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TO THE EDITOR: BCR-ABL -negative myeloproliferative neoplasms (MPNs) are a group of clonal stem cell disorders characterized by the overproduction of mature myeloid cells. However, MPN patients also have a 2.8- to 3.4-fold increased risk of developing a lymphoproliferative disorder (LPD) compared

Background: The Canadian tyrosine kinase inhibitor (TKI) discontinuation trial, named "Treatment Free Remission Accomplished By Dasatinib " (NCT#02268370), has reported 56.8% molecular relapse-free survival (mRFS) rate at 12 months after imatinib (IM) discontinuation. MMR loss occurred quickly after IM discontinuation, typically within 2-4 months, while those who lost MR4 on two consecutive measurements tended to lose their molecular response more gradually. BCR-ABL transcript doubling time (DT) after TKI discontinuation is a reciprocal concept to transcript halving time following TKI therapy. Due to inter-individual differences in DT after TKI discontinuation, DT can be used as a potential biomarker to identify those patients at high-risk for TFR failure when measured before they experience a clinically significant event of molecular relapse. The present study has not only evaluated the kinetics of BCR-ABL transcript rise after IM discontinuation, but also explored the predictive/prognostic role of DT of BCR-ABL transcript level as an early predictor of TFR failure. Patients and methods: Changes of BCR-ABL1 transcript level in each patient were assessed monthly by estimating the number of days required for BCR-ABL1 to double from the previous expression level/measurement, termed the DT. Based on the BCR-ABL1 qPCR value taken monthly in the first 6 months after IM discontinuation, DT was calculated monthly, as x = ln(2)/K, where x is the DT and K is the fold BCR-ABL1 change from the previous value divided by the number of days between each measurement. K was determined as follows: K = [ln(b) - ln(a)]/t, where a is the BCR-ABL1 value of the previous measurement, b is the BCR-ABL1 at the relevant time point, and t is the number of days between measurements. The baseline qPCR level from the prior month to TKI discontinuation was referenced. The distribution of DT was assessed at each time point of DT measurement within the first 6 months. In order to define cut-off levels for BCR-ABL1 qPCR and DT for the first 6 months, multiple statistical parameters were taken into account including positive (PPV) and negative predictive value (NPV), accuracy and F1 score of DT value, resulting in the DT value of 12.75 days at 2 months as the optimal cut-off value of DT value. Patients were stratified into the 3 groups based on the DT value of 12.75 days at 2 months after IM discontinuation. The high-risk group was defined as the patients showing DT < 12.75 days but above 0, i.e. rapidly proliferating CML cells, implying a high risk for TFR failure with a shorter DT. The intermediate-risk group was defined as those patients with DT ≥ 12.75 days, i.e. more slowly proliferating CML cells implying intermediate risk for TFR failure. The low-risk group was defined as patients showing DT of zero or below, i.e. no increase in the size of the pool of cells expressing BCR-ABL, implying a low risk for TFR failure. The mRFS was analyzed for each of these risk groups at 6 monthly intervals after TKI discontinuation. Results: We compared the DT values of the patients that failed TFR with those from the patients who maintained their molecular response at last follow-up. The DT values at 2 months were much shorter in patients who failed TFR after IM cessation (median 8.32 days) compared to those who maintained molecular response (median 20.7 days; p The DT value of 12.75 days was defined as the optimal value for DT at 2 months with the NPV, PPV, accuracy and F1 score of 80.90%, 96.43%, 84.62% and 0.75, respectively, as the -log10(p-value), accuracy and F1 score reached a plateau at a DT of 12.75 days as presented in the Figure A. At a DT value of 12.75 days at 2 months after IM discontinuation, patients were stratified into 3 groups: high- (n=26), intermediate- (n=16) and low-risk groups (n=71; Figure B). With respect to mRFS rate, the high-risk group showed 7.7% mRFS rate at 12 months compared to 53.6% in the intermediate-risk group or 90.0% in the low-risk group (p Conclusion: Monthly assessment of DT based on the monthly BCR-ABL qPCR is useful to identify the patients with an imminent risk of molecular recurrence after IM cessation for TFR. Figure Disclosures Bence-Bruckler: Merck: Membership on an entity's Board of Directors or advisory committees. Keating:Takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees; Hoffman La Roche: Membership on an entity's Board of Directors or advisory committees; Sanofi: Membership on an entity's Board of Directors or advisory committees; Seattle Genetics: Consultancy; Merck: Membership on an entity's Board of Directors or advisory committees; Janssen: Membership on an entity's Board of Directors or advisory committees; Servier: Membership on an entity's Board of Directors or advisory committees; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Shire: Membership on an entity's Board of Directors or advisory committees; Taiho: Membership on an entity's Board of Directors or advisory committees; Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding. Busque:Novartis: Honoraria; BMS: Honoraria; Pfizer: Honoraria. Delage:Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding. Lipton:BMS: Consultancy, Research Funding; Takeda: Consultancy, Honoraria, Research Funding; Bristol-Myers Squibb: Honoraria; Ariad: Consultancy, Research Funding; Pfizer: Consultancy, Honoraria, Research Funding; Novartis: Consultancy, Research Funding. Leber:Pfizer: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Abbvie: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; BMS/Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees; Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Treadwell: Honoraria, Membership on an entity's Board of Directors or advisory committees; Takeda/Palladin: Honoraria, Membership on an entity's Board of Directors or advisory committees; Alexion: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Lundbeck: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Otsuka Pharmaceutical: Honoraria, Membership on an entity's Board of Directors or advisory committees.

Introduction: Acute myeloid leukemia (AML) is driven by a subpopulation of leukemia stem cells (LSCs), which possess properties such as quiescence and self-renewal that are linked to therapy resistance and relapse. The LSC17 score was derived from genes differentially expressed between functionally validated LSC+ and LSC- fractions from 78 AML patients and is strongly associated with survival and response to standard therapy. A critical advantage of the LSC17 test over cytogenetic and molecular analysis is its rapid turnaround time (24-48h on a NanoString platform), providing clinicians with a rapid and powerful tool for upfront risk stratification. We have developed a clinical assay for the LSC17 score validated in a CAP/CLIA-lab setting. Methods: We conducted a prospective, multicenter validation and feasibility study to test the prognostic value of the LSC17 assay under real-world conditions in AML patients treated with curative intent. Patients with a possible new diagnosis of AML were eligible. Patients with a confirmed diagnosis of acute promyelocytic leukemia were excluded from analysis. Standard prognostic markers including cytogenetics, molecular studies and targeted sequencing using a standard AML panel were performed in parallel to the LSC17 score. Treatment was administered according to physician preference, based on patient history and results of standard prognostic assays, when available. Survival data was censored on June 14th, 2020. Results: 381 patients were recruited to the study between June 2016 and March 2020. 4 patients were excluded for quality control reasons (one sample had insufficient RNA and three samples failed quality control checks). 103 were excluded as they had alternative diagnoses. 84 patients were excluded because they did not receive intensive chemotherapy. LSC17 scores ranged from 0 to 1.25, and were classified as high or low according to the median score of 0.51 from a previously validated reference cohort (Ng et al, Nature 2016). Of the 190 patients included in this analysis, 84 had a low LSC17 score and 106 had a high LSC17 score. The median age was 61 years (range 18-79); 86 (45%) were female. When stratified according to ELN 2017 criteria, 48 (27%), 51 (29%), and 77 (44%) patients had favorable, intermediate, and adverse risk disease, respectively. Low LSC17 score was associated with normal cytogenetics (high vs low, 33% vs 58%; P We first considered response to induction chemotherapy (Table 1). 141 patients had standard induction chemotherapy with 3+7, 40 had Flag-IDA and 9 had CPX-351. High score patients had inferior responses to 3+7 with only 59% achieving complete remission (CR) after 1 cycle of chemotherapy compared to 96% of low score patients; responses for LSC17 high score patients were better in the Flag-IDA group with 80% achieving CR after 1 cycle. When considering overall CR rates after 2 cycles of induction, patients with a high LSC17 score were less likely to achieve CR (high vs low, 87% vs 98%; P=0.02). However, this difference was predominantly observed in patients treated with 3+7 (87% vs 99% CR rate in high vs low score patients, respectively); response rates to Flag-IDA were not significantly different between the 2 groups. Measurable residual disease (MRD) monitoring by flow cytometry was performed at the time of CR in 135 (71%) patients enrolled at Princess Margaret Cancer Centre. Patients with a high LSC17 score were significantly more likely to have MRD compared to low score patients (46% vs 10% respectively, P Conclusion: AML patients with a high LSC17 score have inferior outcomes following 3+7 induction chemotherapy. The LSC17 score should be considered as a tool to identify and stratify high-risk patients to alternative upfront therapies such as Flag-IDA. A risk adapted study is planned to validate these results. Disclosures Gupta: Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Sierra Oncology: Consultancy, Membership on an entity's Board of Directors or advisory committees; Pfizer: Consultancy; Bristol MyersSquibb: Honoraria, Membership on an entity's Board of Directors or advisory committees; Incyte: Honoraria, Research Funding. Maze:Novartis: Honoraria; Takeda: Research Funding; Pfizer: Consultancy. McNamara:Novartis: Honoraria. Schimmer:Medivir AB: Research Funding; AbbVie Pharmaceuticals: Other: owns stock ; Takeda: Honoraria, Research Funding; Novartis: Honoraria; Jazz: Honoraria; Otsuka: Honoraria. Leber:Takeda/Palladin: Honoraria, Membership on an entity's Board of Directors or advisory committees; Treadwell: Honoraria, Membership on an entity's Board of Directors or advisory committees; Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; BMS/Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees; Abbvie: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Pfizer: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Otsuka Pharmaceutical: Honoraria, Membership on an entity's Board of Directors or advisory committees; Lundbeck: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Alexion: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Tierens:Amgen: Membership on an entity's Board of Directors or advisory committees; Jazz Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees; Astellas Pharma: Membership on an entity's Board of Directors or advisory committees. Wang:Trilium therapeutics: Patents & Royalties: There is an existing license agreement between TTI and University Health Network and J.C.Y.W. may be entitled to receive financial benefits further to this license and in accordance with UHN's intellectual property policies. .

Background: AML is driven by a small subpopulation of leukemia stem cells (LSCs), which possess stem-cell properties such as quiescence and self-renewal that are linked to therapy resistance and relapse. The LSC17 score was derived from genes differentially expressed between functionally validated LSC+ and LSC- cell fractions from 78 AML patients. The LSC17 score was strongly associated with survival in 4 independent cohorts of AML patients treated with curative intent (n = 908), and accurately predicted initial response. Patients with high LSC17 scores had poor outcomes with standard treatment strategies. The LSC17 score remained highly significant in multivariate analyses, independent of commonly used prognostic factors. A critical advantage of the LSC17 test over cytogenetic analysis is its rapid turnaround time (24-48h on a NanoString platform), providing clinicians with a powerful tool for upfront risk stratification. To date, no RNA-based, stem cell-derived score has been transitioned into a Clinical Laboratory Improvement Amendments (CLIA) certified laboratory. Study design and methods: The study consists of 2 phases. Phase 1 aims to validate the assay in a CLIA certified laboratory setting. Phase 2 aims to determine prospectively the feasibility and prognostic power of LSC17 score testing in newly diagnosed AML patients in the real-world setting. Clinical endpoints include primary induction failure rate, relapse free survival and overall survival. All patients with a suspected diagnosis of de novo or secondary AML, who are deemed fit and appropriate by their treating physician to undergo intensive induction chemotherapy, are considered for this study. Patients who received any prior anti-leukemia treatments (except hydroxyurea) and patients with a confirmed diagnosis of acute promyelocytic leukemia are excluded. Current participating centres include Princess Margaret Cancer Centre (Toronto), Juravinski Cancer Centre (Hamilton), and The Ottawa Hospital Cancer Centre (Ottawa). Pre-study sample size analysis suggests that 150 patients will be required to demonstrate a hazard ratio for death of 2.3 between patients with a high and low LSC17 score (α = 0.05, power = 0.8). The survival for the high and low LSC17 score groups will be compared using the Cox proportional hazards model. Traditional risk stratification will also be tested within a Cox proportional hazards model. Phase 1 of the study has been completed and several key quality control measures have been created. Initial derivation and validation of the LSC17 score was performed using standard chemistry on the NanoString platform; for CLIA lab validation, the assay was transitioned to Elements© chemistry, which does not require custom codeset manufacture by NanoString. The original AML reference cohort was retested using Elements© chemistry to derive an absolute median threshold for prospective LSC17 score determination in individual patients. The lab validation process compared and found no difference in LSC17 scores between samples processed by Ficoll or collected in Paxgene for ease of processing. A standardised quality assurance (QA) process was completed to identify optimal sample requirements as well as specimen storage conditions, score stability during sample storage and turnaround time for testing. An algorithm has been created using the laboratory information system to allow standardised and rapid calculation of the LSC17 score from NanoString nCounter output data. The LSC17 score can be tested on peripheral blood or bone marrow, although bone marrow samples are preferred for patients with very low peripheral blast counts. Samples are ideally stored in RNA Paxgene tubes for RNA stability and to maximize RNA yield. The prospective phase of the study (Phase 2) opened in April 2018 and as of June 2019, 233 patients have been enrolled, of which 120 received induction chemotherapy. 54 patients were excluded due to an alternative diagnosis or failed QA. The remaining patients had non-intensive therapy based on patient choice. Standard prognostic markers including cytogenetics, molecular studies and targeted sequencing using a 49-gene AML panel are performed in parallel to the LSC17 score. Treatment was administered according to physician preference, based on patient history and results of standard prognostic assays, when available. The study continues to recruit and is open to collaborations in other centres. Disclosures Ng: Celgene: Research Funding. Leber:Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Pfizer: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Celgene Corporation: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; AbbVie: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Astellas: Honoraria, Membership on an entity's Board of Directors or advisory committees; Jazz: Honoraria, Membership on an entity's Board of Directors or advisory committees; Alexion: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Sabloff:Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees; Astellas Pharma Canada: Honoraria, Membership on an entity's Board of Directors or advisory committees; ASTX: Membership on an entity's Board of Directors or advisory committees, Research Funding; Jazz Pharmaceuticals: Honoraria, Membership on an entity's Board of Directors or advisory committees; Pfizer Canada: Honoraria, Membership on an entity's Board of Directors or advisory committees; Actinium Pharmaceuticals, Inc: Membership on an entity's Board of Directors or advisory committees; Novartis Pharmaceuticals: Honoraria, Membership on an entity's Board of Directors or advisory committees; Sanofi Canada: Research Funding. Minden:Trillium Therapetuics: Other: licensing agreement. Wang:NanoString: Other: Travel and accommodation; Trilium therapeutics: Other: licensing agreement, Research Funding; Pfizer AG Switzerland: Honoraria, Other: Travel and accommodation; Pfizer International: Honoraria, Other: Travel and accommodation.

Introduction: The introduction of next-generation sequencing (NGS) has expedited the discovery of novel genetic lesions in acute myeloid leukemia (AML), thereby allowing better risk stratification with respect to overall survival (OS). We have previously reported that AML patients with PTPN11 and NPM1 mutations had longer OS following chemotherapy, while those carrying mutations in ASXL1, JAK2, RUNX1, TP53 and SRSF2 had a shorter OS (Daher-Reyes,ASH 2018). Little is known, however, regarding the impact of genetic profiles (somatic mutations and cytogenetic abnormalities) at initial AML diagnosis on the treatment outcomes following allogeneic hematopoietic stem cell transplantation (HCT). Methods & Patients: We enrolled AML patients who had available NGS data at time of initial diagnosis as part of the AGILE project between February 2015 and December 2018, and who subsequently underwent allogeneic HCT. NGS was performed on DNA samples isolated from peripheral blood or bone marrow samples at diagnosis. Analysis was performed using the TruSight Myeloid Sequencing Panel on the MiSeq sequencer (Illumina; San Diego, CA). Transplant outcomes (overall survival (OS), relapse-free survival (RFS), relapse incidence (RI), and non-relapse mortality (NRM)) after HCT were compared according to genetic profiles defined at diagnosis. Survival analysis for OS and RFS was performed using Cox's proportional hazard model, while the Fine-Gray model was used for RI and NRM analyses. Variables considered in the model included CR status prior to HCT (CR1 vs. beyond CR1), de novo AML (vs. secondary/therapy-related AML), induction chemotherapy used (3+7 vs. others), conditioning regimen (myeloablative vs. reduced intensity), WBC, age, donor type, mutation status of commonly mutated genes, and the composite adverse genetic profile (defined as having at least one of monosomal karyotype (MK), TP53 mutation, del(5), complex karyotype (CK), and monosomy 7), given that these 5 features were highly co-occurring, adverse prognostic factors (Figure 1A). Results: We identified 435 patients in whom frontline NGS was performed, of whom a total of 178 patients (40.9%) received HCT and were included in the final analysis. A total of 598 (median 4, IQR 2-5) mutations were identified in 165 patients (n=165/178, 92.7%). Among 54 genes in the panel, 12 genes were mutated in more than 10% of the cohort, with the most commonly mutated genes being DNMT3A (30.3%), TET2 (25.3%), NPM1 (22.5%), RUNX1 (18.5%), IDH2 (16.9%), FLT3 (15.7%), ASXL1 (12.4%), BCOR (12.4%), CEBPA (11.2%), NRAS (11.2%), IDH1 (10.1%), and SRSF2 (10.1%). In univariate analysis, the groups with a composite adverse genetic profile (n=30/178, 16.9%) showed decreased OS (HR 2.19 [1.30-3.67]; p=0.003), while patients harbouring spliceosome gene (SF3B1, SRSF2, U2AF1, and ZRSR2) mutations (n=37/178, 20.8%) had longer OS (HR 0.39 [0.18-0.85]; p=0.018), with 2-year OS rates of 24.9% and 57.9%, respectively (p=0.002)) (Figure 1B). The composite adverse genetic profile was also associated with shorter RFS (HR 2.23 [1.34-3.69]; p=0.002), while spliceosome gene mutations were associated with longer RFS (HR 0.42 [0.20-0.88]; p=0.022), with 2-year RFS rates of 23.7% vs. 57.9%, respectively (p=0.001)). The composite adverse genetic profile was also associated with higher RI (HR 2.94 [1.52-5.66]; p=0.001), with 2-year RI rates of 47.2% vs. 17.2%, respectively, for patients with and without adverse genetic features (p=0.002) (Figure 1C). Neither the composite adverse genetic profile, nor spliceosome gene mutations, were associated with NRM, with HR of 1.21 [0.55-2.65], p=0.64) and 0.45 [0.16-1.31], p=0.15, respectively (Figure 1D). Multivariate analyses confirmed that the composite adverse genetic profile and spliceosome gene mutations were independent prognostic factors for OS, RFS, and RI (p=0.004, p=0.002, and p=0.001, respectively) and for OS and RFS (p=0.020 and p=0.022, respectively). Conclusion: In our cohort, the composite adverse genetic profile (i.e. having at least one of MK, TP53 mutation, del(5), CK and monosomy 7 remained as a poor prognostic factor even after allogeneic HCT. To clarify the role of genetic risk stratification in HCT, further analysis using a larger cohort is warranted. In addition, a comparative analysis between HCT vs no-HCT groups according to the genetic profile, is ongoing in a in a larger patient cohort. Figure 1 Disclosures Michelis: CSL Behring: Other: Financial Support. Mattsson:Gilead: Honoraria; Celgene: Honoraria; Therakos: Honoraria. Schimmer:Novartis Pharmaceuticals: Consultancy; Otsuka Pharmaceuticals: Consultancy; Jazz Pharmaceuticals: Consultancy; Medivir Pharmaceuticals: Research Funding. McNamara:Novartis Pharmaceutical Canada Inc.: Consultancy. Maze:Pfizer Inc: Consultancy; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees. Gupta:Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees; Sierra Oncology: Honoraria, Membership on an entity's Board of Directors or advisory committees; Incyte: Honoraria, Research Funding; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding. Yee:Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Astex: Research Funding; Hoffman La Roche: Research Funding; MedImmune: Research Funding; Pfizer: Honoraria, Membership on an entity's Board of Directors or advisory committees; Merck: Research Funding; Millennium: Research Funding; Astellas: Membership on an entity's Board of Directors or advisory committees; Takeda: Membership on an entity's Board of Directors or advisory committees. Minden:Trillium Therapetuics: Other: licensing agreement. Schuh:Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees; AbbVie: Honoraria, Membership on an entity's Board of Directors or advisory committees; Agios: Honoraria; Teva Canada Innovation: Honoraria, Membership on an entity's Board of Directors or advisory committees; Astellas: Honoraria, Membership on an entity's Board of Directors or advisory committees; Jazz: Honoraria, Membership on an entity's Board of Directors or advisory committees; Pfizer: Honoraria, Membership on an entity's Board of Directors or advisory committees; Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees.

Introduction: Although induction chemotherapy results in a complete remission (CR) in ~70% of newly diagnosed AML patients, post-remission therapies are needed to eliminate minimal residual disease (MRD) and prevent relapse. Consolidation chemotherapy, either as definitive therapy or bridge to bone marrow transplantation (BMT), is currently the most common form of post-remission therapy. Yet, our understanding of its impact on MRD remains limited. In this study, we investigated the effects of consolidation chemotherapy on molecular MRD (mMRD) burden using ultra-deep next generation sequencing (NGS) and correlated treatment response with disease characteristics and survival outcomes in AML patients. Patients and Methods: 91 newly diagnosed AML patients who achieved CR following standard induction chemotherapy were evaluated. Targeted conventional NGS using a 54-gene panel was performed on whole blood (PB) or bone marrow samples collected at diagnosis. PB samples were collected during remission at two consecutive time points (T1 and T2), before and after 1 (n=79) or 2 (n=12) cycles of consolidation chemotherapy, for each patient. To detect mMRD, we used a custom 37-gene hybrid-capture panel and error-corrected NGS based on the duplex sequencing approach with a variant allele frequency (VAF) detection limit of ~1x10-4. For 10 patients, we also performed duplex sequencing analysis on their relapsed samples. Results: NGS of the diagnostic samples identified a total of 298 putative oncogenic mutations in 92% (n=84) of the 91 patients. Ninety percent of these mutations (n=267) were trackable by the custom hybrid-capture panel. Duplex sequencing detected persistence of 56% (n=149) of the trackable mutations in T1 samples; 34% (n=50) of which were clonal hematopoiesis-associated DTA mutations (those involving DNMT3A, TET2, or ASXL1), and the remaining 66% (n=99) were non-DTA mutations. Analysis of T2 samples showed that consolidation chemotherapy reduced the VAF of non-DTA mutations by a median of 73% and cleared 27% (n=27) of them at T2. In contrast, the burden of DTA mutations increased by 0.5% (P < 0.0001 by Mann-Whitney test), and only 2% (n=1) of the mutations was cleared (P = 0.0001 by Fisher's exact test). These findings are consistent with prior studies demonstrating that non-DTA mutations are more reliable markers of leukemic burden than DTA mutations. To study the impact of consolidation chemotherapy at the level of individual patients, the mean VAF of all persistent non-DTA mutations was calculated for each sample and used as a composite measure of mMRD burden (henceforth referred to as "cmMRD"). Analysis of the 10 patients with relapsed samples showed that cmMRD levels tracked well with achievement of remission and disease progression (Fig. 1). In the subset of patients with persistent non-DTA mutations at T1 (n=61), consolidation chemotherapy decreased cmMRD levels by a median of 36% at T2. However, we observed high interpatient variability (Fig. 2); 36% (n=22) of the patients experienced an increase in cmMRD burden after consolidation chemotherapy, and 36% (n=22) had less than a 1 log reduction. Only 28% (n=17) of the patients achieved a log reduction of greater than 1. The likelihood and magnitude of cmMRD response were significantly associated with cytogenetic risk (P = 0.026 by 3x3 Chi-square test; Fig. 3). The proportion of patients with favorable, intermediate, and poor-risk cytogenetics who experienced cmMRD expansion was 17%, 27%, and 71%, respectively. Consistent with these findings, a suboptimal response (defined as cmMRD ratio [T2/T1] > 0.4) was associated with inferior overall survival (HR = 3.29, P = 0.007 by log-rank test; Fig. 4). Conclusions: Our analysis showed that mMRD response to consolidation chemotherapy was highly variable among patients. Although consolidation chemotherapy was effective in deepening the remission for a subset of patients, it failed to lower MRD levels for a substantial proportion of patients, especially those with poor risk cytogenetics. These findings challenge the practice of using consolidation chemotherapy to achieve a deeper remission prior to BMT for high-risk patients and indicate that the opposite outcome may occur instead. NGS-based monitoring of mMRD can potentially be used to distinguish between patients who can remain on consolidation chemotherapy as definitive therapy and those who require a switch in post-remission therapy. Disclosures Gupta: Sierra Oncology: Honoraria, Membership on an entity's Board of Directors or advisory committees; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Incyte: Honoraria, Research Funding. Maze:Pfizer Inc: Consultancy; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees. McNamara:Novartis Pharmaceutical Canada Inc.: Consultancy. Minden:Trillium Therapetuics: Other: licensing agreement. Schimmer:Medivir Pharmaceuticals: Research Funding; Jazz Pharmaceuticals: Consultancy; Novartis Pharmaceuticals: Consultancy; Otsuka Pharmaceuticals: Consultancy. Schuh:Pfizer: Honoraria, Membership on an entity's Board of Directors or advisory committees; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees; Jazz: Honoraria, Membership on an entity's Board of Directors or advisory committees; Agios: Honoraria; Astellas: Honoraria, Membership on an entity's Board of Directors or advisory committees; Teva Canada Innovation: Honoraria, Membership on an entity's Board of Directors or advisory committees; AbbVie: Honoraria, Membership on an entity's Board of Directors or advisory committees; Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees. Yee:Novartis, Pfizer: Honoraria, Membership on an entity's Board of Directors or advisory committees; Astellas, Celgene, Otsuka, Shire, Takeda: Membership on an entity's Board of Directors or advisory committees; Agensys, Astex, Hoffman La Roche, MedImmune, Merck, Millenium, Roche/Genentech: Research Funding. Bratman:SVB: Other: is co-inventor of a patent relating to circulating tumor DNA detection technology, which has been licensed to Roche Molecular Diagnostics.. Chan:Agios: Honoraria; AbbVie Pharmaceuticals: Research Funding; Celgene: Honoraria, Research Funding.

Introduction Core-binding factor (CBF) acute myeloid leukemias (AML) are characterized by the chromosomal abnormalities t(8;21) or inv(16)/t(16;16) and their fusion proteins RUNX1/RUNX1T1 and CBFB-MYH11, respectively. Despite their relatively favorable prognosis, it has been reported that up to 45% of patients with CBF-AML relapse. Current guidelines recommend monitoring the peripheral blood (PB) or bone marrow (BM) for molecular evidence of residual disease (RD) every 3 months for 2 years following remission. By monitoring patients for rising molecular transcripts, those at risk of impending relapse can be identified and treated prior to the emergence of overt disease. However, the relapse kinetics of CBF-AML are poorly-understood, and it is unknown if serial RD monitoring can detect molecular relapses with sufficient lead-time to intervene and prevent morphologic relapse. Methods After local REB approval, we identified patients with CBF-AML treated at the Princess Margaret Cancer Centre in Toronto, Canada between 2000 and 2017. Patients underwent induction and consolidation chemotherapy according to standard protocols followed by RD monitoring with polymerase chain reaction (qPCR) of RUNX1/RUNX1T1 or CBFB-MYH11 transcripts in a CAP/CLIA certified lab every 3 months for a median of 1.2 years (range 0-5.3). RD assessment was performed on BM aspirates, but PB could be tested in patients who could not tolerate repeat BM aspirates. Morphologic relapse was defined as emergence of >5% blasts in the PB or BM, and molecular relapse as a positive transcript PCR (if previous PCR measurements were undetectable) or an increase by 1 log (if previous PCR measurements were detectable) on 2 successive samples without morphologic relapse. Rapid relapse was defined as Results We included 114 patients with CBF-AML. Median age was 46.5 years (range 18-79). t(8;21) was present in 59% and inv(16)/t(16;16) in 41% of patients. All patients achieved remission with 7+3 induction chemotherapy. Over a median follow-up time of 3.7 years (range 0.2-14.3), RD measurements were performed a mean of 5 times per patient with mean sampling interval of 103±54 days. Remission was maintained in 71 (62%) patients but 43 (38%) developed morphological (n=34) or isolated molecular relapse (n=9), with median time to relapse of 4.4 months (range 1.4-31.4). Patients with relapsed disease were significantly less likely to have achieved ≥3 log reduction in RUNX1/RUNX1T1 or CBFB-MYH11 BM transcripts at the end of consolidation chemotherapy compared to patients who remained in remission (75% vs 90%, p=0.046). Of the 43 patients who relapsed, the majority (74.4%, n=32) had rapid relapse kinetics. Of these 43 patients, 25 received reinduction chemotherapy with achievement of CR2, 6 had refractory disease or death, 1 was lost to follow-up, and 17 went on to receive allotransplantation. RD monitoring enabled timely detection of impending relapse and permitted intervention prior to morphologic relapse in only 11 patients (25.6%). Among these 11 patients with slower relapse kinetics, 6 received reinduction chemotherapy with achievement of CR2, 2 received reinduction chemotherapy with refractory disease, and 8 went on to receive allotransplantation. Median overall survival was 20 months (range 3-128) for patients with rapid relapse kinetics and 28 months (range 14-166) for patients with slow relapse kinetics (p=0.02). Clinical features, BM vs PB RD measurements, additional molecular mutations, and cytogenetic abnormalities did not distinguish patients with rapid vs slow relapse kinetics. Conclusions Current guidelines recommend molecular RD monitoring every 3 months for CBF-AML. However, in the majority of patients who relapsed at our institution, RD monitoring every 3 months provided insufficient lead-time to identify molecular relapses prior to morphologic relapse. Further research is warranted to identify the patients with CBF at the highest risk of relapse and the best strategies to monitor these patients over time. Disclosures Gupta: Novartis: Consultancy, Honoraria, Research Funding; Incyte: Research Funding. Maze:Novartis: Consultancy, Honoraria. Schuh:Celgene: Consultancy; Novartis: Consultancy; Pfizer: Consultancy; Jazz: Consultancy; Amgen Inc.: Consultancy; Shire: Consultancy; Teva: Consultancy; Otsuka: Consultancy. Yee:Celgene, Novartis, Otsuka: Membership on an entity's Board of Directors or advisory committees; Agensys, Astex, GSK, Onconova, Genentech/Roche: Research Funding. Schimmer:Otsuka Pharmaceuticals: Consultancy; Jazz Pharmaceuticals: Consultancy; Medivir AB: Research Funding; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees.

Acute myeloid leukemia (AML) is a clinically and biologically heterogeneous disease. Traditionally, cytogenetic analysis has been the backbone for prognostication and treatment decisions. Outcomes vary between age groups with older adults generally having a poorer prognosis. Next Generation Sequencing (NGS) has expedited the discovery of novel genetic lesions in AML to better predict response to intensive chemotherapy and overall survival (OS). The aims of our study were to describe the genetic profile of older adults with AML and to determine its impact on treatment response and survival. We included all new patients with a diagnosis of AML (≥20% blasts in peripheral blood or bone marrow; acute promyelocytic leukemia and myeloid sarcoma were excluded), treated at Princess Margaret Cancer Centre between February 2015 and August 2017. NGS was performed on DNA isolated from peripheral blood or bone marrow samples at diagnosis. Analysis was performed using the TruSight Myeloid Sequencing Panel (Illumina; San Diego, CA) on the MiSeq benchtop genome sequencer (Illumina). Of the 54 genes included in the panel, the complete coding region was sequenced in 15, with hotspot region coverage provided for 39. Demographic and clinical data were obtained from the Princess Margaret Cancer Centre Registry. We identified 454 patients with a new diagnosis of AML in whom frontline NGS was performed. Of these, 300 were 60 years (range 60-92) or older. Demographic and clinical data are shown in Table 1. The median age overall at presentation was 67 yrs (range 18-92) and 57% were male. de novo AML was diagnosed in 329 patients (72%), secondary AML in 17%, and therapy related myeloid neoplasm in 11%. Secondary AML (sAML) was more frequently seen in the ≥60 vs the In total 283 patients (62%) received intensive chemotherapy (95% in the younger group and 45% in the older cohort). 216 patients (76%) achieved a response (CR/CRi/morphologic leukemia free state). No statistically significant difference was seen between age groups (P=0.73) NGS detected 1655 variants. Of these, 1353 classified as oncogenic and 302 as variants of unknown significance (the latter were excluded from subsequent analysis). 14 patients had no mutations identified by NGS. Forty three genes were recurrently mutated in the study cohort: 36 were mutated in >1% of patients, and 11 genes were mutated in >10% of patients. The most commonly mutated genes included DNMT3A (25%), NPM1 (21%), TET2 (19%), RUNX1 (16%), TP53 (16%), ASXL1 (15%), IDH2 (15%), SRSF2 (15%), NRAS (12%), and IDH1 (11%). Older patients had a greater number of mutations overall compared to younger adults (median: 3 vs 2; P = 0.001). In total 986 oncogenic variants were identified in the older group (median 3, range 1-12), while 367 oncogenic variants (median 0, range 0-2) were present in patients < 60 years old (P < 0.001). The older group more commonly harbored mutations in TET2 (25 vs 10%), ASXL1 (21 vs 4%), RUNX1 (20 vs 8 %), SRFS2 (20 vs 6 %), STAG2 (11 vs 6%) and U2AF1 (8 vs 2%). Patients with PTPN11 and NPM1 mutations had longer OS, while patients carrying mutations in ASXL1, JAK2, RUNX1, TP53 and SRSF2 had a shorter OS (Table 2). No differences in OS between age groups (P= 0.2). Multivariate Cox regression analysis showed that male sex (P= 0.0057), sAML (P We then analyzed the correlation between mutations and response rate in patients receiving intensive treatment. PTPN11 and NPM1 mutations were associated with a greater likelihood of achieving a response, while patients with mutations in BCOR, TP53, SF3B1 and U2AF1 had a lower chance of response. Multivariate Cox regression analysis of mutations known to affect response did not show any differences by age, gender, or diagnosis. Mutations in BCOR (P= 0.045), TP53 (P= 0.032) and U2FA1 (P=0.019) were significantly associated with primary induction failure. Overall, older AML patients harbored a greater number of mutations than did their younger counterparts. No age-related differences were observed in mutations known to affect response and/or OS. TP53 mutations, adverse cytogenetics and sAML, were poor prognostic factors regardless of age. Disclosures Schimmer: Medivir AB: Research Funding; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees; Jazz Pharmaceuticals: Consultancy; Otsuka Pharmaceuticals: Consultancy. Yee:Agensys, Astex, GSK, Onconova, Genentech/Roche: Research Funding; Celgene, Novartis, Otsuka: Membership on an entity's Board of Directors or advisory committees. Gupta:Novartis: Consultancy, Honoraria, Research Funding; Incyte: Research Funding. Maze:Novartis: Consultancy, Honoraria. Schuh:Novartis: Consultancy; Otsuka: Consultancy; Pfizer: Consultancy; Teva: Consultancy; Celgene: Consultancy; Amgen Inc.: Consultancy; Shire: Consultancy; Jazz: Consultancy.

Introduction:Induction chemotherapy debulks the leukemic burden in AML patients. Blood count recovery usually occurs during the fourth week of starting chemotherapy in patients who achieve a morphologic remission in bone marrow. However, a subset of patients experience significantly delayed recovery. The relevance of delayed recovery on long-term clinical outcomes and its contributing factors have not been well studied. Specifically, the association between recurrent mutations in AML and hematologic recovery is unknown. Methods:We studied a total of 262 newly diagnosed adult AML patients treated between September 2014 and December 2017 at Princess Margaret Cancer Centre who achieved a complete remission (CR) or CR with incomplete count recovery (CRi) after one cycle of induction chemotherapy. The regimens consisted of 3+7 (N=194) and FLAG-IDA (N=68). We collected information on disease characteristics and blood count results at baseline and during chemotherapy. Mutation profiling of diagnostic samples was performed using a 54-gene next generation sequencing panel (TruSight Myeloid Sequencing Panel, Illumina). Detection of persistent mutations in remission samples was performed using a custom 37-gene duplex sequencing platform with a lower detection limit of ~0.05% variant allele frequency (VAF). Results:Of the cohort of 262 patients, 256 patients (97.7%) achieved neutrophil recovery (defined as > 1x109/L), with time to recovery ranging from 17 to 84 days. Two hundred forty-four (93.1%) patients achieved platelet recovery (defined as > 100x109/L); time to recovery ranged from 17 to 117 days. The percentage of patients who achieved neutrophil and platelet count recovery before day 35 was 82.4% and 84.0% respectively (Fig. 1). To evaluate the prognostic significance of delayed recovery, we categorized patients who achieved CR into two groups, "normal" or "delayed" recovery, according to whether they achieved recovery before or after day 35, respectively. Relapse-free survival (RFS) of patients with delayed recovery was significantly worse than those with normal recovery and only marginally better than those with CRi (P=0.02; Fig. 2). Analysis restricted to 3+7 treated patients showed the same trend (P=0.02), excluding the possibility that the inferior outcome was due to treatment of higher risk patients with more intensive regimens. To study the factors associated with delayed recovery, we performed multivariable Cox regression analysis that included clinical factors and mutations identified at the time of diagnosis as covariates. Four factors were found to be independently correlated with delayed recovery: treatment with FLAG-IDA, truncating ASXL1mutations, SRSF2mutations, and DNMT3AR882 mutations (Table 1). Because FLAG-IDA is the preferred frontline regimen for higher risk patients at our institution, we performed a secondary analysis restricted to patients treated with 3+7 to exclude chemotherapy regimen as a potential confounding variable. This analysis identified six independent factors: AML with myelodysplasia-related changes, lower hemoglobin levels at presentation, truncating ASXL1mutations, TET2mutations, CEBPAmutations, and DNMT3AR882 mutations (Table 1). Somatic mutations in DNMT3A, TET2, ASXL1, and SRSF2(DTAS) mutations are associated with preleukemic conditions, such as myelodysplastic syndrome and age-related clonal hematopoiesis, and frequently persist in remission. These mutations are acquired in hematopoietic stem cells resulting in their propagation to progenitors and terminally differentiated blood cells. We hypothesized that the persistence of DTAS mutations in progenitors might compromise their capacity for reconstitution of normal hematopoiesis resulting in delayed recovery. To test this hypothesis, we performed duplex sequencing on peripheral blood DNA samples collected from a random subset of 43 patients during remission. The detection of DTAS mutations in remission above a VAF of 2% was strongly associated with delayed recovery (P=0.0004; Fig. 3). Conclusion:Delayed hematologic recovery in AML patients after induction chemotherapy is associated with inferior RFS and persistence of preleukemic mutations (i.e., DTAS mutations). Our results support a model in which progenitors harboring DTAS mutations have reduced repopulation capacity leading to delayed hematologic recovery after induction chemotherapy. Disclosures Gupta: Incyte: Research Funding; Novartis: Consultancy, Honoraria, Research Funding. Schimmer:Otsuka Pharmaceuticals: Consultancy; Jazz Pharmaceuticals: Consultancy; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees; Medivir AB: Research Funding. Yee:Agensys, Astex, GSK, Onconova, Genentech/Roche: Research Funding; Celgene, Novartis, Otsuka: Membership on an entity's Board of Directors or advisory committees. Maze:Novartis: Consultancy, Honoraria. Bratman:Roche: Other: SVB is a co-inventor on a patent describing methods for circulating tumor DNA analysis, which has been licensed to Roche Molecular Diagnostics.. Schuh:Shire: Consultancy; Jazz: Consultancy; Novartis: Consultancy; Otsuka: Consultancy; Teva: Consultancy; Pfizer: Consultancy; Celgene: Consultancy; Amgen Inc.: Consultancy.

Background: The prognostication of cytogenetically normal AML (CN-AML) continues to evolve with the use of NGS-based risk stratification. Emerging data indicate that the presence of additional mutations in good- and intermediate-risk patients (as defined by conventional cytogenetic and molecular analyses) changes the behavior of their disease, suggesting that more personalized treatment approaches are needed. Methods: We analyzed the mutational profile of newly diagnosed AML patients with DNMT3A mutations (N = 48) seen at our center and described their clinical characteristics and associated mutations. These patients were identified as part of the Advanced Genomics in Leukemia (AGILE) clinical project currently underway at the Princess Margaret Cancer Centre, Toronto. NGS molecular profiling was performed using the TruSight Myeloid Sequencing Panel (TMSP; Illumina) on the MiSeq benchtop genome sequencer (Illumina). This process permitted profiling of 54 genes (39 in the hotspot region; 15 complete coding region coverage) using amplicon-based library preparation and sequencing by synthesis. 160 patients with newly diagnosed AML were evaluated for this project from February 2015 to February 2016. All were analyzed in parallel by the standard cytogenetic and molecular (NPM1, FLT3-ITD/TKD) diagnostic algorithm. Results: 48 unique patients were identified bearing mutated DNMT3A. Of these, 31 patients had a normal karyotype. Their clinical characteristics are depicted in Table 1. The R882X DNMT3A variant was detected in 12 patients. A total of 100 additional mutations were identified on sequencing (Figure1). The most common associated mutations were in NPM1 (38.7%) followed by IDH1 (29%), RUNX1 (25.8%) and TET2 (22.6%). PTPN11 mutations were identified in 6 patients, 75% of which also had mutated NPM1. Two patients were found to have biallelic CEBPA mutations. Potential gene-gene interactions were also examined and led to the identification of subgroups such as NPM1-FLT3-DNMT3A mutated (n=4), DNMT3A-IDH2R140 (n=3) and DNMT3A-IDH2R172 (n=3) based on recent data by Papaemmanuil, et al (New England Journal of Medicine, 2016) defining these subgroups as being prognostically relevant.( Patients >60 years of age had more frequent mutations in NRAS, BCOR, BCORL1 and TET2. NRAS and BCOR mutations were mutually exclusive with NPM1. RUNX1, IDH2, SRSF2 and U2AF1 mutations were also seen exclusively in the NPM1 negative group. Eligible patients (n=25) received induction therapy with daunorubicin and cytarabine leading to CR1 in 18 patients (72%). Primary induction failure occurred in 6 cases (24%). All 6 cases were NPM1 negative and had missense mutations in DNMT3A including 3 R882X variants. (Figure 2) Additional mutations were identified in IDH1, RUNX1 and/or TET2 in all 6 patients. During the median follow up of 8 months (range 1 - 15 months), 4 patients relapsed, 2 of which had mutated NPM1 with wild type FLT3-ITD. Sixteen patients are alive at this point and 12 are in CR, six having received allogeneic stem cell transplants. One patient with relapsed disease entered a clinical trial of an IDH1 inhibitor Conclusion: Genomic analysis is increasingly recognized as a vital adjunct to conventional diagnostic and prognostic approaches. With ongoing advancements in technology leading to increasing cost effectiveness and decreased turnaround times, the use of NGS is likely to become an up-front investigation resulting in a more personalized approach to therapy. Also, unique patient subgroups defined by gene-gene interactions can be identified to further predict clinical behavior and potentially identify druggable targets for therapy. Disclosures Gupta: Novartis: Consultancy, Honoraria, Research Funding; Incyte Corporation: Consultancy, Research Funding. Schimmer:Novartis: Honoraria. Yee:Novartis Canada: Membership on an entity's Board of Directors or advisory committees, Research Funding. Kamel-Reid:BMS: Research Funding. Schuh:Amgen: Membership on an entity's Board of Directors or advisory committees.

Introduction. Recent genome profiling studies have increased our understanding of the mutation landscapes of myeloid malignancies. Molecular testing of AMLs (NPM1, FLT3-ITD, KIT) and MPNs (JAK2, CALR) constitute current diagnostic standard-of-care. Evidence for the diagnostic, prognostic and/or therapeutic impact of a growing set of genes and variants in myeloid malignancies allows for more accurate patient stratification and enhanced patient management. This has led to consideration of next-generation sequencing (NGS) approaches to simultaneously detect multiple variants in myeloid malignancies for use in the clinical diagnostic setting, to supplant single-gene molecular assays. We designed the Princess Margaret Advanced Genomics in Leukemia (AGILE) trial to prospectively assess the utility of NGS molecular profiling in the management of patients with myeloid malignancies. Methods. Patients for the AGILE trial are consented at the time of diagnosis using an REB approved written consent. Bone marrow or peripheral blood samples are collected at consent, accessioned within CoPath, and DNA extracted for NGS testing. NGS molecular profiling was performed using the TruSight Myeloid Sequencing Panel (TMSP; Illumina) on the MiSeq benchtop genome sequencer (Illumina) by the University Health Network Advanced Molecular Diagnostics Laboratory. The TMSP enables profiling of 54 genes (39 hotspot region; 15 complete coding region coverage) using amplicon-based library preparation and sequencing by synthesis. The TMSP detects the CALR 52 base pair deletion relevant to myelofibrosis, but not FLT3 internal tandem duplications greater than 30 base pair in size. Data were analyzed by NextGENe (v.2.3.1, SoftGenetics) and MiSeq Reporter v2.4.60. A specific script enabling alignment and calling of CALR deletions was added to the analysis to ensure there were no false negative calls. Additional testing and verification of CEBPA variants was performed by Sanger sequencing. Variants were interpreted according to Sukhai et al (Genetics in Medicine, 2015), reviewed by lab directors and reported in the Electronic Patient Record. Impact on patient care was defined as: potential for post-consolidation clinical trials; changes to frequency of monitoring; and, changes to transplant management. Cases were discussed in an interdisciplinary Genomic Tumor Board setting, at which NGS profiling data were reviewed in the context of all other diagnostic information for the patient, to determine impact on patient care. Results. Between February 11 and July 24, 2015, 162 patients were consented for AGILE; 148/162 were profiled by NGS, and to date 124/148 have been reviewed and interpreted. 62/124 (50%) of interpreted cases had a diagnosis of acute myeloid leukemia (AML); 21/124 (20%) with myeloproliferative neoplasms (MPNs); 13/124 (10%) with myelodysplastic syndromes (MDS); 6/124 (5%) with MDS/MPN; and, 15% with other hematologic malignancies. 90% of all cases profiled were informative for at least one variant (range 1-9 variants, average 3.1 variants/case). AML, MDS and MDS/MPN cases exhibited slightly more variants (3.4-4.4 variants/case) than did MPN cases (2.6 variants/case). Overall, 69% of variants were potentially actionable (Sukhai et al, 2015: 23% class 1; 8% class 2; 38% class 3), with a large fraction of cases (90/124, 72.6%) demonstrating at least one class 1 or class 3 variant. Additionally, 73/124 (58.9%) of patients exhibited actionable, class 1, variants not currently being identified by routine molecular diagnostics. In AMLs and MPNs, 88-90% of cases exhibited at least one potentially actionable variant; NGS profiling was more informative in AMLs (62% of cases exhibiting potentially actionable variants not profiled in standard of care testing, compared to 12% of MPN cases). Conclusions. We report the results of a prospective analysis of integrated NGS profiling in the context of diagnosis and management of patients with myeloid malignancies. Using a targeted NGS panel, molecular profiling of patients yielded significant information benefit over current standard approaches in 58.9% of cases analyzed, enabling potential impact on patient management. These data highlight the utility of NGS profiling to complement the initial diagnostic evaluation of myeloid malignancies. Disclosures Gupta: Incyte: Honoraria, Research Funding; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees.