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Background MDS is a heterogeneous disease and the revised International Prognostic Scoring System (IPSS-R) is utilized in prognostication. The percentage (%) of blasts in the bone marrow is determined in the aspirate morphologically. Though the former is the standard of care the blast percentage is also reported by flow cytometry and biopsy which can many times be inconsistent. We previously presented the utilization of biopsy based blast percentage which showed meaningful prognostic groups compared to aspirate. In this study we compare the blasts as reported by the aspirate and flow cytometry in MDS-EB in calculating IPSS-R. Methods The MDS database was reviewed for cases of MDS-EB after due IRB approval at the Mayo clinic. We calculated IPSS-R scores based on the aspirate blast % (IPSS-RAsp) and flow blast% (IPSS-Rfl). The aspirate blast percentage was reported morphologically. Suboptimal aspirates were excluded from the study. The flow blast percentage was determined by immunophenotyping. The overall survival (OS) was determined by IPSS-RAsp and IPSS-RFl. OS estimates were calculated by Kaplan-Meier curves and log-rank testing using JMP v.13. Uno's concordance statistic was used to compare the 2 risk scoring systems. Results Of 1322 patients, 431 (33%) cases were identified with MDS-EB out of which 120 (29%) cases had blasts reported in the aspirate and flow. Based on aspirate MDS EB1: 54% (n=65), MDS EB2 46% (n=55). The hematological, cytogenetic and R-IPSS categories were compared between MDS-EB1 and MDS- EB 2. The blast percentage and hemoglobin levels was significantly different between MDS-EB1 and EB2 as seen in table 1, however the IPSS-R risk groups were not significantly different. The flow cytometry was concordant with aspirate in 66/120 (55%) cases. Out of the dis-concordant cases only 20% (11/54) was upstaged by flow cytometry with most of the patients being down staged as expected by the techniques used in processing the blood and hence not reliable when reported low (Figure 1). The OS outcomes based on the IPSS- R asp, IPSS-Rfl areshown in figure 2A,2B .The p value with aspirate based R-IPSS was more significant than flow cytometry based R-IPSS (p= 0.0007 vs 0.0174). We compared the two models for observed OS differences using the Uno model which was not statistically significant. (p= 0.6) Conclusions Both models did not show a difference which is likely due to the very small sample size. However flow cytometry did down stage more patients when disconcordant and may have less value in that setting. It would be ideal to compare all 3 models aspirate, biopsy and flow cytometry however we did not have enough number of patients to do the comparison. Disclosures Patnaik: Stem Line Pharmaceuticals.: Membership on an entity's Board of Directors or advisory committees. Al-Kali:Astex Pharmaceuticals, Inc.: Research Funding.

Introduction: Whereas morphological assessment and cytogenetics have been the cornerstone for the diagnosis of myelodysplastic syndrome (MDS), flow cytometry and mutational analyses are novel, evolving techniques. These diagnostic procedures play a role in identifying pre-MDS cases including idiopathic cytopenia of undetermined significance (ICUS) and clonal cytopenia of undetermined significance (CCUS). Aim: To assess flow cytometric findings in ICUS and CCUS and their correlation with progression to MDS or myeloid neoplasm (MN), concurrent genetic aberrations, and underlying pathological evolution. Methods: Patients (Pts) who had undergone evaluation to rule out MDS and had retrospectively undergone flow cytometry, cytogenetic, mutational and morphological assessment were included. Flow cytometry results were classified as normal (no abnormality or 1 equivocal result), abnormal (2 abnormalities or at least 1 abnormality and 1 equivocal result), or atypical (1 abnormality or 2-3 equivocal results). Next generation sequencing included mutation analysis of: ASXL1, BCOR, BRAF, CALR, CBL, CEBPA, CSF3R, DNMT3A, ETV6, EZH2, FLT3, GATA1, GATA2, IDH1, IDH2, JAK2, KIT, KRAS, MPL, MYD88, NOTCH1, NPM1, NRAS, PHF6, PTPN11, RUNX1, SETBP1, SF3B1, TERT, TET2, TP53, U2AF1, WT1, ZRSR2. Results: A) Characteristics: 229 pts were assessed (median age 60 and 69% were males). Based on pathologist interpretation, 87 (38%) pts met diagnostic criteria of MDS, 106 (46%) pts had normal/reactive bone marrow (BM), and 36 (16%) pts had BM findings suspicious for MDS. Median time to follow-up was 24 months for MDS pts, and 32 months for pts with cytopenias. B) Morphology: Pts who had a BM biopsy that was suspicious for MDS by pathologist interpretation were more likely to develop MDS compared to pts with normal/reactive pathology report with an incidence rate (IR) of 16% versus 0.9% (p= .0005). Pts who were suspicious for MDS based on the BM biopsy were more likely to have underlying mutations compared to pts with normal/reactive BM (IR 83% versus 69%, p= .2). C) Flow cytometry: In the non-MDS cohort, 96 (67%) pts had normal flow results, 29 (20%) pts had atypical flow, and 17 (12%) pts had abnormal flow results compared to 16 (18%) pts, 18 (21%) pts, and 53 (61%) pts in the MDS cohort, respectively. Of the pts who had normal flow result (n=112), 16 were MDS, 16 were suspicious for MDS/MN, and 80 were normal/reactive. Pts who had biopsy interpretation suspicious for MDS/MN were more likely to have abnormal flow cytometry compared to normal/reactive BM biopsy (IR 55% versus 24%, p=.0003). IR of MDS was 4% in normal flow, 3% in atypical flow, and 12% in abnormal flow (p= .5). Likewise, IR of MN was 4% in normal flow, 20% in atypical flow, and 30% in abnormal flow (p= .1). D) Genetics (cytogenetics and mutation profiling): Cytogenetics was normal in 123 (86%) pts and abnormal in 19 (13%) pts. Pts who had abnormal cytogenetics were more likely to develop MN (IR 57% versus 5%, p= .002). Out of the 50 non-MDS pts tested for NGS, 38 (76%) were positive for mutations. 15 (39%) pts had 1 mutation, 8 (21%) pts had 2, 3 (8%) pts had 3, 6 (16%) pts had 4, 2 (5%) pts had 5, 1 (3%) pt had 7, and 1 (3%) pt had 8 mutations (61% had >1 mutation). Pts with positive mutations were more likely to develop MDS during follow-up compared to pts who did not have mutations (IR 16% versus 0%, p=.06). Additionally, flow cytometric aberrations significantly correlate with the number of mutations (p= .03). MN correlated significantly with BCOR mutation and RUNX1 (IR 60% (p= .008) and 50% (p=.02), respectively. E) Interaction between variables: In pts with positive mutations, flow cytometry did not correlate with progression to MDS with an IR of 17% of MDS in normal flow, 11% in atypical flow, and 17% in abnormal flow, (p= .9). There was no impact on overall survival neither in pts with abnormal flow results vs normal nor in pts with positive mutations vs wild type. Conclusion: Conventional diagnostic techniques remain the cornerstone of MDS diagnosis with flow cytometry and NGS arising as novel techniques that correlate significantly with progression of pre-MDS pts to MDS. Flow had an impact on pathology final interpretation but did not add value in pt with a positive mutation analysis. Larger studies are needed to confirm our findings. Disclosures Patnaik: Stem Line Pharmaceuticals.: Membership on an entity's Board of Directors or advisory committees. Al-Kali:Astex Pharmaceuticals, Inc.: Research Funding.

Introduction: Patients who develop therapy-related myeloid neoplasms (t-MN) have dismal outcomes. Previous studies reported the incidence and risk factors associated with t-MN development. Lenalidomide, in the setting of oral, but not intravenous, melphalan is associated with a higher risk of t-MN (Palumbo et. al, Lancet Oncology, 2014). We carried out this study to evaluate the clinical and pathologic features of t-MN, therapies employed, and factors that predict long-term survival after diagnosis. Patients and methods: We identified patients who received the first ASCT 1998-2016 at our institution. t-MN was defined per the WHO 2016 classification. Median overall survival (OS) was calculated from the time of t-MN diagnosis to last follow-up or death. Statistical analyses were performed using SAS (JMP v14.1) or GraphPad Prism (v7). Results: Out of 2115 patients that underwent at least one ASCT, 53 (2.5%) developed t-MN. Thirty-five of 53 (66%) patients who developed t-MN had received lenalidomide. Among 2062 patients that did not develop t-MN, 916 (44.4%) patients received lenalidomide. Lenalidomide exposure was associated with development of t-MN (χ2 with Yate's correction 8.9, p=0.003). Ten patients were excluded from further analyses due to lack of follow up. Clinical characteristics are shown in Table 1a (N=43). Median age at t-MN diagnosis was 70 years (range 44-79). Median time from ASCT to t-MN was 5 years (range 1-15). After a median follow-up of 70 months (95% CI, 38-134), the median OS was 12 months (95% CI, 9-17, Figure). Primary causes of death were t-MN (71%), MM (12%), both (6%), and other including infection, GVHD, and unknown (12%). Seven (16%) had t-AML and 36(84%) had t-MDS. Three (42%) of 7 patients with t-AML had pure erythroid phenotype. At the time of last follow-up, 9 (21%) were alive. Seven (17%) underwent two ASCT, 16 (36%) received more than 2 years cumulative dose of lenalidomide. Median number of cycles of alkylator therapy including high-dose melphalan (HDM) used for ASCT was 2 (range 1-6). On univariate analysis, factors predicting OS from t-MN diagnosis were ≥ 2 alkylator vs. < 2 cycles (11 vs. 27 months, p=0.02), ≥10% vs. <10% blast at the time of t-MN diagnosis (5.5 vs. 17 months, p=0.01), and the presence of complex karyotype (CK) vs. not (11 vs. 17 months, p=0.03). There was no difference in survival among t-MDS patients who transformed to t-AML vs. those who did not, those who received 1 vs. 2 ASCT, and those with lenalidomide duration ≥ 2 vs. <2 years. On multivariate analysis, the number of alkylator therapies and CK, but not % blasts predicted OS from t-MN diagnosis (Figure). Eight (19%) patients proceeded to receive an autologous (n=4) or allogeneic (n=4) transplant for t-MN (Table 1b). There was no survival advantage for patients who underwent SCT for t-MN, compared to those who did not (17 vs. 10 months, p=0.3). Similarly, there was no survival advantage for patients who received allo SCT compared to auto SCT (21 vs. 16 months, p=0.7). Survival for t-MDS and t-AML was also not different (15 vs. 6 months, p=0.2). There is only one long-term survivor in the transplant group (s/p allogeneic SCT). Four of seven (57%) patients died of progressive t-MN, 1 died of progressive MM, progressive MM and t-MN, and TRM each. Conclusions: Lenalidomide, in the setting of HDM, is associated with an increased risk of t-MN. Increased exposure to alkylators, a higher tumor burden, and the presence of CK predict poor survival in t-MN. As HDM/ASCT followed by lenalidomide maintenance remains the standard of care for eligible patients, minimizing exposure to other alkylator regimens may be prudent. While considered the standard, only a minority undergo transplant; and post-transplant outcomes remain poor. Studies to identify prognostic genetic and epigenetic risk factors are ongoing. Disclosures Al-Kali: Astex Pharmaceuticals, Inc.: Research Funding. Kumar:Celgene: Consultancy, Research Funding; Janssen: Consultancy, Research Funding; Takeda: Research Funding. Patnaik:Stem Line Pharmaceuticals.: Membership on an entity's Board of Directors or advisory committees.

BACKGROUND: CMML is a myelodysplastic/myeloproliferative neoplasm with a median survival of 32 months and no therapies that improve its natural history. We have previously demonstrated that CMML bone marrow mononuclear cells (BMNCs) are hypersensitive to GM-CSF and that the GM-CSF axis is a viable therapeutic target (Padron et al., Blood 2013). Lenzilumab is a novel, humaneered IgG1κ monoclonal antibody, with high affinity for human GM-CSF that has activity in preclinical models of CMML. We report a Phase 1 clinical trial testing the safety and preliminary efficacy of this agent in CMML. METHODS: The study was approved by scientific and ethical review boards. This was a multicenter Phase 1 study designed to evaluate the safety and determine the recommended phase 2 dose of lenzilumab in subjects with CMML. Dose escalation proceeded using a standard 3+3 study design to determine the maximum tolerated dose (MTD). Three dose cohorts included 200 mg, 400 mg, and 600 mg, were given IV on day 1 and 15 of cycle 1 and then only on day 1 of subsequent 28-day cycles. Key inclusion criteria included a WHO-defined diagnosis of CMML and a platelet count greater than 20 x103 cells/dL. Response was evaluated utilizing the MDS/MPN International Working Group Criteria (Savona Blood 2015). Pharmacokinetic analysis and pharmacodynamics were evaluated by pSTAT5 by flow cytometry. RESULTS: Between July 2016 and June 2018, a total of 15 patients were enrolled. The median age at study entry was 74 years (range 52-85) and 80% were male. Nine patients were classified as CMML-0, 3 as CMML-1, and 3 as CMML-2. Seventy three percent of patients had normal cytogenetics or -Y. The most commonly mutated genes at screening included TET2 60%, ASXL1 53%, SRSF2 47%, and RAS pathway (i.e. NRAS or CBL) mutations 40%. Nine patients were previously treated with hypomethylating agents and/or experimental therapies, 3 were treated with hydroxyurea only, and 3 were untreated. The mean Hgb was 9.7g/dL (7.6-14g/dL), the mean platelet count was 147 x103 cells/dL (16-942 x103 cells/dL), and 66% of cases were MPN-CMML by the French-American-British classification at study entry. Three patients were enrolled at each dose level and an additional 6 patients were enrolled at 600mg as planned. Consistent with prior studies of lenzilumab, no dose limiting toxicities were identified and no treatment emergent grade 3 or 4 toxicities were reported. The mean duration on therapy was 221.8 days (14-787 days) and the majority of patients discontinued study drug because of disease progression or lack of response (69%). Five of 15 (33%) patients enrolled achieved clinical benefit by MDS/MPN IWG criteria with 3 platelet responses, 1 neutrophil response, and 1 spleen response. An additional patient had bone marrow myeloblast reduction from 6% to 1% which allowed that patient to undergo allogeneic stem cell transplantation. Clinical response was not statistically associated with somatic mutations or changes in pSTAT5 between screening and cycle 3. However, 3 of 4 patients with NRAS mutation achieved clinical benefit or had clinical meaningful bone marrow myeloblast reductions. CONCLUSION: Lenzilumab is well tolerated in patients with CMML, with no grade 3 or 4 treatment emergent adverse events or DLTs reported. Durable clinical benefit was achieved in 33% of patients and one patient was bridged to allogenic transplant, providing proof of concept that GM-CSF inhibition has activity in CMML. The favorable safety and activity profile of lenzilumab warrants future evaluation as part of a combination regimen targeted to specific subtypes more likely to respond, including patients with NRAS mutations. Disclosures Patnaik: Stem Line Pharmaceuticals.: Membership on an entity's Board of Directors or advisory committees. Sallman:Celgene: Research Funding, Speakers Bureau; Celyad: Membership on an entity's Board of Directors or advisory committees; Incyte: Speakers Bureau; Abbvie: Speakers Bureau; Novartis: Speakers Bureau; Jazz: Research Funding. Al-Kali:Astex Pharmaceuticals, Inc.: Research Funding. Komrokji:celgene: Consultancy; Agios: Consultancy; JAZZ: Consultancy; Novartis: Speakers Bureau; JAZZ: Speakers Bureau; pfizer: Consultancy; DSI: Consultancy; Incyte: Consultancy. Lo:Humanigen: Employment. Durrant:Humanigen: Employment. Chappell:Humanigen: Employment. Ahmed:Humanigen: Employment. List:Celgene: Membership on an entity's Board of Directors or advisory committees, Research Funding.

Abstract Background: The persistence of detectable MRD in complete remission (CR/CRi - CR with incomplete CBC recovery) has been reported to contribute to inferior outcome in younger AML patients (pts) in retrospective studies, however MRD has not been studied prospectively in older adults (age ≥60 yrs) receiving intensive therapy with curative intent. We performed a planned prospective study of MRD status after AML induction therapy in older adults, integrated into the large multicenter ECOG-ACRIN (E-A) E2906 Phase III trial. Methods Eligible patients age ≥60 yrs with AML were randomized 1:1 to receive either 'Standard' 7&3 (Dauno 60mg/m2) induction, with 2 cycles of intermediate dose Ara-C (1.5g/m2 x 12 doses; 6 doses if age ≥70) consolidation (Arm A); or single agent clofarabine (CLO) induction and consolidation (2 cycles) (Arm B). The design and primary clinical results for E2906 (n=727) have been reported previously (Foran et al, ASH #217a, 2015), demonstrating superior overall survival (OS) with standard therapy despite similar CR/CRi rates using stringent criteria, and similar 30-day induction mortality rates. Submission of diagnostic & remission bone marrow or peripheral blood samples was protocol mandated for prospective MRD assessment, and analysis was performed in the central E-A Leukemia Translational Research Lab (LTL) using 6-color multiparameter flow cytometry. MRD-positive (MRD+) was defined as ≥0.1%. LTL flow cytometric analysis was done blinded to treatment arm and outcome of patients. Only pt samples collected within +/-6 days of CR/CRi confirmation were included in this analysis. Statistical analysis was performed using X2 (categories) and Wilcoxon rank sum (continuous) tests to compare baseline patient and disease characteristics. Log-rank tests and multivariate Cox models stratified by treatment arm and adjusted for patient and disease variable (including WBC, cytogenetics, sex, performance status, secondary AML) were used to examine the MRD effect on OS and disease-free survival (DFS, relapse or death). Results The median follow-up is 47.8 months, and 297 of 685 evaluable patients (43.4%) achieved CR/CRi (Standard 44.6%; CLO 42.0%, p=ns). Remission MRD samples were only available for 147 CR/CRi patients (49.5%), owing to variability in sample viability and AML involvement, collection practices and timing of sample collection at individual sites, and patient/physician decision. 58/147 evaluable CR/CRi patients achieved MRD-negative (MRD-) status (Standard 40.7%, CLO 47.9%, p=0.74). Women (56.9% vs. men 43.1%, p=0.003) were more likely to be MRD-, but there was no other significant difference in MRD status stratified by clinical or disease features. MRD+ status at CR/CRi was associated with significantly inferior OS (p=0.031, Figure 1) and also inferior overall DFS (p=0.02); this was most pronounced for DFS after CLO (Arm B, Figure 2) (p=0.005), but not Standard (Arm A) therapy (p=0.41). The impact of MRD+ was confirmed on multivariate analysis using Cox Model Fitting, for OS: OS for All MRD+ pts, HR 1.64 (95% CI 1.00-2.68) (p=0.05); OS for Standard (Arm A) MRD+ pts, HR 1.06 (95% CI 0.51-2.21) (p=0.87); and OS for CLO (Arm B) MRD+ pts, HR 2.30 (95% CI 1.05-5.06) (p=0.04). There was a similar impact for DFS on multivariate analysis using Cox Model Fitting: DFS for All MRD+ pts, HR 1.86 (95% CI 1.16-2.98) (p=0.01); DFS for Standard (Arm A) MRD+ pts, HR 1.15 (95% CI 0.60-2.19) (p=0.67); and DFS for CLO (Arm B) MRD+ pts, HR 3.45 (95% CI 1.47-8.09) (p=0.004). Post-remission therapy was not stratified by MRD in E2906, and 33% of MRD-evaluable pts underwent allogeneic transplantation (no difference in transplant rate for MRD+ vs. MRD-). Conclusions MRD+ ≥0.1% is common (60.5%) after induction therapy in older adults & is significantly associated with inferior OS and DFS in 1st CR/CRi. However we observed excellent outcomes for MRD- pts in first CR/CRi regardless of induction regimen or post-remission therapy used. MRD+ pts in CR/CRi who went on to receive CLO consolidation had significantly poorer outcomes than those who went on to receive intermediate dose Ara-C consolidation. This observation differs strikingly from younger AML, and suggests that intensified Ara-C may abrogate the adverse impact of MRD in older pts in CR. These results strongly support incorporation of centralized MRD at the time of remission into future studies to guide optimal post-remission strategies in older pts with AML. Disclosures Foran: Agios: Research Funding; Xencor, Inc.: Research Funding. Lazarus:Pluristem Ltd.: Consultancy. Altman:Bayer: Other: payment to the institution to conduct clinical trial work; Pfizer: Other: payment to the institution to conduct clinical trial work; Boeringer Ingelheim: Other: payment to the institution to conduct clinical trial work; Epizyme: Other: payment to the institution to conduct clinical trial work; Janssen Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees; Immune Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees; Cyclacel: Other: payment to the institution to conduct clinical trial work; Incyte: Other: payment to the institution to conduct clinical trial work; GSK: Other: payment to the institution to conduct clinical trial work; Agios: Other: Payment to the institution to conduct the trial ; Astellas Pharma: Other; Celgene: Membership on an entity's Board of Directors or advisory committees, Other: payment to the institution to conduct clinical trial work; BMS: Membership on an entity's Board of Directors or advisory committees; Syros: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees; Ariad: Other: payment to the institution to conduct clinical trial work; FujiFilm: Other: payment to the institution to conduct clinical trial work; Genetech: Other: Payment to the institution to conduct clinical trial work; Celator: Other: payment to the institution to conduct clinical trial work. Al-Kali:Novartis: Research Funding. Pratz:Millenium/Takeda: Research Funding; Agios: Research Funding; AbbVie: Consultancy, Research Funding; Astellas: Consultancy, Research Funding; Boston Scientific: Consultancy. Powell:Rafael Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees. Tallman:ADC Therapeutics: Research Funding; BioSight: Other: Advisory board; Daiichi-Sankyo: Other: Advisory board; Orsenix: Other: Advisory board; AROG: Research Funding; AbbVie: Research Funding; Cellerant: Research Funding.

Abstract Background: Chronic myelogenous leukemia (CML) is a BCR-ABL1 driven myeloid neoplasm, with excellent response rates to tyrosine kinase inhibitors (TKI). TKI such as imatinib (IM), dasatinib (DAS), nilotinib (NIL), bosutinib (BOS), and ponatinib (PON) currently US FDA approved, have dramatically changed survival outcomes. That being said, two main challenges exist; suboptimal responses and TKI intolerance. The reason why some patients tolerate/respond to TKI better than others is unknown, but is potentially explainable based on drug metabolism. The field of pharmacogenomics (PGX) is rapidly evolving, with commercial panel's rapidly assessing metabolic pathways such as cytochrome P450 (CYP), UGTA1A, p-glycoprotein/ABCB1. We carried out this study using a 22 gene-PGX panel to assess potential causes of TKI related intolerance and suboptimal responses in compliant patients. Methods: Twenty-nine Mayo Clinic patients with CML were prospectively recruited after informed consent. Buccal swabs were utilized for PGX testing to assess variations/polymorphisms involving CYP3A4/5, 1A2, 2C9, UGT1A1, amongst others (www.Oneome.com). Three groups of patients were recruited, those with i) TKI intolerance, ii) suboptimal responses by ELN criteria, iii) and newly diagnosed cases, to assess if PGX testing could explain TKI intolerance or resistance, or alter choice of therapy in newly diagnosed cases. A pharmacology review was obtained to interpret reports in all cases. Results: 29 patients with CML were prospectively enrolled, median age 64 years, 15 (52%) male. At last follow up (median 21 months), 3 (10%) deaths and no disease progressions were documented. 82% received first line IM, whereas 18% received first line DAS. Major metabolic pathways assessed for IM included, CYP3A4 and 5, while minor pathways included 2C19, 2C9 and 2D6. Majority (83%) of IM patients had normal major pathways with 17% being intermediate-normal. With regards to the minor pathways, 25% were rapid metabolizers for 2C19, whereas 29% were intermediate and 4% poor metabolizers for 2C9 and 50% and 16% were intermediate and poor metabolizers for 2D6. In all IM treated patients PGX testing did not completely explain intolerance or resistance and did not change clinical decision making. Front line DAS was used in 18% and the major pathway assessed was CYP 3A4, with 80% being normal and 20% being intermediate metabolizers. Once again PGX testing did not completely explain intolerance/resistance and no therapeutic changes were based on PGX analysis. Seventeen (59%) patients received second line TKI therapy (50% each for intolerance and resistance), with DAS (58%) and NIL (29%), being the two most common. Once again for DAS, 90% had normal 3A4 metabolism while 10% were intermediate and for NIL 80% were normal and 20% intermediate. Only one of 2 NIL treated patients with UGTA1A polymorphisms developed indirect hyperbilirubinemia (grade 1). In the second line setting, PGX testing did not completely explain or alter treatment decisions. BOS was used as a third line agent in 3 (>10%) patients, 2 who remained refractory and one with intolerance, and all three were normal CYP3A4 metabolizers. None of these patients developed diarrhea a common side effect of BOS. PON was used in one patient with intermediate CYP3A4 metabolism as a 5th line agent and the patient continues to have refractory disease with no thrombotic events. In all cases, no changes were made to concomitant medications based on PGX testing. Conclusion: In conclusion, while PGX testing has rapidly evolved and become commercially available, in the context of TKI therapy for CML, while it offers useful insights on minor metabolic derangements and side effects like NIL induced hyperbilirubinemia, in our study, currently limited by a small sample size, it did not completely explain TKI intolerance or resistance. Recruitment of additional patients (n=100) and correlations with plasma drug levels are currently ongoing. Table. Table. Disclosures Al-Kali: Novartis: Research Funding. Stewart:Amgen Inc., Celgene, Roche, Seattle Genetics: Research Funding; Amgen Inc., BMS, Celgene, Takeda, Roche, Seattle Genetics, Janssen, Ono: Consultancy.

Abstract Introduction: Chronic myelomonocytic leukemia (CMML) is a chronic myeloid malignancy associated with monocytosis, autoimmunity (~30%) & an inherent risk for leukemic transformation. Bone marrow (BM) dendritic cell (DC) populations occur in ~30% of patients, with a poorly defined biological & prognostic role. The malignant immune microenvironment is regulated by indoleamine 2,3-dioxygenase-1 (IDO-1) expressing DCs, which modulate regulatory T (Treg) cells & block their conversion into proinflammatory T helper (Th17)-like cells. IDO-1 is a known immune checkpoint & functions by catabolizing tryptophan, an amino acid essential for T cell function. We hypothesized that distinct IDO-1 expressing DC populations in CMML modulate Tregs & contribute towards immune tolerance & aggressive disease biology. Methods: Primary diagnostic CMML peripheral blood mononuclear cells (PBMC) & BM biopsy specimens were obtained after Mayo Clinic IRB approval. A DC population was defined on H&E stained biopsy sections as focal collections (>10) of cells with characteristic elongated nuclei & cytoplasmic extensions. Transcriptomic & protein expression studies assessing IDO-1 expression were done by previously described methods. In addition, IHC expression of PD-1, PD-L1 & CTLA-4 was also done. IDO-1 promoter methylation studies with DIP-seq were performed. The impact on immune tolerance was assessed using mass cytometry (CyTOF). Results: Cohort: Twenty eight patients with CMML were included in the study, median age 70 (range: 51-80) years; 71% males. Eleven (39%) patients had coexisting autoimmune conditions. Of these, 8 (73%) had detectable DC populations either at diagnosis, or during the course of their disease. At a median follow-up of 46 (95% CI 27, 84) months, there were 14 (50%) deaths & 9 (32%) leukemic transformations.IHC results: Nine (32%) patients were identified to have a DC population at CMML diagnosis. CD123 & TCL1 staining was performed in 5 (56%) patients, with 3 being positive for both, & 2 positive for CD123 only (additional IHC studies ongoing). IDO1 expression by IHC was documented in all 9 (100%) cases (Fig 1A & 1B), while rare populations of PD-1, PD-L1 & CTLA-4 lymphocytes were also seen in all cases. Due to the low DC burdens (median cellularity ≤ 5%) & uniform staining intensity, IHC-based grading was not done. Samples at serial time-points, post-HMA therapy & at the time of blast transformation, were available in 5 & 3 patients respectively. Among the patients who did not have DC populations at diagnosis, 5 (42%) developed them post-HMA therapy, while 3 (50%) developed them at the time of LT. The development of DC populations was associated with loss of response to HMA (50%) & disease progression (50%).Transcriptomic analysis: RNA expression data was available on 7 (25%) patients, of whom only 1 (14%) had DC populations at diagnosis. The IDO-1 RPKM value in the former was higher than the mean pooled value in the latter group (330 versus 74, p=0.05).Methylation studies: DIP-seq was performed on 12 (43%) cases from the primary IHC cohort. Qualitative analysis of IDO-1 promoter hypomethylation was conducted & confirmed in all 9 (100%) cases with 5-mC & 5-hmC marks compared to input as displayed in figure 1C.Immune profiling: CyTOF was performed on 4 CMML samples (3 with IDO-1 expressing DC populations at diagnosis) from the primary IHC cohort & compared to a normal PBMC control. Results confirmed an increase in DC populations (fig 1D& 1E), & reduced % of Th17-like T cells in CMML samples compared to control (1.1 versus 5.07, p=0.05, fig 1F).Clinical correlates & survival analysis: With the exception that CMML patients with DC populations had a higher frequency of NRAS (P=0.007) mutations, the two groups were comparable for cytogenetic & molecular abnormalities. The median OS for the cohort was 45 (95% CI 29, 84) months. CMML patients with IDO-1 expressing DC populations at diagnosis had a shorter median OS, in comparison to those without (median OS 30 vs 45, p=0.03, Kaplan-Meier analysis in fig 1G). Conclusions: In conclusion, we demonstrate that DC populations are seen in ~30% of patients with CMML with a uniform expression of IDO-1 & limited expression of PD-1, PD-L1 & CTLA-4. CMML patients with BM DC populations have a higher frequency of NRAS mutations & DC IDO-1 expression is associated with tumor induced immune tolerance. Additional IHC, genomic & preclinical studies with IDO-1 inhibitors are ongoing. Figure 1. Figure 1. Disclosures Al-Kali: Novartis: Research Funding.

Abstract Introduction: Primary refractory and early relapsed acute myeloid leukemia (RR-AML) continue to pose a therapeutic challenge. Salvage therapy treatment regimens for refractory and relapsed disease are not standardized but include the commonly-used mitoxantrone, etoposide, and cytarabine (MEC) and cladribine, cytarabine, filgrastim, and mitoxantrone (CLAG-M). Previous studies have suggested a potential benefit of CLAG-M, and therefore we performed an analysis of consecutive patients selected to receive either CLAG-M or MEC as salvage therapy for RR-AML. Methods: The study included 150 consecutive patients with RR-AML who received either CLAG-M or MEC between 09/01/2009 and 12/31/2017. Patients were identified through a pharmacy database based on use of mitoxantrone. Baseline disease and patient-related characteristics and clinical outcomes including allogeneic transplantation (ASCT) were obtained by systematic review of EMR. Overall survival (OS) and progression free survival (PFS) were estimated according to the Kaplan Meier method and log-rank test was used to compare outcomes between patients who received either of the two regimens. Results: There were 150 consecutive treated patients with RR-AML included in this analysis, 34 patients received CLAG-M and 116 patients received MEC. The median age was 57 years (18-76), and, and 52% were male. Forty-seven (31%) were treated for early relapsed disease (<6 months after successful induction), 17% (>6 months after induction), and the remainder had primary refractory disease (mean number of induction regimens was 1.8, range 1-6). AML risk was defined by cytogenetic criteria. There were a predominance of intermediate-risk subtypes at 47% (71/150) and followed by high-risk at 37% (55/150). Overall CR/CRi rates for CLAG-M and MEC were 74% (23/31) and 58% (63/108) in patients eligible for analysis (p=0.18). The median follow-up from relapse was 23.5 months (1-76). The median OS was 9.5 months for CLAG-M and 10.0 months for MEC (HR=0.88, 95%CI=0.54-1.41, p=0.59). In total, 76 patients (51%) were able to proceed to ASCT following salvage therapy with either CLAG-M or MEC. Among transplant recipients 56% (19/34) and 49% (57/116) were treated with CLAG-M and MEC, respectively. Median OS after ASCT was 13.0 months for CLAG-M and 31.0 months for MEC (HR=1.76, 95%CI=0.87-3.56, p=0.12). The median OS for refractory AML was 13.0 and 66.0 months for CLAG-M and MEC recipients, respectively (HR=0.92, 95%CI=0.46-1.84, p=0.24). Median OS for those with early relapse was 12.0 months for CLAG-M and 10.0 months for MEC (HR=0.69, 95%CI=0.22-2.11, p=0.51). Lastly, among those who had late relapse, median OS was 9.0 and 48.0 months for CLAG-M and MEC, respectively (HR=17.6, 95%CI=1.57-198, p<0.001). A univariate analysis was performed to investigate the impact of factors associated with OS, including treatment, age, gender, whether they proceeded to ASCT, cytogenetic risk type, and donor source. ASCT was associated with significant improvement in both PFS (HR=0.24, 95%CI=0.16- 0.37, p<0.001) and OS (HR=0.26, 95%CI=0.17-0.40, p<0.001) in this cohort. Age greater than 65 was associated with worse PFS (HR=1.02, 95%CI=1.00-1.03, p=0.04) but not OS (HR=1.01, 95%CI=1.00-1.03, p=0.06) after controlling for other variables including the impact of ASCT. Discussion: Despite a lower 30-day induction mortality we did not identify significant differences in outcomes among patients selected to receive CLAG-M vs. MEC. There was a statistically significant improvement in survival in patients who had late relapses and were treated with MEC, and a trend towards improvement in OS of those treated with MEC who proceeded to ASCT. As expected, ASCT was associated with significant improvement in OS in this cohort, and our results strongly support the use of ASCT as consolidation of remission after relapse for AML. Our data suggests that MEC may be a superior regimen, in particular including those with late relapse. Figure. Figure. Disclosures Foran: Agios: Research Funding; Xencor, Inc.: Research Funding. Al-Kali:Novartis: Research Funding. Palmer:Novartis: Research Funding.

Abstract Background: Acute leukemias of ambiguous lineage (ALAL), including acute undifferentiated leukemia and mixed phenotype acute leukemia (MPAL), are rare hematologic malignancies, accounting for only 2-5% of cases of acute leukemia. Outcomes are generally poor, and retrospective studies have suggested that patients have better outcomes when treated with regimens used for acute lymphoblastic leukemia (ALL) rather than acute myeloid leukemia (AML). Due to heterogeneous definitions and rarity of these leukemias, no single ALL regimen has been studied extensively. Hyperfractionated cyclophosphamide, vincristine, doxorubicin, and dexamethasone (hyperCVAD) is one of the most widely used adult ALL regimens in the United States. We retrospectively examined the effectiveness of this regimen as initial therapy in patients with ALAL. Methods: We retrospectively reviewed records from adult patients treated initially with hyperCVAD-based chemotherapy for ALAL as defined by the World Health Organization at five academic institutions. Only patients whose diagnosis was verified at a participating institution were examined. Philadelphia (Ph) chromosome-positive ALAL patients treated concurrently with tyrosine kinase inhibitors were included. The primary objective of the study was to determine the overall response rate (ORR) and median overall survival (OS). Descriptive statistics were used for baseline characteristics and responses, and Kaplan-Meier estimates were used to calculate all time-to-event outcomes. Results: Twenty-two patients were identified, and pre-treatment characteristics are shown in the Table. Median age was 50 years (range, 22-69), with an even distribution of male and female patients (50% each). The majority (77%) were Caucasian. Two patients (9%) had acute undifferentiated leukemia, 11 (50%) T/myeloid MPAL, 8 (36%) B/myeloid MPAL, and 1 (5%) B/T MPAL. Seven (32%) had a complex karyotype (at least 3 abnormalities), 6 (27%) had a normal karyotype, 3 (14%) were Ph-positive and were treated concurrently with dasatinib, and 1 (5%) had an 11q23 rearrangement. FLT3-ITD was detected in 5 of 8 patients (63%) with an available mutation panel. Three (15%) had central nervous system (CNS) involvement at presentation, and one additional patient developed CNS disease during the course of therapy. There were no deaths within the first 30 days, and the median number of cycles given was 4 (range, 1-8). The CR rate was 73% (n=16) and an additional 14% (n=3) had CR with incomplete count recovery (CRi), for an ORR rate of 86%. One patient had a partial response, and 2 patients had no response. Of the 19 patients achieving CR or CRi, median number of cycles to CR was 1.5, and 12 (63%) proceeded to allogeneic hematopoietic stem cell transplantation (alloHSCT). Of the 7 responders who did not receive alloHSCT, 3 relapsed shortly after initial CR and 4 are alive and in remission 77, 39, 37 and 10 months from treatment initiation. All 3 patients with Ph-positive disease achieved CR. Only 1 proceeded with alloHSCT and all 3 patients are alive and in remission at 51, 39, and 10 months. With a median follow up of 37 months, 14 (64%) patients were alive and in remission, including 11 who had undergone alloHSCT. Four of the 6 patients who died had a complex karyotype. Median overall survival for the entire cohort was not reached (Figure). Conclusions: HyperCVAD results in high remission rates in patients with ALAL, with low incidence of early mortality and high ability to proceed to allogeneic transplantation following response. HyperCVAD can be considered an effective front-line therapy for patients with ALAL. Additionally, hyperCVAD may be a backbone for incorporation of novel immunotherapies and targeted therapies, which may improve results in patients with appropriate targets. Disclosures Sweet: Astellas: Consultancy; Agios: Consultancy; Novartis: Consultancy, Honoraria, Speakers Bureau; Novartis: Consultancy, Honoraria, Speakers Bureau; Jazz: Speakers Bureau; Celgene: Honoraria, Speakers Bureau; Agios: Consultancy; Celgene: Honoraria, Speakers Bureau; BMS: Honoraria; Phizer: Consultancy; Jazz: Speakers Bureau; Astellas: Consultancy; Phizer: Consultancy; BMS: Honoraria. Wang:Novartis: Speakers Bureau; Amgen: Consultancy; Abbvie: Consultancy, Membership on an entity's Board of Directors or advisory committees; Abbvie: Consultancy, Membership on an entity's Board of Directors or advisory committees; Pfizer: Consultancy, Membership on an entity's Board of Directors or advisory committees; Pfizer: Consultancy, Membership on an entity's Board of Directors or advisory committees; Jazz: Speakers Bureau; Novartis: Speakers Bureau; Jazz: Speakers Bureau; Amgen: Consultancy. Al-Kali:Novartis: Research Funding.

Abstract Introduction: The revised international prognostic scoring system (IPSS-R) for myelodysplastic syndrome (MDS) is widely accepted and has been validated in multiple studies. Patients with adverse cytogenetics do poorly and that is reflected in this scoring system by having the highest score for cytogenetics; 2 for intermediate, 3 for poor and 4 for very poor. Little is known about the effect of marrow blasts in adverse cytogenetic in the high-grade MDS defined by IPSS-R intermediate (>3), high (>4.5) and very high (>5). The goal is to examine the effect of marrow blast percentage on outcome in patients with adverse cytogenetics that is present in the high-grade MDS. Methods: We performed data collection from the Mayo clinic records for patients with confirmed MDS after obtaining appropriate IRB approval. Patients were divided based on their total IPSS-R score and we extracted high-grade MDS cases with intermediate, high and very-high IPSS-R only. Cytogenetics and baseline CBC were available for analysis. We calculated the survival difference in patients with blasts <5% and patient with blasts of 5% to 19% for every group. Survival estimates were calculated by Kaplan-Meier method and compared by log-rank testing using JMP v.13. Results: Our database had 1300 patients with confirmed MDS, 41% (N=536) are high-grade MDS. From those, the median age was 70 and 70% were males. Median bone marrow blast was 6% (0-19). Baseline hemoglobin is 9.2 g/dL, WBC 2.7, ANC 1.05, and platelets 69. Their cytogenetics were 1% very good, 31% good, 23% intermediate, 16% poor and 29% very poor. The total IPSS-R groups were 39%,31%, and 30% for the intermediate, high, and very-high groups respectively. The overall survival (OS) for the high-grade MDS with marrow blast <5% was 12.3 months and for patients with marrow blasts ≥5% 11.4 months (P=.4). At each high-grade MDS; intermediate, high and very high, there were no statistically significant differences for patients with marrow blasts below or above 5%. In term of risk of progression to AML, patients with blasts ≥5% were at higher risk of progression compared with <5% (25% vs 10% , P<.001), with no statistically significant difference in term of time-to-AML progression. Conclusion: The percentages of bone marrow blasts had no impact on overall survival among patients with high grade MDS. However, patients with ≥5% marrow blasts are at a higher risk for progression to AML. Disclosures Al-Kali: Novartis: Research Funding.