Levine, Ross L.

Background: ENA is an oral, selective inhibitor of IDH2 approved for the treatment (Tx) of patients (pts) with relapsed/refractory IDH2 mutated (IDH2m) AML. Here we report the results of a Phase 2 expansion and Phase 1b of the Beat AML Master Trial Phase 2/1b sub-study to assess the efficacy of Tx of newly diagnosed (ND) IDH2m AML pts ≥ 60 years of age with ENA monotherapy (ENAm) and subsequent response-driven addition of AZA Tx. (ClinicalTrials.gov NCT03013998). Methods: The study initiated with a 3-outcome, 2-stage Phase 2 design, which enrolled patients on ENAm for up to 5 cycles. Pts without CR/CRi after 5 cycles of ENAm, or progression/intolerance prior to this time, were transferred to Phase 1b to receive ENA + AZA (Figure 1). Key eligibility included ND IDH2m AML pts with age ≥ 60 years and ECOG performance status 0-2. Pts received ENAm 100 mg/day in continuous 28-day cycles and ENA + AZA (75 mg/m2 days 1-7 every 28 days) for Phase 1b. Response was assessed using 2017 ELN AML criteria. The primary endpoint was CR/CRi rate. The 2-stage design required 24 pts and tested the null hypothesis (H0) that CR/CRi rate equaled 20% vs 50% and then expanded to test a revised H0 of 30% vs 50% in 60 pts (conditional alpha=0.025, power=77%). Expansion also allowed further assessment of safety of this treatment regimen. Results: At data cut off (06/18/2020), 60 pts enrolled, received ENAm, and were evaluable for the primary endpoint. Median age was 75 years and 52% were female (Table 1). Median time on ENAm was 4.7 months (mos). At data cut off, 12 pts were still on ENAm Tx. Most common reasons for discontinuing ENAm were Tx failure (defined as no response to treatment) (23 or 38%), disease progression (loss of response to treatment) (7 or 12%) and adverse events (AEs; 6 or 10%). Five pts (8%) went to transplant. CR/CRi was achieved in 28 pts (47%; adjusted 95% CI 28-59, unadjusted exact 95% CI 34-60) (Table 2). Responses were higher (p=0.04) among the 44 pts with IDH2 R140 (55%) as compared to the 16 with IDH2 R172 mutation (25%) further supporting distinct biology between these subsets. After a median follow up of 14.6 mos, the median overall survival (mOS) was 24.4 mos (95% CI 10.6-not reached). The median duration of response was not reached with 12 mos estimation of 57% (95% CI 34-75). Overall, 20 ENA-related serious adverse events (SAEs) occurred in 15 pts, the most common was differentiation syndrome (12 or 20%) and 1 had ENA-related SAE of tumor lysis syndrome (1.7%). One pt had ENA-related Grade 5 AE (renal failure/death). Most common AEs of any grade (in ≥20%) were nausea, anemia, and low potassium (Table 3). The 7-day/30-day/60-day deaths observed with ENAm were 2%/5%/11%, respectively. Phase 1b: Seventeen pts had inadequate response to ENAm and transferred to Phase 1b to receive ENA + AZA. Median time on Tx (including ENAm) was 6.2 mos and median time on Tx after pts started ENA + AZA was 2.1 mos (Table 2). Most common reasons for discontinuing ENA + AZA included Tx failure (5 or 29%), disease progression (2 or 12%), transplant, death and AEs (each 2 or 12%). CR/CRi was 41% (exact 95% CI 18-67). After a median follow up of 12.7 mos, the mOS from start of ENA + AZA combination Tx was 8.9 mos. Four ENA-related SAEs occurred in 3 pts on ENA + AZA Tx and the most common was differentiation syndrome (2 or 12.5%). One dose-limiting toxicity (Grade 3 nausea) related to both Txs was observed. Most common AEs (≥20%) of any grade were anemia, low albumin and vomiting (Table 3). One death occurred at day 13 of ENA + AZA. Conclusions: In newly diagnosed pts ≥60 years old with IDH2m AML, ENA had a low early death rate, high CR/CRi rate (47%, adjusted 95% CI 28-59), and yielded durable remissions. The most common unique toxicity with ENA was differentiation syndrome that occurred in 20% of patients. In pts who did not achieve CR/CRi with ENAm, a subset of patients achieved CR/CRi with addition of AZA. This combined approach of serial therapy with ENA monotherapy followed by AZA addition in pts with sub-optimal response resulted in a mOS exceeding 2 years for pts enrolled on study. Further focus on improving response among patients with IDH2 R172 mutations, identifying subsets of pts not responding to ENA monotherapy, and integrating new targeted agents into this treatment regimen are warranted. Figure 1 Disclosures Stein: Syndax: Consultancy, Research Funding; Celgene Pharmaceuticals: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Daiichi-Sankyo: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Astellas Pharmaceuticals: Consultancy, Membership on an entity's Board of Directors or advisory committees; Seattle Genetics: Consultancy; Agios Pharmaceuticals: Consultancy, Membership on an entity's Board of Directors or advisory committees; Bayer: Research Funding; Genentech: Consultancy, Membership on an entity's Board of Directors or advisory committees; Amgen: Consultancy; Biotheryx: Consultancy; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; PTC Therapeutics: Membership on an entity's Board of Directors or advisory committees; Syros: Membership on an entity's Board of Directors or advisory committees; Abbvie: Consultancy. Borate:Genentech: Membership on an entity's Board of Directors or advisory committees; Daiichi Sankyo: Membership on an entity's Board of Directors or advisory committees; Takeda: Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Membership on an entity's Board of Directors or advisory committees, Research Funding; Jazz Pharmaceuticals: Research Funding; AbbVie: Other: Investigator in AbbVie-funded clinical trials; Pfizer: Membership on an entity's Board of Directors or advisory committees, Research Funding. Baer:Takeda: Other: Institutional research funding; AbbVie: Other: Institutional research funding; Astellas: Other: Institutional research funding; Forma: Other: Institutional research funding; Kite: Other: Institutional research funding; Oscotec: Other: Institutional research funding; Incyte: Other: Institutional research funding. Kovacsovics:Agios: Honoraria; Astella: Honoraria; Pfizer: Research Funding; Novartis: Research Funding; AbbVie: Research Funding; Jazz: Honoraria. Schiller:Astellas Pharma: Honoraria, Research Funding; Celator: Research Funding; Constellation: Research Funding; Abbvie: Research Funding; Actinium: Research Funding; Ariad: Research Funding; Stemline: Speakers Bureau; Cyclacel: Research Funding; Daiichi Sankyo: Research Funding; Deciphera: Research Funding; DeltaFly: Research Funding; Bristol-Myers Squibb: Current equity holder in publicly-traded company, Research Funding; Forma: Research Funding; FujiFilm: Research Funding; Gamida: Research Funding; Genentech-Roche: Research Funding; Geron: Research Funding; Jazz Pharmaceuticals: Research Funding; Karyopharm: Research Funding; Kite Pharma: Research Funding; Mateon: Research Funding; MedImmune: Research Funding; Onconova: Research Funding; Pfizer: Current equity holder in publicly-traded company, Research Funding; Regimmune: Research Funding; Samus: Research Funding; Sangamo: Research Funding; Tolero: Research Funding; Trovagene: Research Funding; Kaiser Permanente: Consultancy; Johnson & Johnson: Current equity holder in publicly-traded company; Agios: Consultancy, Research Funding, Speakers Bureau; Amgen: Consultancy, Current equity holder in publicly-traded company, Research Funding, Speakers Bureau; AstraZeneca: Consultancy; Incyte: Consultancy, Research Funding, Speakers Bureau; Novartis: Consultancy, Research Funding; Ono Pharma: Consultancy; Celgene: Research Funding, Speakers Bureau; Sanofi: Speakers Bureau; Gilead: Speakers Bureau. Olin:Astellas: Other: Site PI; Genentech: Other: Site PI; Pfizer: Other: Site PI; Daiichi Sankyo: Other: Site PI; Genentech: Consultancy; Amgen: Consultancy. Foran:Trillium: Research Funding; Xencor: Research Funding; H3Biosciences: Research Funding; Agios: Honoraria, Research Funding; Pfizer: Membership on an entity's Board of Directors or advisory committees; BMS: Membership on an entity's Board of Directors or advisory committees; Abbvie: Research Funding; Boehringer Ingelheim: Research Funding; Actinium: Research Funding; Aprea: Research Funding; Aptose: Research Funding; Kura Oncology: Research Funding; Takeda: Research Funding; Revolution Medicine: Consultancy; Novartis: Membership on an entity's Board of Directors or advisory committees; Servier: Membership on an entity's Board of Directors or advisory committees. Lin:Trovagene: Research Funding; Tolero Pharmaceuticals: Research Funding; Seattle Genetics: Research Funding; Prescient Therapeutics: Research Funding; Abbvie: Research Funding; Bio-Path Holdings: Research Funding; Astellas Pharma: Research Funding; Aptevo: Research Funding; Incyte: Research Funding; Pfizer: Research Funding; Mateon Therapeutics: Research Funding; Ono Pharmaceutical: Research Funding; Jazz: Research Funding; Gilead Sciences: Research Funding; Genetech-Roche: Research Funding; Celyad: Research Funding; Celgene: Research Funding. Patel:DAVA Pharmaceuticals: Honoraria; Celgene: Consultancy, Speakers Bureau; Agios: Consultancy; France Foundation: Honoraria. Foster:Daiichi Sankyo: Consultancy; Bellicum Pharmaceuticals: Research Funding; Macrogenics: Consultancy, Research Funding. Druker:Leukemia & Lymphoma Society: Research Funding; Henry Stewart Talks: Patents & Royalties; Iterion Therapeutics (formerly Beta Cat Pharmaceuticals): Membership on an entity's Board of Directors or advisory committees; Vivid Biosciences: Membership on an entity's Board of Directors or advisory committees; GRAIL: Consultancy, Current equity holder in private company, Membership on an entity's Board of Directors or advisory committees; Patient True Talks: Consultancy; The RUNX1 Research Program: Membership on an entity's Board of Directors or advisory committees; Third Coast Therapeutics: Membership on an entity's Board of Directors or advisory committees; VB Therapeutics: Membership on an entity's Board of Directors or advisory committees; Gilead Sciences: Consultancy, Membership on an entity's Board of Directors or advisory committees; Millipore (formerly Upstate Biotechnology): Patents & Royalties; MolecularMD (acquired by ICON): Consultancy, Current equity holder in publicly-traded company, Membership on an entity's Board of Directors or advisory committees; Novartis Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees, Patents & Royalties, Research Funding; McGraw Hill: Patents & Royalties; Merck & Co: Patents & Royalties; Cepheid: Consultancy, Membership on an entity's Board of Directors or advisory committees; Dana-Farber Cancer Institute: Patents & Royalties; EnLiven: Consultancy, Research Funding; Aptose Therapeutics Inc. (formerly Lorus): Consultancy, Current equity holder in publicly-traded company, Membership on an entity's Board of Directors or advisory committees; ARIAD: Research Funding; Blueprint Medicines: Consultancy, Current equity holder in private company, Membership on an entity's Board of Directors or advisory committees; ALLCRON: Consultancy, Membership on an entity's Board of Directors or advisory committees; Amgen: Current equity holder in publicly-traded company, Membership on an entity's Board of Directors or advisory committees; Bristol-Myers Squibb: Research Funding; Aileron Therapeutics: Membership on an entity's Board of Directors or advisory committees; Pfizer: Research Funding; Oregon Health & Science University: Patents & Royalties. Byrd:Acerta Pharma: Research Funding; Syndax: Research Funding; Vincera: Research Funding; Pharmacyclics LLC, an AbbVie Company, Janssen, Novartis, Gilead, TG Therapeutics: Other; Pharmacyclics LLC, an AbbVie Company, Gilead, TG Therapeutics, Novartis, Janssen: Speakers Bureau; Novartis: Research Funding; Kartos Therapeutics: Research Funding; Trillium: Research Funding; Leukemia and Lymphoma Society: Other; Janssen: Consultancy; Pharmacyclics LLC, an AbbVie Company, Gilead, TG Therapeutics, BeiGene: Research Funding. Levine:Loxo: Current equity holder in private company, Membership on an entity's Board of Directors or advisory committees; C4 Therapeutics: Current equity holder in private company, Membership on an entity's Board of Directors or advisory committees; Imago: Current equity holder in private company, Membership on an entity's Board of Directors or advisory committees; Celgene: Consultancy, Honoraria, Research Funding; Qiagen: Current equity holder in publicly-traded company, Membership on an entity's Board of Directors or advisory committees; Prelude Therapeutics: Research Funding; Amgen: Honoraria; Astellas: Consultancy; Morphosys: Consultancy; Novartis: Consultancy; Isoplexis: Current equity holder in private company, Membership on an entity's Board of Directors or advisory committees; Janssen: Consultancy; Lilly: Consultancy, Honoraria; Roche: Consultancy, Honoraria, Research Funding; Gilead: Honoraria. Mims:Abbvie: Membership on an entity's Board of Directors or advisory committees; Kura Oncology: Membership on an entity's Board of Directors or advisory committees; Leukemia and Lymphoma Society: Other: Senior Medical Director for Beat AML Study; Jazz Pharmaceuticals: Other: Data Safety Monitoring Board; Syndax Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees; Agios: Consultancy; Novartis: Speakers Bureau. OffLabel Disclosure: Enasidenib is not approved for the treatment of newly diagnosed AML.

Background: Somatic mutations in the IDH genes are common in acute myeloid leukemia (AML). Mutations occur at active site arginine residues in IDH1 (R132) and IDH2 (R140, R172). IDH inhibitors, ivosidenib (IDH1) and enasidenib (IDH2), have shown improved clinical outcomes in patients with relapsed/refractory IDH-mutant AML and are approved for use in this setting, while investigations in combination with chemotherapy are underway in de novo AML. The prognostic significance of IDH mutations remains controversial. We hypothesize that refining our understanding of IDH-mutated AML will contribute to risk-adapted treatment strategies, including optimal use of IDH-targeted agents. The objective of our study was to identify characteristics that affect outcome in de novo IDH-mutated AML across the age spectrum utilizing a large cohort of patients enrolled on several pediatric and adult trials. Methods: The total cohort (N=3588) included patients age <1 month - 88 years. Pediatric and young adult (YA) patients were treated on recent CCG/COG AML trials (CCG2961, COG 03P1, 0531, 1031, N=2231) and YA/adult patients were treated on SWOG S0106 (N=396), ECOG E1900 AML trials (N=398), Beat AML (N=363), or included in the TCGA biology study (N=200; outcomes not evaluated for this group). Patients were analyzed according to three defined age groups: "younger" 0-29 years of age (N=2401), "intermediate" 30-59 years of age (N=819) and "older" 60 years of age and above (N=319). Data regarding clinical characteristics and treatment outcomes were collected and evaluated according to the standard practices of each cooperative or research groups for the respective studies. Mutational profiling was performed by targeted sequencing for patient samples from COG trials, Beat-AML, ECOG, and SWOG; whole-genome or whole-exome sequencing for the TCGA cohort. Prevalence of IDH mutations, co-occurring mutations, and outcomes (5-year event-free survival [EFS]) were analyzed across the defined age groups. Results: The prevalence of IDH mutations among the entire cohort was 8.6% (N=276). Analysis according to mutation type demonstrated that IDH2 mutations comprised 57% (N=158) and IDH1 mutations 43% (N=118). The prevalence of IDH mutations was strongly correlated with increased age (Fig 1A); according to the age-defined cohorts was 4.0% (N=82) in younger, 15.2% (N=126) in intermediate, and 20.3% (N=65) in older patients (p<0.001). The co-occurring mutational profile demonstrated that IDH mutations commonly co-occurred with NPM1,DNMT3A, and FLT3-ITD mutations (Fig 1B). Among IDH-mutant patients, 48% (N=132) harbored dual mutations (IDHmut/NPM1mut); 11.6% (N=32) triple mutations (IDHmut/NPM1mut/DNMT3Amut), the latter particularly prevalent in intermediate-aged adults (N=27/32, 85%). Analysis of the cohort with outcome data (N=2824) demonstrated that IDHmut and IDH-WT patients experienced similar EFS of 39% vs. 40%, respectively (p=0.723). Given the favorable prognostic significance of NPM1, we subsequently analyzed outcomes of this dual mutant group and found that NPM1 mutations retained favorable prognostic impact in the context of IDH mutant patients (Fig 2A). Notably, this effect was age-dependent, as those with IDHmut/NPM1mut had a favorable EFS compared to IDHmut/NPM1-WT for younger (76% vs. 24%, p<0.001) and intermediate patients (43% vs. 15%, p=0.001, Fig 2B) but this favorable effect was lost in older patients (29% vs. 34%, p=0.456, Fig 2C). Among intermediate age patients, outcome was further stratified by DNMT3A status, and IDHmut/NPM1mut/DNMT3Amut patients experienced an inferior EFS of 25% vs. 57% in IDHmut/NPMmut (p=0.003, Fig 2D). Conclusion: Analysis of this large patient cohort provides the most comprehensive description of IDH mutations in AML across the age spectrum. We confirm age-associated prevalence of IDH mutations and frequent co-occurrence with NPM1 mutation in all ages and in further combination with DNMT3A mutation in intermediate-aged adults. We definitively demonstrate that IDH mutation status is not an independent prognostic determinant of outcome in any age group. Co-occurrence of NPM1 and IDH mutations favorably impacts outcome in patients < 60 years of age with AML, particularly in the absence of DNMT3A mutation. Our data support that IDH inhibitors may be of particular interest in older adults and in patients <60 according to co-occurring NPM1 and DNMT3A mutations. Disclosures Othus: Marck: Consultancy; Daiichi Sankyo: Consultancy; Celgene: Membership on an entity's Board of Directors or advisory committees; Glycomimetics: Membership on an entity's Board of Directors or advisory committees. Radich:Jazz: Consultancy; Novartis Pharmaceuticals Corporation: Consultancy, Research Funding; Amgen: Consultancy; Bristol-Myers Squibb: Consultancy. Abdel-Wahab:Merck: Consultancy; Janssen: Consultancy; Envisagenics Inc.: Current equity holder in private company; H3 Biomedicine Inc.: Consultancy, Research Funding. Tallman:UpToDate: Patents & Royalties; ADC Therapeutics: Research Funding; BioSight: Membership on an entity's Board of Directors or advisory committees, Research Funding; Glycomimetics: Research Funding; Rafael: Research Funding; Amgen: Research Funding; Bioline rx: Membership on an entity's Board of Directors or advisory committees; Daiichi-Sankyo: Membership on an entity's Board of Directors or advisory committees; KAHR: Membership on an entity's Board of Directors or advisory committees; Rigel: Membership on an entity's Board of Directors or advisory committees; Delta Fly Pharma: Membership on an entity's Board of Directors or advisory committees; Oncolyze: Membership on an entity's Board of Directors or advisory committees; Jazz Pharma: Membership on an entity's Board of Directors or advisory committees; Roche: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees; Abbvie: Research Funding; Cellerant: Research Funding; Orsenix: Research Funding. Atallah:Jazz: Consultancy; Genentech: Consultancy; Abbvie: Consultancy; Takeda: Consultancy, Research Funding; Pfizer: Consultancy; Novartis Pharmaceutical Corporation: Consultancy. Luger:Daiichi-Sankyo: Honoraria; Pfizer: Honoraria; Bristol-Myers Squibb: Honoraria; Acceleron: Honoraria; Agios: Honoraria; Loxo Oncology: Honoraria; Onconova: Research Funding; Kura: Research Funding; Biosight: Research Funding; Ariad: Research Funding; Hoffman La Roche: Research Funding. Levine:Novartis: Consultancy; Loxo: Current equity holder in private company, Membership on an entity's Board of Directors or advisory committees; Morphosys: Consultancy; Astellas: Consultancy; Janssen: Consultancy; Prelude Therapeutics: Research Funding; Amgen: Honoraria; Gilead: Honoraria; Lilly: Consultancy, Honoraria; Qiagen: Current equity holder in publicly-traded company, Membership on an entity's Board of Directors or advisory committees; Imago: Current equity holder in private company, Membership on an entity's Board of Directors or advisory committees; C4 Therapeutics: Current equity holder in private company, Membership on an entity's Board of Directors or advisory committees; Isoplexis: Current equity holder in private company, Membership on an entity's Board of Directors or advisory committees; Celgene: Consultancy, Honoraria, Research Funding; Roche: Consultancy, Honoraria, Research Funding. Cooper:Celgene: Other: Spouse was an employee of Celgene (through August 2019).

Nearly 20% of patients with myelofibrosis progress to blast phase disease; an aggressive form of acute myeloid leukemia. Although previous studies have implicated loss of TP53 or JARID2 in progression, by and large the genetic events that lead to conversion to blast phase remain unknown. To identify genes whose loss drives progression, we performed a focused CRISPR/Cas9 screen in which murine Jak2V617F bone marrow cells expressing Cas9 were transduced with two separate sgRNA libraries of known tumor suppressor genes and subjected to colony replating assays. Transduction of one of the two libraries led to serial replating and enhanced self-renewal of the Jak2V617F cells. Subsequent DNA sequencing revealed enrichment of all four guides targeting STK11, the gene that encodes LKB1 which regulates a number of key cellular pathways including energy utilization by activation of AMPK. To confirm that loss of Stk11 is the event that leads to increased clonogenicity, we collected cells from Jak2V617F/Vav-Cre+ and control Vav-Cre+ mice and induced Stk11 knockout by electroporating Cas9-Stk11 sgRNA ribonucleoprotein complexes. Consistent with the screening results, only Jak2V617F Vav-Cre+ cells with Cas9-Stk11 sgRNA showed serial replating. To determine whether Stk11 is required for growth of cells with a different driver of enhanced JAK/STAT signaling, we doubly transduced Stk11 homozygous floxed bone marrow cells with MPLW515L-mCherry and Cre-GFP to delete Stk11. As expected, cells with both MPLW515L and Cre recombinase showed enhanced self-renewal, while singly infected control cells failed to replate. These results demonstrate that activation of JAK/STAT signaling can overcome the requirement for Stk11 in normal hematopoiesis and suggest that STK11 loss may be a strong driver of malignant transformation in combination with enhanced JAK-STAT signaling. We next investigated the mechanism by which loss of STK11 cooperates with enhanced JAK/STAT signaling to promote leukemia. RNA-sequencing of wild-type, Stk11+/+/ MPLW515L, and Stk11-/-/MPLW515L hematopoietic cells revealed enrichment of a number of pathways related to hypoxia, oxidative phosphorylation and mitochondrial translation in cells lacking LKB1. Western blot assays confirmed activation of mTOR signaling as well as HIF1a stabilization and pathway activation, both of which have been reported to lie downstream of LKB1 loss. We also performed a number of studies to determine the relevance of reduced LKB1 expression to leukemic progression. First, we induced deletion of Stk11 in mice that were transplanted with HSPCs expressing MPLW515L after development of the MPN phenotype. Loss of Stk11 caused a rapid lethality that was associated with enhanced bone marrow fibrosis and osteosclerosis. We also observed accumulation of leukemic blasts in small clusters consistent with AML transformation arising in the spent phase MPN. Additionally, we deleted STK11 by CRISPR/Cas9 in primary MPN patient samples and monitored their engraftment in immunocompromised mice. We observed enhanced engraftment and increased reticulin fibrosis and osteosclerosis in mice that received the STK11 edited cells compared to those with non-targeted sgRNA. Third, we compared the expression of STK11 in paired blast and chronic phase myelofibrosis patient samples by RT-PCR. Consistent with the hypothesis that loss of STK11 facilitates leukemia, we found that its expression was decreased by more than 50% in five of seven paired post-MPN AML patient samples, with two having STK11 levels below 20%. We further validated downregulation of LKB1 by immunohistochemistry on paired chronic and blast phase MPN specimens and observed little staining in the blast phase specimens. Finally, to further show that the mechanism of in vitro enhanced self-renewal is related to leukemia progression, we stained the paired marrows for HIF1a and saw a dramatic increase in staining at the AML phase. We also analyzed RNA-seq data of paired chronic versus blast phase MPNs specimens and observed that there is a strong congruence of enriched pathways that are associated with the in vitro mouse HSPC phenotype and the human blast phase progression, such as oxidative phosphorylation and hypoxia. Together, our study demonstrates that loss of LKB1/STK11 promotes transformation of cells with activated JAK/STAT signaling and that STK11 is a prominent candidate tumor suppressor gene in post-MPN AML. Disclosures Gurbuxani: UpToDate: Honoraria. Hoffman:Dompe: Research Funding; Protagonist: Consultancy; Abbvie: Membership on an entity's Board of Directors or advisory committees; Forbius: Consultancy; Novartis: Membership on an entity's Board of Directors or advisory committees. Levine:Astellas: Consultancy; Amgen: Honoraria; Gilead: Honoraria; Qiagen: Current equity holder in publicly-traded company, Membership on an entity's Board of Directors or advisory committees; Morphosys: Consultancy; Novartis: Consultancy; Prelude Therapeutics: Research Funding; Loxo: Current equity holder in private company, Membership on an entity's Board of Directors or advisory committees; Imago: Current equity holder in private company, Membership on an entity's Board of Directors or advisory committees; C4 Therapeutics: Current equity holder in private company, Membership on an entity's Board of Directors or advisory committees; Isoplexis: Current equity holder in private company, Membership on an entity's Board of Directors or advisory committees; Celgene: Consultancy, Honoraria, Research Funding; Roche: Consultancy, Honoraria, Research Funding; Lilly: Consultancy, Honoraria; Janssen: Consultancy. Rampal:Galecto: Consultancy; Incyte: Consultancy, Research Funding; Constellation: Research Funding; Stemline: Consultancy, Research Funding; Celgene: Consultancy; Jazz Pharmaceuticals: Consultancy; CTI Biopharma: Consultancy; Abbvie: Consultancy; Pharmaessentia: Consultancy; Promedior: Consultancy; Blueprint: Consultancy.

Abstract Myeloproliferative neoplasms (MPN) that have evolved into accelerated or blast phase disease (MPN-AP/BP) have poor outcomes with limited treatment options and therefore represent an urgent unmet need. We have previously demonstrated in a multicenter, phase 1 trial conducted through the Myeloproliferative Neoplasms Research Consortium that the combination of ruxolitinib and decitabine is safe and tolerable and is associated with a favorable overall survival (OS). In this phase 2 trial, 25 patients with MPN-AP/BP were treated at the recommended phase 2 dose of ruxolitinib 25 mg twice daily for the induction cycle followed by 10 mg twice daily for subsequent cycles in combination with decitabine 20 mg/m2 for 5 consecutive days in a 28-day cycle. Nineteen patients died during the study follow-up. The median OS for all patients on study was 9.5 months (95% confidence interval, 4.3-12.0). Overall response rate (complete remission + incomplete platelet recovery + partial remission) was 11/25 (44%) and response was not associated with improved survival. We conclude that the combination of decitabine and ruxolitinib was well tolerated, demonstrated favorable OS, and represents a therapeutic option for this high-risk patient population. This trial was registered at www.clinicaltrials.gov as #NCT02076191.

Abstract Background: We recently reported on MPLW515L/K mutations in 1182 patients with myeloid disorders (Blood, First Edition July 25, 2006) and found low frequency occurrence in in agnogenic myeloid metaplasia (AMM) (~5%) and essential thrombocythemia (ET) (~1%), but not polycythemia vera (PV). Of the 20 MPLW515L/K-positive patients in that series, 6 (30%) also carried a low burden of the JAK2V617F mutation. Studies of mutation prevalence in individuals with clonal granulopoiesis as well as familial myeloproliferative disorders (MPD) studies suggest that these mutations (JAK2V617F) may be acquired as secondary genetic events. Aim: to gain additional insight regarding the aforementioned two mutations and MPD pathogenesis by determining (i) concordance between mutation expression and clonal hematopoiesis, (ii) the instructive role of each mutation in determining lineage fate, iii) differences in pattern and lineage restriction of these mutations between various MPD, and (iv) chronology of clonal emergence and clonal dominance for the 2 mutations. Methods: Sixteen MPD patients were studied (13 JAK2V617F+ and 3 MPLW515L/K+); 9 had PV (all JAK2V617F+), 2 ET (both JAK2V617F+), 1 CMML (JAK2V617F+), and 4 AMM (2 MPLW515K+, and one each with MPLW515L and JAK2V617F). CD34+ progenitor cells were plated in methylcellulose and resulting hematopoietic colonies were scored on day 10–12. Colonies were obtained with (all patients) and without (10 patients; 5 with PV, 1 ET, and 4 AMM) cytokine support. Individual colonies were screened for presence of either mutation by DNA sequencing. In addition, MPLW515L/K analysis was performed in T and B lymphocytes in 3 informative cases. Finally, serially stored bone marrow was examined in 3 patients with co-expression of MPL515 and JAK2V617F mutations. Results: A total of 552 hematopoietic colonies from 16 MPD patients were genotyped. We found cohabitation of both mutation-positive and mutation-negative endogenous colonies in PV as well as other MPD. For JAK2V617F+ patients, the majority (75–100%) of erythropoietin-independent erythroid colonies (EEC) but not endogenous granulocyte colonies (20–70%) were mutation-positive. In contrast, no EEC were obtained from progenitors from the 3 MPLW515L/K+ patients. For 2 of the 3 patients, the endogenous myeloid colonies were predominantly mutation-positive (~90%). A mixed allele pattern (homozygous and/or heterozygous) was seen with both mutations regardless of MPD phenotype, but the overall mutant colony burden was higher with MPLW515L/K mutations relative to JAK2V617F. When such testing was possible, MPL515 mutations were detected in T-lymphocytes (2 of 3 patients) as well as B-lymphocytes (2 of 2 patients). Finally, among 3 patients carrying both mutations, serial marrow studies (25 time points over 4–8 years) revealed the occurrence of both mutations at diagnosis and persistent dominance of MPLW515L/K over JAK2V617F over time. Conclusions: Our observations provide direct evidence for clonal hematopoiesis that antedates acquisition of either MPLW515L/K or JAK2V617F that bias towards myeloid and erythroid fates, respectively. Furthermore, both mutations appear to occur early in the disease course and lineage studies suggest a hierarchically earlier stem cell origin for MPLW515L/K as compared to JAK2V617F.

Introduction: Inherited predisposition to myeloid malignancies in adults may be more common than previously suggested with recent studies suggesting a prevalence of candidate predisposition alleles in 15-20% of patients. An inherited predisposition may not be considered in older AML patients despite significant clinical implications for family members as potential stem cell transplant donors. To better define the role of inherited genetic alterations in older AML patients , we analyzed a unique cohort of newly diagnosed older (>60 years) patients enrolled in) Beat AML® Master Trial(BAMT) for candidate genes associated with a known or putative inherited cancer predisposition. Methods: We analyzed extracted DNA from skin and/or saliva samples compared to paired leukemia samples of 176 AML patients enrolled in the BAMT. All samples underwent genomic profiling using a modified FoundationOne®Heme platform (capture-based) and/or the Oregon Health Sciences University panel (amplicon-based), evaluating 477 and 220 genes respectively, with a known role in hematologic malignancies. Germline(GL) variants were identified by the haplotype-based Bayesian genetic variant detector FreeBayes and using variant allele frequency(VAF) values. The pathogenicity and clinical significance of the variants was interpreted according to the 2015 ACMG/AMP guidelines while the AMP/CAP/ASCO guidelines and various disease databases were used in the somatic variant calls. Results: -The mutational landscape of the 176 newly diagnosed older AML patients is detailed in Table 1. Our cohort has a higher proportion of adverse risk patients, consistent with an older AML patient population. 27 pathogenic or likely pathogenic GL variants were detected in 24 AML patients, with a germline mutation prevalence of 14% in this cohort. Deleterious GL mutations were found in the gene DDX41 (5), followed by SBDS (4), CHEK2 (4), MPL (3), BRCA2 (2), HAX1 (2), DNAH9 (2), FANCA (1), FANCL (1), SAMD9 (1), BLM (1), and ATM (1) (Table 2). The types of mutations included missense mutations (9), nonsense mutations (8), frameshift mutations (7), splice site mutations (2), and an exonic deletion (1). Family history of leukemia was available on 129 patients from this cohort. 12 patients have at least one family member with AML. Of these 12 patients, 2 had a deleterious GL alteration identified. Along with the 14% prevalence of pathogenic/likely pathogenic GL mutations , there were an additional 181 GL variants of unknown significance (VUS) in 102 patients, seen in genes implicated in inherited predisposition to hematologic malignancies, most commonly variants in DOCK8 and CREBBP(>5% VUS) with both genes being implicated in leukemogenesis . As skin and/or saliva samples were collected at the time of AML diagnosis, tumor-in-normal presence was expectedly observed. The median VAF for somatic mutations was significantly lower (p < 0.0001) in skin (median 6%; mean 9%; standard deviation (SD) 10%; N=562 variants) than in saliva (median 17%; mean 21%; SD 16%; N=368 variants). In 37 patients who had both saliva and skin tissue concomitantly ,skin had a significantly lower tumor-in-normal presence (median VAF 5%, mean 8%, SD 8%;) than saliva (median 15%, mean 20%, SD 16%)(p < 0.0001). Conclusions: We found a prevalence of 14% pathogenic/ likely pathogenic GL mutations in cancer predisposition genes in this unique cohort of newly diagnosed older AML patients. This finding has potential clinical implications for patients and family members. We also found a large number of VUS in genes implicated in hematological malignancies. Additional studies linking candidate VUS' to familial predisposition to understand contribution to AML predisposition are needed. We are in the process of comparing the manual curation of ACMG classification of pathogenicity with a computational curation algorithm to assess the potential for automated classification of GL variants. Our study suggests the choice of source for germline DNA in patients with AML is variably impacted by leukemic contamination. Cultured skin fibroblasts are the current standard for tumor-normal paired genotyping, with the caveat of being labor intensive and not routinely performed in clinical diagnostic laboratories. This is a critical consideration for rapid GL screening of patients and family members with hematologic malignancies and suspected cancer predisposition. Disclosures Borate: Novartis: Consultancy; Takeda: Consultancy; Pfizer: Consultancy; Daiichi Sankyo: Consultancy; AbbVie: Consultancy. Mims:Abbvie: Membership on an entity's Board of Directors or advisory committees; Agios Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees; PTC Therapeutics: Membership on an entity's Board of Directors or advisory committees; Astellas Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees; Jazz Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees. Stein:Agios: Consultancy, Membership on an entity's Board of Directors or advisory committees; Astellas Pharma US, Inc: Membership on an entity's Board of Directors or advisory committees; Celgene Corporation: Membership on an entity's Board of Directors or advisory committees; Daiichi Sankyo, Inc.: Membership on an entity's Board of Directors or advisory committees; Bioline: Membership on an entity's Board of Directors or advisory committees; Genentech: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees; PTC Therapeutics: Membership on an entity's Board of Directors or advisory committees; Syros: Membership on an entity's Board of Directors or advisory committees. Patel:Celgene: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Dava Oncology: Honoraria; France Foundation: Honoraria. Baer:Astellas: Research Funding; Abbvie: Research Funding; AI Therapeutics: Research Funding; Forma: Research Funding; Incyte: Research Funding; Kite: Research Funding; Takeda: Research Funding. Stock:Agios: Membership on an entity's Board of Directors or advisory committees; Astellas: Membership on an entity's Board of Directors or advisory committees; UpToDate: Honoraria; Daiichi: Membership on an entity's Board of Directors or advisory committees; Pfizer: Membership on an entity's Board of Directors or advisory committees; Kite, a Gilead Company: Membership on an entity's Board of Directors or advisory committees; Research to Practice: Honoraria. Schiller:Bristol Myer Squibb: Research Funding; Celgene: Research Funding, Speakers Bureau; Constellation Pharmaceutical: Research Funding; Daiichi Sankyo: Research Funding; Agios: Research Funding, Speakers Bureau; Amgen: Other, Research Funding; Astellas: Research Funding; Biomed Valley Discoveries: Research Funding; Eli Lilly and Company: Research Funding; FujiFilm: Research Funding; Genzyme: Research Funding; Gilead: Research Funding; Incyte: Research Funding; J&J: Research Funding; Jazz Pharmaceuticals: Honoraria, Research Funding; Karyopharm: Research Funding; Novartis: Research Funding; Onconova: Research Funding; Pfizer Pharmaceuticals: Equity Ownership, Research Funding; Sangamo Therapeutics: Research Funding. Blum:AmerisourceBergen: Consultancy; Forma: Research Funding; Xencor: Research Funding; Boehringer Ingelheim: Research Funding; Celgene: Research Funding; Astellas,: Research Funding. Shami:JSK Therapeutics: Employment, Equity Ownership; Amgen: Research Funding; Pfizer: Research Funding; Cantex: Research Funding; Aptevo: Research Funding; Jazz: Consultancy, Honoraria; Abbvie: Consultancy, Honoraria; Agios: Consultancy, Honoraria; Lone Star Thiotherapies: Equity Ownership. Foran:Agios: Honoraria, Research Funding. Byrd:Acerta: Research Funding; Gilead: Other: Travel Expenses, Research Funding, Speakers Bureau; Genentech: Research Funding; Novartis: Other: Travel Expenses, Speakers Bureau; Pharmacyclics LLC, an AbbVie Company: Other: Travel Expenses, Research Funding, Speakers Bureau; TG Therapeutics: Other: Travel Expenses, Research Funding, Speakers Bureau; Ohio State University: Patents & Royalties: OSU-2S; BeiGene: Research Funding; Janssen: Consultancy, Other: Travel Expenses, Research Funding, Speakers Bureau. Druker:OHSU (licensing fees): Patents & Royalties: #2573, Constructs and cell lines harboring various mutations in TNK2 and PTPN11, licensing fees ; Bristol-Myers Squibb: Other: PI or co-investigator on clinical trial(s) funded via contract with OHSU., Research Funding; Novartis: Other: PI or co-investigator on clinical trial(s) funded via contract with OHSU., Patents & Royalties: Patent 6958335, Treatment of Gastrointestinal Stromal Tumors, exclusively licensed to Novartis, Research Funding; Monojul: Other: former consultant; Vivid Biosciences: Membership on an entity's Board of Directors or advisory committees, Other: Stock options; Beat AML LLC: Other: Service on joint steering committee; Merck & Co: Patents & Royalties: Dana-Farber Cancer Institute license #2063, Monoclonal antiphosphotyrosine antibody 4G10, exclusive commercial license to Merck & Co; Dana-Farber Cancer Institute (antibody royalty): Patents & Royalties: #2524, antibody royalty; Aileron Therapeutics: #2573, Constructs and cell lines harboring various mutations in TNK2 and PTPN11, licensing fees , Membership on an entity's Board of Directors or advisory committees; Bristol-Myers Squibb: Patents & Royalties, Research Funding; Pfizer: Research Funding; ALLCRON: Membership on an entity's Board of Directors or advisory committees; Amgen: Equity Ownership, Membership on an entity's Board of Directors or advisory committees; Aptose Biosciences: Consultancy, Equity Ownership, Membership on an entity's Board of Directors or advisory committees; Beta Cat: Membership on an entity's Board of Directors or advisory committees, Other: Stock options; The RUNX1 Research Program: Membership on an entity's Board of Directors or advisory committees; Patient True Talk: Consultancy; GRAIL: Equity Ownership, Other: former member of Scientific Advisory Board; Cepheid: Consultancy, Honoraria; Blueprint Medicines: Consultancy, Equity Ownership, Membership on an entity's Board of Directors or advisory committees; Burroughs Wellcome Fund: Membership on an entity's Board of Directors or advisory committees; Celgene: Consultancy; Pfizer: Other: PI or co-investigator on clinical trial(s) funded via contract with OHSU., Research Funding; ICON: Other: Scientific Founder of Molecular MD, which was acquired by ICON in Feb. 2019; CureOne: Membership on an entity's Board of Directors or advisory committees; Gilead Sciences: Other: former member of Scientific Advisory Board. Vergilio:Foundation Medicine, Inc.: Employment; F. Hoffman La Roche, Ltd.: Equity Ownership. Levine:Imago Biosciences: Membership on an entity's Board of Directors or advisory committees; Prelude Therapeutics: Research Funding; C4 Therapeutics: Membership on an entity's Board of Directors or advisory committees; Roche: Consultancy, Research Funding; Celgene: Consultancy, Research Funding; Amgen: Honoraria; Gilead: Consultancy; Lilly: Honoraria; Qiagen: Membership on an entity's Board of Directors or advisory committees; Isoplexis: Membership on an entity's Board of Directors or advisory committees; Loxo: Membership on an entity's Board of Directors or advisory committees; Novartis: Consultancy.

*equal contribution of AB, RLL, BD and JCB Background: Acute myeloid leukemia (AML) is common with increasing age, and older adults with AML rarely achieve long-term remission with chemotherapy. Gene discovery studies in older adults with AML have shown that this malignancy is characterized by a multitude of somatic genomic alterations beginning with initiating somatic events followed by acquisition of collaborative transforming mutations. Despite these important biologic insights, current therapeutic approaches to AML remain limited, particularly in adults ≥ 60 years of age. The Beat AML trial was designed to assess the feasibility of using genetic profiling to assign patients (pts) to molecularly defined, subtype-specific therapies within 7 days of the initial diagnosis in a multi-center clinical trial setting, and to delineate the role of molecularly informed first-line treatment of AML with mechanism based novel therapies. Methods: Treatment-naïve patients with AML were enrolled in this prospective trial which offered accelerated cytogenetic and comprehensive mutational testing within 7 days followed by treatment assignment using these molecular data. Pt eligibility included age ≥ 60 years with non-APML AML, no known CNS leukemia, no prior hypomethylating agent (HMA) therapy and no clinical need for emergent therapy. Eligible pts were profiled by local cytogenetics analysis and using a central next generation sequencing (NGS) assay (Foundation Medicine, Inc.) with all molecular data required for treatment assignment (TA) obtained < 7 days. TA was made centrally using a pre-determined algorithm considering somatic cytogenetic and molecular alterations in the dominant clone, available targeted therapeutics for specific AML subsets, and the likelihood of cure with intensive chemotherapy. Results: From November 2016 to January 2019, 487 pts with a suspected diagnosis of AML had enrolled at 14 clinical sites; 395 were eligible for the study (77% of the patients not eligible for the study had an alternative diagnosis). The median age of eligible patients was 72 years (range: 60 to 92) with 38% being≥ 75 years and 16% with treatment-related AML. From the 395 eligible patients, 374 (94.7%) were centrally assigned to the different cytogenetic/genomic groups within 7 days. The most common groups were TP53 mutated (19%) and marker negative (18%) molecular groups. The Beat AML trial is dynamic by design, thereby allowing different arms to open over time; all trial arms are designed to evaluate for substantial clinical efficacy in small, molecularly defined patient subsets. As shown in Figure 1, 224 patients (57%) had a TA and consented to a BEAT AML sub-study. Of the remaining 171 patients, 103 received standard therapy defined as induction therapy (7+3) or hypomethylation agent (25 before TA and 78 after TA), 28 received an alternative investigational agent (5 before TA and 23 after TA), 38 received palliative care, and 2 had an unknown treatment status and are grouped with the palliative care patients in subsequent analyses; 9 patients died before TA (2 who received standard therapy and 7 in the palliative care group). Demographic, clinical, performance and molecular characteristics were not largely different between pts who elected targeted therapy as part of the BEAT AML trial versus those who elected standard therapy. As shown in Figure 2, the overall survival was significantly longer for patients enrolled in a targeted therapy arm as part of the BEAT AML trial compared to those who elected standard therapy. (p<0.0001). The 30-day estimated death rate was 3.7% (95% CI: 1.9-7.2) for patients electing treatment on a BEAT AML sub-study, 20.4% (95% CI: 13.0-31.2) for those receiving standard therapy, 0% for those receiving an investigational therapy, and 72.6% (95% CI: 57.8-85.7) for the palliative care group. Conclusion: Our data support the feasibility of a rapid precision medicine approach in older patients with previously untreated AML. Patients with AML who elected treatment assigned based upon cytogenetic and molecular alterations in the dominant clone using a novel precision medicine approach had significantly improved overall survival versus those who elected standard of care treatment. Disclosures Levine: Gilead: Consultancy; Prelude Therapeutics: Research Funding; Celgene: Consultancy, Research Funding; Novartis: Consultancy; Isoplexis: Membership on an entity's Board of Directors or advisory committees; Roche: Consultancy, Research Funding; Qiagen: Membership on an entity's Board of Directors or advisory committees; Loxo: Membership on an entity's Board of Directors or advisory committees; Imago Biosciences: Membership on an entity's Board of Directors or advisory committees; C4 Therapeutics: Membership on an entity's Board of Directors or advisory committees; Amgen: Honoraria; Lilly: Honoraria. Mims:Abbvie: Membership on an entity's Board of Directors or advisory committees; Agios Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees; Astellas Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees; PTC Therapeutics: Membership on an entity's Board of Directors or advisory committees; Jazz Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees. Borate:Novartis: Consultancy; Takeda: Consultancy; Pfizer: Consultancy; Daiichi Sankyo: Consultancy; AbbVie: Consultancy. Stein:Agios: Consultancy, Membership on an entity's Board of Directors or advisory committees; Astellas Pharma US, Inc: Membership on an entity's Board of Directors or advisory committees; Celgene Corporation: Membership on an entity's Board of Directors or advisory committees; PTC Therapeutics: Membership on an entity's Board of Directors or advisory committees; Syros: Membership on an entity's Board of Directors or advisory committees; Daiichi Sankyo, Inc.: Membership on an entity's Board of Directors or advisory committees; Bioline: Membership on an entity's Board of Directors or advisory committees; Genentech: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees. Patel:France Foundation: Honoraria; Dava Oncology: Honoraria; Celgene: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Baer:Takeda: Research Funding; Incyte: Research Funding; Kite: Research Funding; Forma: Research Funding; AI Therapeutics: Research Funding; Abbvie: Research Funding; Astellas: Research Funding. Stock:Daiichi: Membership on an entity's Board of Directors or advisory committees; Agios: Membership on an entity's Board of Directors or advisory committees; Astellas: Membership on an entity's Board of Directors or advisory committees; Research to Practice: Honoraria; UpToDate: Honoraria; Kite, a Gilead Company: Membership on an entity's Board of Directors or advisory committees; Pfizer: Membership on an entity's Board of Directors or advisory committees. Deininger:Pfizer: Consultancy, Honoraria, Research Funding; Ascentage Pharma: Consultancy, Honoraria; TRM: Consultancy; Sangoma: Consultancy; Fusion Pharma: Consultancy; Adelphi: Consultancy; Takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees; Humana: Honoraria; Incyte: Honoraria; Novartis: Honoraria; Sangamo: Consultancy; Blueprint: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees. Blum:Boehringer Ingelheim: Research Funding; Celgene: Research Funding; Astellas,: Research Funding; Xencor: Research Funding; Forma: Research Funding; AmerisourceBergen: Consultancy. Schiller:Amgen: Other, Research Funding; Agios: Research Funding, Speakers Bureau; Celgene: Research Funding, Speakers Bureau; Constellation Pharmaceutical: Research Funding; Daiichi Sankyo: Research Funding; Eli Lilly and Company: Research Funding; FujiFilm: Research Funding; Genzyme: Research Funding; Gilead: Research Funding; Incyte: Research Funding; J&J: Research Funding; Jazz Pharmaceuticals: Honoraria, Research Funding; Karyopharm: Research Funding; Novartis: Research Funding; Onconova: Research Funding; Pfizer Pharmaceuticals: Equity Ownership, Research Funding; Sangamo Therapeutics: Research Funding; Bristol Myer Squibb: Research Funding; Astellas: Research Funding; Biomed Valley Discoveries: Research Funding. Olin:Daiichi Sankyo: Research Funding; Astellas: Research Funding; Genentech: Consultancy, Research Funding; Pfizer: Research Funding; Jazz Pharmaceuticals: Consultancy, Honoraria; Revolution Medicine: Consultancy; AstraZeneca: Research Funding; Clovis: Research Funding; Ignyta: Research Funding; MedImmune: Research Funding; Mirati Therapeutics: Research Funding; Novartis: Research Funding; Spectrum: Research Funding. Foran:Agios: Honoraria, Research Funding. Lin:Pfizer: Membership on an entity's Board of Directors or advisory committees; Jazz Pharmaceuticals: Honoraria. Traer:AbbVie: Consultancy; Agios: Consultancy; Astellas: Consultancy; Daiichi Sankyo: Consultancy; Notable Labs: Equity Ownership. Odenike:AbbVie: Consultancy, Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees, Research Funding; Incyte: Research Funding; Astra Zeneca: Research Funding; Astex Pharmaceuticals: Research Funding; NS Pharma: Research Funding; Gilead Sciences: Research Funding; Janssen Oncology: Research Funding; Oncotherapy: Research Funding; Agios: Research Funding; CTI/Baxalta: Research Funding. Arellano:Gilead: Consultancy. Vergilio:Roche Holding AG: Equity Ownership; Foundation Medicine: Employment. Brennan:Foundation Medicine: Employment. Vietz:Foundation Medicine: Employment. Druker:ALLCRON: Membership on an entity's Board of Directors or advisory committees; Pfizer: Research Funding; Aileron Therapeutics: #2573, Constructs and cell lines harboring various mutations in TNK2 and PTPN11, licensing fees , Membership on an entity's Board of Directors or advisory committees; Bristol-Myers Squibb: Patents & Royalties, Research Funding; Burroughs Wellcome Fund: Membership on an entity's Board of Directors or advisory committees; Cepheid: Consultancy, Honoraria; The RUNX1 Research Program: Membership on an entity's Board of Directors or advisory committees; GRAIL: Equity Ownership, Other: former member of Scientific Advisory Board; Patient True Talk: Consultancy; Dana-Farber Cancer Institute (antibody royalty): Patents & Royalties: #2524, antibody royalty; Pfizer: Other: PI or co-investigator on clinical trial(s) funded via contract with OHSU., Research Funding; Merck & Co: Patents & Royalties: Dana-Farber Cancer Institute license #2063, Monoclonal antiphosphotyrosine antibody 4G10, exclusive commercial license to Merck & Co; OHSU (licensing fees): Patents & Royalties: #2573, Constructs and cell lines harboring various mutations in TNK2 and PTPN11, licensing fees ; Amgen: Equity Ownership, Membership on an entity's Board of Directors or advisory committees; Aptose Biosciences: Consultancy, Equity Ownership, Membership on an entity's Board of Directors or advisory committees; Beta Cat: Membership on an entity's Board of Directors or advisory committees, Other: Stock options; Blueprint Medicines: Consultancy, Equity Ownership, Membership on an entity's Board of Directors or advisory committees; Vivid Biosciences: Membership on an entity's Board of Directors or advisory committees, Other: Stock options; Beat AML LLC: Other: Service on joint steering committee; CureOne: Membership on an entity's Board of Directors or advisory committees; Celgene: Consultancy; Gilead Sciences: Other: former member of Scientific Advisory Board; ICON: Other: Scientific Founder of Molecular MD, which was acquired by ICON in Feb. 2019; Monojul: Other: former consultant; Novartis: Other: PI or co-investigator on clinical trial(s) funded via contract with OHSU., Patents & Royalties: Patent 6958335, Treatment of Gastrointestinal Stromal Tumors, exclusively licensed to Novartis, Research Funding; Bristol-Myers Squibb: Other: PI or co-investigator on clinical trial(s) funded via contract with OHSU., Research Funding. Byrd:Novartis: Other: Travel Expenses, Speakers Bureau; BeiGene: Research Funding; Pharmacyclics LLC, an AbbVie Company: Other: Travel Expenses, Research Funding, Speakers Bureau; Acerta: Research Funding; Ohio State University: Patents & Royalties: OSU-2S; Genentech: Research Funding; Gilead: Other: Travel Expenses, Research Funding, Speakers Bureau; TG Therapeutics: Other: Travel Expenses, Research Funding, Speakers Bureau; Janssen: Consultancy, Other: Travel Expenses, Research Funding, Speakers Bureau.

Key Points c-KIT activating mutations cause resistance to PARP inhibitor in AML1-ETO–positive leukemias. c-KIT inhibitor avapritinib downregulates BRCA1/2 and DNA-PK catalytic subunit to restore the sensitivity to PARP inhibitor.

Abstract Background: Novel therapies are required to improve the outcome of patients with AML. New agents are asked to demonstrate an overall survival (OS) benefit before qualifying for FDA approval. The long duration of clinical trials required in order to achieve this endpoint hampers quick evaluation of candidate therapies, including novel agents. Identification of reliable surrogate endpoints for OS in AML is needed. Here we compare the results of therapy for patients with untreated AML ages 16-60 years on the Eastern Cooperative Oncology Group 1900 trial (E1900) of induction chemotherapy followed by consolidation and autologous transplant in order to evaluate the validity of an event free survival (EFS) endpoint as a surrogate for OS. Methods:OS was measured from randomization for induction therapy to death from any cause (censored at last contact). EFS was measured from randomization to induction treatment failure, relapse after compete response (CR), or death in remission (censored at last contact). Hazard ratios (HR) were computed using Cox proportional hazards models. The association between EFS and OS was evaluated using the Kendall tau-a rank correlation for censored data. Results:There were657 patients enrolled of which 426 patients relapsed or had induction treatment failure before death or date of last contact. Median EFS and OS were 8.0 months (95% CI, 6.3 to 9.7 months) and 23.6 months (95% CI, 16.9 to 23.6 months), respectively. With a median follow-up of 80.1 months, there is a statistically significant correlation between EFS and OS (Kendall tau-a = 0.467, 95% confidence interval (CI) = (0.425, 0.510), p<0.001). This correlation was similarly significant at a median follow-up of 25.2 months (Kendall tau-a = 0.361, 95% CI (0.323, 0.400), p <0.001) when the E1900 trial was originally reported (Fernandez et al. NEJM 2009). Key findings reported based on the original OS endpoint are similar when analyzed with an EFS endpoint (Table 1). High-dose daunorubicin (90 mg/m2) (DNR 90) confers both an EFS and OS benefit in patients aged < 50 years and patients with intermediate cytogenetic risk, and does not confer an EFS or OS benefit in older patients and patients with unfavorable cytogenetic risk, on univariate analysis. Divergent results are only seen in the small subset of favorable cytogenetic risk patients, where DNR 90 conferred an OS benefit (p=0.027) without an EFS benefit (p=0.32). Both EFS and OS endpoints consistently reflect the impact of mutation status on survival. The presence of a FLT3-ITD or DNMT3A mutation has a negative impact on both EFS and OS while an IDH2 mutation has a favorable impact on EFS and OS. The presence of a NPM1 mutation confers a favorable impact on EFS and OS in patients who received DNR 90 and did not impact EFS or OS in patients receiving standard-dose daunorubicin (45 mg/m2) (DNR 45). The presence of an IDH1 mutation does not impact EFS or OS. Conclusions:The results of E1900 demonstrating superiority of DNR 90 in AML induction in patients up to age 60 are concordant when using an EFS or OS endpoint. This is true for the group as a whole as well as for subgroups for which targeted agents are in development (FLT3/IDH2 inhibitors). Further investigation of whether EFS is a reliable surrogate for OS is warranted in AML. If confirmed, its use as a primary endpoint could be adopted by regulatory agencies in order to allow more rapid completion of clinical trials in AML and bring new therapies to AML patients in a timely fashion. Table 1. Results of E1900 based on an EFS endpoint versus an OS endpoint. Subgroup N OS HR (DNR 90/DNR 45) & 95% CI Wald P EFS HR (DNR 90/DNR 45) & 95% CI Wald P DNR 45 DNR 90 Age < 50 yrs ³ 50 yrs 188 142 172 155 0.66 (0.50, 0.85) 0.81 (0.62, 1.06) 0.002 0.118 0.64 (0.50, 0.82) 0.86 (0.67, 1.10) 0.0004 0.23 Cytogenetic Favorable Intermediate Unfavorable 38 141 59 51 127 63 0.51 (0.28, 0.93) 0.68 (0.50, 0.92) 0.79 (0.54, 1.16) 0.027 0.012 0.225 0.76 (0.44, 1.31) 0.63 (0.47, 0.83) 0.72 (0.49, 1.05) 0.32 0.001 0.09 Subgroup N OS HR (MUT/WT) & 95% CI Wald P EFS HR (MUT/WT) & 95% CI Wald P FLT3-ITD WT MUT 456 147 1.62 (1.31, 2.01) <.0001 1.48 (1.21, 1.82) 0.0002 DNMT3A WT MUT 371 119 1.30 (1.03, 1.65) 0.03 1.23 (0.98, 1.54) 0.07 IDH1 WT MUT 465 36 0.88 (0.59, 1.33) 0.55 0.91 (0.62, 1.34) 0.64 IDH2 WT MUT 451 50 0.63 (0.43, 0.93) 0.02 0.68 (0.48, 0.97) 0.03 NPM1 DNR 45 DNR 90 245 257 0.84 (0.61, 1.16) 0.60 (0.41, 0.89) 0.30 0.01 0.90 (0.66, 1.22) 0.59 (0.41, 0.84) 0.49 0.004 Disclosures No relevant conflicts of interest to declare.

Background: Pegylated Interferon-alpha (PEG-IFNa) improves hematologic parameters and reduces mutant allele fraction in patients with myeloproliferative neoplasms (MPNs); however, widespread clinical use is limited by frequent discontinuation due to side effects. Identifying biomarkers of response to PEG-IFNa therapy might identify patient subsets most likely to derive benefit from this therapy. Serum pro-inflammatory cytokine levels are increased in MPN patients and associated with adverse clinical outcomes. The effect of PEG-IFNa therapy on cytokine levels in MPN patients and correlation with clinical response has not been elucidated. We hypothesized that identification of cytokine signatures could predict for clinical/molecular response to PEG-IFNa in MPNs. Methods: Pre- and post-treatment serum samples were collected from available patients enrolled on the Myeloproliferative Disorders Research Consortium (MPD-RC) 111/112 trials-multicenter studies assessing efficacy of PEG-IFNa in patients with high-risk polycythemia vera/essential thrombocythemia either up front or in the setting of hydroxyurea failure/intolerance. Serum was prepared using the Millipore MAP Human 41-Cytokine Magnet Bead System (Millipore; Cat:HCYTOMAG-60K) and run on the Luminex FLEXMAP 3D platform. Data was analyzed using Luminex xPonent 4.3 software. Correlative mutational data on 156 genes implicated in myeloid malignancies was also available for all patients. Age-matched serum from healthy individuals (N=6) was obtained from AllCellsTM for use as wild-type (WT) controls. Baseline cytokine samples were compared between groups of interest by use of Wilcoxon rank-sum test. Change from baseline in cytokines for each group were compared to the null hypothesis of zero change. P values <0.05 were considered statistically significant. Results: Pre- and post-treatment serum samples were available on 29 MPN patients from the MPN-RC 111/112 cohorts. 21 patients were classified as complete responders (CRs) vs. 8 non-responders (NRs) using European LeukemiaNet criteria. Baseline cytokine levels were generally increased in both CRs and NRs compared to WT, including significant increases in Eotaxin (p=0.023), IL3 (p=0.048), IP10 (p=0.04), and TNFa (p=0.006) (Table 1), as well as a non-significant trend increase in IL8 (p=0.076). Notably, other cytokines were decreased at baseline in comparison to WT, including EGF (p<0.001), as well as MDC (p=0.040) and PDGFaabb (p=0.02), in line with previous studies. Compared to CRs, NRs displayed significantly lower levels of GRO (p=0.020), MDC (p=0.003), and PDGFaabb (p=0.026) at baseline along with elevated levels of IP10 (p=0.028) suggesting pre-treatment levels of these cytokines might predict response to therapy. Comparison of pre- and post- treatment samples revealed a general increase in median cytokine levels in CRs, with significant changes in GM-CSF (p=0.012), IP10 (p<0.001), MCP1 (p=0.015) and IFNa itself (p=0.010). Notably, median cytokine levels in NRs post-treatment, including IFNa, were relatively unchanged from baseline despite on-going PEG-IFNa therapy. Additional pre-treatment serum samples, as well as correlative analysis of cytokine changes with JAK-STAT driver mutant allele fraction and mutational profiling are underway and will be presented at the meeting. Conclusions: Preliminary findings suggest individual cytokines are affected by PEG-IFNa in MPNs. Furthermore, baseline levels of GRO, MDC, PDGFaabb, and IP10 correlate with response to PEG-IFNa. These data may identify MPN patients most likely to respond to PEG-IFNa therapy and those for whom this therapy may be most appropriate. Further analysis with a larger cohort of treatment-naïve patients is underway to validate these findings and identify additional molecular and cytokine signatures of response to PEG-IFNa therapy. Disclosures Yacoub: Agios: Speakers Bureau; Hylapharm: Equity Ownership; Dynavax: Equity Ownership; Cara: Equity Ownership; Ardelyx: Equity Ownership; Incyte: Consultancy, Honoraria, Speakers Bureau; Seattle Genetics: Honoraria, Speakers Bureau; Novartis: Consultancy, Speakers Bureau. Mascarenhas:Incyte: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Research Funding; Roche: Consultancy, Research Funding; Merck: Research Funding; Celgene: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; CTI Biopharma: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Janssen: Research Funding; Promedior: Research Funding; Merus: Research Funding; Pharmaessentia: Consultancy, Membership on an entity's Board of Directors or advisory committees. Levine:Lilly: Honoraria; Qiagen: Membership on an entity's Board of Directors or advisory committees; Imago Biosciences: Membership on an entity's Board of Directors or advisory committees; Loxo: Membership on an entity's Board of Directors or advisory committees; Prelude Therapeutics: Research Funding; Isoplexis: Membership on an entity's Board of Directors or advisory committees; Roche: Consultancy, Research Funding; Gilead: Consultancy; Amgen: Honoraria; C4 Therapeutics: Membership on an entity's Board of Directors or advisory committees; Celgene: Consultancy, Research Funding; Novartis: Consultancy. Hoffman:Merus: Research Funding. Rampal:Constellation, Incyte, and Stemline Therapeutics: Research Funding; Agios, Apexx, Blueprint Medicines, Celgene, Constellation, and Jazz: Consultancy.