiently and accurately identify ITDs and classify them based on their nucleotide composition into newly defined categories of “typical” or “atypical”. Typical ITDs insert sequences are entirely endogenous to theFLT3locus whereas atypical ITDs contain nucleotides exogenous to the wildtypeFLT3. We applied HeatITup to our cohort ofde novoand relapsed AML patients. Individuals with AML carrying typical ITDs benefited significantly more from FLT3i than patients with atypical ITDs, regardless of whether FLT3i was used after initial induction or at relapse. Furthermore, analysis of the TCGA AML cohort demonstrated improved survival for patients with typical ITDs treated with induction chemotherapy. These results underscore the importance of structural discernment of complex somatic mutations such as ITDs in progressing towards personalized treatment for AML patients.

This randomized, open-label, phase 2b study (NCT01565668) evaluated the efficacy and safety of 2 dosing regimens of quizartinib monotherapy in patients with relapsed/refractory (R/R)

Quizartinib elicits differential responses that correlate with karyotype and genotype of the leukemic clone

High-dose melphalan with autologous stem cell support improves survival for patients with myeloma. For selected patients, we have been using a protocol of short hospitalization, discharging patients to home with careful outpatient monitoring in the office, which we hypothesized would reduce complications and utilization of inpatient beds.We reviewed 301 initial autologous transplants for myeloma, categorized as brief stay (≤ 4 days, 82 patients) or prolonged stay (≥ 5 days, 219 patients). Selection for a brief stay was determined by clinical characteristics, availability of caregivers at home, distance from our medical center, and patient preference.Within the brief stay population, 67% required readmission before day + 100, but this group still had fewer cumulative hospital days (9 vs. 18, P.0001). There were fewer documented infections among brief stay patients (22% vs. 46% P.001) and fewer admissions to intensive care units (0% vs. 5.9%, P = .02). The groups had similar rates of bleeding (1.2% vs. 1.4% P = 1.0) and thrombosis (3.7% vs. 4.6% P = 1.0). No patients in the brief stay group died within 100 days, compared with mortality of 1.8% (P = .6) in the prolonged stay group.Carefully selected patients receiving an autologous stem cell transplant for treatment of myeloma can be managed with a brief initial hospitalization and outpatient follow-up, with low morbidity and mortality.

Genomic studies have revealed significant branching heterogeneity in cancer. Studies of resistance to tyrosine kinase inhibitor therapy have not fully reflected this heterogeneity because resistance in individual patients has been ascribed to largely mutually exclusive on-target or off-target mechanisms in which tumors either retain dependency on the target oncogene or subvert it through a parallel pathway. Using targeted sequencing from single cells and colonies from patient samples, we demonstrate tremendous clonal diversity in the majority of acute myeloid leukemia (AML) patients with activating FLT3 internal tandem duplication mutations at the time of acquired resistance to the FLT3 inhibitor quizartinib. These findings establish that clinical resistance to quizartinib is highly complex and reflects the underlying clonal heterogeneity of AML.

Acute myeloid leukemia (AML) is a malignant hematopoietic disease and the most common type of acute leukemia in adults. The mechanisms underlying drug resistance in AML are poorly understood. Activating mutations in FMS-like tyrosine kinase 3 (FLT3) are the most common molecular abnormality in AML. Quizartinib (AC220) is a potent and selective second-generation inhibitor of FLT3. It is in clinical trials for the treatment of relapsed or refractory FLT3-ITD–positive and –negative AML patients and as maintenance therapy. To understand the mechanisms of drug resistance to AC220, we undertook an unbiased approach with a novel CRISPR-pooled library to screen new genes whose loss of function confers resistance to AC220. We identified SPRY3, an intracellular inhibitor of FGF signaling, and GSK3, a canonical Wnt signaling antagonist, and demonstrated reactivation of downstream FGF/Ras/ERK and Wnt signaling as major mechanisms of resistance to AC220. We confirmed these findings in primary AML patient samples. Expression of SPRY3 and GSK3A was dramatically reduced in AC220-resistant AML samples, and SPRY3-deleted primary AML cells were resistant to AC220. Intriguingly, expression of SPRY3 was greatly reduced in GSK3 knockout AML cells, which positioned SPRY3 downstream of GSK3 in the resistance pathway. Taken together, our study identified novel genes whose loss of function conferred resistance to a selective FLT3 inhibitor, providing new insight into signaling pathways that contribute to acquired resistance in AML. Cancer Res; 77(16); 4402–13. ©2017 AACR.

BACKGROUND: Mammalian Target of Rapamycin Complex 1 (mTORC1) inhibitors enhance chemotherapy response in acute myelogenous leukemia (AML) cells in vitro. However whether inhibiting mTORC1 enhances clinical response to AML chemotherapy remains controversial. We previously optimized measurement of mTORC1’s kinase activity in AML blasts during clinical trials using serial phospho-specific flow cytometry of formaldehyde-fixed whole blood or marrow specimens. To validate mTORC1 as a therapeutic target in AML, we performed two clinical trials combining an mTORC1 inhibitor (sirolimus) and MEC (mitoxantrone, etoposide, cytarabine) in patients with relapsed, refractory, or untreated high-risk AML. METHODS: Flow cytometric measurements of ribosomal protein S6 phosphorylation (pS6) were performed before and during sirolimus treatment to determine whether mTORC1 inhibition enriched for chemotherapy response. RESULTS: In 51 evaluable subjects, the overall response rate (ORR) to the combination regimen was 47% (95% confidence interval 33 – 61%, 33% CR, 2% CRi, 12% PR) and similar toxicity to historic experience with MEC alone. 37 subjects had baseline pS6 measured pre-sirolimus, of whom 27 (73%) exhibited mTORC1 activity. ORR was not significantly different between subjects with and without baseline mTORC1 activity (52% vs 40%, respectively, p=0.20). The ORR among subjects with baseline target activation and mTORC1 inhibition during therapy was 71% (12/17) compared to 20% (2/10) in subjects without target inhibition. CONCLUSIONS: Fixed, whole blood pS6 by flow cytometry may be a predictive biomarker for clinical response to mTORC1 inhibitor-based regimens. These data provide clinical confirmation that mTORC1 activation mediates chemotherapy resistance in patients with AML.

Tyrosine kinase inhibitors (TKIs) represent transformative therapies for several malignancies. Two critical features necessary for maximizing TKI tolerability and response duration are kinase selectivity and invulnerability to resistance-conferring kinase domain (KD) mutations in the intended target. No prior TKI has demonstrated both of these properties. Aiming to maximize selectivity, medicinal chemists have largely sought to create TKIs that bind to an inactive (type II) kinase conformation. Here we demonstrate that the investigational type I TKI crenolanib is a potent inhibitor of Fms tyrosine kinase-3 (FLT3) internal tandem duplication, a validated therapeutic target in human acute myeloid leukemia (AML), as well as all secondary KD mutants previously shown to confer resistance to the first highly active FLT3 TKI quizartinib. Moreover, crenolanib is highly selective for FLT3 relative to the closely related protein tyrosine kinase KIT, demonstrating that simultaneous FLT3/KIT inhibition, a prominent feature of other clinically active FLT3 TKIs, is not required for AML cell cytotoxicity in vitro and may contribute to undesirable toxicity in patients. A saturation mutagenesis screen of FLT3-internal tandem duplication failed to recover any resistant colonies in the presence of a crenolanib concentration well below what has been safely achieved in humans, suggesting that crenolanib has the potential to suppress KD mutation-mediated clinical resistance. Crenolanib represents the first TKI to exhibit both kinase selectivity and invulnerability to resistance-conferring KD mutations, which is unexpected of a type I inhibitor. Crenolanib has significant promise for achieving deep and durable responses in FLT3-mutant AML, and may have a profound impact upon future medicinal chemistry efforts in oncology.

Background: The initial treatment of FLT3 wild type acute myeloid leukemia (AML) has not significantly changed since induction therapy with Ara-C and anthracyclines was first developed. Preclinical data suggests constitutive activation of the AKT3/mammalian target of rapamycin (mTOR) pathway may play a role in pathogenesis of this disease in a subset of AML patients. Previous data from our group has shown that the presence of phosphorylated ribosomal S6 (pS6) in AML blasts as detected by flow cytometry may predict response to the combination of sirolimus and induction chemotherapy. Here we report the clinical and pharmacodynamics results of a phase II study of the combination of these drugs. Methods: Subjects had newly diagnosed AML based on WHO criteria. Subjects received oral sirolimus starting on day 1 (12 mg loading dose) then 4 mg daily on days 2-10 with idarubicin 12mg/m2 days 4-7 and cytarabine 100mg/m2 days 4-10. Clinical response was assessed at hematologic recovery or by day 42 using IWG for response. Samples for pharmacodynamic studies of blasts were drawn prior to treatment with sirolimus on day 1, and then again prior to dosing of idarubicin and cytarabine on day 4. Assessment of pS6 on gated blasts, a biomarker of mTORC1 activation, was assessed by flow cytometry using previously described methods. Results: 55 patients enrolled on this trial received sirolimus with an average age of 58 years. Toxicity was similar to published 7+3 data and prolonged aplasia without recovery was not observed. Twenty-nine patients (53%) had high risk cytogenetic or molecular mutations, 15 (27%) had intermediate risk disease, and 11 (20%) patients had lower risk disease. As a whole, 35 patients (64%) entered into CR or CRp, 1 had a PR, 17 (27%) were non-responders. Two (4%) patients (ages 64 and 71) died during induction. Thirteen (45%) patients with high risk disease had a CR or CRp, 14 (48%) were non-responders, and 2 died in induction. Of the 15 subjects with intermediate risk disease, 11 (79%) patients had a CR or CRp, 1 had a partial response, and 3 were non-responders. All low risk patients had a CR, and 9 of 11 are alive and in remission at the time of censoring of data with a median time on study of 674 days. One patient with low risk disease subsequently relapsed, went to stem cell transplant, and is currently in CR. Two patients with low risk disease refused to proceed with standard of care consolidation; of these, 1 is alive and in remission 946 days from study entry, and 1 died in relapse. Fifteen patients (27%) subsequently underwent allogeneic stem cell transplantation in CR, and 8 (53%) are still alive an average of 358 days after transplant. Thirty-seven of 55 patients had adequate samples for pharmacodynamic analysis. Surprisingly, all patients demonstrated activation of ribosomal S6 prior to therapy in contrast to 67% positivity seen in previous studies that focused on patients with relapsed AML. mTORC1 was inhibited greater than 40% in 28/37 (76%) of patients. Inhibition did not correlate with either overall survival or age of patients. Conclusions: Sirolimus and 7+3 is a well-tolerated regimen. mTORC1 appears to be activated in almost all patients at the time of diagnosis of AML as assessed by flow cytometric assessment of ribosomal S6. Inhibition of mTORC1 did not correlate with response, suggesting that AML cells may have redundant signaling pathways that regulate chemosensitivity when mTORC1 is inhibited. Given the large percentage of samples with mTORC1 activation in this upfront AML study, future research into dual mTORC inhibitors may prove valuable. Disclosures Carroll: Astellas Pharmaceuticals: Research Funding; Incyte Pharmaceuticals: Research Funding. Porcu: Innate Pharma: Research Funding; Kura: Research Funding; Miragen: Research Funding; Kiowa: Research Funding; Galderma: Research Funding; Tetralogic: Research Funding; Cell Medica: Research Funding; Celgene: Research Funding. Perl: Arog Pharmaceuticals: Consultancy; Novartis: Other: Advisory Board; Pfizer: Other: Advisory Board; Seattle Genetics: Other: Advisory board; Asana Biosciences: Other: Scientific advisory board; Astellas: Consultancy; Daiichi Sankyo: Consultancy; Actinium Pharmaceuticals: Other: Scientific Advisory Board.

Introduction: In the phase 3 QuANTUM-R trial, once-daily, oral, highly potent and selective FLT3 inhibitor Q improved clinical benefits vs SC (median overall survival [mOS], 6.2 vs 4.7 mo [HR, 0.76 (95% CI, 0.58-0.98); P = .02]; composite complete remission [CRc], 48% vs 27%; median duration of CRc, 12.1 vs 5.0 wk) in 367 pts with R/R FLT3-ITD AML (Cortes et al. Lancet Oncol, 2019; NCT02039726). Prior to randomization, 25% (Q) and 23% (SC) of pts had 1 prior HSCT. An OS sensitivity analysis, with censoring at the time of any subsequent HSCT during QuANTUM-R, was supportive (mOS, 5.7 vs 4.6 mo [HR, 0.79 (95% CI, 0.59-1.05)]; P = .05). Post hoc analyses of characteristics and clinical outcomes in pts who underwent subsequent HSCT in QuANTUM-R are reported. Methods: Pts aged ≥ 18 y with FLT3-ITD R/R AML receiving Q (60 mg [30-mg lead-in]) or 1 of 3 prespecified high- or low-intensity SC regimens and underwent subsequent HSCT as part of the open-label, randomized QuANTUM-R trial were analyzed. Pts receiving HSCT in the Q arm could resume maintenance Q 30-100 days after HSCT. Decisions to proceed to HSCT and resume Q after HSCT were made per investigator discretion/institutional policies. Results: Of 367 randomized pts, 85 in the Q arm underwent any subsequent HSCT (allogenic HSCT [allo-HSCT], 84 [6 with and 78 w/o additional AML therapy]; autologous HSCT, 1) and 19 in the SC arm underwent any HSCT (5 with and 14 w/o additional AML therapy]). Median age (range) was lower in pts with any HSCT (Q, 49 [19-71] y; SC, 44 [23-67] y) vs pts w/o (Q, 58 [19-81] y; SC, 59 [18-78] y). Q + SC pooled data showed a longer mOS (95% CI) in 104 pts with any HSCT vs 263 w/o (12.2 [10.0-24.1] vs 4.4 [4.1-4.9] mo; P < .0001; Fig 1); 1-year OS probabilities (95% CI) were 50% (40%-60%) vs 13% (9%-18%). Among pts preselected for high-intensity therapy (Q [n = 188] + SC [n = 93]), mOS in the pooled high-intensity group was 11.9 (10.0-24.0) mo with any HSCT vs 4.6 (4.1-5.4) mo w/o. Among pts preselected for low-intensity therapy, 13/57 in the Q arm and 0/29 in the SC arm underwent any HSCT; mOS in the pooled low-intensity group was 32.4 (6.2-NA) mo with any HSCT vs 4.1 (2.7-4.6) mo w/o. In pts with CRc (last recorded response prior to allo-HSCT), mean time (range) to allo-HSCT was 13.3 (5.9-26.9) wk with Q and 12.1 (6.3-28.6) wk with SC. Q + SC pooled data showed that mOS (95% CI) was longer in pts with a CRc prior to allo-HSCT vs pts w/o CRc (20.1 [11.7-NA] vs 8.8 [7.0-11.4] mo). Survival outcomes by treatment were similar regardless of study treatment, with longer mOS in pts with any HSCT vs pts w/o (Q, 11.9 [10.2-25.1] vs 4.5 [4.1-5.4] mo; SC, 12.7 [6.1-NA] vs 4.0 [2.7-5.0] mo); respective 1-year OS probabilities (95% CI) were 50% (39%-60%) vs 13% (8%-20%) and 51% (26%-70%) vs 12% (6%-21%). In the Q arm, mOS (95% CI) was longer in pts with a best response of CRc who resumed Q after allo-HSCT (27.1 [18.2-NA] mo) vs pts not resuming Q (5.4 [4.7-11.4] mo; Fig 2). In 48 pts (62%) in the Q arm resuming Q after allo-HSCT, median time (range) from allo-HSCT to Q resumption was 65 (30-106) d. Four pts (5%) in the Q arm died < 30 days after allo-HSCT. As of 2/22/2018, 46 of 78 pts in the Q arm (59%) and 9 of 14 pts in the SC arm (64%) with allo-HSCT w/o additional AML therapy died, primarily due to AML disease progression (Q, 31 [40%]; SC, 7 [50%]). The frequency of treatment-emergent adverse events (TEAEs) was mostly lower in pts resuming Q after allo-HSCT than in the overall Q population (Table 1); TEAEs of interest were similar. Long-term survivor data will be presented. Conclusions: Independent of HSCT, Q improved survival vs SC in pts with FLT3-ITD R/R AML in QuANTUM-R. Q + SC pooled analyses showed longer survival in pts with HSCT vs pts w/o and in pts with CRc prior to allo-HSCT. Importantly, survival post-HSCT was similar in the Q and SC arms, indicating that pts eligible for HSCT were appropriately transplanted, and the higher HSCT rate in the Q arm was beneficial to pts. More pts treated with Q underwent HSCT, likely due to a higher rate and duration of CRc with Q vs SC and better overall fitness. In pts preselected for low-intensity SC at study entry, 13 were able to undergo HSCT after Q treatment. Resumption of Q after HSCT was associated with better survival outcomes and was tolerable. These data illustrate the value of using Q to target the FLT3-ITD mutation as a part of the overall treatment sequence in pts with FLT3-ITD R/R AML. Disclosures Ganguly: Seattle Genetics: Speakers Bureau; Janssen: Honoraria, Other: Advisory Board; Kite Pharma: Honoraria, Other: Advisory Board; Daiichi Sankyo: Research Funding. Cortes:Bristol-Myers Squibb: Consultancy, Research Funding; BiolineRx: Consultancy; Daiichi Sankyo: Consultancy, Honoraria, Research Funding; Pfizer: Consultancy, Honoraria, Research Funding; Astellas Pharma: Consultancy, Honoraria, Research Funding; Jazz Pharmaceuticals: Consultancy, Research Funding; Sun Pharma: Research Funding; Immunogen: Consultancy, Honoraria, Research Funding; Takeda: Consultancy, Research Funding; Novartis: Consultancy, Honoraria, Research Funding; Forma Therapeutics: Consultancy, Honoraria, Research Funding; Biopath Holdings: Consultancy, Honoraria; Merus: Consultancy, Honoraria, Research Funding. Krämer:Daiichi-Sankyo: Honoraria, Membership on an entity's Board of Directors or advisory committees; Roche: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; BMS: Research Funding; Bayer: Research Funding. Levis:Amgen: Consultancy, Honoraria; Agios: Consultancy, Honoraria; Daiichi Sankyo Inc: Consultancy, Honoraria; Astellas: Consultancy, Research Funding; Novartis: Consultancy, Research Funding; Menarini: Consultancy, Honoraria; FUJIFILM: Consultancy, Research Funding. Martinelli:Daiichi Sankyo: Consultancy, Honoraria; Pfizer: Consultancy, Other: trial grant; Celgene: Consultancy, Honoraria, Other: trial grant; Janssen: Consultancy, Other: trial grant; Incyte: Consultancy, Other: trial grant; Amgen: Consultancy, Other: trial grant; Abbvie: Consultancy, Honoraria, Other: trial grant; Novartis: Consultancy, Other: trial grant; Roche: Consultancy, Other: trial grant; Ariad: Consultancy, Other: trial grant. Perl:Novartis: Honoraria, Other: Advisory board, Non-financial support included travel costs for advisory board meetings as well as a medical writing company that assisted with manuscript preparation/submission and slide deck assembly for academic meeting presentations of the data., Research Funding; Bayer: Research Funding; BioMed Valley Discoveries: Research Funding; FujiFilm: Research Funding; Takeda: Consultancy, Honoraria, Other: Non-financial support included travel costs for advisory board meetings.; Astellas: Consultancy, Honoraria, Other: Non-financial support included travel costs for advisory board meetings as well as a medical writing company that assisted with manuscript preparation/submission and slide deck assembly for academic meeting presentations of trial data., Research Funding; Daiichi Sankyo: Consultancy, Honoraria, Other, Research Funding; Arog: Consultancy, Other: Non-financial support included travel costs for advisory board meetings.; AbbVie: Consultancy, Honoraria, Other: Non-financial support included travel costs for advisory board meetings.; Actinium Pharmaceuticals: Consultancy, Honoraria, Other: Clinical Advisory Board member, Research Funding; Agios: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Non-financial support included travel costs for advisory board meetings.; Jazz: Consultancy, Honoraria, Other: Non-financial support included travel costs for advisory board meetings.; NewLink Genetics: Consultancy, Honoraria, Other: Non-financial support included travel costs for advisory board meetings.. Russell:Astellas: Consultancy, Honoraria, Speakers Bureau; Pfizer Inc: Consultancy, Honoraria, Speakers Bureau; Jazz: Consultancy, Honoraria, Speakers Bureau; DSI: Consultancy, Honoraria, Speakers Bureau. Arunachalam:Daiichi Sankyo: Employment. Gammon:Daiichi Sankyo: Consultancy. Lesegretain:Daiichi-Sankyo Inc.: Employment, Equity Ownership. Mires:Daiichi Sankyo: Employment. Namuyinga:Daiichi Sankyo: Employment. Zhang:Daiichi Sankyo: Employment. Khaled:Omeros: Consultancy; Daiichi Sankyo: Other: Travel support; Alexion: Consultancy, Speakers Bureau.

Background: Philadelphia chromosome-like acute lymphoblastic leukemia (Ph-like ALL) is a high-risk subtype occurring in 15-40% of older children, adolescents, and adults with B-ALL and is associated with high relapse rates and poor survival. Approximately 50% of Ph-like ALL cases have CRLF2 (cytokine receptor-like factor 2 rearrangements (CRLF2-R), often with concomitant JAK2 point mutations. We and others have shown that targeted inhibition of JAK/STAT and PI3K/AKT signaling in CRLF2-rearranged Ph-like ALL only partially inhibits leukemia proliferation. Our preliminary data indicates that modified B cell receptor signaling results in ERK activation and Ph-like ALL cell growth that appears independent of CRLF2-activated signaling. This study aimed to define the extent to which BCR signaling mediates drug resistance in Ph-like ALL after cytokine receptor signaling inhibition and to develop novel combinatorial treatment strategies. Methods and Results: We first validated high basal levels of JAK/STAT and PI3K pathway phosphoproteins via immunoblotting of cell lysates from >20 primary childhood and adult Ph-like ALL samples and patient-derived xenograft (PDX) models. Despite lack of B-cell receptor (BCR) μ heavy chain on Ph-like ALL cells by flow cytometry analysis, we detected high expression levels of the BCR-associated proteins CD79A, CD79B, and BLNK. We further identified constitutive phosphorylation of downstream BCR-associated signaling molecules, including SRC family kinases (SFKs), BTK, and ERK. Given these new observations, we then sought to delineate more precisely alternative pathways in Ph-like ALL (beyond JAK/STAT and PI3K) that may contribute to adaptive signaling regulation and confer resistance to kinase inhibitor monotherapy. We hypothesized that JAK inhibitor (JAKi) resistance is mediated by compensatory activation of PI3K/AKT/mTOR through 'BCR-like' signaling via CD79/CD19/SRC/BTK/ERK. To test this hypothesis, we treated CRLF2-R Ph-like ALL cells in vitro with selective inhibitors of JAK1/2 (ruxolitinib) or PI3Kd (INCB050465) and assessed effects upon signaling via immunoblotting. We observed i) effective dephosphorylation of STAT5 and moderate dephosphorylation of AKT with full reactivation within 72h following JAKi or PI3Kdi monotherapy, respectively, ii) combined JAKi and PI3Kdi prevented PI3K pathway, reactivation, and iii) JAKi and PI3Kdi had no effects upon ERK signaling. These results suggested that oncogene-independent activation of BCR and PI3K pathway signaling occurs in Ph-like ALL. We then performed immunofluorescence analysis and detected distinct clustering and homodimerization of CD79B at the cell membrane of Ph-like ALL cells, as well as physical proximity of CD79B and CD19, suggesting that CD19 could be phosphorylated by SRC/SFKs independently of an activated BCR. Interestingly however, CRISPR-mediated deletion of CD19 or CD79B resulted in hyperactivation of ERK signaling. Finally, we tested if triple inhibition of JAK/STAT, PI3K, and SRC/SFKs signaling is sufficient to eradicate Ph-like ALL. Strikingly, combined JAKi (ruxolitinib), PI3Kdi (INCB050465), and SRCi (dasatinib) silenced STAT5, PI3K, and ERK signaling and induced near-complete cytotoxicity in vitro and in vivo in Ph-like ALL cell lines and patient-derived xenograft (PDX) models. While triple inhibitor treatment appeared well-tolerated in mice, we also assessed dual kinase inhibition of JAK2 and PI3K with dexamethasone (a known repressor of BCR signaling) as a more clinically relevant combinatorial strategy. We observed similarly robust inhibition of signaling pathways and leukemia eradication in vitro and in vivo in our Ph-like ALL cell lines and PDX models. Conclusions: Children and adults with Ph-like ALL have a >60% risk of relapse despite maximally intensive chemotherapy, demonstrating need for alternative therapeutic approaches. While earlier studies by our group and others have reported partial anti-leukemia activity of JAKi and PI3Ki monotherapies, our new data provide compelling evidence that three essential cooperating signaling pathways are required for Ph-like leukemogenesis. We postulate that triple JAK, PI3K, and SRC inhibition or dual kinase inhibition with chemotherapy can overcome innate compensatory mechanisms of signaling resistance and may in fact be necessary to eradicate Ph-like ALL in patients. Disclosures Perl: Daiichi Sankyo: Consultancy, Honoraria, Other, Research Funding; Arog: Consultancy, Other: Non-financial support included travel costs for advisory board meetings.; AbbVie: Consultancy, Honoraria, Other: Non-financial support included travel costs for advisory board meetings.; Actinium Pharmaceuticals: Consultancy, Honoraria, Other: Clinical Advisory Board member, Research Funding; Agios: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Non-financial support included travel costs for advisory board meetings.; Jazz: Consultancy, Honoraria, Other: Non-financial support included travel costs for advisory board meetings.; NewLink Genetics: Consultancy, Honoraria, Other: Non-financial support included travel costs for advisory board meetings.; Astellas: Consultancy, Honoraria, Other: Non-financial support included travel costs for advisory board meetings as well as a medical writing company that assisted with manuscript preparation/submission and slide deck assembly for academic meeting presentations of trial data., Research Funding; Takeda: Consultancy, Honoraria, Other: Non-financial support included travel costs for advisory board meetings.; Bayer: Research Funding; BioMed Valley Discoveries: Research Funding; FujiFilm: Research Funding; Novartis: Honoraria, Other: Advisory board, Non-financial support included travel costs for advisory board meetings as well as a medical writing company that assisted with manuscript preparation/submission and slide deck assembly for academic meeting presentations of the data., Research Funding. Carroll:Astellas Pharmaceuticals: Research Funding; Incyte: Research Funding; Janssen Pharmaceuticals: Consultancy. Tasian:Gilead Sciences: Research Funding; Incyte Corportation: Research Funding; Aleta Biotherapeutics: Membership on an entity's Board of Directors or advisory committees.

Introduction: Patients (pts) with relapsed/refractory (R/R) acute myeloid leukemia (AML) with FLT3-ITD mutations have a dismal prognosis and limited treatment options. Given the aggressiveness of FLT3-ITD AML, therapies that produce rapid and sustained disease control are needed. Quizartinib (Q), a once-daily, oral, highly potent and selective FLT3 inhibitor, demonstrated a clinically meaningful overall survival (OS) benefit in pts with R/R FLT3-ITD AML vs salvage chemotherapy (SC; 6.2 vs 4.7 mo [HR, 0.76 (95% CI, 0.58-0.98); P = .02]) in the phase 3 QuANTUM-R trial (NCT02039726; Cortes et al. Lancet Oncol, 2019). In this post hoc analysis, we characterize clinical outcomes in pts who achieved a composite complete remission (CRc) in QuANTUM-R, including pts with CR with incomplete hematologic recovery (CRi) and transfusion independence. Methods: Pts aged ≥ 18 years with FLT3-ITD AML R/R after standard AML therapy, with or without hematopoietic stem cell transplant (HSCT), were randomized 2:1 to Q (60 mg [30-mg lead-in]) or 1 of 3 prespecified SC regimens. Pts receiving HSCT in the Q arm could resume Q after HSCT. Response was assessed per modified International Working Group criteria (Table 1). Transfusion dependence at baseline (BL) was defined as any platelet (PLT) or red blood cell (RBC) transfusion within 28 days of first dose. Post-BL transfusion independence was defined as no PLT or RBC transfusions for any consecutive 56-day period on treatment. Results: Of 367 randomized pts, 245 and 122 were randomized to Q and SC, respectively. Median duration of treatment was 97 days with Q (including post-HSCT resumption) and ranged from 5 to 10 days with SC depending on the regimen. Median follow-up was 23.5 mo. In the intent-to-treat population, CRc was consistent across prespecified subgroups (eg, sex, response to prior therapy, FLT3-ITD variant allele frequency). Median time to CRc was 1.1 mo with Q and 0.9 mo with SC; median duration of CRc was 2.8 mo with Q and 1.2 mo with SC (Table 2). Most responses in both arms were CRi, achieved in 99 pts (40%) in the Q arm and 32 pts (26%) in the SC arm. Peripheral blood counts in pts who achieved CRi are shown in Table 3. Of pts with CRi, 45 (Q) and 13 (SC) underwent HSCT. Outcomes with HSCT included engraftment failure in 11% (Q), rejection in 2% (Q), relapse in 33% (Q) and 46% (SC), and successful transplant in 47% (Q) and 46% (SC) and were unknown in 7% (Q) and 8% (SC). Of the 205 pts in the Q arm who were transfusion dependent at BL, 46 (22%) became transfusion independent post-BL (29 with HSCT; 17 without). Mean (SD) duration of post-BL transfusion independence was 255 (216.6) days. By response, 24 of 91 pts (26%) with CRi, 7 of 48 (15%) with a partial response (PR), and 4 of 47 (9%) with no response (NR) became transfusion independent post-BL; respective mean (SD) durations were 297.6 (268.3), 84.6 (21.7), and 211.3 (111.9) days. Of the 36 pts in the Q arm who were transfusion independent at BL, 20 (55.6%) maintained transfusion independence post-BL (12 with HSCT; 8 without; mean [SD] duration, 208 [203.1] days). Transfusion independence could not be assessed in the SC arm. Transfusion data was not collected after the end of treatment, and most pts in the SC arm were treated for < 56 days. In the Q arm, median OS (95% CI) was longer in pts with CRi (7.5 [5.4-9.9] mo) vs pts with PR (6.1 [5.1-7.2] mo) or NR (4.1 [3.3-5.9] mo) (Figure 1); respective medians in the SC arm were 8.8 (6.3-20.8), 7.8 (5.4-28.2), and 3.8 (2.7-4.7) mo. In the 34 pts in the Q arm with a last response of CRi prior to allogeneic HSCT, median OS (95% CI) was 25.1 (9.9-NA) mo; in the SC arm (n = 9), median OS (95% CI) was 20.1 (4.3-NA) mo. In the Q arm, median OS (95% CI) was longer in pts with CRi who became transfusion independent post-BL vs pts who did not (27.1 [10.4-NA] vs 5.3 [4.6-6.4] mo); similarly, median OS (95% CI) was longer in pts who maintained transfusion independence vs pts who did not (25.1 [11.4-NA] vs 9.6 [4.6-NA] mo). Conclusions: Q induced rapid, durable, and consistent tumor control in pts with FLT3-ITD R/R AML irrespective of prior therapy, including HSCT. A high proportion of pts with CRi became eligible for HSCT, the only potential curative treatment option. Moreover, a high proportion achieved durable transfusion independence regardless of HSCT, which is also associated with clinical benefit. These data highlight the clinical benefit of achieving CRi with Q in pts with FLT3-ITD R/R AML, a population with a high unmet need. Disclosures Levis: Novartis: Consultancy, Research Funding; Daiichi Sankyo Inc: Consultancy, Honoraria; Agios: Consultancy, Honoraria; Astellas: Consultancy, Research Funding; Amgen: Consultancy, Honoraria; FUJIFILM: Consultancy, Research Funding; Menarini: Consultancy, Honoraria. Ganguly:Daiichi Sankyo: Research Funding; Seattle Genetics: Speakers Bureau; Kite Pharma: Honoraria, Other: Advisory Board; Janssen: Honoraria, Other: Advisory Board. Khaled:Alexion: Consultancy, Speakers Bureau; Daiichi Sankyo: Other: Travel support; Omeros: Consultancy. Krämer:BMS: Research Funding; Bayer: Research Funding; Roche: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Daiichi-Sankyo: Honoraria, Membership on an entity's Board of Directors or advisory committees. Martinelli:Novartis: Consultancy, Other: trial grant; Pfizer: Consultancy, Other: trial grant; Roche: Consultancy, Other: trial grant; Incyte: Consultancy, Other: trial grant; Ariad: Consultancy, Other: trial grant; Daiichi Sankyo: Consultancy, Honoraria; Celgene: Consultancy, Honoraria, Other: trial grant; Amgen: Consultancy, Other: trial grant; Abbvie: Consultancy, Honoraria, Other: trial grant; Janssen: Consultancy, Other: trial grant. Perl:BioMed Valley Discoveries: Research Funding; FujiFilm: Research Funding; Novartis: Honoraria, Other: Advisory board, Non-financial support included travel costs for advisory board meetings as well as a medical writing company that assisted with manuscript preparation/submission and slide deck assembly for academic meeting presentations of the data., Research Funding; Takeda: Consultancy, Honoraria, Other: Non-financial support included travel costs for advisory board meetings.; Bayer: Research Funding; NewLink Genetics: Consultancy, Honoraria, Other: Non-financial support included travel costs for advisory board meetings.; Actinium Pharmaceuticals: Consultancy, Honoraria, Other: Clinical Advisory Board member, Research Funding; Agios: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Non-financial support included travel costs for advisory board meetings.; Jazz: Consultancy, Honoraria, Other: Non-financial support included travel costs for advisory board meetings.; Astellas: Consultancy, Honoraria, Other: Non-financial support included travel costs for advisory board meetings as well as a medical writing company that assisted with manuscript preparation/submission and slide deck assembly for academic meeting presentations of trial data., Research Funding; Daiichi Sankyo: Consultancy, Honoraria, Other, Research Funding; Arog: Consultancy, Other: Non-financial support included travel costs for advisory board meetings.; AbbVie: Consultancy, Honoraria, Other: Non-financial support included travel costs for advisory board meetings.. Russell:Astellas: Consultancy, Honoraria, Speakers Bureau; DSI: Consultancy, Honoraria, Speakers Bureau; Pfizer Inc: Consultancy, Honoraria, Speakers Bureau; Jazz: Consultancy, Honoraria, Speakers Bureau. Choi:Daiichi Sankyo: Employment. Lesegretain:Daiichi-Sankyo Inc.: Employment, Equity Ownership. Mendell:Daiichi Sankyo, Inc.: Employment. Mires:Daiichi Sankyo: Employment. Zhang:Daiichi Sankyo: Employment. Cortes:Daiichi Sankyo: Consultancy, Honoraria, Research Funding; Astellas Pharma: Consultancy, Honoraria, Research Funding; Sun Pharma: Research Funding; Jazz Pharmaceuticals: Consultancy, Research Funding; Merus: Consultancy, Honoraria, Research Funding; Forma Therapeutics: Consultancy, Honoraria, Research Funding; BiolineRx: Consultancy; Novartis: Consultancy, Honoraria, Research Funding; Pfizer: Consultancy, Honoraria, Research Funding; Bristol-Myers Squibb: Consultancy, Research Funding; Biopath Holdings: Consultancy, Honoraria; Takeda: Consultancy, Research Funding; Immunogen: Consultancy, Honoraria, Research Funding.

BACKGROUND: The FLT3 tyrosine kinase inhibitor (TKI) gilteritinib improves the survival of patients with relapsed/refractory (R/R) FLT3 mutated (FLT3mut+) acute myeloid leukemia (AML) compared to standard salvage chemotherapy; however, single agent TKI therapy is not curative and long-term survival remains low. Combination therapy with agents that induce apoptosis may enhance cytotoxicity against FLT3mut+ and WT clones and potentially delay or prevent drug resistance. Preclinical data demonstrate that the combination of venetoclax with a FLT3 tyrosine kinase inhibitor is highly synergistic, and BCL-2 inhibition by venetoclax directly triggers apoptosis, which may help overcome resistance to FLT3-targeted therapy. Therefore, we sought to define the safety and activity of venetoclax plus gilteritinib in R/R AML. METHODS: This is a multicenter, open-label, phase 1b clinical trial (NCT03625505) evaluating the safety and efficacy of venetoclax in combination with gilteritinib for patients with relapsed or refractory (R/R) AML. Patients had to have R/R AML and an Eastern Cooperative Oncology Group (ECOG) performance status of 0-2. Here, we present data in patients that had either wild type (WT) or mutated FLT3, and were treated with 400 mg venetoclax in combination with 80 mg or 120 mg gilteritinib daily, from the dose escalation portion of the study. For study purposes, gilteritinib was administered alone for one day. On day two venetoclax was initiated in a three-day ramp-up from 100 to 200 to 400 mg; thereafter, target doses of each were administered, daily, in 28-day cycles unless venetoclax was shortened for cytopenia recovery. Interruptions of venetoclax or both drugs simultaneously were permitted for adverse events (AEs). RESULTS: Data cutoff was July 10, 2019. Of 15 patients enrolled and treated, 5 had WT FLT3 and 10 had mutant FLT3 (8 ITD, 1 TKD, and one with both included with the ITD group). The median age for all patients was 58 (range: 23-81). Both patients with WT or mutant FLT3 had a median of 2.0 prior lines of therapy, with ranges of 2-4 and 1-4 prior lines, respectively. Six (60%) of the FLT3 mutant patients had previously received a FLT3 blocking TKI (2 of those receiving both midostaurin and sorafenib), and 5 (50%) had prior stem cell transplant (SCT). None of the patients with WT FLT3 were FLT3 inhibitor-experienced, and one patient had prior stem cell transplant. Key treatment emergent grade ≥3 AEs across all patients were: febrile neutropenia (47%), anemia (27%), thrombocytopenia (7%) and neutropenia (7%). One patient receiving 80 mg of gilteritinib had a protocol-defined dose limiting toxicity of prolonged neutropenia, and one receiving 120 mg of gilteritinib was still within the protocol-defined count recovery period at analysis. Seven (47%) patients had venetoclax interrupted, the majority due to neutropenia; 3 (20%) patients had gilteritinib interrupted. No cases of tumor lysis syndrome were observed. Pharmacokinetic studies showed comparable drug levels to those observed with single agent use of each drug. Key efficacy results are shown in the Table. Fifty percent of patients with mutant FLT3 achieved CRc, and another 40% of patients achieved morphologic leukemia free state, for an ORR of 90% (9/10). The ORR in patients with WT FLT3 was 20% (1/5). 0-32); this patient had WT FLT3. Among the 5 patients who achieved CRc, 2 had relapse after documented CRi (at 2.6 months and 1.6 months). Patient monitoring is ongoing, and enrollment in an expansion cohort has also commenced (FLT3 mutant patients treated with 400 mg venetoclax plus 120 mg of gilteritinib); results will be updated for the presentation. CONCLUSIONS: Venetoclax in combination with gilteritinib was well tolerated and demonstrated blast clearance in 90% of patients with FLT3 mutated AML. The high overall rate of response in patients with FLT3 mutated AML, particularly in patients with previous FLT3 TKI exposure, suggests venetoclax in combination with gilteritinib may be a highly effective treatment option for AML patients with FLT3mut+, even in patients with relapsed/refractory AML. Disclosures Perl: Bayer: Research Funding; AbbVie: Consultancy, Honoraria, Other: Non-financial support included travel costs for advisory board meetings.; Takeda: Consultancy, Honoraria, Other: Non-financial support included travel costs for advisory board meetings.; NewLink Genetics: Consultancy, Honoraria, Other: Non-financial support included travel costs for advisory board meetings.; FujiFilm: Research Funding; Novartis: Honoraria, Other: Advisory board, Non-financial support included travel costs for advisory board meetings as well as a medical writing company that assisted with manuscript preparation/submission and slide deck assembly for academic meeting presentations of the data., Research Funding; BioMed Valley Discoveries: Research Funding; Actinium Pharmaceuticals: Consultancy, Honoraria, Other: Clinical Advisory Board member, Research Funding; Agios: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Non-financial support included travel costs for advisory board meetings.; Daiichi Sankyo: Consultancy, Honoraria, Other, Research Funding; Astellas: Consultancy, Honoraria, Other: Non-financial support included travel costs for advisory board meetings as well as a medical writing company that assisted with manuscript preparation/submission and slide deck assembly for academic meeting presentations of trial data., Research Funding; Jazz: Consultancy, Honoraria, Other: Non-financial support included travel costs for advisory board meetings.; Arog: Consultancy, Other: Non-financial support included travel costs for advisory board meetings.. Daver:Otsuka: Consultancy; Immunogen: Consultancy, Research Funding; Forty-Seven: Consultancy; Genentech: Consultancy, Research Funding; Agios: Consultancy; Agios: Consultancy; Otsuka: Consultancy; Sunesis: Consultancy, Research Funding; Celgene: Consultancy; BMS: Consultancy, Research Funding; Daiichi Sankyo: Consultancy, Research Funding; Servier: Research Funding; Incyte: Consultancy, Research Funding; BMS: Consultancy, Research Funding; Abbvie: Consultancy, Research Funding; Glycomimetics: Research Funding; Astellas: Consultancy; Jazz: Consultancy; Jazz: Consultancy; Daiichi Sankyo: Consultancy, Research Funding; Hanmi Pharm Co., Ltd.: Research Funding; Sunesis: Consultancy, Research Funding; NOHLA: Research Funding; Karyopharm: Consultancy, Research Funding; Celgene: Consultancy; Pfizer: Consultancy, Research Funding; Abbvie: Consultancy, Research Funding; Novartis: Consultancy, Research Funding; Incyte: Consultancy, Research Funding; Hanmi Pharm Co., Ltd.: Research Funding; Forty-Seven: Consultancy; Servier: Research Funding; Genentech: Consultancy, Research Funding; Novartis: Consultancy, Research Funding; Immunogen: Consultancy, Research Funding; Glycomimetics: Research Funding; Karyopharm: Consultancy, Research Funding; Pfizer: Consultancy, Research Funding; NOHLA: Research Funding; Astellas: Consultancy. Pratz:Astellas Pharma: Consultancy, Research Funding; AbbVie: Consultancy, Research Funding; Agios: Consultancy, Research Funding; Boston Biomedical: Consultancy; Millenium/Takeda: Research Funding. Hong:Genentech Inc.: Employment, Equity Ownership; Roche: Equity Ownership. Bahceci:Astellas: Employment, Patents & Royalties. Tong:AbbVie: Employment, Other: stock or options. Tian:AbbVie, Inc.: Employment, Other: stock or options. Dilley:AbbVie, Inc.: Employment, Other: stock or options.

Background: Quizartinib is a once-daily, oral, highly potent and selective FLT3 inhibitor with proven single-agent activity and a manageable safety profile in FLT3-ITD R/R AML. In the global, phase 3 QuANTUM-R study, quizartinib demonstrated a significant survival benefit over salvage chemotherapy(Cortes, et al. Lancet Oncol, 2019; NCT02039726). Additional support for the safety profile of quizartinib at the proposed dosing regimen (60 mg QD with a 30-mg starting dose) is provided by a pooled analysis of over 600 patients with R/R AML. Methods: We pooled data from four studies: one phase 3 (QuANTUM-R), two phase 2, (ACC220-002 and 2689-CL-2004; Cortes, et al. Lancet Oncol, 2018; Cortes, et al. Blood, 2018), and one phase 1 (CP0001: only patients assigned to continuous daily dosing regimens are included in this analysis; Cortes, et al. J Clin Oncol, 2013) to provide an integrated safety summary of quizartinib monotherapy for the treatment of R/R AML. Treatment-emergent adverse events (TEAEs), on-treatment deaths, and adverse events of special interest (AESIs; QT prolongation and potential ventricular arrhythmias, hepatic disorders, and sequelae of cytopenias such as infections and bleeding) with quizartinib were analyzed. Results: The pooled data set included 673 patients; 51% were male, and median age was 59 years. Thirty-eight patients were assigned to quizartinib 30 mg, 277 to 60 mg, and 358 to >60 mg up to 300 mg. Overall, median treatment duration was 79 days (range, 1-1296 days) and was longest in the 60-mg dose group (95 days) vs the >60-mg (70.5 days) and 30-mg (66 days) groups. The overall TEAE profile was consistent with the results from the phase 3 QuANTUM-R study. Most on-treatment deaths (215 of 599 evaluable patients [36%]; defined as taking place between the first dose and ≤30 days after the last dose) were attributed to AML disease progression (130/599 [22%]), followed by TEAEs (83/599 [14%]), which were predominantly respiratory tract infections and events related to sepsis. TEAEs leading to discontinuation of quizartinib occurred in 173/673 patients (26%). In the 60-mg dose group (quizartinib proposed dosing regimen), the only TEAE associated with discontinuation in >2% of patients was pneumonia (6/277 patients [2%]). The most frequently reported grade ≥3 TEAEs were febrile neutropenia (240/673 [36%]), anemia (188/673 [28%]) and thrombocytopenia (182/673 [27%]) in the hematologic category and pneumonia (119/673 [18%]) and sepsis/septic shock (124/673 [18%]) in the nonhematologic category (Table 1A). In the 60-mg dose group, the most frequent AESI was infection (210/277 [76%]; Table 1B). Epistaxis and petechiae, mainly grade 1/2, were the most frequently reported hemorrhage TEAEs. TEAEs in the hemorrhage category occurred more frequently in the >60-mg dose group than the 60-mg dose group (215/358 [60%] and 136/277 [49%], respectively). The most frequent serious hemorrhage TEAEs were gastrointestinal hemorrhages (15/673 [2%]) and intracranial hemorrhage (10/673 [2%]). QTcF prolongation >500 ms (grade 3) occurred in 75/673 patients (11%), mostly in those receiving quizartinib >60 mg (n = 64) (Table 1C). In the 60-mg dose group, QTcF prolongation >500 ms occurred in 9/277 patients (3%). The median time to onset of QTcF prolongation >500 ms was shorter in the >60-mg dose group than in the 60-mg dose group (9 and 46 days, respectively). Arrhythmias potentially related to QTcF prolongation were infrequent; one event of torsade de pointes, and one event of fatal cardiac arrest (both at doses >60 mg) were observed. No dose effects were seen with hepatic disorders, cardiac arrhythmias, or cardiac failure AESI categories. Conclusions: The overall safety profile of quizartinib in this R/R AML pooled analysis is consistent with that observed in QuANTUM-R. A reduction in the incidence of QTcF prolongation was noted with lower doses of quizartinib (30 or 60 mg vs >60 mg). There was also a reduced incidence of gastrointestinal symptoms, infections, and bleeding at lower doses of quizartinib (30 or 60 mg vs >60 mg). Results from this pooled analysis demonstrate that quizartinib is well tolerated at the proposed dosing regimen (60 mg QD with a 30-mg starting dose) in patients with R/R AML. Disclosures Cortes: BiolineRx: Consultancy; Biopath Holdings: Consultancy, Honoraria; Takeda: Consultancy, Research Funding; Novartis: Consultancy, Honoraria, Research Funding; Merus: Consultancy, Honoraria, Research Funding; Daiichi Sankyo: Consultancy, Honoraria, Research Funding; Pfizer: Consultancy, Honoraria, Research Funding; Forma Therapeutics: Consultancy, Honoraria, Research Funding; Astellas Pharma: Consultancy, Honoraria, Research Funding; Jazz Pharmaceuticals: Consultancy, Research Funding; Sun Pharma: Research Funding; Immunogen: Consultancy, Honoraria, Research Funding; Bristol-Myers Squibb: Consultancy, Research Funding. Ganguly:Kite Pharma: Honoraria, Other: Advisory Board; Janssen: Honoraria, Other: Advisory Board; Seattle Genetics: Speakers Bureau; Daiichi Sankyo: Research Funding. Krämer:Roche: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Daiichi-Sankyo: Honoraria, Membership on an entity's Board of Directors or advisory committees; Bayer: Research Funding; BMS: Research Funding. Levis:FUJIFILM: Consultancy, Research Funding; Menarini: Consultancy, Honoraria; Novartis: Consultancy, Research Funding; Daiichi Sankyo Inc: Consultancy, Honoraria; Amgen: Consultancy, Honoraria; Agios: Consultancy, Honoraria; Astellas: Consultancy, Research Funding. Martinelli:Daiichi Sankyo: Consultancy, Honoraria; Amgen: Consultancy, Other: trial grant; Pfizer: Consultancy, Other: trial grant; Ariad: Consultancy, Other: trial grant; Incyte: Consultancy, Other: trial grant; Roche: Consultancy, Other: trial grant; Celgene: Consultancy, Honoraria, Other: trial grant; Janssen: Consultancy, Other: trial grant; Novartis: Consultancy, Other: trial grant; Abbvie: Consultancy, Honoraria, Other: trial grant. Perl:Takeda: Consultancy, Honoraria, Other: Non-financial support included travel costs for advisory board meetings.; Daiichi Sankyo: Consultancy, Honoraria, Other, Research Funding; Astellas: Consultancy, Honoraria, Other: Non-financial support included travel costs for advisory board meetings as well as a medical writing company that assisted with manuscript preparation/submission and slide deck assembly for academic meeting presentations of trial data., Research Funding; Arog: Consultancy, Other: Non-financial support included travel costs for advisory board meetings.; AbbVie: Consultancy, Honoraria, Other: Non-financial support included travel costs for advisory board meetings.; Actinium Pharmaceuticals: Consultancy, Honoraria, Other: Clinical Advisory Board member, Research Funding; Bayer: Research Funding; BioMed Valley Discoveries: Research Funding; FujiFilm: Research Funding; Novartis: Honoraria, Other: Advisory board, Non-financial support included travel costs for advisory board meetings as well as a medical writing company that assisted with manuscript preparation/submission and slide deck assembly for academic meeting presentations of the data., Research Funding; NewLink Genetics: Consultancy, Honoraria, Other: Non-financial support included travel costs for advisory board meetings.; Agios: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Non-financial support included travel costs for advisory board meetings.; Jazz: Consultancy, Honoraria, Other: Non-financial support included travel costs for advisory board meetings.. Russell:Jazz: Consultancy, Honoraria, Speakers Bureau; DSI: Consultancy, Honoraria, Speakers Bureau; Astellas: Consultancy, Honoraria, Speakers Bureau; Pfizer Inc: Consultancy, Honoraria, Speakers Bureau. Choi:Daiichi Sankyo: Employment. Mendell:Daiichi Sankyo, Inc.: Employment. Namuyinga:Daiichi Sankyo: Employment. Pham:Daiichi Sankyo: Employment. Said:Daiichi Sankyo: Employment. Wang:Daiichi Sankyo: Employment. Mitov:Daiichi Sankyo UK Ltd: Employment. Kim:Daiichi Sankyo: Employment. Khaled:Alexion: Consultancy, Speakers Bureau; Daiichi Sankyo: Other: Travel support; Omeros: Consultancy.

Introduction: R/R FLT3-ITD AML is an aggressive hematologic malignancy with a generally poor prognosis and high relapse rate even after allogeneic hematopoietic stem cell transplantation (HSCT). QuANTUM-R (NCT02039726), a large, global, phase 3, randomized, controlled trial, showed that single-agent quizartinib significantly prolonged overall survival (OS) vs salvage chemotherapy (SC) in patients with R/R FLT3-ITD AML after first-line treatment with or without HSCT (Cortes et al, Lancet Oncol 2019). To evaluate both quality and quantity of life for patients with R/R FLT3-ITD AML, we conducted a Q-TWiST analysis of QuANTUM-R data to compare survival between patients receiving quizartinib and SC adjusted for quality of life (QOL). Methods: The primary analysis cohort was the intent-to-treat (ITT) QuANTUM-R population, which included 367 patients (245 patients receiving quizartinib; 122 patients receiving SC). The secondary analysis cohort was the per-protocol analysis set (PPS), which excluded patients randomized but not treated and patients with major protocol violations who would affect assessment of efficacy endpoints (231 patients receiving quizartinib; 88 patients receiving SC). Each patient's OS was partitioned into 3 health states: time with any grade 3/4 treatment-emergent adverse events (TEAEs) before relapse (TOX), time without relapse or grade 3/4 toxicity (TWiST), and time after relapse (REL). Q-TWiST was assessed at 104 weeks (approximate median follow-up of QuANTUM-R) as the mean time spent in each state weighted by its respective QOL, represented by health utility (u; 0.0-1.0). Q-TWiST was calculated as follows: Q-TWiST = u(TWiST) × TWiST + u(TOX) × TOX + u(REL) × REL for which u(TWiST), u(TOX), and u(REL) represent the utilities applied to the restricted mean time in TWiST, TOX, and REL, respectively. Relative Q-TWiST gain (ie, Q-TWIST gain divided by mean OS of salvage chemotherapy) of ≥ 15% was considered clinically important, based on published minimally important difference norms (Revicki et al, Qual Life Res 2006). The base case that assessed the Q-TWiST difference between quizartinib and SC for the ITT population included any grade 3/4 TEAEs and set utilities at commonly assumed values: u(REL) = u(TOX) = 0.5, relative to u(TWiST) = 1.0. A sensitivity analysis was conducted for which u(TOX) and u(REL) were varied from 0.0 to 1.0. The following additional scenarios analyses were conducted: (1) including only treatment-related (TR) grade 3/4 TEAEs, (2) assessing Q-TWiST difference between quizartinib and SC for the PPS cohort, and (3) including only TR grade 3/4 TEAEs for the PPS cohort. 95% CIs were estimated via nonparametric bootstrap. Results: For the ITT population, quizartinib was associated with a mean OS gain of 8.5 weeks vs SC at 104 weeks from randomization (Table). In base case, the mean (95% CI) Q-TWiST gain at 104 weeks for quizartinib vs SC was 6.7 weeks (1.7-12.3; relative gain, 20.3%), which was statistically significant and clinically meaningful (Table). For the sensitivity analysis for which u(TOX) and u(REL) were varied from 0.0 to 1.0, Q-TWiST gains for quizartinib ranged from 5.0 (u[REL] = u[TOX] = 0.0) to 8.5 weeks (u[REL] = u[TOX] = 1.0). The relative Q-TWiST gains for quizartinib vs SC remained clinically important, irrespective of the values for u(TOX) and u(REL) and ranged from 15.2% to 25.5% (Figure). In the scenario analyses (Table), (1) when only TR grade 3/4 TEAEs were included, the Q-TWiST gain for quizartinib was 7.4 weeks (2.2-13.0; relative gain, 22.5%), (2) in the PPS cohort, the mean (95 % CI) Q-TWiST gain for quizartinib was 6.9 weeks (0.8-13.5; relative gain, 20.7%), and (3) when including only TR grade 3/4 TEAEs in the PPS, the Q-TWiST gain for quizartinib was 7.5 weeks (1.5-14.2; relative gain, 22.5%). Conclusions: Quizartinib significantly prolonged quality-adjusted survival vs SC in patients with R/R FLT3-ITD AML after disease control, safety, and QOL were accounted for, providing evidence of meaningful clinical benefit in a patient population with few treatment options. To put these results in perspective, the relative Q-TWiST gains for quizartinib reported herein are larger than nearly 90% of the relative Q-TWiST gains reported in a recent systematic review of 81 Q-TWiST comparisons across 13 cancers (Solem et al, Exp Rev Pharmacoecon Outcomes Res 2018). Disclosures Cortes: Astellas Pharma: Consultancy, Honoraria, Research Funding; Jazz Pharmaceuticals: Consultancy, Research Funding; Bristol-Myers Squibb: Consultancy, Research Funding; Takeda: Consultancy, Research Funding; Pfizer: Consultancy, Honoraria, Research Funding; Novartis: Consultancy, Honoraria, Research Funding; Daiichi Sankyo: Consultancy, Honoraria, Research Funding; Merus: Consultancy, Honoraria, Research Funding; Immunogen: Consultancy, Honoraria, Research Funding; Forma Therapeutics: Consultancy, Honoraria, Research Funding; Biopath Holdings: Consultancy, Honoraria; BiolineRx: Consultancy; Sun Pharma: Research Funding. Ganguly:Daiichi Sankyo: Research Funding; Kite Pharma: Honoraria, Other: Advisory Board; Janssen: Honoraria, Other: Advisory Board; Seattle Genetics: Speakers Bureau. Khaled:Omeros: Consultancy; Alexion: Consultancy, Speakers Bureau; Daiichi Sankyo: Other: Travel support. Krämer:Roche: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Daiichi-Sankyo: Honoraria, Membership on an entity's Board of Directors or advisory committees; Bayer: Research Funding; BMS: Research Funding. Levis:Daiichi Sankyo Inc: Consultancy, Honoraria; Agios: Consultancy, Honoraria; Amgen: Consultancy, Honoraria; Menarini: Consultancy, Honoraria; Novartis: Consultancy, Research Funding; Astellas: Consultancy, Research Funding; FUJIFILM: Consultancy, Research Funding. Martinelli:Janssen: Consultancy, Other: trial grant; Celgene: Consultancy, Honoraria, Other: trial grant; Abbvie: Consultancy, Honoraria, Other: trial grant; Pfizer: Consultancy, Other: trial grant; Roche: Consultancy, Other: trial grant; Incyte: Consultancy, Other: trial grant; Daiichi Sankyo: Consultancy, Honoraria; Amgen: Consultancy, Other: trial grant; Novartis: Consultancy, Other: trial grant; Ariad: Consultancy, Other: trial grant. Perl:Bayer: Research Funding; BioMed Valley Discoveries: Research Funding; FujiFilm: Research Funding; Novartis: Honoraria, Other: Advisory board, Non-financial support included travel costs for advisory board meetings as well as a medical writing company that assisted with manuscript preparation/submission and slide deck assembly for academic meeting presentations of the data., Research Funding; Jazz: Consultancy, Honoraria, Other: Non-financial support included travel costs for advisory board meetings.; AbbVie: Consultancy, Honoraria, Other: Non-financial support included travel costs for advisory board meetings.; Actinium Pharmaceuticals: Consultancy, Honoraria, Other: Clinical Advisory Board member, Research Funding; Agios: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Non-financial support included travel costs for advisory board meetings.; Daiichi Sankyo: Consultancy, Honoraria, Other, Research Funding; Arog: Consultancy, Other: Non-financial support included travel costs for advisory board meetings.; Astellas: Consultancy, Honoraria, Other: Non-financial support included travel costs for advisory board meetings as well as a medical writing company that assisted with manuscript preparation/submission and slide deck assembly for academic meeting presentations of trial data., Research Funding; NewLink Genetics: Consultancy, Honoraria, Other: Non-financial support included travel costs for advisory board meetings.; Takeda: Consultancy, Honoraria, Other: Non-financial support included travel costs for advisory board meetings.. Russell:Astellas: Consultancy, Honoraria, Speakers Bureau; Jazz: Consultancy, Honoraria, Speakers Bureau; DSI: Consultancy, Honoraria, Speakers Bureau; Pfizer Inc: Consultancy, Honoraria, Speakers Bureau. Botteman:Pharmerit International: Employment, Equity Ownership; Alnylam Pharmaceuticals: Consultancy; Daiichi Sankyo: Consultancy, Research Funding. Shah:Merck: Research Funding; Bayer: Research Funding; Pfizer: Research Funding. Luo:Pharmerit International: Employment. Shun:Daiichi Sankyo: Employment. Ray:Daiichi Sankyo: Employment, Equity Ownership.

Background: Quizartinib, a once-daily, oral, highly potent and selective FLT3 inhibitor, demonstrated a significant improvement in survival vs SC in FLT3-ITD-positive R/R AML in the global, randomized, phase 3 QuANTUM-R study (Cortes et al. Lancet Oncol, 2019; NCT02039726). Patients with R/R FLT3-ITD-positive AML were randomized 2:1 to receive single agent quizartinib or investigator's choice of pre-selected SC. We investigated the effects of baseline co-mutations and FLT3-ITD VAF on overall survival (OS) and response (composite complete remission [CRc]) to quizartinib and SC in QuANTUM-R. Methods: We analyzed 37 recurrently mutated genes in AML in baseline bone marrow samples from 304 patients (82.8% of ITT population [N = 367; quizartinib, n = 245; SC, n = 122]) with R/R FLT3-ITD-positive AML using next-generation sequencing and a customized Archer® Core Myeloid panel. Positive mutation status was defined as ≥ 1 mutation detected in the gene region using a VAF cutoff of 2.7%. FLT3-ITD VAF was measured separately by the Navigate BioPharma FLT3 Mutation Assay (polymerase chain reaction-based, VAF cutoff of 3%). Low and high FLT3-ITD VAF were defined as ≤25% and >25%, respectively. Results: In addition to FLT3-ITD, 5 key co-mutations were detected: DNMT3Amut (n = 182/304 [59.9%]), NPM1mut (n = 168/304 [55.3%]), TET2mut (n = 98/304 [32.2%]), IDH1/2mut (n = 49/304 [16.1%]) and CEBPAmut (n = 46/304 [15.1%]). Median OS was numerically longer with quizartinib vs SC in patients with DNMT3Amut, TET2mut, IDH1/2mut and NPM1mut, but not CEBPAmut (Table). CRc rates were numerically higher with quizartinib vs SC for each of the 5 key baseline co-mutations. For single gene mutations, the longest median OS was seen in patients with CEBPAmut treated with quizartinib or SC (37 and 37.6 weeks, respectively). As the majority of NPM1mut patients were also DNMT3Amut (138/168, 82%), we examined various permutations of these two mutations. Patients with NPM1wt/DNMT3Amut had significantly longer median OS with quizartinib vs SC (39.3 vs 19.6 weeks, respectively; HR, 0.239; P = 0.003 [Table]) while NPM1mut/DNMT3Amut patients had lower and similar median OS between the 2 arms (23.6 vs 23.4 weeks, respectively). Quizartinib treatment showed significantly longer median OS vs SC in patients with high FLT3-ITD VAF (23.9 vs 17 weeks respectively; HR, 0.689, P = 0.0148), while the median OS in patients with low FLT3-ITD VAF was similar (34.1 vs 26.6 weeks, respectively; HR, 0.857, P = 0.535). Conclusions: This is the first evaluation of the effect of baseline co-mutations on clinical outcomes in a large trial of R/R AML patients with FLT3-ITD mutations treated with quizartinib. Key co-mutations identified in this analysis were found to potentially impact treatment response and OS with quizartinib, relative to SC. Despite relatively low CRc rates in patients with IDH1/2mut, this group-as well as those with NPM1wt-derived the greatest OS benefit from quizartinib compared with SC on QuANTUM-R. CEBPA mutations were associated with high CRc rates and relatively long median OS, regardless of treatment arm. Patients with NPM1mut had a higher CRc rate with quizartinib vs SC, but this did not translate into longer survival on either arm compared with NPM1wt. A high allelic burden of FLT3-ITD at the time of salvage therapy was associated with relatively poorer median OS; quizartinib significantly improved survival of patients with high FLT3-ITD VAF relative to SC. Although these results require confirmation in an independent dataset, the modulatory effects of baseline co-mutations on treatment response and OS with quizartinib appear to differ from other FLT3 inhibitors. Our results indicate that a subset of R/R AML patients may particularly derive clinical benefit from quizartinib. Table Disclosures Perl: Daiichi Sankyo: Consultancy, Honoraria, Other, Research Funding; Arog: Consultancy, Other: Non-financial support included travel costs for advisory board meetings.; AbbVie: Consultancy, Honoraria, Other: Non-financial support included travel costs for advisory board meetings.; Actinium Pharmaceuticals: Consultancy, Honoraria, Other: Clinical Advisory Board member, Research Funding; Agios: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Non-financial support included travel costs for advisory board meetings.; Jazz: Consultancy, Honoraria, Other: Non-financial support included travel costs for advisory board meetings.; NewLink Genetics: Consultancy, Honoraria, Other: Non-financial support included travel costs for advisory board meetings.; Takeda: Consultancy, Honoraria, Other: Non-financial support included travel costs for advisory board meetings.; Bayer: Research Funding; BioMed Valley Discoveries: Research Funding; FujiFilm: Research Funding; Novartis: Honoraria, Other: Advisory board, Non-financial support included travel costs for advisory board meetings as well as a medical writing company that assisted with manuscript preparation/submission and slide deck assembly for academic meeting presentations of the data., Research Funding; Astellas: Consultancy, Honoraria, Other: Non-financial support included travel costs for advisory board meetings as well as a medical writing company that assisted with manuscript preparation/submission and slide deck assembly for academic meeting presentations of trial data., Research Funding. Cortes:Astellas Pharma: Consultancy, Honoraria, Research Funding; Jazz Pharmaceuticals: Consultancy, Research Funding; Merus: Consultancy, Honoraria, Research Funding; Forma Therapeutics: Consultancy, Honoraria, Research Funding; Biopath Holdings: Consultancy, Honoraria; BiolineRx: Consultancy; Pfizer: Consultancy, Honoraria, Research Funding; Takeda: Consultancy, Research Funding; Novartis: Consultancy, Honoraria, Research Funding; Daiichi Sankyo: Consultancy, Honoraria, Research Funding; Bristol-Myers Squibb: Consultancy, Research Funding; Sun Pharma: Research Funding; Immunogen: Consultancy, Honoraria, Research Funding. Ganguly:Kite Pharma: Honoraria, Other: Advisory Board; Janssen: Honoraria, Other: Advisory Board; Seattle Genetics: Speakers Bureau; Daiichi Sankyo: Research Funding. Khaled:Omeros: Consultancy; Alexion: Consultancy, Speakers Bureau; Daiichi Sankyo: Other: Travel support. Krämer:Roche: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Daiichi-Sankyo: Honoraria, Membership on an entity's Board of Directors or advisory committees; Bayer: Research Funding; BMS: Research Funding. Martinelli:Novartis: Consultancy, Other: trial grant; Roche: Consultancy, Other: trial grant; Janssen: Consultancy, Other: trial grant; Incyte: Consultancy, Other: trial grant; Pfizer: Consultancy, Other: trial grant; Amgen: Consultancy, Other: trial grant; Celgene: Consultancy, Honoraria, Other: trial grant; Ariad: Consultancy, Other: trial grant; Abbvie: Consultancy, Honoraria, Other: trial grant; Daiichi Sankyo: Consultancy, Honoraria. Russell:Pfizer Inc: Consultancy, Honoraria, Speakers Bureau; Astellas: Consultancy, Honoraria, Speakers Bureau; Jazz: Consultancy, Honoraria, Speakers Bureau; DSI: Consultancy, Honoraria, Speakers Bureau. Chang:Daiichi Sankyo: Employment. Mires:Daiichi Sankyo: Employment. Kato:Daiichi Sankyo, Inc.: Employment; Celgene: Employment, Equity Ownership. Zhang:Daiichi Sankyo: Employment. Korkhov:Precision for Medicine, Inc.: Employment; Daiichi Sankyo: Consultancy. Wang:Precision for Medicine, Inc.: Employment; Daiichi Sankyo: Consultancy. Günnel:Precision for Medicine, Inc.: Employment; Daiichi Sankyo: Consultancy. Sumi:Daiichi Sankyo, Inc.: Employment. Isoyama:Daiichi Sankyo Co, Ltd: Employment. Lesegretain:Daiichi-Sankyo Inc.: Employment, Equity Ownership. Berisha:Daiichi Sankyo: Employment. Dos Santos:Daiichi Sankyo: Employment. Levis:Agios: Consultancy, Honoraria; Amgen: Consultancy, Honoraria; Novartis: Consultancy, Research Funding; FUJIFILM: Consultancy, Research Funding; Menarini: Consultancy, Honoraria; Astellas: Consultancy, Research Funding; Daiichi Sankyo Inc: Consultancy, Honoraria.

Introduction: Clonal selection occurring under the selective pressure of Fms-like tyrosine kinase 3 (FLT3) tyrosine kinase inhibitor (TKI) therapy is not fully understood. To date, the most common mutations found at the time of resistance to potent and selective type II FLT3 TKIs, like quizartinib, are on-target kinase domain (KD) mutations. Activating RAS pathway mutations are a common mechanism of resistance to type I FLT3 TKIs (McMahon et al., 2019 and Zhang et al., 2019). Changes in the acute myeloid leukemia (AML) genetic landscape at relapse on single agent or combination type II FLT3 TKI therapy have not been well-characterized at the single cell (SC) level. Methods: We performed SC sequencing with a novel high-throughput SC DNA sequencing platform, Mission Bio Tapestri, on bone marrow or peripheral blood samples from 11 patients with FLT3-mutant relapsed/refractory (R/R) AML treated with quizartinib. We analyzed 13 samples from 7 patients treated with quizartinib monotherapy and 12 samples from 4 patients treated with a combination of quizartinib and omacetaxine. Results: We analyzed a mean of 6,636 cells/sample (range 2,437-13,538). Each leukemia was made up of an average of 5 clonal sub-populations (range 2-7). 5/10 patients with serial samples demonstrated increased polyclonality at relapse, with a mean of 4 clones pretreatment (range 2-6) and 5 at relapse (range 2-7). All patients had an internal tandem duplication in FLT3 (FLT3-ITD) in at least 1 clone. Using SC sequencing, we visualized distinct clones with both hetero -and homo-zygous FLT3-ITD mutations. At the time of relapse after quizartinib, 7 patients (6 on monotherapy and 1 with combination therapy) developed at least one additional FLT3 KD mutation. These on-target mutations were found either as co-mutations within the FLT3-ITD clone or in a native FLT3 clone without an ITD. 4 of these 7 patients had polyclonal KD mutations (mean 2 distinct KD mutations; range 1-3), most commonly at the D835 locus. In 6/7 patients, each KD mutation was found in separate cellular subclones. However, 1 patient had multiple KD mutations within the same subclone (at the D835 and S838 loci). In 6/7 patients who relapsed with a KD mutation, the KD mutation was the dominant clone at relapse. No clones with on-target KD mutations were present prior to therapy. However, all relapse clones containing off-target mutations, found in 3/11 patients, were present in small subclones prior to clinical relapse. As an example, 1 patient who relapsed with 2 NRAS mutations had 2 distinct pre-existing clonal NRAS mutant populations, without FLT3-ITD co-mutations, detectable at Conclusions: Single cell (SC) sequencing allows for direct measurement of clonality, co-mutational status, zygosity, and clonal evolution, which can only be inferred through traditional bulk NGS. This detail reveals that individual mutations may be present in a number of different combinations and confirms that polyclonality is common even within a single leukemia. From time of diagnosis, knowledge of which mutations co-exist in the same clone can suggest potential mechanisms of resistance and help direct treatment. On therapy, SC sequencing can conclusively demonstrate clonal selection. SC sequencing allows for detection of clones not detectable by bulk NGS. The fact that all 4 patients sequenced at the time of morphologic remission had measurable residual disease (MRD) by SC sequencing suggests the benefit of SC sequencing as a strategy for MRD detection. At the time of relapse, identifying the dominant as well as smaller clonal subsets can help direct appropriate combination targeted therapy. Despite the fact that highly selective type II agents, like quizartinib, have historically been thought to select for on-target resistance, SC sequencing highlights more diverse mechanisms of resistance including off-target mutations. Our data supports the need for effective combination therapy to delay or suppress outgrowth of resistant clones. Disclosures Jacob: Mission Bio Inc.: Employment. Durruthy-Durruthy:Mission Bio Inc.: Employment. Levis:FUJIFILM: Consultancy, Research Funding; Daiichi Sankyo Inc: Consultancy, Honoraria; Agios: Consultancy, Honoraria; Menarini: Consultancy, Honoraria; Novartis: Consultancy, Research Funding; Astellas: Consultancy, Research Funding; Amgen: Consultancy, Honoraria. Perl:Novartis: Honoraria, Other: Advisory board, Non-financial support included travel costs for advisory board meetings as well as a medical writing company that assisted with manuscript preparation/submission and slide deck assembly for academic meeting presentations of the data., Research Funding; Astellas: Consultancy, Honoraria, Other: Non-financial support included travel costs for advisory board meetings as well as a medical writing company that assisted with manuscript preparation/submission and slide deck assembly for academic meeting presentations of trial data., Research Funding; Daiichi Sankyo: Consultancy, Honoraria, Other, Research Funding; Actinium Pharmaceuticals: Consultancy, Honoraria, Other: Clinical Advisory Board member, Research Funding; Takeda: Consultancy, Honoraria, Other: Non-financial support included travel costs for advisory board meetings.; BioMed Valley Discoveries: Research Funding; NewLink Genetics: Consultancy, Honoraria, Other: Non-financial support included travel costs for advisory board meetings.; Arog: Consultancy, Other: Non-financial support included travel costs for advisory board meetings.; FujiFilm: Research Funding; Bayer: Research Funding; Agios: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Non-financial support included travel costs for advisory board meetings.; AbbVie: Consultancy, Honoraria, Other: Non-financial support included travel costs for advisory board meetings.; Jazz: Consultancy, Honoraria, Other: Non-financial support included travel costs for advisory board meetings.. Smith:Astellas Pharma: Research Funding; Abbvie: Research Funding; Revolution Medicines: Research Funding; fujiFilm: Research Funding.

Introduction: The phase 3 ADMIRAL trial demonstrated that gilteritinib, a novel, potent, oral FLT3 inhibitor, significantly prolonged overall survival and resulted in higher remission rates compared with salvage chemotherapy in patients with FLT3-mutation-positive (FLT3mut+) relapsed/refractory (R/R) acute myeloid leukemia (AML; Perl AE, et al. AACR 2019), even in the presence of common co-occurring AML mutations (DNMT3A, NPM1, and WT1) (Levis MJ, et al. J Clin Oncol. 2019;37[suppl 15]:7000). However, as with other FLT3 inhibitors, patients often develop resistance after an initial response to gilteritinib. Evidence suggests that expansion of leukemic clones containing mutations in Ras/MAPK pathway genes NRAS and KRAS mediates secondary resistance to gilteritinib in patients with FLT3mut+ R/R AML, and confirms that cells with Ras/MAPK pathway mutations are FLT3mut+ (McMahon CM, et al. Cancer Discov. 2019; doi: 10.1158/2159-8290). We evaluated emerging mutations in patients who relapsed while receiving gilteritinib therapy in the ADMIRAL trial. Methods: Blood or bone marrow samples were available for 361 patients at baseline (97.3% of the intention-to-treat population [N=371]) and for 40 patients who relapsed on gilteritinib treatment. Samples were analyzed by next-generation sequencing using the Archer Core Myeloid Panel. Data were analyzed using Archer Analysis software; the variant allele frequency (VAF) cutoff was ≥2.7%. Results: Of 371 patients enrolled in the ADMIRAL trial, 247 were assigned to 120-mg/day gilteritinib and 75 (30.5%) relapsed during the study. Most relapses (n=72/75; 96.0%) occurred ≤4 weeks from the last gilteritinib dose. Forty patients who had samples available at baseline also had samples at relapse for comparison. No samples were available from patients who relapsed on chemotherapy. At relapse, 27/40 patients (67.5%) had new mutations, including mutations in Ras/MAPK pathway genes (n=18), FLT3 (n=6), WT1 (n=3), IDH1 (n=1), and GATA2 (n=1) (Table). Thirteen patients (32.5%) had no new mutations. Of the 18 patients with Ras/MAPK pathway gene mutations at relapse, 11 (61.1%) had >1 new mutation at relapse (range, 2-6). The most frequently mutated Ras/MAPK pathway gene was NRAS (n=11). Patients were also assessed for Ras/MAPK gene pathway mutations prior to gilteritinib therapy. Among all FLT3mut+ patients analyzed for co-mutated genes at baseline (n=361), 25 (6.9%) had Ras/MAPK pathway gene mutations detected (gilteritinib, n=18; salvage chemotherapy, n=7; median VAF, 13% [range, 3.4%-50%]). In contrast to the 12.0% of patients (n=3/25) who had >1 Ras/MAPK pathway gene mutation at baseline, 61.1% (n=11/18) had >1 Ras/MAPK pathway gene mutation at relapse. Notably, a considerable number of gilteritinib-treated patients who had Ras/MAPK pathway gene mutations at baseline achieved remission: the rate of CRc (ie, composite complete remission: complete remission [CR] or CR with incomplete hematologic/platelet recovery) was 38.9% (n=7/18); the rate of CR/CRh (ie, CR or CR with partial hematologic recovery) was 27.8% (n=5/18). Six patients acquired new FLT3 mutations at relapse. Five of these six patients acquired a F691L gatekeeper mutation; one of these five patients also acquired a FLT3 juxtamembrane domain point mutation. Of the three patients who acquired a WT1 mutation at relapse, one also acquired a FLT3 F691L gatekeeper mutation. The acquisition of Ras/MAPK pathway gene mutations and FLT3 F691L gatekeeper mutations at relapse was mutually exclusive. Conclusions: In patients with FLT3mut+ R/R AML who relapsed on gilteritinib therapy, Ras/MAPK pathway gene mutations and FLT3 F691L gatekeeper mutations were the most common mutational events. The presence of a Ras/MAPK pathway gene mutation at baseline did not preclude benefit from gilteritinib therapy, possibly due to fewer Ras/MAPK pathway gene mutations per patient at baseline than at relapse. The acquisition of multiple Ras/MAPK pathway gene mutations at relapse likely mediates continued engagement of Ras/MAPK signaling in patients with FLT3mut+ R/R AML receiving gilteritinib. The frequency of emergent FLT3 F691 gatekeeper mutations at relapse in patients who received 120-mg/day gilteritinib in the ADMIRAL study was similar to that observed in relapsed patients who received 20- to 450-mg/day gilteritinib (Levis MJ, et al. Blood. 2017;130[suppl 1]:2705). Table Disclosures Smith: Revolution Medicines: Research Funding; Astellas Pharma: Research Funding; fujiFilm: Research Funding; Abbvie: Research Funding. Levis:Astellas: Consultancy, Research Funding; FUJIFILM: Consultancy, Research Funding; Menarini: Consultancy, Honoraria; Novartis: Consultancy, Research Funding; Agios: Consultancy, Honoraria; Amgen: Consultancy, Honoraria; Daiichi Sankyo Inc: Consultancy, Honoraria. Perl:Astellas: Consultancy, Honoraria, Other: Non-financial support included travel costs for advisory board meetings as well as a medical writing company that assisted with manuscript preparation/submission and slide deck assembly for academic meeting presentations of trial data., Research Funding; BioMed Valley Discoveries: Research Funding; Daiichi Sankyo: Consultancy, Honoraria, Other, Research Funding; Arog: Consultancy, Other: Non-financial support included travel costs for advisory board meetings.; AbbVie: Consultancy, Honoraria, Other: Non-financial support included travel costs for advisory board meetings.; Actinium Pharmaceuticals: Consultancy, Honoraria, Other: Clinical Advisory Board member, Research Funding; Agios: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Non-financial support included travel costs for advisory board meetings.; Jazz: Consultancy, Honoraria, Other: Non-financial support included travel costs for advisory board meetings.; NewLink Genetics: Consultancy, Honoraria, Other: Non-financial support included travel costs for advisory board meetings.; Takeda: Consultancy, Honoraria, Other: Non-financial support included travel costs for advisory board meetings.; Bayer: Research Funding; FujiFilm: Research Funding; Novartis: Honoraria, Other: Advisory board, Non-financial support included travel costs for advisory board meetings as well as a medical writing company that assisted with manuscript preparation/submission and slide deck assembly for academic meeting presentations of the data., Research Funding. Martinelli:Daiichi Sankyo: Consultancy, Honoraria; Roche: Consultancy, Other: trial grant; Ariad: Consultancy, Other: trial grant; Janssen: Consultancy, Other: trial grant; Amgen: Consultancy, Other: trial grant; Pfizer: Consultancy, Other: trial grant; Abbvie: Consultancy, Honoraria, Other: trial grant; Celgene: Consultancy, Honoraria, Other: trial grant; Novartis: Consultancy, Other: trial grant; Incyte: Consultancy, Other: trial grant. Berman:Astellas: Membership on an entity's Board of Directors or advisory committees, Research Funding. Montesinos:Karyopharm: Membership on an entity's Board of Directors or advisory committees, Other: Research support; Pfizer: Membership on an entity's Board of Directors or advisory committees, Other: Research support, Research Funding, Speakers Bureau; Celgene: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other: Research support, Speakers Bureau; Teva: Membership on an entity's Board of Directors or advisory committees, Other: Research support, Research Funding, Speakers Bureau; Abbvie: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees, Other: Research support, Research Funding, Speakers Bureau; Daiichi Sankyo: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other: Research support, Speakers Bureau; Janssen: Membership on an entity's Board of Directors or advisory committees, Other: Research support, Research Funding, Speakers Bureau; Incyte: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Baer:Abbvie: Research Funding; Astellas: Research Funding; Al Therapeutics: Research Funding; Forma: Research Funding; Incyte: Research Funding; Kite: Research Funding; Takeda: Research Funding. Larson:Celgene: Consultancy; Agios: Consultancy; Novartis: Honoraria, Other: Contracts for clinical trials. Yokoyama:Astellas: Other: Travel expenses. Recher:Incyte: Honoraria; Astellas: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Sunesis: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Jazz: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Amgen: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Abbvie: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Astellas: Consultancy, Membership on an entity's Board of Directors or advisory committees; Macrogenics: Consultancy, Membership on an entity's Board of Directors or advisory committees. Yoon:MSD: Consultancy; Kyowa Hako Kirin: Research Funding; Janssen: Consultancy; Genentech, Inc.: Research Funding; Amgen: Consultancy, Honoraria; Yuhan Pharma: Research Funding; Novartis: Consultancy, Honoraria. Hill:Astellas: Employment; Ligacept, LLC.: Other: Stock, Patents & Royalties. Rosales:Astellas: Employment. Bahceci:Astellas: Employment, Patents & Royalties.

Introduction: Older patients with high-risk myeloid malignancies are now eligible for either induction chemotherapy (IC) or novel treatment strategies including liposomal cytarabine and daunorubicin (Vyxeos) or hypomethylating agent (HMA)/venetoclax. Vyxeos and HMA/venetoclax may be associated with less early mortality, but no trials have demonstrated significantly less mortality compared to IC. In this context, we need a better tool to determine a patient's risk of early mortality by strategy in order to inform therapy selection for older patients. The current methods to assess a patient's fitness for IC are the Eastern Cooperative Oncology Group (ECOG) or Karnofsky Performance Status (KPS) assessments, clinician subjective evaluations [i.e. gestalt (CG)], and often age itself (>75-80 years). None of these include objective measures of fitness. The Fried frailty phenotype (FP) uses both subjective (exhaustion and activity level) and objective measures (weight loss, gait speed, and grip strength) of frailty to categorize patients into fit, pre-frail, and frail. We hypothesized that FP would correlate with early mortality in this population and could be used to guide initial treatment selection. Methods: From September, 2018 to June, 2019 we prospectively enrolled 30 patients age 60 years or older with newly diagnosed, untreated acute myeloid leukemia (AML) or high-risk myelodysplastic syndrome (MDS) on an ongoing institutional review board approved clinical trial. We performed FP, CG, hematopoietic cell transplantation-comorbidity index (HCT-CI), and ECOG assessments on all patients prior to initiation of any therapy for their high grade myeloid disease. The primary endpoints were 60 and 100-day mortality. Results: Median patient age and follow up were 70.9 (range 61-82) years and 111 days, respectively. Patients had high-risk disease features as shown in Table 1, with the vast majority of AML patients being adverse risk by European Leukemia Network criteria and all MDS patients being high or very high-risk by the Revised International Prognostic Scoring System. The most common molecular mutations were TP53, ASXL1, RUNX1, IDH1/2, FLT3, and DNMT3A. IC consisting of either 7+3 or Vyxeos was used in 11 patients, HMA alone or in combination in 16, targeted therapy with enasidenib alone in 1, and best supportive care (BSC) in 2 (Table 1). Four patients who were frail by FP received IC (3 with Vyxeos). By FP assessments, 17% of patients were fit (score 0), 33% were pre-frail (score 1-2), and 50% were frail (score 3-5). In contrast, CG categorized 37% of patients as fit, 30% as pre-frail, and 33% as frail. Seven of 15 frail patients by FP were categorized as pre-frail or fit by CG. FP and ECOG scores also differed with 7 patients having low-risk ECOG scores of 0-1 and a high-risk FP of ≥3 (frail). For entire cohort, 60- and 100-day mortality rates were 15% and 25%, respectively. Frail patients by FP had 60-day and 100-day mortality rates of 32% and 51%, respectively, which was significantly worse than fit and pre-frail patients, all of whom were alive at 100 days (Figure 1/2, p=.016). Of the 6 out of 15 FP frail patients who died, 1 received a HMA alone, 3 HMA with venetoclax, and 2 BSC. In patients with ECOG scores of 0-1 or those categorized as fit by CG, 100-day mortalities were 8% and 10%, respectively. Mortality for patients with HCT-CI scores of 1-2 was unexpectedly higher (34% at both 60 days and 100 days) than for patients with higher risk HCT-CI scores ≥3 (13% and 29%, respectively). Conclusion: In newly diagnosed older patients with advanced myeloid neoplasms, being frail by FP was associated with increased 60 and 100-day mortality, owing to high mortality rates with HMA based therapies. While HCT-CI scores have been significantly associated with mortality after allogeneic transplantation, we observed that these scores were not linearly associated with survival or mortality in newly diagnosed AML and high/very-high risk MDS patients. By ECOG and CG, even the low risk groups contained patient deaths, suggesting that these standard metrics may not capture certain at-risk patients. CG tended to down grade frailty scores, categorizing patients as fitter than they were by FP. As such, FP may be a useful tool to predict early mortality. Further research is warranted to determine whether mortality differs by treatment within a given FP category, which may support the use of FP to select initial therapy. Disclosures Frey: Novartis: . Gill:Novartis: Research Funding; Tmunity Therapeutics: Research Funding; Carisma Therapeutics: Research Funding; Amphivena: Consultancy; Aro: Consultancy; Intellia: Consultancy; Sensei Bio: Consultancy; Carisma Therapeutics: Equity Ownership. Perl:Bayer: Research Funding; BioMed Valley Discoveries: Research Funding; FujiFilm: Research Funding; Novartis: Honoraria, Other: Advisory board, Non-financial support included travel costs for advisory board meetings as well as a medical writing company that assisted with manuscript preparation/submission and slide deck assembly for academic meeting presentations of the data., Research Funding; Jazz: Consultancy, Honoraria, Other: Non-financial support included travel costs for advisory board meetings.; NewLink Genetics: Consultancy, Honoraria, Other: Non-financial support included travel costs for advisory board meetings.; Takeda: Consultancy, Honoraria, Other: Non-financial support included travel costs for advisory board meetings.; Astellas: Consultancy, Honoraria, Other: Non-financial support included travel costs for advisory board meetings as well as a medical writing company that assisted with manuscript preparation/submission and slide deck assembly for academic meeting presentations of trial data., Research Funding; Agios: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Non-financial support included travel costs for advisory board meetings.; Daiichi Sankyo: Consultancy, Honoraria, Other, Research Funding; Arog: Consultancy, Other: Non-financial support included travel costs for advisory board meetings.; AbbVie: Consultancy, Honoraria, Other: Non-financial support included travel costs for advisory board meetings.; Actinium Pharmaceuticals: Consultancy, Honoraria, Other: Clinical Advisory Board member, Research Funding. Maillard:Genentech: Consultancy; Regeneron: Consultancy. Pratz:Millenium/Takeda: Research Funding; AbbVie: Membership on an entity's Board of Directors or advisory committees, Research Funding; Agios: Membership on an entity's Board of Directors or advisory committees, Research Funding; Astellas: Membership on an entity's Board of Directors or advisory committees, Research Funding. Porter:Kite: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees, Patents & Royalties, Research Funding; Incyte: Membership on an entity's Board of Directors or advisory committees; Glenmark Pharm: Membership on an entity's Board of Directors or advisory committees; Immunovative: Membership on an entity's Board of Directors or advisory committees; American Board of Internal Medicine: Membership on an entity's Board of Directors or advisory committees; Wiley and Sons: Honoraria; Genentech: Employment. Carroll:Astellas Pharmaceuticals: Research Funding; Incyte: Research Funding; Janssen Pharmaceuticals: Consultancy. Luger:Seattle Genetics: Research Funding; Biosight: Research Funding; Ariad: Research Funding; Agios: Honoraria; Genetech: Research Funding; Daichi Sankyo: Honoraria; Onconova: Research Funding; Kura: Research Funding; Jazz: Honoraria; Celgene: Research Funding; Cyslacel: Research Funding; Pfizer: Honoraria.

Background FLT3-ITD mutations occur in about 25% of patients (pts) with acute myeloid leukemia (AML) and are associated with poor outcomes. Pts with relapsed/refractory (R/R) FLT3-ITD AML have worse prognosis and high unmet medical need. Quizartinib (Q) is a potent and selective FLT3i with promising activity and a manageable safety profile. QuANTUM-R was a global, phase 3, randomized trial of Q vs chemotherapy (SC) in pts with R/R FLT3-ITD AML (NCT02039726). Methods Pts with R/R FLT3-ITD AML w/wo hematopoietic stem cell transplant (HSCT) were randomized to receive Q or a preselected investigator choice SC: low-dose cytarabine; mitoxantrone, etoposide, and intermediate-dose cytarabine (MEC); or fludarabine, cytarabine, and G-CSF with idarubicin (FLAG-IDA). Prior midostaurin was allowed. Pts receiving HSCT after Q could resume Q after HSCT. Primary and secondary endpoints were overall survival (OS) and event-free survival (EFS), respectively. Exploratory endpoints included response rate, time to and duration of response, and transplant rate. Results 367 pts were randomized; 245 to Q and 122 to SC. Median follow-up was 23.5 mo. OS hazard ratio (HR) of Q relative to SC was 0.76 (95% CI, 0.58-0.98; P=.0177). Median OS was 6.2 (95% CI, 5.3-7.2) vs 4.7 (95% CI, 4.0-5.5) mo in Q and SC arms, respectively. EFS HR was 0.90 (95% CI, 0.70-1.16; P=.1071); median EFS was 1.4 (95% CI, 0.0-1.9) vs 0.9 (95% CI, 0.4-1.3) mo, respectively. Sensitivity analyses and OS subgroup analyses supported Q vs SC. Composite complete response (CRc) was 48% and 27% in Q and SC arms, respectively. Transplant rate was 32% (Q) and 12% (SC). Median time to first CRc was 4.9 wk for Q. The most common grade ≥ 3 TEAEs in both arms were infections and those associated with cytopenia. Conclusion OS benefit was observed with single-agent Q vs SC in pts with R/R FLT3-ITD AML with a favorable Q safety profile, providing evidence of meaningful clinical benefit in pts with limited treatment options.

Introduction: Gilteritinib is a potent/selective oral inhibitor of FMS-like tyrosine kinase 3 (FLT3). Based upon interim analysis response rates from the ADMIRAL Phase III study of gilteritinib vs salvage chemotherapy (SC) in patients (pts) with R/R FLT3mut+ AML (NCT02421939), gilteritinib became the first FLT3 inhibitor approved as single agent therapy in this population. Here we present the final results of this pivotal trial. Methods: Adults with confirmed FLT3mut+ AML (FLT3-ITD and/or FLT3-TKD D835 or I836 mutations) refractory to induction chemotherapy or in untreated first relapse were randomized (2:1) to receive continuous 28-day cycles of 120 mg/day gilteritinib or pre-randomization selected SC: low-dose cytarabine (LoDAC), azacitidine (AZA), mitoxantrone/etoposide/cytarabine (MEC), or fludarabine/cytarabine/granulocyte colony-stimulating factor/idarubicin (FLAG-IDA). Prior FLT3 inhibitor use, other than midostaurin or sorafenib, was excluded. Overall survival (OS) and the combined rate of complete remission/complete remission with partial hematologic recovery (CR/CRh) were co-primary endpoints. Secondary endpoints were event-free survival (EFS) and CR rate; safety/tolerability was also examined. Results: A total of 371 pts were randomized: 247 to gilteritinib and 124 to SC (MEC, 25.7%; FLAG-IDA, 36.7%; LoDAC, 14.7%; AZA, 22.9%). Median age was 62 years (range, 19-85). Baseline FLT3 mutations were: FLT3-ITD, 88.4%; FLT3-TKD, 8.4%; both FLT3-ITD and FLT3-TKD, 1.9%; unconfirmed, 1.3%. Overall, 39.4% of pts had refractory AML and 60.6% had relapsed AML. Patients randomized to gilteritinib had significantly longer OS (9.3 months) than SC (5.6 months; hazard ratio [HR] for death = 0.637; P=0.0007); 1-year survival rates were 37.1% and 16.7%, respectively. The CR/CRh rates for gilteritinib and SC were 34.0% and 15.3%, respectively (P=0.0001); CR rates were 21.1% and 10.5% (2-sided P=0.0106). Median EFS was 2.8 months and 0.7 months in the gilteritinib and SC arms, respectively (HR 0.793, P=0.0830). Common adverse events (AEs) in all randomized pts were febrile neutropenia (43.7%), anemia (43.4%), and pyrexia (38.6%). Common grade ≥3 AEs related to gilteritinib were anemia (19.5%), febrile neutropenia (15.4%), thrombocytopenia (12.2%), and decreased platelet count (12.2%). Adjusted for exposure duration, serious treatment-emergent AEs per patient year were less common with gilteritinib (7.1%) than SC (9.2%). Conclusions: In patients with R/R FLT3mut+ AML, the potent, selective FLT3 inhibitor gilteritinib resulted in significantly longer OS and higher response rates compared with chemotherapy and had a favorable safety profile. These results change the treatment paradigm for salvage therapy of R/R FLT3mut+ AML and establish gilteritinib as the new standard of care. Citation Format: Alexander E. Perl, Giovanni Martinelli, Jorge E. Cortes, Andreas Neubauer, Ellin Berman, Stefania Paolini, Pau Montesinos, Maria R. Baer, Richard A. Larson, Celalettin Ustun, Francesco Fabbiano, Antonio Di Stasi, Robert Stuart, Rebecca Olin, Margaret Kasner, Fabio Ciceri, Wen-Chien Chou, Nikolai Podoltsev, Christian Recher, Hisayuki Yokoyama, Naoko Hosono, Sung-Soo Yoon, Je-Hwan Lee, Timothy Pardee, Amir T. Fathi, Chaofeng Liu, Xuan Liu, Erkut Bahceci, Mark J. Levis. Gilteritinib significantly prolongs overall survival in patients with FLT3-mutated (FLT3mut+) relapsed/refractory (R/R) acute myeloid leukemia (AML): Results from the Phase III ADMIRAL trial [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr CT184.

7000 Background: The FLT3 inhibitor, gilteritinib, showed superior response and overall survival (OS) compared with salvage chemotherapy (SC) in patients (pts) with FLT3mut+ R/R AML in the phase 3 ADMIRAL study. We analyzed the impact of baseline co-mutations and FLT3-ITD allelic ratio (AR) on response and OS. Methods: A total of 37 recurrently mutated genes in AML (Archer Core Myeloid Panel) were analyzed by next-generation sequencing; the cutoff for co-mutation positivity (co-mut+) was ≥0.027. Baseline FLT3-ITD AR ( FLT3-ITD to FLT3 wild-type DNA) was measured by the LeukoStrat CDx FLT3 Mutation Assay. The median FLT3-ITD AR value of 0.77 was used to define high (≥0.77) vs low (mut+ pts identified four major co-mutation cohorts, each with ≥10% of pts: NPM1 (n=173; 47.9%), DNMT3A (n=115; 31.9%), DNMT3A/NPM1 (n=86; 23.8%) , and WT1 (n=65; 18.0%). In addition, seven pts (1.9%) had all three co-mutations (ie, NPM1, DNMT3A, and WT1). The gilteritinib arm had superior response rates and OS across all four major co-mutation cohorts, with the greatest survival benefit in pts with DNMT3A/NPM1 co-mut+ (Table). In FLT3-ITD AR analyses (n=335), gilteritinib conferred longer OS than SC in pts with a high or low FLT3-ITD AR (gilteritinib: high FLT3-ITD AR, 7.1 mos vs low FLT3-ITD AR, 10.6 mos; SC: high FLT3-ITD AR, 4.3 mos vs low FLT3-ITD AR, 6.9 mos). In both arms, OS was longer in the low FLT3-ITD AR cohort than the high FLT3-ITD AR cohort but the difference in the gilteritinib arm was not statistically significant (gilteritinib: HR=1.341, P=0.0712; SC: HR=2.01, P=0.0021). Conclusions: The ADMIRAL trial shows that the clinical benefit of gilteritinib in FLT3mut+ R/R AML is maintained regardless of NPM1, DNMT3A, DNMT3A/ NPM1, or WT1 co-mut+ or high FLT3-ITD AR. Clinical trial information: NCT02421939. [Table: see text]

Introduction Grade (gr) 2-4 mucositis complicates myeloablative (MAC) allogeneic hematopoietic transplantation (HCT) in 90% of patients. Methotrexate (MTX) GVHD prophylaxis (ppx) contributes to mucositis and delays engraftment. Severe mucositis increases patient-controlled analgesia (PCA) and TPN (total parenteral nutrition) use, length of stay (LOS) and precludes completion of post HCT MTX. Leucovorin (LCV) following MTX is controversial. Objectives To address exacerbation of mucositis by MTX, we implemented routine LCV post MAC alloHCT and compared outcomes with historical controls. The primary endpoint was the duration of gr 2-4 mucositis. Secondary endpoints were the incidence of gr 3-4 mucositis, time to engraftment, TPN and PCA use, LOS, incidence of GVHD and relapse. Methods Thirty-two consecutive adults received MAC alloHCT and MTX ppx with LCV 15 mg PO q6h x 4 doses, 12 h post d+3, +6, and +11 MTX and were compared to 33 consecutive historical controls. Controls did not receive routine LCV, but may have received ≥ 1 dose post d+6 or +11 MTX at physician discretion. Results Baseline characteristics were similar between the groups. All patients received tacrolimus and MTX GVHD ppx, most with Cy/TBI conditioning. Forty percent received peripheral blood stem cells and 60% had a matched unrelated donor. The median age was 46 y and 50% had AML. Thirty percent of controls received ≥ 1 LCV dose (most post d+11 MTX). The mean duration of gr 2-4 mucositis was shorter with LCV vs. control (7.4 vs. 11 d, p = 0.02). A trend towards lower incidence of gr 3-4 mucositis was observed with LCV (34% vs. 58%, p = 0.08). TPN use was similar between groups (25% vs. 36%, p = 0.4), however duration was shorter with LCV (8.6 vs. 21 d, p = 0.02). A trend towards less frequent PCA use was observed with LCV (34% vs. 58%, p = 0.08). Neutrophil engraftment was faster with LCV (17.6 vs. 20 d, p = 0.04) and a trend towards faster platelet engraftment was observed (15 vs. 20 d, p = 0.06). LOS was shorter with LCV (27 vs. 33 d, p = 0.01). LCV did not impact the incidence of GVHD. Relapse was less common in the LCV group (3% vs. 27%, p = 0.01) albeit with a shorter follow up (mean 202 d vs. 560 d). Conclusion Routine LCV addition to MAC alloHCT with MTX ppx shortened the duration of gr 2-4 mucositis, expedited neutrophil engraftment, shortened TPN and LOS and showed trends towards reduction in clinically important endpoints related to mucositis incidence, severity and associated supportive care. Our small sample size and non-randomized design may limit the strength of these conclusions. Differences between the groups may have been biased towards the null as 30% of controls received ≥ 1 LCV dose. LCV ppx warrants prospective evaluation to assess effects on mucositis, engraftment, GVHD, resource utilization and LOS.

Leukemia cutis (LC), the infiltration of the epidermis, dermis, or subcutis with leukemia cells, complicates 5–10% of cases of acute myeloid leukemia (AML) in adults and is considered a marker of poor prognosis.1–3 While the association between AML with monocytic features and LC has been described, little is known about the association of other AML characteristics and LC.2,4,5 Recently, a number of recurrent gene mutations have been described in AML; however, the association of these mutations and LC has not been systematically investigated.6,7 Using amplicon-based next-generation sequencing (NGS) of a panel of recurrent, hematologic malignancy-associated mutations, we sought to determine the association between molecular markers and LC. We identified 284 patients diagnosed with AML at the University of Pennsylvania (2001–2014) who had undergone targeted NGS analysis of 33 genes associated with hematologic malignancy;8 of these, 23 are recurrently mutated in AML and were studied (listed in Table 2). These 284 cases were identified either from the Hematologic Malignancies Tissue Bank at the University of Pennsylvania (2001–2013), or from a pathology database of patients tested in a clinical context (after February 2013). Using a clinical database of acute leukemia patients (February 2011 – August 2014) who were evaluated for NPM1 mutations by a targeted method, an additional 276 patients with known NPM1 status were identified. Redundant cases were excluded. Table 2. AML-Associated Somatic Mutations and Leukemia Cutis (n=284). All cases of AML were confirmed by a hematopathologists review of the diagnostic material. The presence of monocytic features was determined by a combination of morphology and immunophenotypic analysis, as well as cytochemistry, as appropriate. For each AML patient, a dermatopathology database was reviewed to identify cases of skin biopsy-proven LC at any time during the disease course. Independent dermatopathology review was obtained for indeterminate cases of LC; cases still classified as indeterminate after re-review were excluded from the analysis. Information regarding clinical and disease characteristics was determined by review of the medical records. Targeted NGS testing of 33 genes associated with hematologic malignancies (including NPM1) was conducted by the Center for Personalized Diagnostics at the University of Pennsylvania. Average read depth was 3000X, minimal depth was 250x, and reporting frequency cutoff for variants was 5%.8 Mutations were classified into four categories: pathogenic, likely disease-associated, variant of uncertain significance (VUS), or likely benign based on review of publically available data; only pathogenic or likely disease-associated mutations were included in this analysis. Targeted NPM1 analysis was performed in the Department of Pathology at the University of Pennsylvania. The targeted NPM1 test consists of multiplex RT-PCR followed by detection on a liquid bead array. This assay allows for the simultaneous detection of the most common NPM1 mutations in exon 12 (type A, B, and D). The analytical sensitivity of the assay is approximately 0.01%. The Institutional Review Board of the University of Pennsylvania approved this research. Patient and clinical characteristics were summarized by descriptive statistics. Association between the presence of mutation and LC was assessed by the chi-square test or logistic regression, stratified by monocytic subtype when appropriate. Only genes with a mutation frequency ≥ 5% (n=24) were assessed for association with LC. All statistical tests were two-sided, with P values 90%) of NPM1 status at diagnosis and relapse.9 A further limitation of our study is the lack of response and survival data in this cohort. NPM1-mutant AML in the absence of FLT3-ITD mutation is reported to have a favorable association in both younger and older patients, while the presence of LC has been associated with unfavorable outcome.2,10–12 The implication of having both of these prognostic features is unknown and should be the subject of further investigation. The cellular mechanisms through which NPM1 mutations might alter leukemic myeloblasts homing to the skin require further study. Regardless of mechanism, our data support the World Health Organization’s provisional classification of NPM1-mutated AML as a distinct biological entity. We note that an association between NPM1 mutation and myeloid sarcoma has formerly been described, supporting the unique biology of NPM1-mutated AML.13 In summary, our data suggests that the previously described association between AML with monocytic features and LC may largely be explained by an association between NPM1 and LC.

Cancer-associated isocitrate dehydrogenase (IDH) mutations produce the metabolite 2-hydroxyglutarate (2HG), but the clinical utility of 2HG has not been established. We studied whether 2HG measurements in acute myeloid leukemia (AML) patients correlate with IDH mutations, and whether diagnostic or remission 2HG measurements predict survival. Sera from 223 de novo AML patients were analyzed for 2HG concentration by reverse-phase liquid chromatography-mass spectrometry. Pretreatment 2HG levels ranged from 10 to 30 000 ng/mL and were elevated in IDH-mutants (median, 3004 ng/mL), compared to wild-type IDH (median, 61 ng/mL) (P.0005). 2HG levels did not differ among IDH1 or IDH2 allelic variants. In receiver operating characteristic analysis, a discriminatory level of 700 ng/mL optimally segregated patients with and without IDH mutations, and on subsequent mutational analysis of the 13 IDH wild-type samples with 2HG levels700 ng/mL, 9 were identified to have IDH mutations. IDH-mutant patients with 2HG levels200 at complete remission had shorter overall survival compared to 2HG ≤200 ng/mL (hazard ratio, 3.9; P = .02). We establish a firm association between IDH mutations and serum 2HG concentration in AML, and confirm that serum oncometabolite measurements provide useful diagnostic and prognostic information that can improve patient selection for IDH-targeted therapies.

Abstract 2600 Background: Older patients diagnosed with acute lymphoblastic leukemia (ALL) receiving intensive induction therapy often suffer from poor outcomes due to therapy-related toxicity and high rates of relapse. We previously reported that patients age ≥60 diagnosed with ALL and treated at our institution with either hyperfractionated cyclophosphamide, vincristine, doxorubicin and dexamethasone alternating with high-dose methotrexate and cytarabine (hyperCVAD) or daunorubicin, vincristine and prednisone (DVP) induction therapies achieved comparable rates of survival. Now with longer follow-up and further analysis, we describe additional outcomes and factors predictive of survival in this patient population. Methods: Thirty-seven patients diagnosed with ALL at age ≥60 and treated at the University of Pennsylvania between July 2003 and June 2011 who received induction therapy with either hyperCVAD (≥1 A+B cycle) or DVP (phase I+II) were analyzed. HyperCVAD was administered as first described at the MD Anderson Cancer Center and DVP per the ECOG 2993/UKALL XII protocol. Therapy adjustments and bone marrow biopsy to confirm remission were performed at the discretion of the treating physician. Almost all Philadelphia chromosome (Ph) positive patients received a tyrosine kinase inhibitor. Event-free survival (EFS) was defined as the time from diagnosis to either relapse or death from any other cause. Results: Table 1 describes baseline characteristics. Table 2 describes outcomes. If achieved, morphologic remission was recognized upon the first bone marrow assessment performed while on therapy, which occurred after a median of 4 (2 A+B) cycles of hyperCVAD and by completion of phase II induction of DVP. EFS and overall survival (OS) trended in favor of DVP. HyperCVAD patients were more likely to complete intensive therapy but less likely to receive maintenance therapy, and more likely to relapse with the majority of relapses occurring off active treatment. Primary reasons for not starting or stopping maintenance therapy were infections and cytopenias. Relapsed disease was the most frequent cause of death. Table 3 describes univariate Cox regression analysis. Receipt of maintenance therapy demonstrated the strongest association with survival (p=0.0001, hazard ratio 0.06 for EFS; p=0.0002, hazard ratio 0.05 for OS). Valid multivariate analysis could not be performed due to small sample size. Conclusions: In older ALL patients treated with aggressive induction therapies and achieving remission, receipt of maintenance therapy appears to be most predictive of EFS and OS. Outcomes in the DVP and hyperCVAD groups were similar although a trend towards prolonged survival in the DVP group was seen, which may be explained by a lower rate of relapse due to a higher likelihood of remaining on therapy over time. Our findings suggest that these patients may benefit from attenuated courses of intensive initial therapy in order to avoid developing toxicities that may prohibit tolerance of prolonged maintenance therapy. Disclosures: No relevant conflicts of interest to declare.

Genetic heterogeneity contributes to clinical outcome and progression of most tumors, but little is known about allelic diversity for epigenetic compartments, and almost no data exist for acute myeloid leukemia (AML). We examined epigenetic heterogeneity as assessed by cytosine methylation within defined genomic loci with four CpGs (epialleles), somatic mutations, and transcriptomes of AML patient samples at serial time points. We observed that epigenetic allele burden is linked to inferior outcome and varies considerably during disease progression. Epigenetic and genetic allelic burden and patterning followed different patterns and kinetics during disease progression. We observed a subset of AMLs with high epiallele and low somatic mutation burden at diagnosis, a subset with high somatic mutation and lower epiallele burdens at diagnosis, and a subset with a mixed profile, suggesting distinct modes of tumor heterogeneity. Genes linked to promoter-associated epiallele shifts during tumor progression showed increased single-cell transcriptional variance and differential expression, suggesting functional impact on gene regulation. Thus, genetic and epigenetic heterogeneity can occur with distinct kinetics likely to affect the biological and clinical features of tumors. Refereed/Peer-reviewed

A hallmark of cancer is the disruption of differentiation within tumor cells. Internal tandem duplication mutations of the FLT3 kinase (FLT3/ITD) occur commonly in acute myeloid leukemia (AML) and are associated with poor survival, leading to efforts to develop FLT3 kinase inhibitors. However, FLT3 inhibitors have thus far met with limited success, inducing only a clearance of peripheral blasts with minimal BM responses. Quizartinib is a novel potent and selective FLT3 inhibitor currently being studied in clinical trials. In 13 of 14 FLT3/ITD AML patients with normal karyotype treated with quizartinib, we observed terminal myeloid differentiation of BM blasts in association with a clinical differentiation syndrome. The single patient whose blasts failed to differentiate had a preexisting C/EBPα mutation and another developed a C/EBPα mutation at disease progression, suggesting a mechanism of resistance to FLT3 inhibition. In vitro, in primary blasts cocultured with human BM stroma, FLT3 inhibition with quizartinib induced cell-cycle arrest and differentiation rather than apoptosis. The present study is the first description of terminal differentiation of cancer cells in patients treated with a tyrosine kinase inhibitor. These data highlight the importance of the differentiation block in the patho-genesis of AML.

The proto-oncogene c-Myc paradoxically activates both proliferation and apoptosis. In the pathogenic state, c-Myc–induced apoptosis is bypassed via a critical, yet poorly understood escape mechanism that promotes cellular transformation and tumorigenesis. The accumulation of unfolded proteins in the ER initiates a cellular stress program termed the unfolded protein response (UPR) to support cell survival. Analysis of spontaneous mouse and human lymphomas demonstrated significantly higher levels of UPR activation compared with normal tissues. Using multiple genetic models, we demonstrated that c-Myc and N-Myc activated the PERK/eIF2α/ATF4 arm of the UPR, leading to increased cell survival via the induction of cytoprotective autophagy. Inhibition of PERK significantly reduced Myc-induced autophagy, colony formation, and tumor formation. Moreover, pharmacologic or genetic inhibition of autophagy resulted in increased Myc-dependent apoptosis. Mechanistically, we demonstrated an important link between Myc-dependent increases in protein synthesis and UPR activation. Specifically, by employing a mouse minute (L24+/–) mutant, which resulted in wild-type levels of protein synthesis and attenuation of Myc-induced lymphomagenesis, we showed that Myc-induced UPR activation was reversed. Our findings establish a role for UPR as an enhancer of c-Myc–induced transformation and suggest that UPR inhibition may be particularly effective against malignancies characterized by c-Myc overexpression.

In a randomized trial of therapy for FMS-like tyrosine kinase-3 (FLT3) mutant acute myeloid leukemia in first relapse, 224 patients received chemotherapy alone or followed by 80 mg of the FLT3 inhibitor lestaurtinib twice daily. Endpoints included complete remission or complete remission with incomplete platelet recovery (CR/CRp), overall survival, safety, and tolerability. Correlative studies included pharmacokinetics and analysis of in vivo FLT3 inhibition. There were 29 patients with CR/CRp in the lestaurtinib arm and 23 in the control arm (26% vs 21%; P = .35), and no difference in overall survival between the 2 arms. There was evidence of toxicity in the lestaurtinib-treated patients, particularly those with plasma levels in excess of 20μM. In the lestaurtinib arm, FLT3 inhibition was highly correlated with remission rate, but target inhibition on day 15 was achieved in only 58% of patients receiving lestaurtinib. Given that such a small proportion of patients on this trial achieved sustained FLT3 inhibition in vivo, any conclusions regarding the efficacy of combining FLT3 inhibition with chemotherapy are limited. Overall, lestaurtinib treatment after chemotherapy did not increase response rates or prolong survival of patients with FLT3 mutant acute myeloid leukemia in first relapse. This study is registered at www.clinicaltrials.gov as #NCT00079482.

Background After induction therapy for acute myelogenous leukemia (AML), the presence of minimal residual disease (MRD) by targeted next-generation sequencing (NGS) during complete remission (CR) predicts relapse and survival, particularly after exclusion of pre-leukemic mutations. MRD assessment is not routinely performed for AML prior to transplant, partly because consensus regarding assay methodology, appropriate timing, interpretation of results, and therapeutic value prior to SCT is lacking. We therefore sought to describe the rates of mutational clearance and correlate these with relapse rates post-transplant. Methods We conducted a retrospective review of sequential AML or myelodysplastic syndrome (MDS) patients undergoing allogeneic hematopoietic cell transplant (alloHCT) at our institution between 2014 and 2017. There were 119 patients with AML/MDS who were treated with either myeloablative or reduced intensity conditioning regimens. Of the 119 patients transplanted, 60 had both pre- and post-treatment NGS results and were included in the analysis. 56 patients had somatic mutations on initial NGS and were therefore eligible for mutational clearance analysis. Twelve patients were in active disease and excluded from further analyses. The remaining patients (n=44) represent the core dataset. Blood and/or marrow specimens were analyzed via a clinical NGS panel targeting 68 leukemia-associated genes. Median coverage (across 88 samples) was 2817 reads. Mutations were considered persistent if present at variant allele frequencies (VAF) ≥ 1% for single nucleotide variants (SNV) or ≥ 2 copies for insertions and deletions (indels). Validated laboratory reporting practice at our institution reports VAF > 4% for SNVs and ≥ 1% for indels with a minimum of 250 total reads. We therefore defined three levels of mutational clearance on the basis of the VAF of residual mutations: VAF for SNV 4% (and/or indels > 1%). Patients with ≥ 1 mutation meeting these thresholds were designated NGS(-), NGS-low and NGS(+), respectively. The median follow-up was 332 days. Results On review of NGS data, 120 mutations were present in initial sequencing, with 64 mutations persistent in pre-transplant samples from 26 patients. The most commonly mutated genes from initial samples were FLT3 (18), ASXL1 (11), TET2 (10), NPM1 (9), RUNX1 (8), SRSF2 (8), and DNMT3A (7) (Figure 1A). Mutational clearance varied widely, with the putative pre-leukemic genes DNMT3A, TET2, and ASXL1 (DTA) demonstrating low rates of mutational clearance (Figure 1A). Mutations persisting below the validated reporting threshold were present in 20 patients, including 10 patients otherwise negative by NGS. There were 16 patients categorized as NGS(+), 10 NGS-low, and 18 NGS(-), with relapse rates of 31%, 22%, and 30%, respectively. No difference in relapse risk was observed between NGS(-) and NGS-low subgroups (p = 0.72), and no RFS benefit was observed for patients without persistent mutations > 4% relative to the NGS(+) subgroup (p = 0.56, Figure 1B). Recent work has shown a survival benefit in AML patients in CR without persistent mutations that is enhanced when DTA genes were excluded from the analysis (Jongen-Lavrencic, NEJM 2018). In our cohort, after exclusion of DTA mutations, 6 patients were reclassified by mutational clearance status, and 2 were excluded from the analysis as they had only DTA mutations in pre-treatment samples. Similar to the more comprehensive cohort, no RFS benefit based on NGS status was observed in the post-transplant period (p = 0.42, Figure 1C). Conclusions There were similar outcomes regardless of molecular MRD findings by NGS for patients with advanced myeloid malignancies who were in morphologic CR prior to alloHCT. These results contrast with those in the published literature that address a more uniform patient population of clinical trial participants, not all of whom went on to transplant. Further detailed analyses from larger more homogeneous populations will be useful to determine the prognostic significance of MRD by NGS prior to allogeneic HCT. Figure 1 Figure 1. Disclosures Frey: Servier Consultancy: Consultancy; Novartis: Consultancy. Perl:Novartis: Membership on an entity's Board of Directors or advisory committees; AbbVie: Membership on an entity's Board of Directors or advisory committees; Actinium Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees; NewLink Genetics: Membership on an entity's Board of Directors or advisory committees; Arog: Consultancy; Pfizer: Membership on an entity's Board of Directors or advisory committees; Astellas: Consultancy; Daiichi Sankyo: Consultancy. Stadtmauer:Takeda: Consultancy; Celgene: Consultancy; AbbVie, Inc: Research Funding; Amgen: Consultancy; Janssen: Consultancy. Porter:Genentech: Other: Spouse employment; Kite Pharma: Other: Advisory board; Novartis: Other: Advisory board, Patents & Royalties, Research Funding. Gill:Extellia: Consultancy, Membership on an entity's Board of Directors or advisory committees; Carisma Therapeutics: Equity Ownership; Novartis: Research Funding.

Background: Older patients (pts) with AML unfit for intense induction chemotherapy have a poor prognosis with a 5 year survival of 6 weeks and 5 CRi patients did not reach an ANC of ≥ 500/µL. Therefore, the activity level was reduced to 1.5 µCi/kg/dose for further evaluation. Methods: This study enrolled older pts with untreated AML who were considered to be unfit for standard induction chemotherapy. Pts aged 60 to 74 years were required to have significant co-morbidities, while all pts ≥ 75 years were eligible. Other eligibility criteria included ECOG PS 0-2, CD33 expression on > 25% of blasts, and a peripheral blast count Results: 18 pts were included in this prespecified Interim Analysis. An additional 9 pts were treated at this dose and will be included in an updated analysis at the ASH meeting. The median age of the 18 pts was 73.5 years (range 60-87) and median ECOG Performance Status was 1 (0 in 3 pts, 1 in 9 pts, & 6 in 2 pts). 11 pts had prior AHDs (6 MDS, 2 CMML, 2 NHL, 1 myelofibrosis), and 9 had prior treatment for AHDs. Of the pts with known cytogenetic and molecular genetic results, 1 had favorable-risk, 3 had intermediate-risk, and 5 had adverse-risk AML using NCCN guidelines. The median baseline BM blast % was 40.5% (range, 22-66%) with a median CD33 expression of 62% (range, 26-100%) of AML cells. Objective responses were seen in 4 pts (22%): 3 complete remissions with incomplete platelet count recovery (CRp) and 1 complete remission with incomplete hematologic recovery (CRi). Among the responders with known cytogenetics, 1 pt had adverse genetics and 1 had Intermediate-risk genetics.Of the pts with remission, 3 had CT genotype for the CD33 splicing polymorphism SNP rs12459419 (including 2 CRp) and 1 had CC genotype. 3 of the responders are in follow up at Days 59, 169 and 266 without further treatment. Myelosuppression was seen in all pts including Grade 4 thrombocytopenia with marrow aplasia for > 6 weeks after the first dose in 4 pts. 1 pt with prior MDS had pancytopenia for > 4 months. The 3 pts with CRp achieved an ANC ≥ 1000/µL at Days 28, 38, and 40 from the first dose of 225Ac-lin. The pt with CRi did not reach an ANC of 500/µL. Non hematologic Grade ≥3 Treatment-Emergent adverse events (AEs) that were at least possibly related were 4 patients with febrile neutropenia, as well as 1 patient each with fungal pneumonia, acute respiratory failure, pulmonary edema, chest pain, sepsis, gastric hemorrhage, generalized muscle weakness, atrial fibrillation with rapid ventricular response and typhilitis. No pts had an infusion-related reaction requiring dose interruption. Veno-occlusive disease did not occur. The 30-day mortality rate was 16.7% (1 cardiac arrest and 2 with multi organ failure). Conclusions: Preliminary data from this Interim Analysis of 225Ac-lin monotherapy in older AML pts unfit for intensive therapy indicate a lower rate of myelosuppression at 1.5 µCi/kg/dose but also a lower response rate than was seen at 2.0 µCi/kg/dose. Although the study met the prespecified response criteria for continuing enrollment, it will be closed to further accrual in recognition that targeted radiation, like other therapies, will likely have the best outcomes when used in combination with other therapies in pts with active AML. An extensive development program in AML, MDS, and multiple myeloma is planned. One study will utilize 225Ac-lin in combination with salvage chemotherapy and another with venetoclax. 225Ac-lin will be used as a single agent for AML postremission therapy. In addition, 225Ac-lin will be used as targeted conditioning prior to hematopoietic stem cell transplant in pts with MDS with a complex karyotype and as a conditioning agent prior to autologous transplant in MM. Table. Table. Disclosures Atallah: Jazz: Consultancy; Novartis: Consultancy; Pfizer: Consultancy; Abbvie: Consultancy; BMS: Consultancy. Orozco:Actinium Pharmaceuticals: Research Funding. Craig:Novartis: Research Funding; Actinium Pharmaceuticals: Research Funding; Celgene: Research Funding. Levy:Takeda (Millennium Pharmaceuticals, Inc.): Consultancy. Finn:Ochsner Clinic Foundation: Employment. Perl:NewLink Genetics: Membership on an entity's Board of Directors or advisory committees; Actinium Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees; AbbVie: Membership on an entity's Board of Directors or advisory committees; Arog: Consultancy; Astellas: Consultancy; Novartis: Membership on an entity's Board of Directors or advisory committees; Daiichi Sankyo: Consultancy; Pfizer: Membership on an entity's Board of Directors or advisory committees. Park:Amgen: Consultancy, Membership on an entity's Board of Directors or advisory committees; Juno Therapeutics: Consultancy, Research Funding; Shire: Consultancy; AstraZeneca: Consultancy; Adaptive Biotechnologies: Consultancy; Kite Pharma: Consultancy; Pfizer: Consultancy; Novartis: Consultancy. Roboz:Astex Pharmaceuticals: Consultancy; Bayer: Consultancy; Aphivena Therapeutics: Consultancy; Celltrion: Consultancy; Celgene Corporation: Consultancy; Novartis: Consultancy; Celgene Corporation: Consultancy; Pfizer: Consultancy; Argenx: Consultancy; Roche/Genentech: Consultancy; AbbVie: Consultancy; Cellectis: Research Funding; Aphivena Therapeutics: Consultancy; Roche/Genentech: Consultancy; Sandoz: Consultancy; Bayer: Consultancy; Sandoz: Consultancy; Jazz Pharmaceuticals: Consultancy; Otsuka: Consultancy; Astex Pharmaceuticals: Consultancy; Daiichi Sankyo: Consultancy; Orsenix: Consultancy; Janssen Pharmaceuticals: Consultancy; AbbVie: Consultancy; Jazz Pharmaceuticals: Consultancy; Argenx: Consultancy; Janssen Pharmaceuticals: Consultancy; Eisai: Consultancy; Otsuka: Consultancy; Pfizer: Consultancy; Eisai: Consultancy; Orsenix: Consultancy; Cellectis: Research Funding; Daiichi Sankyo: Consultancy; Novartis: Consultancy; Celltrion: Consultancy. Tse:Brown Cancer Center, University of Louisville School of Medicine: Employment; Jazz: Consultancy; Amgen: Consultancy; Amgen: Honoraria; Amgen: Honoraria. Mawad:Swedish Cancer Institute: Employment. Rizzieri:Novartis: Consultancy; Pfizer: Consultancy, Membership on an entity's Board of Directors or advisory committees; Amgen: Consultancy, Membership on an entity's Board of Directors or advisory committees; Jazz: Consultancy, Membership on an entity's Board of Directors or advisory committees; Incyte: Consultancy, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Teva: Consultancy, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Arog: Consultancy, Membership on an entity's Board of Directors or advisory committees; Gilead: Consultancy, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Berger:Actinium Pharmaceuticals: Employment, Equity Ownership. Jurcic:Astellas: Research Funding; Daiichi-Sankyo: Research Funding; Incyte: Consultancy; Celgene: Research Funding; AbbVie: Consultancy, Research Funding; Novartis: Membership on an entity's Board of Directors or advisory committees; Forma Therapeutics: Research Funding; Syros Pharmaceuticals: Research Funding; Actinium Pharmaceuticals, Inc: Research Funding; Genetech: Research Funding; Kura Oncology: Research Funding.

AML (acute myeloid leukemia) is increasingly being treated with precision medicine. To better inform treatment, the mutational content of patient samples must be determined. However, current tumor sequencing paradigms are inadequate to fully characterize many instances of the disease. A major challenge has been the unambiguous identification of potentially rare and genetically heterogeneous neoplastic cell populations, capable of critically impacting tumor evolution and the acquisition of therapeutic resistance. Standard bulk population sequencing is unable to identify rare alleles and definitively determine whether mutations co-occur within the same cell. Single-cell sequencing has the potential to address these key issues and transform our ability to accurately characterize clonal heterogeneity in AML. Previous single-cell studies examining genetic variation in AML have relied upon laborious, expensive and low-throughput technologies that are not readily scalable for routine analysis of the disease. We applied a newly developed platform technology to perform targeted single-cell DNA sequencing on over 140,000 cells and generated high-resolution maps of clonal architecture from AML tumor samples. Marrow and/or peripheral blood samples were collected prior to, during treatment, and at clinical progression to the FLT3 inhibitor gilteritinib given on a clinical trial for relapsed/refractory AML with FLT3 mutation. Single-cell sequencing of multiple patient samples demonstrated that relapse clones acquired oncogenic RAS mutations. We utilized the high-throughput and sensitivity of our single-cell approach to more definitively assess where in the course of treatment these RAS mutated clones were acquired. Oncogenic RAS harboring clones, comprising between 0.4%, and 0.1% of tumor populations, were identified in patient samples either prior to or shortly after onset of treatment. Significantly, these RAS variant alleles were not detectable with targeted bulk sequencing. Throughout the course of treatment with the FLT3 inhibitor gilteritinib, the RAS mutant clones selectively expanded and were responsible for resistance to therapy and relapse. These findings point to the presence of underlying genetic heterogeneity in AML and demonstrate the utility of sensitively assaying clonal architecture to better inform patient stratification and therapy selection. Disclosures Eastburn: Mission Bio, Inc.: Employment, Equity Ownership. Durruthy-Durruthy:Mission Bio, Inc.: Employment, Equity Ownership. Smith:Astellas Pharma: Research Funding. Perl:Actinium Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees; NewLink Genetics: Membership on an entity's Board of Directors or advisory committees; Pfizer: Membership on an entity's Board of Directors or advisory committees; Daiichi Sankyo: Consultancy; Arog: Consultancy; Novartis: Membership on an entity's Board of Directors or advisory committees; Astellas: Consultancy; AbbVie: Membership on an entity's Board of Directors or advisory committees.

Introduction: Midostaurin was the first multikinase inhibitor approved in combination with daunorubicin and cytarabine induction and high-dose cytarabine (HiDAC) consolidation chemotherapy for the treatment of adults with newly diagnosed FLT3-mutation-positive (mut+) acute myeloid leukemia (AML). Approval was largely based on the results from the phase 3 RATIFY trial; patients who received midostaurin had significantly improved overall and event-free survival than those who received placebo (Stone et al, N Engl J Med, 2017). RADIUS-X (NCT02624570) is an expanded treatment protocol (ETP) designed to provide access to midostaurin during the US Food and Drug Administration's review process and to extend the understanding of the safety and tolerability of midostaurin in patients with newly diagnosed FLT3-mut+ AML. The safety profile of midostaurin in preliminary data from RADIUS-X was consistent with that in the RATIFY study (Roboz et al, Blood, 2017 [abstract 1338]). Here we report updated safety data for midostaurin during induction and consolidation and safety data during the maintenance phase. Methods: In this open-label, single-arm ETP, patients (aged ≥18 years) received 1-2 cycles of induction therapy (cytarabine plus daunorubicin [60-90 mg/m2/day] or idarubicin [12 mg/m2/day]) and up to 4 cycles of HiDAC consolidation chemotherapy plus midostaurin (50 mg twice daily [bid] on days 8-21 of each 28-day cycle), followed by up to 12 months of single-agent midostaurin (50 mg bid on days 1-28). Patients could enroll at any point before completion of a second cycle of consolidation. Patients achieving complete remission (CR) or CR with incomplete hematologic recovery (CRi) after induction proceeded to consolidation; patients who maintained a response were eligible to proceed to maintenance. The primary endpoints were safety and tolerability of midostaurin. Results: Of 111 patients screened, 103 were enrolled in the study: 47 during induction (46%) and 56 during consolidation (54%) (Figure). The median age was 58 y (range, 19-79 y); all patients were FLT3-mut+ (Table). Of 47 patients enrolled during induction, 15 received daunorubicin and 32 received idarubicin as the anthracycline. Of 35 patients who completed consolidation and entered maintenance, 9 had completed the protocol treatment and 3 remained on therapy at the data cutoff date (March 30, 2018). The CR/CRi rate for the induction phase was 74% (57% CR, 17% CRi). The relapse rate was 14% overall. The most common reason for study discontinuation was proceeding to transplant (overall, 52%; induction, 11%; consolidation, 42%; maintenance, 34%). The median duration of midostaurin exposure was 35 days (range, 3-426 days). Dose adjustment or interruption due to adverse events (AEs) occurred in 26 patients, most commonly due to febrile neutropenia (n=9) and gastrointestinal disorders (n=6). No new safety events were observed with longer follow-up. Most patients (99%) experienced ≥1 any-grade AE, mostly during induction and/or consolidation. Due to the timing of patient enrollment (up to the second cycle of consolidation), hematologic AEs were lower than reported in comparable studies. The most common AEs occurring in ≥20% of patients were febrile neutropenia (53%), nausea (42%), diarrhea (37%), anemia (36%), platelet count decreased (31%), fatigue (23%), headache (22%), and vomiting (22%). Serious AEs occurred in 50% of patients overall, most commonly febrile neutropenia (37%). AEs during induction were generally similar, regardless of anthracycline received. Overall, 9 patients discontinued due to AEs: 5 during induction (febrile neutropenia, blood bilirubin increased, electrocardiogram QT prolonged, renal impairment, and respiratory distress), 1 during consolidation (sepsis), and 1 during maintenance (leukocytosis). During maintenance, 16 of 35 patients (46%) reported any-grade AEs with midostaurin monotherapy; the most common any-grade and grade 3/4 AEs occurring in >1 patient were platelet count decrease (11% and 3%), nausea (9% and 0%), and oropharyngeal pain (6% and 0%).The rate of death during the study was low, with 1 death reported (disease progression). Conclusions: Midostaurin continued to demonstrate a manageable safety profile with longer follow-up and was associated with high transplant and low relapse rates. Maintenance therapy with midostaurin was well tolerated; no new safety signals were observed. Disclosures Perl: Daiichi Sankyo: Consultancy; Arog: Consultancy; AbbVie: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees; Pfizer: Membership on an entity's Board of Directors or advisory committees; Actinium Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees; Astellas: Consultancy; NewLink Genetics: Membership on an entity's Board of Directors or advisory committees. Sweet:Agios: Consultancy; Novartis: Consultancy, Honoraria, Speakers Bureau; Pfizer: Consultancy, Honoraria; Incyte: Research Funding; Bristol Myers Squibb: Honoraria; Jazz Pharmaceuticals: Honoraria, Speakers Bureau; Celgene: Speakers Bureau. Roboz:Novartis: Consultancy; Daiichi Sankyo: Consultancy; Pfizer: Consultancy; Eisai: Consultancy; Janssen Pharmaceuticals: Consultancy; Argenx: Consultancy; Orsenix: Consultancy; Aphivena Therapeutics: Consultancy; Daiichi Sankyo: Consultancy; Roche/Genentech: Consultancy; Orsenix: Consultancy; Celgene Corporation: Consultancy; Celltrion: Consultancy; Jazz Pharmaceuticals: Consultancy; Celltrion: Consultancy; Cellectis: Research Funding; Jazz Pharmaceuticals: Consultancy; Sandoz: Consultancy; Otsuka: Consultancy; Otsuka: Consultancy; Roche/Genentech: Consultancy; Pfizer: Consultancy; AbbVie: Consultancy; Janssen Pharmaceuticals: Consultancy; Bayer: Consultancy; Astex Pharmaceuticals: Consultancy; Eisai: Consultancy; Aphivena Therapeutics: Consultancy; Argenx: Consultancy; Celgene Corporation: Consultancy; AbbVie: Consultancy; Bayer: Consultancy; Novartis: Consultancy; Astex Pharmaceuticals: Consultancy; Cellectis: Research Funding; Sandoz: Consultancy. Strickland:Astellas Pharma: Consultancy; Boehringer Ingelheim: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees; Pfizer: Consultancy, Membership on an entity's Board of Directors or advisory committees; Baxalta: Consultancy, Membership on an entity's Board of Directors or advisory committees; CTI Biopharma: Consultancy, Membership on an entity's Board of Directors or advisory committees; Sunesis Pharmaceuticals: Consultancy, Research Funding; Tolero Pharmaceuticals: Consultancy, Membership on an entity's Board of Directors or advisory committees. Bonifacio:Novartis: Employment. Haines:Novartis: Employment. Barbera:Novartis: Employment. Purkayastha:Novartis Pharmaceuticals Corporation: Employment.