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Abstract Background: KIT D816V is considered the driver mutation in systemic mastocytosis (SM) however this mutation alone does not explain the diverse clinical manifestations of SM. While mutations in other myeloid-relevant genes have been reported in SM, their pattern(s) of co-segregation and prognostic value, independent of age and SM subtype, have not been fully defined in a mature dataset. Objectives: In this pilot study of advanced SM patients, we sequenced a panel of myeloid-relevant genes for known pathogenic mutations, to ascertain: (i) the frequency of individual mutations; (ii) the pattern(s) of mutation co-segregation; and (iii) the prognostic value of mutations, both individually and in combination, on overall- (OS) and leukemia-free survival (LFS). Methods: The current study was approved by the Mayo Clinic institutional review board. SM was classified as per World Health Organization criteria. DNA was isolated from archived bone marrow (BM) cell pellets. Next-generation deep sequencing by HiSeq SBS chemistry (Illumina) was performed to investigate the coding regions of 22 genes: KIT, JAK2, CALR, SRSF2, U2AF1, SF3B1, ASXL1, TET2, EZH2, SETBP1, DNMT3A, IDH-1/2, SUZ12, CBL, NRAS, FLT3, PTPN11, RUNX1, CEBPA, TP53 and NPM1. Results: We studied 19 patients with advanced SM; 6 had aggressive SM (ASM) and 13 had SM with an associated hematological disease (SM-AHD). Of the latter, 5 patients (38%) had myeloproliferative neoplasm-unclassified (MPN-u), 3 (23%) chronic myelomonocytic leukemia (CMML), 2 (15%) acute myeloid leukemia (AML), and 1 (8%) each polycythemia vera, myelodysplastic syndrome, and multiple myeloma. The median follow up from diagnosis was 20 months (range 2 to 84). Over this period, 5 patients (26%) developed leukemic transformation and 12 patients (63%) have died. KIT D816V was identified in 9 (47%) patients; 9 of 10 patients who tested negative by deep sequencing were screened by allele-specific PCR (sensitivity ~0.01%), with 8 additional patients testing positive. Thus, overall KIT D816V frequency was 89%. Fourteen (74%) patients harbored at least one additional non-KIT mutation; of these 7 patients had one additional mutation (ASXL1/TET2/SF3B1 = 2 each and JAK2 =1), 3 patients each had two and three additional mutations, and 1 patient had 4 additional mutations. The most frequently mutated genes (other than KIT) were ASXL1/TET2 (5 patients each, 26%), CBL (4 patients, 21%), SETBP1/SF3B1/DNMT3A (2 patients each, 11%) and JAK2/CALR/FLT3/IDH-1/RUNX1/TP53 (1 patient each, 5%). There was no overlap between patients harboring TET2 and ASXL1 mutations however 2 and 1 CBL-mutated patients concurrently harbored TET2 and ASXL1 mutations, respectively. SETBP1 and SF3B1 but not DNMT3A mutations occurred independently of TET2 and ASXL1 mutations. The distribution of mutations was similar between ASM and SM-AHD subgroups. When considered individually, the following non-KIT mutated genes (present in at least 2 patients) were associated with significantly inferior OS: ASXL1, CBL and SETBP1 (p<0.05). When the 3 mutated genes were considered together, only ASXL1 and CBL maintained their significance, independent of age and SM subtype, for inferior OS (Hazard ratio (95% confidence interval)=34.8 (3.1-393.9) and 59.7 (4.1-861.5), respectively). Patients harboring ASXL1 and/or CBL mutations (n=8, 8 deaths, median OS=11 months) had a significantly worse OS as compared to those without either mutation (n=11, 4 deaths, median OS=84 months) (p=0.0002) (Fig 1). When considering the number of non-KIT mutations (zero, one, two, three and four mutations in 5, 7, 3, 3 and 1 patients, respectively), the group with ≥3 mutations (n=4, 4 deaths, median OS=7 months) had a significantly inferior OS as compared to those with <3 mutations (n=15, 8 deaths, median OS=48 months) (p=0.01) (Fig 2). Presence of mutations was not correlated with LFS in this analysis. Conclusions: In this cohort of advanced SM patients, non-KIT mutations were frequent (prevalence 74%). TET2, ASXL1, SETBP1 and SF3B1, but not CBL or DNMT3A, mutations were mutually exclusive. Presence of ASXL1 and CBL mutations was associated with significantly inferior OS (HR=35 and 60, respectively), independent of known prognostic factors. An increasing number of non-KIT mutations (≥3, HR=5.9) was also associated with a significantly worse survival outcome. Sequencing results from a larger cohort will be presented at the meeting. Figure 1. Figure 1. Figure 2. Figure 2. Disclosures Pardanani: Stemline: Research Funding.

Abstract Background : TET2, located on chromosome 4q24, is frequently mutated in the majority of patients with chronic myelomonocytic leukemia (CMML). TET2 has 11 exons, and variations, especially in exon 3 have been described as a part of age related clonal hematopoiesis (Jaiswal NEJM 2015). In CMML, somatic TET2 mutations in the absence of ASXL1 mutations (ASXL1wt/TET2mt) were previously shown to impart a favorable outcome on survival (Patnaik BCJ 2015). In the current larger CMML patient cohort, we describe the number and type of TET2 mutations and examine their phenotypic and prognostic effects. Methods : 261 patients with CMML were included in the study. All patients had bone marrow (BM) biopsies and cytogenetics performed at diagnosis. Targeted capture assays were carried out on BM DNA specimens obtained at diagnosis for the following genes; TET2, DNMT3A, IDH1, IDH2, ASXL1, EZH2, SUZ12, SRSF2, SF3B1, ZRSR2, U2AF1, PTPN11, Tp53, SH2B3, RUNX1, CBL, NRAS, KRAS, JAK2, CSF3R, FLT3, KIT, CALR, MPL, NPM1, CEBPA, IKZF, and SETBP1. TET2 (NM_001127208.2) coverage extended from exons 3-11, with frame shift, non-sense, and missense variations considered pathogenic. Previously annotated single nucleotide polymorphisms (http//www.hapmap.org) were considered non-pathogenic. Results: Among the 261 study patients, 65% were males and median age was 70 years (range, 28-91). 154 (59%), 64 (25%) and 43 (16%) patients were classified as CMML-0, 1 and 2, respectively. At a median follow-up of 23 months, 174 (67%) deaths and 37 (14%) leukemic transformations were documented. Mutational frequencies ≥4% were encountered in; ASXL1 45%, TET2 42%, SRSF2 40%, NRAS 14%, SETBP1 13%, CBL 10%, JAK2 7%, RUNX1 6%, DNMT3A 6%, U2AF1 6%, SF3B1 5%, ZRSR2 4%, Tp53 4% and IDH2 4%. i) TET2 mutations type, number and phenotypic correlates: TET2 mutations were seen in 109 (42%) patients; these included frameshift 33 (30%), nonsense 29 (27%) and missense 11 (10%) variants whereas 36 (33%) had more than one type of mutation. Overall, 57 (52%) patients had more than 1 TET2 mutations: 52 (48%) patients had 1, 46 (42%) 2 and 11 (10%) ≥3 TET2 mutations. Among all 109 TET2 mutated patients, 65% were male, and median age was 71 years with no significant difference in age and gender distribution between mutated and un-mutated cases, or type of TET2 mutations; however, older patients were more likely to carry multiple TET2 mutations (p=0.01). Compared to their un-mutated counterparts, TET2 mutated cases were less likely to have a low hemoglobin (p<0.001), circulating immature myeloid cells (IMC) (p=0.001), peripheral blood (PB) (p=0.009) and BM blasts (p=0.009), and have high-risk stratification per Mayo Molecular Model (p<0.001); these differences were not affected by the type or number of TET2 mutations. TET2 mutated cases were more likely to have a higher frequency of SRSF2 (p=0.004) and lower frequency of ASXL1 (p=0.03), Tp53 (p=0.04) and IDH1/2 mutations (p<0.001); these associations were also not affected by the type or number of TET2 mutations. ii) Impact on survival: Median survival for the entire cohort (n=261) was 24 months. In univariate analysis, survival was superior in TET2 mutated (median 33 months) versus wild-type (median 21 months) patients [p=0.03; HR 1.3 95% CI 1.12-1.86] (figure 1A). This survival difference remained significant after adjustment for age (p=0.04), leukocyte count (p=0.017), absolute monocyte count (p=0.02), absolute lymphocyte count (p=0.02), platelet count (p=0.015), circulating IMC (p=0.03), DNMT3A (p=0.02) and ASXL1 (p=0.045) mutations; however, significance was lost after adjustment for abnormal karyotype (p=0.32) and the Mayo Molecular Model (p=0.0003). These observations were not affected by the type or number of TET2 mutations. Finally, our previous observation regarding the survival advantage of ASXL1wt/TET2mt versus other genotypes was most apparent for patients with multiple TET2 mutations (p=0.02) (figure 1B). Conclusions: TET2 mutations are common in CMML and constitute approximately equal proportions of frameshift and non-sense mutations, while missense mutations are less frequent. Majority of TET2 mutated CMML cases harbor more than one mutant variant. Regardless, the relevance of type and number of TET2 mutations in CMML was limited to an association between older age and number of mutations and the latter with possibly improved survival in the absence of clonal ASXL1 mutations. Disclosures No relevant conflicts of interest to declare.

Abstract Background The Dynamic International Prognostic Scoring System (DIPSS)-plus currently provides the most comprehensive prognostic model for primary myelofibrosis (PMF) (JCO 2011;29:392). DIPSS-pluse uses eight independent predictors of inferior survival: age >65 years, hemoglobin <10 g/dL, leukocyte count >25 x 109/L, circulating blasts ³1%, constitutional symptoms, unfavorable karyotype, red cell transfusion need and platelet count <100 x 109/L. More recently, type 1/type 1-like CALR driver mutational status and ASXL1 andSRSF2 mutations were identified as additional DIPSS-plus-independent risk factors for survival in PMF (JAMAOncol. 2015;1:97). Based on our earlier preliminary observation (Leuk Res. 2007;31:1503), we conducted the current study to fully examine the additional prognostic relevance of monocytosis (absolute monocyte count ≥1 x 10(9)/L) in PMF. Methods Study patients fulfilled the 2016 WHO criteria for the diagnosis of PMF, including both pre-PMF and overt PMF (Blood. 2016;127:2391). Additional selection criteria included the availability of absolute monocyte count (AMC) and percentage at time of referral. Targeted next generation sequencing was used to screen for prognostically-relevant mutations (Blood 2015 126:354). Statistical analyses considered clinical and laboratory parameters obtained at time of initial referral to the Mayo Clinic. Results Patient characteristics: The study population included 454 patients (median age 64 years; 62% males); 293 (64%) patients harbored JAK2 mutations, 74 (16%) type 1/like CALR, 16 (3%) type 2/like CALR, 24 (5%) MPL and 47 (10%) were "triple-negative". DIPSS-plus risk distribution was 29% high, 38% intermediate-2, 17% intermediate-1 and 15% low; 27% displayed red cell transfusion-dependency, 29% constitutional symptoms, 70% palpable splenomegaly and 36% abnormal karyotype, including 13% with unfavorable karyotype. 301 patients were screened for ASXL1 mutations with 39% mutated, 297 for SRSF2 mutations with 15% mutated, 286 for U2AF1 with 18% mutated, 253 for SF3B1 with 6% mutated, 229 for EZH2 with 5% mutated and 110 for IDH1/2 with 7% mutated. Clinical, cytogenetic and molecular comparisons between PMF patients with and without monocytosis: Among all study patients, 376 (83%) displayed AMC <1 x 10(9)/L; the remaining had either moderate (AMC between 1 and 3 x 10(9)/L; n=65) or marked (AMC >3 x 10(9)/L; n=13) monocytosis. Comparison of these three groups revealed that monocytosis was significantly associated with older age (p=0.0001), higher leukocyte count (p<0.0001), lower platelet count (p=0.01), higher circulating blast percentage (p=0.0002) and higher DIPSS-plus risk distribution (p=0.01). There were no significant differences in the distribution of driver mutations, ASXL1, SRSF2, U2AF, SF3B1, EZH2 or IDH1/2 mutations or incidence of unfavorable karyotype. Survival analysis: After a median follow up of 3.2 years, 265 (58%) deaths and 38 (8%) leukemic transformations were documented. In univariate analysis, all 8 variables included in DIPSS-plus were significantly associated with shortened survival (p<0.001 in all instances). Significant risk factors in univariate analysis also included AMC >3 x 10(9)/L (p<0.0001; HR 5.6, 95% CI 3.1-10.0), AMC 1 to 3 x 10(9)/L (p<0.0001; HR 2.1, 95% CI 1.5-2.9), absence of CALR type 1/type 1-like (p<0.0001) and presence of ASXL1 (p<0.0001) or SRSF2 (p<0.0001) mutations. The significant difference in survival between the three AMC categories (i.e. <1, 1-3 and >3 x 10(9)L) was independent of each one of the eight DIPSS-plus variables, DIPSS-plus, driver mutational status, ASXL1 and SRSF2 mutations (p<0.0001 in all instances). The survival difference between patients with and without monocytosis was evident in both high/intermediate-2 and low/intermediate-1 DIPSS-plus risk groups (Figure). Patients with monocytosis were also more likely to undergo leukemic transformation (HR 3.0, 95% CI 1.4-6.5) and this effect was also independent of karyotype, driver mutational status, ASXL1 or SRSF2 mutations. Conclusion The current study identifies monocytosis as a powerful risk factor for both overall and leukemia-free survival in PMF and the effect was independent of currently established prognostic models and genetic risk factors. It was particularly noteworthy to document similar distribution of driver mutations among the three monocyte categories. Figure Figure. Disclosures No relevant conflicts of interest to declare.

Abstract Background Polycythemia Vera (PV) constitutes one of the three BCR-ABL1-negative myeloproliferative neoplasms and is characterized by clonal erythrocytosis and the almost invariable presence of JAK2 mutation. An absolute monocyte count (AMC) of ≥1 x 10(9)/L defines chronic myelomonocytic leukemia (CMML) but can also be seen in other myeloid disorders including myelodysplastic syndromes (MDS) and myeloproliferative neoplasms (MPN). The presence or development of monocytosis has previously been shown to confer poor prognosis in both primary myelofibrosis (PMF), which is one of the three BCR-ABL1-negative MPN (Leukemia Research 2007;31:1503, Mod Pathol. 2013 Feb;26(2):204) and MDS (Haematologica. 1997;82:25). In the current study, we examined the clinical, prognostic and molecular correlates of monocytosis in PV. Methods Study patients were selected from our institutional database of MPN and fulfilled the 2008 World Health Organization (WHO) criteria for the diagnosis of PV (Blood. 2009;114:937). Cytogenetic and mutational analyses were performed according to conventional methods (Leukemia. 2014;28:2206) any assignment as unfavorable karyotype was per PMF criteria (Leukemia. 2011;25:82). Mutation screening included TET2, ASXL1 and SRSF2 because of their known association with CMML (Leukemia. 2014;28:2206) Statistical analyses considered clinical and laboratory parameters obtained at time of diagnosis. Results Patient characteristics: Analysis was conducted on 587 patients (median age 60 years; 48% males) who met WHO criteria for diagnosis of PV. Amongst them, accurate documentation of AMC was available in 237 patients, cytogenetic information in 239, and ASXL1, TET2 and SRSF2 mutational status in 133 patients. Median (range) values were for AMC 0.6 x 10(9)/L (0-4.7) and leukocytes 11.6 x 10(9)/L (3.8-171.6). 31% of 506 informative patients had palpable splenomegaly, 34% of 551 had microcirculatory symptoms, 30% of 566 had pruritus, 8% of 504 had erythromelalgia, 42% of 581 had hypertension, 9% of 584 had diabetes and 11% of 575 were active tobacco users. 25% of the patients presented with history of thrombosis and 22% developed thrombosis after diagnosis. Cytogenetic findings were abnormal in 19%, of whom 20% were unfavorable. TET2, ASXL1 and SRSF2 mutations were documented in 18%, 11% and 3%, respectively. During follow-up, 224 (38%) patients died and median follow-up for living patients was 109 months. Median survival was 16 years and leukemic or fibrotic transformations were documented in 4% and 14%, respectively. Comparison of patients with and without monocytosis: Among 237 informative patients, 32 (14%) displayed monocytosis (AMC ≥1 x 10(9)/L) at time of diagnosis. PV patients with monocytosis were older (p=0.006) and displayed higher leukocyte count (p<0.0001) and higher incidences of leukocytosis (p=0.024) and unfavorable cytogenetic abnormalities (p=0.02). There was no association between monocytosis and mutations for TET2 (p=0.1), ASXL1 (p=0.7) and SRSF2 (p=0.3) or thrombosis before (p=0.9) or after (p=0.5) diagnosis (p=0.5), palpable splenomegaly (p=0.6), pruritus (p=0.7) or microcirculatory symptoms (p=0.1). Among the 237 PV patients in whom information regarding AMC was available, 70 (30%) died during follow-up and 49 (21%), 23 (10%), 9 (4%) developed thrombosis, leukemic transformation or fibrotic progression, respectively. In univariate analysis, overall (p=0.009; HR 2.0, 95% CI 1.2-3.4) but not leukemia-free (p=0.79), myelofibrosis-free (p=0.13) or thrombosis-free (p=0.48) survivals were different between patients with or without monocytosis. Furthermore, the significant difference in survival was no longer apparent when analysis was adjusted for age (p=0.13), unfavorable karyotype (0.17) or leukocytosis (p=0.06). Conclusions Monocytosis (AMC ≥1 x 10(9)/L) is not infrequent in PV (14%). However, the presence of monocytosis does not appear to represent a significantly different phenotype in terms of molecular characteristics although it is associated with older age, leukocytosis and unfavorable karyotype. The latter associations account for the inferior survival seen in patients with monocytosis. Disclosures No relevant conflicts of interest to declare.

Abstract Background: Myeloid sarcoma is a tumor mass consisting of myeloid blasts occurring at anatomical site other than the bone marrow (Arber et al. Blood 2016;127(20):2391-2405). It is a subgroup of acute myeloid leukemia, which can be localized or disseminated and may involve multiple organs. It can present with or without a positive bone marrow. It may precede or follow bone marrow involvement. It may be identified at diagnosis or relapse, and is not uncommon after stem cell transplantation (Koc et al. Cancer 1999;85(3):608-615; Yoshihara et al. Biol. Blood Marrow Transplant 2012;18(12):1800-1807). Objective: To describe the clinical characteristics, cytogenetics, prognosis and outcome of patients with myeloid sarcoma with or without bone marrow involvement. Methods: The Mayo Clinic database was interrogated using the ICD-9 codes 205.0, 205.2, 205.3, as well as terms "myeloid sarcoma," "chloroma," and "extramedullary sarcoma" in clinical notes and pathology reports. Patients' follow up information was collected until July 2016. Results: Ninety six patients with a diagnosis myeloid sarcoma were identified. The diagnosis was based on biopsy results and in some cases imaging studies in addition to bone marrow biopsy. The median age was 53 (range 17-83) years, and 64 (67%) patients were males. Myeloid sarcoma with de novo (primary) and secondary acute myeloid leukemia (with antecedent hematologic malignancy and therapy related) accounted for 64% (61) and 36% of the cases respectively. The sites involved based on their frequency of occurrence included integumentary system (skin and soft tissues) in 37 (38%), lymphatic system in 17 (18%), the gastrointestinal and genitourinary system in 14 (15%), the nervous system in 9 (9%), the breast in 3 (3%) and multiple and other single sites in 16 (17 %). Bone marrow cytogenetics findings were documented in 74 (77%) patients; favorable, intermediate, and poor cytogenetic abnormalities account for 7 (9%), 45 (61%), and 22 (30%) cases respectively. After a median follow up of 135 weeks, 57 (59%) patients died. The median survival of primary and secondary acute myeloid leukemia with myeloid sarcoma was 52 and 11.5 months (P<0.0001); and that of favorable, intermediate and unfavorable cytogenetics abnormalities was 169, 52 and 17.5 months (P=0.04) respectively. Twenty six (27%) patients had no bone marrow involvement; and 18 (69%) of them were primary myeloid sarcoma (without antecedent malignancy or therapy). The median (range) age of those with and without bone marrow involvement was 53 (17-83) and 56 (17-81) years (P=0.6). At diagnosis patients with and without bone marrow involvement have a median (range) hemoglobin (gm/dL) (10.3 (6.2-15.4) vs 13.1 (9.9-15.2) P=0.0002), white blood cell count (X109/L) (21.4 (1.1-182.5) vs 5.8 (2.4-23.2) P<0.0001), and platelet count (X109/L) (71 (8-437) vs 250 (17-561) respectively. Aggressive chemotherapy therapy was given to 58 (83%) and 20 (77%) of patients with and without bone marrow involvement (P=0.6). The median survival was 17 and 20 months with and without bone marrow involvement (P=0.4). Of those with bone marrow involvement, 49 (70%) achieved complete remission, and 26 (53%) of those individuals subsequently relapsed. Conclusion: The treatment outcome of patients with myeloid sarcoma with or without bone marrow involvement seems the same. The conventional risk factors, antecedent hematological neoplasms and cytogenetic findings, have significant impact on survival. Disclosures Al-Kali: Celgene: Research Funding; Onconova Therapeutics, Inc.: Research Funding.

Abstract Background: Allogeneic hematopoietic stem cell transplantation (HSCT) is a potentially curative treatment for primary myelofibrosis (PMF). Reduced intensity conditioning (RIC) allows otherwise ineligible patients to proceed with HSCT. Host factors in PMF such as bone marrow (BM) fibrosis, massive splenomegaly, and transfusion related allo-immunization increase the risk of engraftment failure, especially with RIC. Spleen directed therapy (SDT) is often used in PMF patients with splenomegaly to help with engraftment, however little data exists supporting this practice. This study was carried out to investigate the role for SDT and the predictors of outcomes with RIC HSCT for PMF. Methods :After IRB approval, the Mayo Clinic HSCT registry was queried for patients with PMF that underwent RIC allo-HSCT from 2005-2014. Disease and transplant related data were retrospectively abstracted and analyzed for HSCT related outcomes. SDT was defined as a therapeutic strategy with specific intent to overcome an enlarged spleen prior to HSCT and included splenectomy, splenic artery embolization, splenic irradiation, or JAK inhibitor therapy that was stopped <30 days before HSCT. Survival estimates were calculated using the Kaplan-Meier method and means were compared using the log-rank test. Univariate and multivariate analyses were performed using Cox regression modeling. Results :51 patients (67% males) with WHO defined PMF with palpable splenomegaly that underwent RIC allo-HSCT were included in the study; median age 57 years (range, 35-68). The median follow-up was 12.2 months, and at last follow up, 19 deaths (37%) and 4 relapses (8%) were documented. The median OS for the group was not reached (mean 34.2 months); 88% at 100 days and 60% at 2 years. 17 deaths were attributed to non-relapse mortality (NRM). There were 3 engraftment failures (6%). 32 patients (63%) developed acute GVHD (grades II-IV) and 24 patients (47%) developed chronic GVHD (all grades). Twenty-one patients (41%) received SDT; 10 (48%) splenectomy, 2 (9%) splenic irradiation, and 9 (43%) JAK inhibitor therapy (ruxolitinib). The SDT group had a median spleen size of 14.5 cm (range, 1-29 cm) below the left costal margin (LCM) and 13 patients (62%) with spleen size >10 cm below LCM, while the no SDT group had a median spleen size of 7 cm (range, 1-19 cm) and 12 patients (40%) with spleen size >10 cm below LCM; p = 0.01. Seven (64%) of 11 patients receiving splenic irradiation (n = 1) or JAK inhibitor therapy (n = 6) were eligible for IWG-MRT spleen response, and 2 (29%) responded (both in JAK inhibitor group). Of the remaining 5 patients, 2 had a response not meeting IWG-MRT criteria. There were no differences in age (p = 0.09), gender (p = 1.0), DIPSS + score (p = 0.35), or HCT-CI (p = 0.61) between the two groups. There was a statistically significant difference in engraftment failure, with all 3 engraftment failures occurring in the SDT group (2 splenectomy patients, 1 splenic irradiation patient; p = 0.02). Engraftment failures were not attributable to insufficient cell dose, donor specific antibodies, or identifiable host factors. The patient with engraftment failure who underwent splenic irradiation had persistent massive splenomegaly. There were similar outcomes with regards to relapse rates, NRM, and acute and chronic GVHD. In the SDT group, the median OS was 13.3 months; 81% at 100 days and 33% at 2 years. In the no SDT group, the median OS was not reached; 94% at 100 days and 68% at 2 years; p=0.13. In a univariate survival analysis that included age, gender, SDT, DIPSS+ score, HCT-CI, CMV status, ABO status, HLA matching, donor source, graft source, engraftment status, and acute and chronic GVHD, predictors of survival were engraftment failure (p = 0.02) and major/bidirectional ABO incompatibility (p = 0.02). Similar results were obtained when JAK inhibitor therapy was considered separately from other forms of SDT. In a multivariate analysis, engraftment failure (HR 8.2, 1.8-27.2; p = 0.01) and major/bidirectional ABO incompatibility (HR 4.1, 1.4-10.9; p = 0.009) retained independent prognostic significance. Discussion:In patients with PMF and splenomegaly, there was no demonstrable benefit from SDT. Predictors of post-HSCT survival included engraftment failure and major/bidirectional ABO incompatibility. These findings need validation in a larger cohort of patients. Disclosures Al-Kali: Celgene: Research Funding. Mesa:Gilead: Research Funding; Incyte Corporation: Research Funding; Pfizer: Research Funding; Genentech: Research Funding; CTI Biopharma: Research Funding; Promedior: Research Funding; Novartis Pharmaceuticals Corporation: Consultancy; NS Pharma: Research Funding.

Abstract Background : Refractory anemia with ring sideroblasts and thrombocytosis (RARS-T) is a provisional entity in the MDS/MPN overlap syndromes, with diagnostic features of RARS, along with a platelet count > 450 x 10(9)/L and large atypical megakaryocytes. Mutations involving SF3B1 (~80%), JAK2 (~60%), TET2 (~25%) and ASXL1 (~15%) have been reported. The frequency of thrombotic events in RARS-T is thought to be similar to that of essential thrombocytosis (ET) (3.6 vs 3.9/100 patient years; Hematologica 2012; 1036-41). However, unlike in ET, it remains unclear as to whether thrombotic events in RARS-T impact overall (OS) or thrombosis-free (TFS) survival. Methods : 82 patients with WHO-defined RARS-T were included in the study. All patients had bone marrow (BM) biopsies, iron stains for detection of BM ring sideroblasts (RS) and cytogenetics performed at diagnosis. Mutational analysis for JAK2, CALR, MPL, SF3B1, SRSF2 and ASXL1 was carried out on BM DNA obtained at the time of diagnosis. Details of type of thrombotic event and cardiovascular (CV) risk factors including; hypertension, diabetes, smoking and dyslipidemia were obtained by careful review of the medical record. OS was calculated from time of initial diagnosis to the time of last follow-up or death. TFS was calculated from the time of diagnosis of RARS-T to development of thrombosis in uncensored patients and date of last follow up or death in patients censored for thrombosis. Conventional statistics were utilized for all analyses. Results: Among the 82 study patients, 46 (56%) were males and median age was 72 years (range, 48-93). At a median follow-up of 26.5 months; 48 (59%) deaths and 2 leukemic transformations were documented. Median OS was 44 months. Karyotype was diploid in 61 (74%) and analyzed mutational frequencies were; SF3B1 67% (28/42), JAK2 V617F 40% (25/61), ASXL1 21% (9/41), SRSF2 6% (2/31), MPL 1% (2/41) and CALR 0, respectively. Cardiovascular risk factors were present in 52 (63%). a) Thrombotic events and their impact on thrombosis free survival: Eight (10%) patients had a thrombotic event prior to or at the time of diagnosis of RARS-T (venous-8, arterial-0). Nine (11%) patients developed subsequent thrombotic events (venous-7, arterial-2), with no fatalities. In univariate analysis, lower hemoglobin level (p=0.008), lower BM RS % (p=0.04), history of thrombosis (p=0.02), and absence of SF3B1 mutations (p=0.017) were associated with an inferior TFS. Age (p=0.07), JAK2 mutation status (p=0.56) and CV risk factors (p=0.95) did not have prognostic impact. Given the association between SF3B1 mutations and BM RS, in a multivariable model that included these two as covariates, only the absence of SF3B1 mutations retained prognostic significance (p=0.02). Absence of SF3B1 mutation remained significant when history of thrombosis or lower hemoglobin level were introduced into the multivariable model. b) Risk factors for overall survival: In univariate analysis, hemoglobin <10 gm/dl (p=0.007), presence of circulating blasts (p=0.002) and presence of CV risk factors (p=0.04) were associated with an inferior OS. Neither history of thrombosis (p=0.59) nor SF3B1 (p=0.12) mutations affected OS. In multivariable analysis, hemoglobin <10 gm/dl (p=0.03) [HR 1.9; 95% CI 1.1-3.5] and circulating blasts (p=0.002) [HR 1.3; 95% CI 1.1-1.6] remained significant. Conclusions: In contrast to what is observed in ET, thrombosis history does not appear to affect either overall or thrombosis-free survival in RARS-T. The current study suggests a lower thrombosis risk in SF3B1 -mutated patients with RARS-T, compared to their SF3B1 wild-type counterparts. Disclosures No relevant conflicts of interest to declare.

Abstract Background: Fludarabine plus busulfan (FB) and fludarabine plus melphalan (FM) are two commonly used reduced intensity conditioning (RIC) regimens for allogeneic hematopoietic stem cell transplantation (SCT). A recent analysis showed that both regimens had similar overall survival (OS) but relapse incidence (RI) was significantly higher with FB with a trend towards higher non-relapse mortality (NRM) in FM (Baron et al., Cancer 2015). However, that cohort included patients treated with oral and intravenous busulfan without pharmakokinetic targeting of intravenous which may impact anti-leukemic activity. Aim: Compare transplant related outcomes of FB vs. FM using intravenous (IV) busulfan targeted to the area under the curve (AUC). Methods: After due IRB approval, patients with acute myelogenous leukemia (AML) and myelodysplastic syndromes (MDS) receiving RIC-SCT from 2008-2014 were identified. All baseline and laboratory features were retrospectively extracted. Busulfan dose in FB was 0.8 mg/kg IV for 10 doses with therapeutic AUC target of 900-1500 mcmol/L (min). All patients received T-cell replete grafts. Categorical and continuous variables were compared using Pearson's chi-squared and Wilcoxon/Kruskal-Wallis, respectively. Survival estimates were calculated using the Kaplan-Meier method and curves were compared using the log-rank test. Cumulative incidence was computed as competing events using Grey's model. Univariate and multivariate analyses were performed using Cox regression modeling. Results: A. Baseline characteristics and AUC monitoring: 134 pts were identified (47 FB and 87 FM). Median follow up of the entire cohort was 40 months (0-63.3) and at last follow up, 60% and 29% have died or relapsed, respectively. Baseline characteristics stratified according to conditioning regimen are shown in table 1. Younger age (60 yrs FB vs. 61 yrs FM, p = 0.015) and a trend towards a higher CMV R-/D- status (28% FB vs. 14% FM p = 0.064) were the only significant differences identified. All patients in the FB group received intravenous busulfan and 46/47 patients had evaluable AUC data with a range of 732-1354 mcmol/L (min). A total of 19 patients were outside of range, all <900 mcmol/L (min) and required a median dose increase of 28.1% (3.3-50.2%) B. Engraftment and toxicity data: The median time for platelet engraftment was 19 days (0-48) for FB vs. 16 days (14-183) for FM (p = 0.0023) whereas the median time to absolute neutrophil count (ANC) engraftment was 18 days (7-30) for FB and 15 days (11-40) for FM (p = 0.077). Cumulative incidence of grade II-IV, III-IV acute GVHD and chronic GVHD at 2-yr was 57.3%, 11% and 52.8% for FB and 48.6%, 17% and 63.4% for FM (p = 0.73, 0.4 and 0.21, respectively). Two patients in the FM group died of cardiac causes (heart failure and sudden cardiac arrest). No cases of sinusoidal obstructive syndrome were observed in either arm C. Transplant outcomes: A significantly higher 2-yr relapse incidence (RI) was associated with FB vs. FM at 35.6% vs 17.3%, respectively (p = 0.0058). 2-yr progression free survival (PFS) was also significantly lower in the FB vs. FM at 51.2% vs. 65.1%, respectively (p 0.031). However, 2-yr OS and NRM was similar for FB vs. FM (53.1% and 22.9% vs 63.9% and 21.9%, respectively p = 0.26 and 0.89). Necessitating a dose adjustment based on AUC did not increase the risk for relapse or affect NRM. In multivariate analysis, FB was associated with increased RI with hazard ratio (HR) 2.29 (1.07-4.88; p = 0.033). Other factors significantly associated with RI on multivariate analysis were secondary/therapy related disease with HR 2.84 (1.34-6.02; p = 0.0067) and CR1 vs. other with HR 0.39 (0.17-5.32; p = 0.019). The significance of the results remained unchanged after exclusion of MDS patients (data not shown) Conclusion: Despite AUC dose adjustment, FB compared to FM was associated with increased RI with a similar OS and NRM. AUC dose adjustment did not impact transplant outcomes and its routine use in RIC should be further evaluated. Given the wide use of FB as a conditioning regimen, these important observations should be prospectively studied in a randomized fashion. Figure 1. Figure 1. Figure 2. Figure 2. Disclosures Al-Kali: Novartis: Research Funding. Wolf:Janssen Scientific Affairs, LLC: Consultancy.

Abstract Background: The 2016 revision to the World Health Organization (WHO) classification of myeloid neoplasms has specifically categorized germline mutations that are associated with myeloid clonal evolution (Arber et al. Blood 2016). This group consists of myeloid neoplasms with an isolated germline predisposition (CEBPA, DDX41), myeloid neoplasms associated with congenital thrombocytopenia (ETV6, RUNX1, ANKRD26) and germline myeloid neoplasms with multi-organ dysfunction (GATA2, chromosomal breakage disorders, telomere biology disorders etc). We carried out this study to describe the clinical spectrum of germline disorders with predisposition to myeloid neoplasms as categorized by the 2016 WHO classification revision. Methods: After Institutional Review Board (IRB) approval, the adult and pediatric bone marrow failure syndrome database (1990-2016) and the electronic medical record were queried for germline disorders involving GATA2, CEBPA, DDX41, ETV6, RUNX1, ANKRD26, Down syndrome and Noonan syndrome. Chromosomal breakage assays (Diepoxybutane/Mitomycin-C), flow-fluorescent in-situ hybridization (FISH) for telomere length assessment, Fanconi anemia complementation assays and Sanger/Next Generation sequencing (NGS) for the aforementioned germline disorders with myeloid predisposition were carried out in Clinical Laboratory Improvement Amendments (CLIA)-certified laboratories. These disorders were then classified based on the 2016 WHO classification revision. Results : 54 individuals (37 families) were included in the study. Eleven (20%) patients belonging to 5 families were identified as having germline mutations with a preexisting platelet disorder: ETV6 (n=1), ANKRD26 (n=5), RUNX1 (n=5). Forty-three (79%) patients (32 families) had inherited syndromes with multi-organ dysfunction: GATA2 (n=11, 26%), bone marrow failure syndromes (n=14, 33%) and telomere biology disorder (n=14, 33%). There was one patient with neurofibromatosis with a germline PTPN11 mutation who developed juvenile myelomonocytic leukemia, while there were three patients with Down syndrome; 2 with transient abnormal myelopoiesis and one who developed acute megakaryocytic leukemia. The clinical phenotype, prevalence and characteristics of myeloid clonal evolution and outcomes are presented in Table 1. No patients with germline CEBPA or DDX41 mutations were identified. Patients with germline platelet disorders did not have any prominent non-hematological manifestations. Erythrocytosis (20%) with long-standing thrombocytopenia (100%) was a unique feature associated with ANKRD26 mutations. Non-hematologic clues such as human papillomavirus (HPV)-driven warts, primary lymphedema (Emberger syndrome) and frequent atypical infections with monocytopenia were seen in patients with germline GATA2 mutations, and preceded myeloid clonal evolution (morphologic, cytogenetic and molecular). Notably, the age at presentation and penetrance of myeloid transformation was variable, with individuals from the same family developing symptoms during the first decade of life and others remaining asymptomatic to date (fifth decade). Somatic ASXL1 mutations were detected in all 3 (100%) patients with GATA2 mutations and in one patient with ANKRD26 mutation that developed myeloid clonal evolution. In our study myeloid clonal evolution was seen in 40% with RUNX1 mutations, 27% with GATA2 mutations, and 20% with ANKRD26 mutations. We could not calculate the same for bone marrow failure syndromes as the total number of cases seen are still being assessed. Outcomes with allogeneic stem cell transplantation were favorable in appropriately selected patients (Table 1). Conclusion : The 2016 WHO revision to the classification of myeloid neoplasms highlights the importance of recognition and molecular characterization of germline mutations (syndromic and non-syndromic) with risk for myeloid clonal evolution. While some of these disorders (GATA2, Fanconi anemia, telomere biology disorders) may have important non-hematological clues, many present with isolated thrombocytopenia (RUNX1, ETV6). The age and frequency of myeloid evolution is highly variable. Acquisition of somatic ASXL1 mutations at the time of clonal myeloid transformation highlights the role of epigenetic dysregulation in disease evolution. Disclosures Kenderian: Novartis: Patents & Royalties, Research Funding.

Abstract Abstract 4009 Trisomy 8 is the most common among sole cytogenetic abnormalities in both acute myeloid leukemia (AML) and myelodysplastic syndromes (MDS). In the very first paper published on isocitrate dehydrogenase (IDH) mutations in AML, 13 of the 16 IDH1 mutations detected were associated with normal karyotype, 2 with trisomy 8 and one with trisomy 13. Trisomy 8 was also recurrent in patients with IDH1/IDH2-mutated post-MDS AML. In the current study we examined the prevalence and disease distribution of IDH1 and IDH2 mutations in a large (n=157) group of patients with hematologic malignancies and isolated trisomy 8. The Mayo Clinic cytogenetic database allowed identification of 157 patients with isolated trisomy 8. Archived bone marrow cell pellets were used to extract DNA for IDH1 and IDH2 mutation analysis. Eighteen IDH mutations were identified: 15 IDH2 (14 R140Q and one R140W) and 3 IDH1 (2 R132C and one R132G). Seventeen of the 18 IDH mutations occurred in myeloid malignancies whereas one (IDH2R140W) occurred in a patient with angioimmunoblastic lymphoma who was not previously exposed to chemotherapy or radiotherapy, and in whom the IDH2 mutation disappeared after effective lymphoma chemotherapy. Among the 17 IDH-mutated myeloid malignancies, disease-specific IDH1/IDH2 mutational frequencies were as follows: 27% (3/11) for post-MDS AML, 25% (3/12) for therapy-related MDS/AML, 15% (8/54) for de novo MDS, 13% (2/15) for de novo AML and 3% (1/32) for myeloproliferative neoplasm (MPN). In contrast, IDH mutational frequencies were significantly lower among 64 additional patients with AML or MDS without isolated trisomy 8: 7% in de novo AML (n=28), 0% in de novo MDS (n=21), 0% in post-MDS AML (n=11) and 0% in therapy-related MDS/AML (n=4). In the 54 patients with trisomy 8-associated de novo MDS, prognosis was similar between IDH mutated (n=8; median survival 14 months) and unmutated (n=46; median survival 16 months) cases (p=0.7). The majority of IDH-mutated cases with de novo MDS belonged to high risk MDS disease category. However, 3 of the 8 IDH-mutated patients with de novo MDS and 2 of the 3 with therapy-related MDS did not display excess bone marrow blasts. The current study suggests a possible association between IDH mutations and trisomy 8 in AML and MDS but not in MPN or MDS/MPN. The fact that the mere presence of trisomy 8 did not result in a more than expected incidence of IDH mutations in MPN or MDS/MPN makes it unlikely that such an association would be secondary to trisomy 8-associated genetic or biologic changes. Instead, it is possible that IDH mutations, which have been shown to cluster with high-risk disease in both MPN and MDS associated with 5q-, promote a selective advantage for the survival of the clone that harbors trisomy 8. Consistent with this contention, we were able to demonstrate in one of our patients with relapsed AML, the presence of IDHR132C both at initial AML diagnosis and time of relapse, whereas the trisomy 8 abnormality was seen only at the time of relapse. Regardless, the presence of molecular heterogeneity among patients with trisomy 8-associated AML or MDS might explain the controversial prognostic influence of the specific cytogenetic abnormality. Disclosures: No relevant conflicts of interest to declare.