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Abstract Background: CD123 (alpha chain of the interleukin-3 receptor [IL-3RA]) heterodimerizes with CD131 (βc, common beta chain) to constitute the high-affinity receptor for IL-3. CD123 is not expressed on hematopoietic stem/progenitor cells from normal bone marrow (BM). In contrast, CD123 is highly expressed in CD34+/CD38- cells from acute myeloid leukemia (AML) patients, which recapitulate the leukemic phenotype in NOD/SCID mice; CD123, therefore, is a marker for leukemic stem cells in AML (Jordan CT et al., Leukemia 2000). CD123 is also highly expressed on CD4+/56+ leukemic cells in patients with blastic plasmacytoid dendritic cell neoplasm (BPDCN), an aggressive hematodermic neoplasm. The validity of CD123 as a rational therapeutic target was illustrated by clinical efficacy data for SL-401, a biologic target therapy directed to IL-3R, in patients with BPDCN and AML, respectively (Frankel AE et al., Blood 2014 andFrankel AE et al., J Clin Oncol 31, 2013 (suppl; abstr 7029)). Objectives: To study CD123 expression as a potential therapeutic target in myeloproliferative neoplasms (MPN). Methods: The study was approved by our institutional review board and patients provided written consent for sample collection. MPN diagnosis was based on WHO 2008 criteria. Surface antigen expression on hematopoietic cells of various lineages was interrogated using the 4-color multiparametric flow cytometer, FACSCaliber TM (BD Biosciences, San Jose, CA). Data analysis was performed using CellQuest Pro Software (BD Biosciences). Results: We studied a total of 21 MPN patients and 3 normal controls. Of the former, 14 patients had systemic mastocytosis (SM) (indolent SM=9, SM with associated myeloid neoplasm=4 and aggressive SM=1), 6 had primary myelofibrosis (PMF) and 1 had eosinophilic leukemia transformed to AML. Normal controls: Three normal BM samples were studied; the number of CD123 positive cells in the total population was <1%. Rare CD34+/CD38- cells were uniformly CD123-. Of the CD123+ cells, only a minor subset (<10%) coexpressed myeloid/granulocyte lineage (CD13+, CD15+ or CD16+) or monocyte/macrophage lineage (CD14+ or CD11b+) markers. Systemic mastocytosis: The data were informative for 6 patients (3 with peripheral blood [PB], 1 with BM, and 2 with paired PB and BM samples) for whom a sufficient number of mast cells (MC) were identified for immunophenotyping. Neoplastic MC were defined as CD117 hi/SSC hi/CD45 hi/CD34-/CD25+/FcεRI+. CD123 expression was seen in the majority of MC for 4 patients (#1-4, CD123 percentage positive, PB/BM): 91%/n.a. (#1), 75%/81% (#2), 84%/n.a. (#3), and 88%/n.a. (#4). In contrast, one patient (#5) had a minority of CD123+ MC (33%/28%). Clonal eosinophilia: PB was studied; the WBC differential count showed 41% leukemic blasts and 57% eosinophils (both confirmed to be clonally related based on FISH studies). Both cell populations were predominantly CD123+ (≥90%). Primary myelofibrosis: We studied PB samples from 6 PMF patients. Approximately 1-2% of circulating cells marked as CD123+; of these, expression was notable on CD34-/CD38+ cells (median 54%; range 41-74% positive). We found a larger proportion (30-50%) of CD123+ cells that coexpressed CD13+, CD16+ or CD11b+ representing monocytes, immature myeloid cells and granulocytes, as compared to normal BM controls. Studies on BM samples from PMF patients are ongoing. Conclusions: CD123 (IL-3RA) is expressed on relevant primary cells of interest in select MPNs, namely neoplastic mast cells in SM patients and eosinophils in clonal eosinophilia patients. In PMF, a minor population of circulating cells was CD123+ with a biased distribution on myeloid lineage cells as compared to normal BM samples. We are currently studying CD123 expression in additional MPN patients, and also analyzing CD123 expression on BM trephine biopsies by immunohistochemistry. In addition, the cytotoxicity assessment of SL-401 against MPN cell lines and primary cells is ongoing. Overall, the aforementioned data support the clinical development of SL-401 in patients with MPNs and clinical trials are currently being planned. Disclosures Brooks: Stemline Therapeutics: Employment, Equity Ownership. Pardanani:Stemline Therapeutics Inc.: Research Funding.

Abstract Background: ENESTop, an ongoing, single-arm, phase 2 study (ClinicalTrials.gov, NCT01698905), is the first trial specifically evaluating treatment-free remission (TFR; ie, stopping tyrosine kinase inhibitor [TKI] treatment without a loss of response) in patients with chronic myeloid leukemia in chronic phase (CML-CP) who achieved a sustained deep molecular response after switching from imatinib (IM) to nilotinib (NIL). Of 126 patients in ENESTop who were eligible to stop NIL, 57.9% (95% CI, 48.8%-66.7%) maintained TFR at 48 weeks. Here we present results from a subgroup analysis based on reasons for switching from IM to NIL, categorized as intolerance, resistance, and physician preference. Methods:Eligible patients were adults with CML-CP who received ≥ 3 years of total TKI therapy (> 4 weeks of IM, followed by ≥ 2 years of NIL) and achieved a sustained MR4.5 (BCR-ABL1 ≤ 0.0032% on the International Scale [BCR-ABL1IS]) on NIL therapy; patients with a documented MR4.5 at the time of switch from IM to NIL were not eligible. Enrolled patients continued NIL treatment in a 1-year consolidation phase, and those without confirmed loss of MR4.5 (ie, consecutive BCR-ABL1IS > 0.0032%) were eligible to stop NIL in the TFR phase. Patients with loss of major molecular response (MMR; ie, BCR-ABL1IS > 0.1%) or confirmed loss of MR4 (ie, consecutive BCR-ABL1IS > 0.01%) during the TFR phase reinitiated NIL treatment. The primary endpoint was the proportion of patients who maintained TFR (ie, no loss of MMR, confirmed loss of MR4, or treatment reinitiation) at 48 weeks after stopping NIL. In this post hoc analysis, rates of TFR at 48 weeks after stopping NIL and a Kaplan-Meier (KM) analysis of treatment-free survival (TFS; defined as the time from the start of TFR to the earliest occurrence of any of the following: loss of MMR, confirmed loss of MR4, reinitiation of NIL due to any cause, progression to accelerated phase/blast crisis, death due to any cause) were evaluated in subgroups of patients who switched from IM to NIL due to intolerance, resistance, or physician preference. These categories were determined by grouping the reasons for switching from IM to NIL, as reported by the investigators, based on relatedness to safety (intolerance), loss of response/treatment failure (resistance), and the physician's clinical judgment (physician preference); individual reasons included within each category are presented in the Figure. Results:A total of 125 patients who entered the TFR phase were included in this analysis; 1 patient who was found to have had atypical transcripts was excluded. Among these 125 patients, the reasons for switching to NIL were categorized as intolerance in 51 patients (40.8%), resistance in 30 patients (24.0%), and physician preference in 44 patients (35.2%). The proportion of patients who maintained TFR at 48 weeks after stopping NIL was generally similar across the 3 subgroups: 30 of 51 (58.8%; 95% CI, 44.2%-72.4%) in the intolerance subgroup, 16 of 30 (53.3%; 95% CI, 34.3%-71.7%) in the resistance subgroup, and 27 of 44 (61.4%; 95% CI, 45.5%-75.6%) in the physician preference subgroup. KM analysis of TFS showed that in all 3 subgroups, the majority of TFS events occurred within the first 24 weeks after stopping NIL (Figure). There were no notable differences in the kinetics of TFS events among subgroups. The KM-estimated median duration of TFS was not reached by the data cutoff date in all 3 subgroups. Conclusion: Primary analysis from ENESTop showed that among patients with CML-CP who achieved a sustained MR4.5after switching from IM to NIL, 57.9% of those who stopped NIL maintained TFR at 48 weeks. In the present analysis, TFR was maintained at 48 weeks after stopping NIL by > 50% of patients in the intolerance, resistance, and physician preference subgroups, with generally similar results across subgroups. These findings suggest that the rate of successful TFR following second-line NIL does not differ based on the reasons for switching from IM to NIL. Figure. Figure. Disclosures Hughes: Ariad: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; BMS: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Australasian Leukaemia and Lymphoma Group (ALLG): Other: Chair of the CML/MPN Disease Group. Boquimpani:Novartis: Research Funding, Speakers Bureau; BMS: Speakers Bureau. Takahashi:Novartis: Honoraria, Research Funding; Pfizer: Honoraria, Research Funding; BMS: Honoraria. Shuvaev:Pfizer: Honoraria; BMS: Honoraria; Novartis pharma: Honoraria. Ailawadhi:Pharmacyclics: Consultancy; Novartis: Consultancy; Amgen Inc: Consultancy; Takeda Oncology: Consultancy. Lipton:Pfizer: Consultancy, Research Funding; Novartis: Consultancy, Research Funding; BMS: Consultancy, Research Funding; Ariad: Consultancy, Research Funding. Turkina:Pfizer: Honoraria; Novartis Pharma: Honoraria; BMS: Honoraria. Moiraghi:BMS: Speakers Bureau; NOVARTIS: Speakers Bureau. Nicolini:Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; BMS: Consultancy, Honoraria; Ariad pharmaceuticals: Honoraria, Membership on an entity's Board of Directors or advisory committees. Sacha:BMS: Consultancy, Honoraria, Speakers Bureau; Incyte: Consultancy, Honoraria, Speakers Bureau; Pfizer: Consultancy, Honoraria, Speakers Bureau; Novartis: Consultancy, Honoraria, Speakers Bureau; Adamed: Consultancy, Honoraria. Kim:Pfizer: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; BMS: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Novartis: Consultancy, Honoraria, Research Funding, Speakers Bureau; ILYANG: Consultancy, Honoraria, Research Funding. Fellague-Chebra:Novartis: Employment. Acharya:Novartis Healthcare Pvt. Ltd.: Employment. Krunic:Novartis: Employment, Equity Ownership. Jin:Novartis: Employment, Equity Ownership. Mahon:BMS: Honoraria; PFIZER: Honoraria; NOVARTIS PHARMA: Honoraria, Research Funding; ARIAD: Honoraria.

Abstract Background: ENESTop (NCT01698905) is an ongoing, single-arm, phase 2 study evaluating treatment-free remission (TFR) in patients (pts) with chronic myeloid leukemia in chronic phase (CML-CP) who achieved sustained molecular response 4.5 (MR4.5; BCR-ABL1 ≤ 0.0032% on the International Scale [BCR-ABL1IS]) on second-line nilotinib (NIL). In the primary analysis, 57.9% (95% CI, 48.8%-66.7%) of pts who stopped NIL maintained TFR (no loss of major molecular response [MMR; ie, BCR-ABL1IS > 0.1%], confirmed loss of MR4 [ie, consecutive BCR-ABL1IS > 0.01%], or treatment reinitiation) at 48 weeks. Adverse events (AEs) were reported in 73.8% of pts during the first 48 weeks of TFR vs 77.0% during the year prior to stopping treatment. The incidence of musculoskeletal pain-related AEs was higher during TFR (42.1% vs 14.3%). To assess the potential effect of stopping NIL on quality of life (QOL), pt-reported outcomes were assessed before and during TFR. Methods: ENESTop enrolled adult pts with CML-CP with ≥ 3 years of prior tyrosine kinase inhibitor (TKI) therapy (> 4 weeks of imatinib [IM], then ≥ 2 years of NIL). Pts must have achieved sustained MR4.5 on NIL after switching from IM. Enrolled pts entered a 1-year NIL treatment consolidation phase; those without confirmed loss of MR4.5 (ie, consecutive BCR-ABL1IS > 0.0032%) entered the TFR phase and stopped NIL. Pts with loss of MMR or confirmed loss of MR4 during the TFR phase reinitiated NIL. QOL was assessed via questionnaires completed by pts at specified time points. The MD Anderson Symptom Inventory for CML (MDASI-CML) questionnaire assessed, for a defined set of symptoms, the levels of severity and interference with daily life on a scale of 0 to 10, with 0 being the lowest level. The EQ-5D-5L questionnaire assessed problems experienced by pts (no, slight, moderate, severe, or extreme [ie, interfering with functioning] problems) in 5 dimensions: mobility, self-care, usual activities, anxiety/depression, and pain/discomfort; additionally, overall level of health was assessed on a scale of 0 to 100 using the EQ VAS, with 0 being the lowest level. Results: Of 163 enrolled pts, 126 met the criteria for stopping NIL in the TFR phase; of these 126, 53 had loss of MMR or confirmed loss of MR4, of whom 51 reinitiated NIL. Among pts who completed each questionnaire at week 48 of the consolidation phase, week 12 of the TFR phase, or week 48 of the TFR phase, mean MDASI-CML severity scores were 1.7, 1.5, and 1.2, respectively; mean MDASI-CML interference scores were 1.7, 1.6, and 1.4, respectively; and mean EQ VAS scores were 82.2, 78.8, and 82.3, respectively (Table). Among pts with sustained TFR and scores at both week 48 of the consolidation phase and week 12 or 48 of the TFR phase, minimal changes were observed in MDASI-CML and EQ VAS scores during TFR vs week 48 of the consolidation phase. Among pts who reinitiated NIL, mean MDASI-CML severity and interference scores and mean EQ VAS scores at 24 weeks after the start of retreatment were 1.6, 1.5, and 78.8, respectively; changes in scores between week 24 after treatment reinitiation and week 48 of the consolidation phase were minimal among pts with scores at both time points. Among pts who completed the EQ-5D-5L questionnaire, the proportions who reported problems (any level of severity) in the 5 dimensions were generally similar across time points, although problems with mobility and pain/discomfort were more common during TFR vs week 48 of the consolidation phase, particularly at week 12 of the TFR phase (Table). Conclusion: Changes in QOL after stopping NIL, as assessed using these questionnaires, were minimal. This may be related to pts having a relatively high QOL prior to stopping treatment given that they had tolerated ≥ 3 years of TKI therapy, including ≥ 2 years of NIL, prior to enrollment. Despite the higher incidence of musculoskeletal pain-related AEs observed during TFR (42.1% vs 14.3%), the overall QOL was generally similar between the TFR and consolidation phases. This suggests that these AEs did not have a significant negative impact on QOL. Longer follow-up in ENESTop will be needed to further evaluate trends in QOL after stopping second-line NIL. Disclosures Mahon: NOVARTIS PHARMA: Honoraria, Research Funding; BMS: Honoraria; ARIAD: Honoraria; PFIZER: Honoraria. Boquimpani:BMS: Speakers Bureau; Novartis: Research Funding, Speakers Bureau. Takahashi:Novartis: Honoraria, Research Funding; Pfizer: Honoraria, Research Funding; BMS: Honoraria. Shuvaev:Novartis pharma: Honoraria; Pfizer: Honoraria; BMS: Honoraria. Ailawadhi:Pharmacyclics: Consultancy; Novartis: Consultancy; Amgen Inc: Consultancy; Takeda Oncology: Consultancy. Lipton:Novartis: Consultancy, Research Funding; Ariad: Consultancy, Research Funding; BMS: Consultancy, Research Funding; Pfizer: Consultancy, Research Funding. Turkina:Novartis Pharma: Honoraria; Pfizer: Honoraria; BMS: Honoraria. Moiraghi:NOVARTIS: Speakers Bureau; BMS: Speakers Bureau. Nicolini:Ariad: 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; BMS: Consultancy, Honoraria. Sacha:Pfizer: Consultancy, Honoraria, Speakers Bureau; Incyte: Consultancy, Honoraria, Speakers Bureau; BMS: Consultancy, Honoraria, Speakers Bureau; Novartis: Consultancy, Honoraria, Speakers Bureau; Adamed: Consultancy, Honoraria. Kim:BMS: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; ILYANG: Consultancy, Honoraria, Research Funding; Pfizer: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Novartis: Consultancy, Honoraria, Research Funding, Speakers Bureau. Fellague-Chebra:Novartis: Employment. Acharya:Novartis Healthcare Pvt. Ltd.: Employment. Brandt:Novartis: Employment. Gnanasakthy:Novartis: Consultancy, Equity Ownership, Research Funding. Jin:Novartis: Employment, Equity Ownership. Hughes:Ariad: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; BMS: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding.

Abstract Introduction: Recent reports have utilized von Willebrand factor (VWF) multimerquantitation in the assessment of native cardiac lesions and prosthetic valve dysfunction. However there is no standardized method for quantitation. We compared 3 methods of assessment which utilized a normal plasma control. Methods: We analyzed 476 samples and their control plasma from 395 patients including normal subjects, patients with aortic stenosis, hypertrophic cardiomyopathy, mitral or aortic regurgitation, normal and abnormal left cardiac valve prostheses, and left ventricular assist device therapy (LVAD). VWF multimers were assessed as normal or abnormal, or as normalized (patient / normal plasma) VWF multimerratios of gel bands >15/2-15 (NMR 15) or gel bands > 10/2-10 (NMR 10). We tested whether one technique was more strongly associated with hemodynamic severity of the cardiac lesion, with a history of acquired bleeding, and compared the results to a separate test of VWF function, platelet function analyzer 15 00 (PFA). Results: Two hundred seventeen patient samples reflected normal or mildly abnormal hemodynamics, 111 moderate, and 113 severely abnormal hemodynamics. Abnormal multimers were present in only 19% of samples with normal or mildly abnormal hemodynamics compared to 79% abnormal in the presence of moderate to severe hemodynamic abnormality. The distinction between moderate and severe hemodynamic abnormality was less striking, 65% versus 88% (figure, left). Quantitative NMR values declined with increasing cardiac lesion severity (figure, middle). The two quantitative multimermethods showed similar relationships to lesion severity by ANOVA, r=0.40 (NMR 15) versus r=0.36 (NMR 10), and by Spearman correlation, r=0.68 for NMR 15, and r=0.66 for NMR 10, and PFA results were comparable (all p< 0.001). Bleeding rates were associated with NMR 15, 10 and PFA (Mann-Whitney p<0.001, figure, right). Conclusion: The dichotomous normal / abnormal VWF multimer method appears to distinguish ≥ moderate hemodynamic disruption, whereas there is a continuous relationship between hemodynamic severity and quantitative multimer methods, which may be clinically useful in circumstances in which clinical estimation of lesion severity is challenging, such as with dysfunctional prosthetic valves. Progressive loss of VWF multimersappears to be associated with bleeding, suggesting that quantitative measures may provide incremental value over the dichotomous normal / abnormal designation. Figure Figure. Disclosures Blackshear: Baxalta, Inc: Consultancy, Research Funding.

Abstract Background:The 2008 World Health Organization (WHO) developed a new classification system for Myelodysplastic Syndrome (MDS). The well-defined categories are refractory anaemia with excess blasts (type 1 or 2 based on the marrow blast count being below or above 10%), refractory anaemia with or without ringed sideroblasts, refractory cytopenias with multilineage dysplasia and myelodysplastic syndromes with isolated deleted 5q. MDS cases that do not meet the diagnostic criteria of the above categories are classified myelodysplastic syndrome (MDS-U). However, few reports in the literature exist in terms of natural progression and clinical outcome of patients with MDS-U. Aim: To study the clinical outcome of patients with MDS-U. Method: A retrospective, IRB-approved, single-institution study through chart review of cases with MDS at Mayo Clinic Rochester between 1993 and 2014 was performed. Patients diagnosed with MDS based on WHO classification were included. MDS classification was based on routine Mayo Clinic pathology reports. Central independent hematopathology review for bone marrow biopsy was performed for cases diagnosed with MDS-U or simply generic MDS. Comparison between groups’ medians was done using Wilcoxon test, while survival estimates were calculated using Kaplan-Meier curves using JMP V10. Result: A total of 802 patients, who met WHO criteria for MDS, were studied. Median age was 71 years (range, 18-99), 69% were males. Median white blood cell (WBC) 3.6 x109, hemoglobin (Hbg) 9.6 g/dl, platelets (PLT) 105 x109, peripheral blood (PB) blasts 0% and bone marrow (BM) blasts 2%. Median overall survival (OS) was 28 months. One hundred nine (14%) cases transformed to AML. Out of the 802 patients, 90 (11%) patients were initially classified as MDS-U according to 2008 WHO criteria, 69% were males with median age 71 years. Upon pathology review, only 42/90 cases (47%) were confirmed to be MDS-U (group 1). Among 47 cases not meeting MDS-U, 40% were best classified as RARS, 17% refractory anemia, and 9% as 5Q del Syndrome, while 2 cases did not have any myeloid neoplasm. Group 1 had median WBC 3 x109, Hbg 9.9g/dL, PLT 71 x109, PB blasts 0% and BM blasts 0%. IPSS grouping was low, intermediate-1, intermediate-2 and high in 27%, 52%, 21% and 0%, respectively. R-IPSS grouping was very low, low, intermediate, high and very high in 15%, 42%, 15%, 21% and 6%, respectively. Median OS in group 1 was 68, 37, 13 and 0 months per IPSS (p=0.04), and 101, 44, 14, 11, 13 months per IPSS-R (p=0.005), respectively. Of the 43 patients with MDS-U, 39 had follow-up; 21 patients (54%) of which progressed. MDS-U became 42% RAEB, 24% RCMD, 14% CMML, 5% RARS, 10% MDS/MPN, and 5% atypical. Group 2 (MDS other than MDS-U) 759 patients had median age 71 years, 69% were males. They had WBC 3.6 x109, Hbg 9.6g/dL, PLT 107 x109(p=0.01), PB blasts 0% and BM blasts 0%. IPSS grouping was low, intermediate-1, intermediate-2 and high in 29%, 44%, 22% and 5% respectively. R-IPSS grouping was very low, low, intermediate, high and very high in 17%, 32%, 20%, 17% and 14% respectively. On comparison between Group 1 vs 2, mOS was 27 vs 29 months (p=0.7), and percentage transformed to AML 14% in both groups. On multivariate analysis for mOS only age, IPSS-R and IPSS but not MDS-U nor gender were statistically significant. Conclusion: MDS-Uis a small subset of MDS. With independent pathology review, half of the MDS-U cases were subclassified into other MDS groups. In follow-up more than half of the cases were subclassified into other MDS groups and some were non-MDS. IPSS and IPSS-R are helpful tools for survival assessment in MDS-U. High risk MDS was infrequent in MDS-U per IPSS. We found no significant difference in mOS nor AML transformation when comparing MDS-U to other groups. Disclosures No relevant conflicts of interest to declare.

Abstract Background: In addition to NBEAL2, a single dominant-negative mutation in the GFIB1 gene has been associated with grey platelet syndrome but no association has been mentioned with dense granule deficiency. Here we describe a child with thrombocytopenia, alpha-delta granule deficiency, and a homozygous missense mutation in GFIB1. Case Report:The patient is an 8y/o Hispanic male born to non-consanguineous parents. Prenatal and birth history were unremarkable. No family history of blood disorders or pediatric malignancies. The boy has 2 healthy older siblings, no dysmorphic features, and normal skin pigmentation and eye findings. Renal function and hearing are normal. At 3mo he was noted to have multiple spontaneous petechiae along with an isolated thrombocytopenia of 46K/uL. At 10 months, a bone marrow evaluation showed increased megakaryocytes suggestive of ITP. By 3years of age, he received three treatments of IVIG without an adequate response. His platelet counts have generally ranged between 30-50K/uL. With acute illnesses, they drop to 15-20K/uL. His bleeding symptoms have primarily been spontaneous bruising and petechiae as well as prolonged epistaxis. His symptoms have been generally controlled with anti-fibrinolytic agents alone. Platelet transfusions have been reserved for surgical procedures or significant bleeding symptoms. Further evaluations over the past 5 years have included peripheral smears, showing atypical large hypo-granular platelets, and two additional bone marrow aspirates, showing megakaryocytic hyperplasia with numerous osteoclast-like forms and occasional small mono-lobated megakaryocytes and evident emperipolesis. Anti-nuclear antibody testing and platelet direct and indirect antibody testing were negative. Platelet electron microscopy showed that platelets virtually contained no dense granules (0.05 dense granules/platelet, 200 platelets) and about 30-40% of the platelets had markedly decreased alpha granules. Some platelets had complex canalicular networks and membrane vacuoles. These features are consistent with an alpha-delta platelet storage-pool deficiency. A myeloid malignancy mutation panel, performed using next generation sequencing, detected no variants of known significance. Gene sequencing for MHY9-related disorders as well as DNA breakage analysis for Fanconi's anemia were negative. However, DNA sequencing of the patient's sample revealed a homozygous missense mutation (c923 T>C; p.Leu308Pro) in the GFIB1gene; each parent carried one copy of this change. Conclusion: GFIB1, mapped to chromosome 9q34.13, encodes a transcriptional repressor that is important for megakaryopoiesis. It has been reported in patients with gray platelet syndrome; an inherited platelet disorder associated with thrombocytopenia and decreased alpha granules. This case points to an association of biallelic GFIB1 mutations with alpha-delta granule deficiency. This case underscores the importance of platelet esoteric testing and molecular analysis in the diagnosis of hereditary platelet disorders. As a targetable mutation in the future, this could revolutionize the early diagnosis and treatment of this rare platelet disorder. Disclosures No relevant conflicts of interest to declare.

Abstract Introduction Midostaurin is an orally available multikinase inhibitor that blocks FLT3 kinase activity. FLT3 mutations are associated with more frequent and earlier relapses and worse survival. The phase 3 RATIFY trial showed that midostaurin compared with placebo improved overall and event-free survival in newly diagnosed pts with FLT3-mutated AML when administered in combination with standard chemotherapy and as single-agent maintenance (Stone et al, ASH 2015). The ongoing RADIUS trial (NCT01883362) is investigating whether adding midostaurin to SOC after alloHSCT reduces the risk of relapse in pts with FLT3-ITD-mutated AML. Here we report safety data from the first 56 enrolled pts. Methods RADIUS is a randomized, open-label, phase 2 study comparing SOC vs midostaurin + SOC after alloHSCT in adult pts with AML with FLT3-ITD mutations (planned enrollment, N = 60). Study treatment started 28-60 days after alloHSCT. SOC was dictated by the treating physician. Pts were randomized to either SOC or midostaurin 50 mg twice daily + SOC (hereafter called the midostaurin arm) continuously for ≤ 12 months and will be followed up for ≥ 24 months. The study was designed to look for any safety or efficacy signals and not powered to find differences between study treatments. The primary endpoint is relapse-free survival at 18 months after alloHSCT. Adverse events (AEs) were followed up for 30 days after treatment. Key inclusion criteria are documented FLT3-ITD mutation, age 18-70 years, and first complete remission status. Pts could enroll after the date of engraftment and hematologic recovery to an absolute neutrophil count > 1000/μL and platelet count ≥ 20,000/μL without requiring transfusion. Results Pts were randomized from Feb 5, 2014, to Jun 13, 2016. The 2 arms (n = 28 each) were balanced regarding age, sex, and race. Most pts (93%) had de novo AML. At data cutoff (Jun 3, 2016), data were not mature enough to evaluate efficacy. Median (range) follow-up in the SOC and midostaurin arms was 240 (3-786) and 234 (3-656) days, respectively. Overall, 18 pts (64%) in the SOC arm and 19 pts (68%) in the midostaurin arm stopped treatment. Of these, 10 (36%) and 8 (29%) in the SOC and midostaurin arms, respectively, completed 12 months of treatment. Other reasons for stopping treatment were relapse (2 [7%] and 2 [7%]), death (2 [7%] and 0 [0%]), administrative problems (2 [7%] and 1 [4%]), withdrawn consent (1 [4%] and 3 [11%]), abnormal test results (1 [4%] and 0 [0%]), and AEs (0 [0%] and 4 [14%]). In the 24 pts who received ≥ 1 dose in the midostaurin arm, the median midostaurin dose was 76.2 (range, 25-100) mg daily. In the 15 pts (54%) who required a dose change, the reasons for dose changes were AEs (13 [46%]), dosing error (3 [11%]), re-escalation (3 [11%]), abnormal test results (2 [7%]), per protocol (2 [7%]), use of concomitant strong CYP3A4 inhibitors (1 [4%]), and other reasons (4 [14%]). The most common any-grade (Gr) AEs were fatigue (29%) and AST, headache, nausea and vomiting (all 25%) in the SOC arm and nausea and vomiting (both 64%) and diarrhea (43%) in the midostaurin arm (Figure 1). The most common Gr 3/4 AEs were nausea and hypertension in the SOC arm (all 3 [11%] each) and diarrhea, increased ALT, neutrophil count decreased (all 3 [11%] each) and platelet count decreased (5 [18%]) in the midostaurin arm. No on-treatment deaths occurred in the midostaurin arm. AEs led to discontinuation of midostaurin in 4 pts and included Gr 1 nausea, Gr 2 nausea and vomiting, Gr 3 lung infection, and Gr 2 elevated liver enzymes (n = 1 each). All of these except the lung infection were considered related to midostaurin. Graft-vs-host disease (GVHD) occurred in 16 pts (57%) in the SOC arm and 18 pts (64%) in the midostaurin arm (Figure 2). No stage ≥ 3 organ involvement occurred. Most cases of GVHD (11 [39%] in the SOC arm and 17 [61%] in the midostaurin arm) were acute. The most commonly affected organ was the skin (11 [39%] and 13 [46%], respectively, of which 5 [18%] and 4 [14%], respectively, were stage 2). Conclusions The preliminary safety data in the post-alloHSCT setting was consistent with data from other studies. Rates of Gr 1/2 nausea, vomiting, and diarrhea were higher in the midostaurin arm. Midostaurin did not change rates of GVHD. Because of the limited duration of follow-up, effects on chronic GVHD are unknown. Follow-up is ongoing, with efficacy data anticipated in 2017. Disclosures Maziarz: Athersys: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Incyte: Membership on an entity's Board of Directors or advisory committees; Novartis Pharmaceuticals Corporation: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding. Scott:Celgene: Consultancy, Membership on an entity's Board of Directors or advisory committees; Novartis: Consultancy, Research Funding, Speakers Bureau; Alexion: Speakers Bureau; Agios: Membership on an entity's Board of Directors or advisory committees. Deol:Jazz Pharmaceuticals: Consultancy. Haines:Novartis: Employment. Bonifacio:Novartis: Employment. Rine:Novartis: Employment. Fernandez:Fate Pharmaceuticals: Honoraria; Chimerix: Honoraria; Sanofi: Speakers Bureau.

Abstract Background:The Janus kinase (JAK) 1/JAK2 inhibitor ruxolitinib has been evaluated for patients with MF in the phase 3 COMFORT studies. In both trials, ruxolitinib prolonged OS, reduced splenomegaly, and improved MF-related symptoms and quality of life compared with controls. Here, we report the results of an exploratory pooled analysis of OS in the COMFORT studies at 5 years of follow-up. Methods: The double-blind COMFORT-I trial and the open-label COMFORT-II trial were randomized phase 3 studies that evaluated the safety and efficacy of ruxolitinib in patients with intermediate-2 (int-2) or high-risk primary MF (PMF), post-polycythemia vera MF (PPV-MF), or post-essential thrombocythemia MF (PET-MF). The comparator was placebo in COMFORT-I and best available therapy (BAT) in COMFORT-II. The ruxolitinib starting dose was 15 or 20 mg twice daily based on baseline platelet counts (100-200 and >200 × 109/L, respectively); dose modifications were permitted for safety and efficacy. Patients were allowed to cross over to ruxolitinib from the control arm for progressive splenomegaly, defined as a ≥25% increase in spleen volume from baseline (COMFORT-I) or study nadir (COMFORT-II), or select protocol-defined progression events; crossover was mandatory following treatment unblinding in COMFORT-I. OS was a secondary endpoint in both studies and was evaluated in an intent-to-treat (ITT) analysis using a Cox proportional hazard model that estimated the treatment effect stratified by clinical trial and International Prognostic Scoring System (IPSS) risk. The crossover-corrected treatment effect was estimated using a rank-preserving structural failure time (RPSFT) method. Results: Overall, 528 patients were randomized: 301 to ruxolitinib (COMFORT-I, n=155; COMFORT-II, n=146) and 227 to placebo (n=154) or BAT (n=73). All ongoing patients in the control arms crossed over to ruxolitinib by the 3-year follow-up. Patient populations were similar between the two trials and their details were previously published. In the combined ruxolitinib group, 162 patients (53.8%) had high-risk MF and 139 (46.2%) had int-2 risk MF based on IPSS criteria. At the 5-year ITT analysis, 128 patients (42.5%) died in the ruxolitinib group compared with 117 (51.5%) in the control group. The risk of death was reduced by 30% with ruxolitinib compared with control (median OS: ruxolitinib, 63.5 mo; control, 45.9 mo; HR, 0.70; 95% CI, 0.54-0.91; P=0.0065; Figure A). After correcting for crossover using RPSFT, OS advantage was more pronounced for patients originally randomized to ruxolitinib (median OS: ruxolitinib, 63.5 mo; control, 27 mo; HR, 0.35; 95% CI, 0.23-0.59; Figure B). An analysis of OS censoring patients at the time of crossover also demonstrated that ruxolitinib prolonged survival compared with control (median OS: ruxolitinib, 63.5 mo; control, 28.3 mo; HR, 0.53; 95% CI, 0.36−0.78; P=0.0013; Figure C). Among all patients treated with ruxolitinib, those with lower-risk disease had longer survival compared with those with high-risk disease (median OS: int-2, not reached [estimated, 102 mo]; high-risk, 50 mo; HR, 2.86; 95% CI, 1.95-4.20; P<0.0001; Figure D). In a subgroup analysis, OS favored ruxolitinib compared with placebo for patients with int-2 or high-risk MF (data not shown). At 5 years, median OS appeared to favor patients with int-2 (n=58) or high-risk (n=89) PMF who were originally randomized to ruxolitinib compared with historical (Cervantes et al; J Clin Oncol 30:2981-2987) controls (int-2 PMF, not reached [estimated, 70 mo] vs 48 mo; high-risk PMF, 34 vs 27 mo); OS was longer among patients with int-2 vs high-risk PMF (P=0.0003). Subgroup analyses showed that ruxolitinib provided an OS advantage regardless of age (>65 or ≤65 y), sex, disease type (PMF, PPV-MF, PET-MF), risk status (int-2 or high), JAK2V617F mutation status, baseline spleen volume (>10 or ≤10 cm), anemia, white blood cell count (>25 or ≤25 × 109L), or platelet count (>200 or ≤200 × 109/L). Conclusion: Long-term treatment with ruxolitinib up to 5 years prolonged survival in patients with MF compared with BAT or placebo. Corrections for patients who crossed over to ruxolitinib suggested that the separation between ruxolitinib and control OS curves was primarily caused by a delay in ruxolitinib treatment. The results suggest that earlier treatment with ruxolitinib may provide a greater survival advantage for patients with MF. Disclosures Gupta: Incyte Corporation: Consultancy, Research Funding; Novartis: Consultancy, Honoraria, Research Funding. Mesa:Incyte: Research Funding; Ariad: Consultancy; Novartis: Consultancy; Celgene: Research Funding; CTI: Research Funding; Promedior: Research Funding; Galena: Consultancy; Gilead: Research Funding. Vannucchi:Novartis: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau. Kiladjian:AOP Orphan: Research Funding; Novartis: Research Funding. Cervantes:AOP Orphan: Membership on an entity's Board of Directors or advisory committees; Baxalta: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Novartis: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Sun:Incyte Corporation: Employment, Equity Ownership. Gao:Incyte Corporation: Employment, Equity Ownership. Dong:Novartis Pharmaceutical Corporation: Employment, Equity Ownership. Naim:Incyte Corporation: Employment, Equity Ownership. Gopalakrishna:Novartis Pharma AG: Employment, Equity Ownership. Harrison:Incyte Corporation: Honoraria, Speakers Bureau; Baxaltra: Consultancy, Honoraria, Speakers Bureau; Gilead: Honoraria, Speakers Bureau; CTI Biopharma: Consultancy, Honoraria, Speakers Bureau; Shire: Honoraria, Speakers Bureau; Novartis: Consultancy, Honoraria, Other: travel, accommodations, expenses, Research Funding, Speakers Bureau.

Abstract DNA methylation at cytosine position 5 (5mC) is a genetic modification that regulates gene expression and is critical for cancer initiation and development. The methylcytosine dioxygenase TET2 participates in active DNA demethylation by converting 5mC to 5-hydroxymethylcytosine (5hmC) and its subsequent intermediates thereby regulating gene expression. TET2 gene is frequently mutated in hematological disorders, including 15-25% of myelodysplastic syndrome (MDS) cases. Loss of TET2 function leads to DNA hypermethylation and subsequent dysregulated gene expression in hematopoietic stem cells, and has been considered as an initial step of myeloid malignant transformation including MDS and acute myeloid leukemia (AML). While enzymatic activity of TET2 is well studied, little is known about post-translational modifications (PTMs) that regulate its activity in hematopoietic cells. Lysine acetylation, one of the most crucial PTMs, occurs in a variety of proteins and modulates protein-protein or protein-nucleic acids interactions. Here, we first observed that ectopic expression of histone acetyltransferase EP300 or CREB binding protein (CBP) increased the endogenous TET2 acetylation in 293T cells. Mass spectrometry analysis of TET2 identified several conserved acetylated lysine residues located on the exterior surface of its catalytic domain (CD), which is predicted to be essential for the interaction of TET2 with DNA. Modeling of TET2/DNA interaction using x-ray crystal structure (PDB code: 4NM6) indicates acetylated TET2 interferes with DNA binding thereby impairing the catalytic activity of the enzyme. Like other acetylated proteins, TET2 modification is reversible, since ectopic expression of the protein deacetylase Sirtuin1 (SIRT1) significantly decreases acetylation of TET2. A domain mapping analysis revealed that SIRT1 preferentially interacts with TET2 CD, further supporting the regulatory role of SIRT1 on TET2. To explore the role of SIRT1 mediated deacetylaion of TET2 in more physiological condition, SIRT1 knockdown (KD) MDS-L cells as well as SIRT1 knockout (KO) murine hematopoietic c-kit+ cells were used. In MDS-L cells derived from a MDS patient, SIRT1 KD promoted hyperacetylation of endogenous TET2 which is associated with 50% decrease in 5hmC levels compared to control (p=0.03, n=3). Similarly, SIRT1 KO murine c-Kit+ cells showed TET2 hyperacetylation and 62% decrease in 5hmC compared to wildtype (WT) counterpart (p=0.009, n=5). Phenotypically, the transforming ability of SIRT1 shRNA transduced MDS-L cells was evaluated in vitro through serial replating assay. In contrast to first plating which showed no difference between two groups, the number of colonies derived from SIRT1 KD cells was 2.39 fold higher than that from the control shRNA transduced group after two rounds of replating (p=0.0002, n=3). Importantly, we tested the in-vivo effect of SIRT1 KD on MDS-L cells engrafted in immunodeficient NSGS mice. SIRT1 KD significantly enhanced MDS-L cell engraftment compared to control shRNA (50±5% of human CD45+ cells in SIRT1 KD group vs. 19±4% human CD45+ cells in control group, p=0.003, n=6). Interestingly, increased transformation capacity of SIRT1 KD MDS-L cells was associated with decreased expression of TET2 regulated tumor suppressor genes. For example, expression levels of Mtss1 and Dusp6 were significantly decreased in SIRT1 KD MDS-L cells compared to control shRNA counterpart (Mtss1, 49±5% decrease compared to control, p=0.005; Dusp6, 25±2% decrease compared to control, p=0.01). Similar results were observed in SIRT1 KO cells. The validation of physical binding of TET2 to its targets is ongoing. Moreover, the effect of an SIRT1 allosteric activator-SRT1720 in MDS-L cells is similar to that of Vitamin C, a known TET2 activator. Specifically, SRT1720 significantly increased Mtss1 expression in MDSL cells (p=0.0005, n=3), indicating that SIRT1 agonist may lead to activation of TET2 downstream tumor suppressor genes. In summary, our data demonstrate that TET2 activity can be functionally modified by acetylation and may be enhanced in MDS patients that do not harbor loss-of-function mutations through the SIRT1 mediated deacetylation. These results support further exploration of molecular mechanisms inducing TET2 acetylation, and evaluation of SIRT1 activation as a potential therapeutic approach in MDS. Disclosures No relevant conflicts of interest to declare.

Abstract Abstract 1122 Background: Continuous flow left ventricular assist device (CF-LVAD) recipients have increased tendency of post-surgical bleeding. We have previously described a universal loss of high molecular weight VWF multimers (HMWM), likely due to enhanced cleavage of the HMWM in CF-LVAD recipients. Among various VWF laboratory tests, VWF multimer analysis remains the reference method for detecting such an acquired VWF abnormality (AVWA). We hypothesize that the severity of AVWA is a predictor for bleeding tendency. In this study, using our in-gel VWF multimer electrophoresis method, we measured the severity of HMWM loss in CF-LVAD recipients by infra-red densitometry analysis and examined its association with other VWF activity test results and patients' bleeding tendency. Design: As part of an on-going prospective multicenter study, pre- and/or post-CF-LVAD implantation (7, 30 days and 5–7 months) blood samples were collected from 20 LVAD recipients during 2008 and 2009. Their clinically significant bleeding episodes were recorded. Plasma VWF antigen (VWF:Ag), VWF:Lx activity [Chen D, et al. J Thromb Haemost. 2011;9(10):1993–2002] and plasma VWF multimer analyses [Pruthi RK, et al. Thromb Res. 2010;126(6):543–9] were performed on all available plasma samples. VWF multimers were quantified by infra-red fluorescent densitometry analysis using Odyssey Infrared Imager version 2.0. VWF:multi ratio defined by density ratio between the high molecular weight multimer (HMWM, bands 11 and above) and low and intermediate molecular weight multimer (band 2 to 9) was calculated. Normal range of VWF:multi ratio was determined from 16 normal donor plasma and 4 pooled normal plasma. Statistical analyses including t-test and kappa test were employed. Result: The normal range of VWF:multi ratio is 0.4–0.76. The CV of VWF:multi ratio of a pooled normal plasma tested in 21 gel runs is 12%. Loss of VWF HMWM is present in three patients before CF-LVAD implantation and all patients after implantation. All samples with loss of HMWM show decreased VWF:multi ratio (<0.4). At a cut-off value of 0.4, the sensitivity and specificity of VWF:multi ratio for detecting HMWM loss are 100% and 95.5% respectively (n=67). Decrease of VWF:multi ratio is observed after implantation (0.41±0.07 pre- vs. 0.29±0.07 post-implantation, P<0.00001). In four patients who received heart transplantation, normalization of VWF multimer pattern and VWF:multi ratio (0.54±0.06) is observed. Ten patients had significant post-implantation bleeding episodes that are associated with significantly decreased VWF:multi ratio (0.26±0.04 bleeding vs. 0.32±0.09 non-bleeding, P=0.002) and VWF Lx/Ag ratio (0.72±0.10 bleeding vs 0.80±0.09 non-bleeding, P=0.001). At a cut-off of 0.26, VWF:multi ratio demonstrates a sensitivity of 64% and specificity of 85.7% for predicting clinically significant bleeding. The VWF:multi ratio shows moderate agreement with VWF:Lx/Ag ratio (Kappa value 0.42). Conclusions: Severity of VWF HMWM losses can be quantitatively measured by the new in-gel infra-red densitometry method (VWF:multi ratio). Severity of VWF HMWM losses defined by the VWF:multi ratios, along with VWF:Lx/Ag ratios are significantly associated with bleeding tendency in LVAD recipients. Disclosures: Milano: Thoratec: Consultancy.