Popat, Uday R

Abstract There is a lack of large comparative study on the outcomes of reduced intensity conditioning (RIC) in acute myeloid leukemia (AML) transplantation using fludarabine/busulfan (FB) and fludarabine/melphalan (FM) regimens. Adult AML patients from Center for International Blood and Marrow Transplant Research who received first RIC allo-transplant between 2001 and 2015 were studied. Patients were excluded if they received cord blood or identical twin transplant, total body irradiation in conditioning, or graft-versus-host disease (GVHD) prophylaxis with in vitro T-cell depletion. Primary outcome was overall survival (OS), secondary end points were leukemia-free survival (LFS), nonrelapse mortality (NRM), relapse, and GVHD. Multivariate survival model was used with adjustment for patient, leukemia, and transplant-related factors. A total of 622 patients received FM and 791 received FB RIC. Compared with FB, the FM group had fewer transplant in complete remission (CR), fewer matched sibling donors, and less usage of anti-thymocyte globulin or alemtuzumab. More patients in the FM group received marrow grafts and had transplantation before 2005. OS was significantly lower within the first 3 months posttransplant in the FM group (hazard ratio [HR] = 1.82, P < .001), but was marginally superior beyond 3 months (HR = 0.87, P = .05). LFS was better with FM compared with FB (HR = 0.89, P = .05). NRM was significantly increased in the FM group during the first 3 months of posttransplant (HR = 3.85, P < .001). Long-term relapse was lower with FM (HR = 0.65, P < .001). Analysis restricted to patients with CR showed comparable results. In conclusion, compared with FB, the FM RIC showed a marginally superior long-term OS and LFS and a lower relapse rate. A lower OS early posttransplant within 3 months was largely the result of a higher early NRM.

Abstract Comparative outcomes of allogeneic hematopoietic cell transplantation (HCT) for BCR-ABL1− myeloproliferative neoplasms (MPNs) in blast phase (MPN-BP) vs de novo acute myeloid leukemia (AML), and AML with prior myelodysplastic syndromes (MDSs; post-MDS AML), are unknown. Using the Center for International Blood and Marrow Transplant Research (CIBMTR) database, we compared HCT outcomes in 177 MPN-BP patients with 4749 patients with de novo AML, and 1104 patients with post-MDS AML, using multivariate regression analysis in 2 separate comparisons. In a multivariate Cox model, no difference in overall survival (OS) or relapse was observed in patients with MPN-BP vs de novo AML with active leukemia at HCT. Patients with MPN-BP in remission had inferior OS in comparison with de novo AML in remission (hazard ratio [HR], 1.40 [95% confidence interval [CI], 1.12-1.76]) due to higher relapse rate (HR, 2.18 [95% CI, 1.69-2.80]). MPN-BP patients had inferior OS (HR, 1.19 [95% CI, 1.00-1.43]) and increased relapse (HR, 1.60 [95% CI, 1.31-1.96]) compared with post-MDS AML. Poor-risk cytogenetics were associated with increased relapse in both comparisons. Peripheral blood grafts were associated with decreased relapse in MPN-BP and post-MDS AML (HR, 0.70 [95% CI, 0.57-0.86]). Nonrelapse mortality (NRM) was similar between MPN-BP vs de novo AML, and MPN-BP vs post-MDS AML. Total-body irradiation–based myeloablative conditioning was associated with higher NRM in both comparisons. Survival of MPN-BP after HCT is inferior to de novo AML in remission and post-MDS AML due to increased relapse. Relapse-prevention strategies are required to optimize HCT outcomes in MPN-BP.

Abstract Allogeneic hematopoietic cell transplantation (HCT) is the only curative therapy for myelofibrosis (MF). In this large multicenter retrospective study, overall survival (OS) in MF patients treated with allogeneic HCT (551 patients) and without HCT (non-HCT) (1377 patients) was analyzed with Cox proportional hazards model. Survival analysis stratified by the Dynamic International Prognostic Scoring System (DIPSS) revealed that the first year of treatment arm assignment, due to upfront risk of transplant-related mortality (TRM), HCT was associated with inferior OS compared with non-HCT (non-HCT vs HCT: DIPSS intermediate 1 [Int-1]: hazard ratio [HR] = 0.26, P < .0001; DIPSS-Int-2 and higher: HR, 0.39, P < .0001). Similarly, in the DIPSS low-risk MF group, due to upfront TRM risk, OS was superior with non-HCT therapies compared with HCT in the first-year post treatment arm assignment (HR, 0.16, P = .006). However, after 1 year, OS was not significantly different (HR, 1.38, P = .451). Beyond 1 year of treatment arm assignment, an OS advantage with HCT therapy in Int-1 and higher DIPSS score patients was observed (non-HCT vs HCT: DIPSS-Int-1: HR, 2.64, P < .0001; DIPSS-Int-2 and higher: HR, 2.55, P < .0001). In conclusion, long-term OS advantage with HCT was observed for patients with Int-1 or higher risk MF, but at the cost of early TRM. The magnitude of OS benefit with HCT increased as DIPSS risk score increased and became apparent with longer follow-up.

Background: Allogeneic hematopoietic stem cell transplantation (HSCT) is currently the only potentially curative therapy in eligible patients with myelodysplastic syndromes (MDS). Reduced-intensity conditioning (RIC) regimens that have been developed to extend HSCT to older patients resulted in encouraging outcomes. However, several retrospective studies have raised concerns about disease control when RIC is used in MDS and the ideal conditioning regimen has not yet been found. In this study, we aimed to compare two most commonly used RIC regimens; intravenous use of fludarabine with busulfan (FluBu) and fludarabine with melphalan (FluMel). Study population: Through the CIBMTR, after excluding patients with ex-vivo T cell depletion, we identified 1045 MDS patients aged ≥ 60 years and underwent first HSCT with matched related or matched (8/8) unrelated donor (MRD and MUD) using RIC between 2007-2016. RIC was defined via CIBMTR criteria as a regimen that incorporated an IV busulfan (BU) total dose ≤ 7.2 mg/kg or low-dose melphalan (MEL) total dose ≤ 150 mg/m2. By that, we identified 697 MDS patients who received FluBu (BU 6.4 mg/kg: 87%, BU 3.2 mg/kg: 13%) and 448 receiving FluMel (MEL 140 mg/m2: 80%, MEL 100 mg/m2: 20%). Results: The two groups, FluBu and FluMel, were comparable for disease and transplant related characteristics except the more frequent use of ATG or Campath in FluBu group (39% vs. 31%). The median age was 67 in both groups, and 26% and 19% of FluBu and FluMel groups were aged ³70, respectively. Hematopoietic comorbidity index (HCT-CI) was ³3 in 61% and 59% of FluBu and FluMel groups and MDS risk score by CIBMTR at HCT was high/very high in 34% in both groups. FluMel was associated with a reduced relapse incidence (RI) after HSCT compared with FluBu as presented in Table 1 and Table 2. Adjusted RI at 1-year was 43% with FluBu and 25% with FluMel (p=<0.0001). On the other hand, transplant related mortality (TRM) was higher with FluMel compared with FluBu (27% vs. 15%, p=<0.0001). The difference persisted at 2- and 3-years after HSCT as presented in the figure. Since the magnitude of improvement in RI was greater with FluMel than the improvement in TRM with FluBu, disease-free survival (DFS) was improved at 1-year and beyond with FluMel compared with FluBu (48% vs. 41% at 1-year, p=0.030, and 38% vs 28% at 3-years, p=0.0030). These outcome differences remained significant when sensitivity analyses were performed excluding patients who received RIC with either BU 3.2 mg/kg or Mel 100 mg/m2. FluMel, did not lead to higher incidence of severe grade 3-4 aGvHD (HR=1.2, 95%CI, 0.9-1.6, p=0.3) or chronic GvHD (HR=0.9, 95%CI=0.7-1.06, p=0.2). However, grade 2-4 aGVHD was observed more often with FluMel than FluBu (HR=1.3, 95%CI, 1.1-1.6, p=0.006). This led to inferior outcomes of GRFS within the first 2 months with FluMel (HR=1.9, HR=1.4-2.6, p<0.001) but superior outcomes of GRFS beyond 2 months with FluMel compared with FluBu (HR=0.7, 95%CI=0.6-0.8, p<0.001). Conclusion: Our results suggest that between the two most commonly used RIC regimens in older MDS patients, FluMel was associated with superior DFS and overall survival compared with FluBu due to reduced RI despite higher TRM. Disclosures Oran: AROG pharmaceuticals: Research Funding; Astex pharmaceuticals: Research Funding. Nakamura:Kirin Kyowa: Other: support for an academic seminar in a university in Japan; Alexion: Other: support to a lecture at a Japan Society of Transfusion/Cellular Therapy meeting ; Celgene: Other: support for an academic seminar in a university in Japan; Merck: Membership on an entity's Board of Directors or advisory committees. Scott:Celgene Corporation: Consultancy, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Alexion: Consultancy, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Novartis: Research Funding; Incyte: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Agios: Speakers Bureau. Popat:Jazz: Consultancy; Incyte: Research Funding; Bayer: Research Funding.

Introduction. Our previous flow cytometry-based comparison of HIV(+) and HIV(-) autologous hematopoietic stem cell transplant (auto-HSCT) recipient immunomes at 56, 180 and 365 days post-transplant to each other and to healthy controls (HCs) showed that both sets of auto-HSCT recipient immunomes approached HCs over time, but retained significant differences. HIV(+), but not HIV(-), auto-AHCT recipients retained pro-inflammatory features consistent with chronic HIV infection. Here, we report the results of a quantitative and functional analysis of immune reconstitution in HIV(+) patients treated with allogeneic hematopoietic stem cell transplant (allo-HSCT), in comparison with HIV(+) auto-HSCT recipients and HCs. Methods. Blood samples were collected for analysis at days 56, 180 and 365 post-transplant from HIV(+) transplant recipients and at 1 time point from HCs. Whole blood analysis was performed by five-color flow cytometry across 100 immune marker combinations. Comparisons were made between HIV(+) allo-HSCT recipients (n=17, acute myeloid leukemia, acute lymphocytic leukemia, myelodysplastic syndrome, Hodgkin and non-Hodgkin lymphoma that received myeloablative or reduced intensity conditioning on the BMT-CTN-0903/AMC-080 trial), HIV(+) auto-HSCT recipients (n=36, aggressive B cell non-Hodgkin lymphoma or Hodgkin lymphoma that received myeloablative conditioning on the BMT-CTN-0803/AMC-071 trial) and 71 HCs. Unsupervised principal component analysis (PCA) examined differences in immune cell proportions, identified by flow cytometry across 100 cell subsets at each time point. Wilcoxon rank-sum tests compared median absolute counts and median proportions of cell subsets. An independent feature importance score analysis (FIS) identified contributions of immune cell populations expressing specific immune marker combinations to the differences between HIV(+) auto-HSCT recipients, HIV(+) allo-HSCT recipients and HCs. Functional responsiveness of HIV(+) allo-HSCT recipients' T cells to stimulation with CD3- and CD28-directed antibodies, NK cells to stimulation with IL-12 and IL-18 and monocytes to stimulation with lipopolysaccharide (LPS) was assessed in a preliminary mass cytometry on peripheral blood mononuclear cells isolated at the same time points (n=2) and compared to HCs (n=2). Results. PCA showed that immunomes of HIV(+) allo-HSCT recipients and HIV(+) auto-HSCT recipients clustered together with each other, but away from HCs at all time points throughout the post-transplant year. FIS identified: 1) 13 cell subsets that defined the difference between HIV(+) allo-HSCT recipients (all visits) and HCs, and 2) 11 immune cell subsets that defined the difference between HIV(+) auto-HSCT recipients (all visits) and HCs; in both of these comparisons, activated CD3+/HLA-DR+ T cells had the greatest impact on the difference between HIV(+) and HC immunomes. At 1 year, both HIV(+) transplant recipient cohorts had higher absolute numbers of activated T cells, effector T cells and CD8+ T cells than HCs (Wilcoxon rank-sum test, p<0.0031). HIV(+) autologous and allogeneic HSCT recipients also had lower numbers of CD4+ T cells, naïve T cells and activated NK cells compared to HCs (p<0.0031). FIS also identified 20 immune cell subsets that defined the difference between HIV(+) autologous and allogeneic HSCT recipients immunomes at 1 year, with CD8+/CD27- effector T cell subset exerting the highest impact on the difference. Preliminary functional mass cytometry analysis of 2 HIV(+) allo-HSCT recipients and 2 HCs showed that: 1) IFNʏ production by CD8+ T cells was increased above that of HCs at all time points. 2) Expanded populations of CD4+/T-bet+ cytotoxic cells expressing granzyme B and perforin, and CD8+ cytotoxic T cells expressing granzyme B and perforin, persisted in HIV(+) allo-HSCT recipients at all time points, but not in HCs. 3) NK cells retained an ability to produce IFNʏ in response to stimulation with IL-12 and IL-18 in HIV(+) allo-SCT recipients. 4) Monocytes showed an enhanced production of TNFα in response to stimulation with LPS in HIV(+) allo-HSCT recipients compared to HCs at 1 year post-HSCT. Conclusion. Chronic HIV infection confers the pro-inflammatory immune features on the phenotypic and functional profiling of the T lymphocyte immunome of stem cell transplant recipients, irrespective of allogeneic or autologous stem cell donor source. Disclosures Devine: Bristol Myers: Other: Grant for monitoring support & travel support; Kiadis Pharma: Other: Protocol development (via institution); Magenta Therapeutics: Other: Travel support for advisory board; My employer (National Marrow Donor Program) has equity interest in Magenta. Noy:Janssen: Consultancy; Medscape: Honoraria; Prime Oncology: Honoraria; NIH: Research Funding; Pharamcyclics: Research Funding; Raphael Pharma: Research Funding. Popat:Bayer: Research Funding; Incyte: Research Funding; Jazz: Consultancy. Hofmeister:Celgene: Honoraria; Janssen: Membership on an entity's Board of Directors or advisory committees; Nektar: Honoraria, Membership on an entity's Board of Directors or advisory committees; Karyopharm: Membership on an entity's Board of Directors or advisory committees; Imbrium: Membership on an entity's Board of Directors or advisory committees; Oncopeptides: Membership on an entity's Board of Directors or advisory committees. Navarro:Atara Biotherapeutics: Employment, Equity Ownership. Behbehani:Fluidigm corporation: Other: Travel funding. Lozanski:Boehringer Ingelheim: Research Funding; Beckman Coulter: Research Funding; Stemline Therapeutics Inc.: Research Funding; Genentec: Research Funding. Baiocchi:Prelude: Consultancy.

Abstract Background: The myeloproliferative neoplasms (MPNs), including essential thrombocythemia (ET), polycythemia vera (PV) and myelofibrosis (MF) can be characterized by heterogeneous symptoms, disease features, and prognosis. Timely monitoring of blood counts and if needed, referral for discussion of stem cell transplant (SCT), are critical to optimizing survival and quality of life. In connection with the MPN SCT Transplantation Timing Taskforce's (MS3T's) work in developing the DIPPS-based Stem Cell Spectrum Timing Tool, the survey was deployed to explore factors contributing to delayed entry to SCT. National Comprehensive Cancer Network (NCCN) guidelines for MPNs strongly recommend referral to specialized centers with expertise in the management of MPNs (Mesa et. al. 2017). To date, efforts to assess the timing and quality of MPN patient care from the patient's perspective have been minimal. Methods: Patients were recruited from MPN-related Facebook pages, subscribers of MPNforum Magazine and E-mail support groups including the MPN-NET, MPDchat, and the MPN Research Foundation. Hematologists, MPN patients, and advocates constructed the 11-item survey questions and content. The survey was available for patient response between July 4-11th2018. Patients were queried on MPN type, time of diagnosis, and details regarding knowledge of their MPN disease features and care. Data: Demographics.Overall 2382 MPN patients responded to the online survey. Of these, 901 (38%) patients had ET, 865 (36%) had PV, 561 (24%) had MF, 41 (2%) had MPN-unclassifiable or MPN/MDS overlap and 15 (1%) did not respond. Among MF patients, 56% reported having primary MF, 42% secondary MF, 1% prefibrotic MF, and 1% reported having already undergone SCT (1% did not specify type of MF or transplant). The majority of patients were diagnosed with their MPN by a hematology/oncology (77.8%) or family practice (15 %) physician. MPN Care provider and monitoring: Out of all respondents, 35% reported being cared for by an MPN specialist, 36% were not cared for by an MPN specialist and 27% were unsure if their provider was an MPN specialist. Overall less than half (42%) of patients reported having sought a second opinion from an MPN specialist. The majority (87%) of participants knew their mutational status relating to the highly publicized and widely tested JAK2 V617F mutation (73.8%) and CALR (10.2%). However, a statistically insignificant number of patients had any idea of other driving and secondary mutations including MPL, EZH2, SRSF2, IDH1/2 or ASLX-1. Blood counts were reviewed by a hematologist for the majority of patients (93% responded "yes", 4% responded "sometimes", 3% responded "no"). SCT Referral: Among ET and PV, <1% of patients reported being referred to SCT. For MF, 34% of participants reported having been referred for SCT discussion (30% for primary MF and 28% for secondary MF). Conclusions: MPN patients often report receiving care outside of the care of an MPN specialist. Additionally, despite the poor outcomes and higher likelihood of progression to AML, less than a third of patients with secondary MF report being referred for SCT discussion. Independent validation of patient responses, particularly in regards to MPN specialized care and timing of transplant discussion should be investigated further. However, these patient responses suggest many patients may be receiving less than optimal MPN care. These results demonstrate the importance of community hematology/oncology physician and patient education regarding optimal MPN care. Disclosures Mesa: UT Health San Antonio - Mays Cancer Center: Employment; Celgene: Research Funding; Novartis: Consultancy; Incyte Corporation: Research Funding; Pfizer: Research Funding; CTI Biopharma: Research Funding; Genentech: Research Funding; Promedior: Research Funding; NS Pharma: Research Funding; Gilead: Research Funding. Palmer:Novartis: Research Funding. Harrison:Novartis: Consultancy, Honoraria, Research Funding, Speakers Bureau; Gilead: Honoraria, Speakers Bureau; CTI BioPharma: Consultancy, Honoraria; Roche: Consultancy, Honoraria; Celgene: Consultancy, Honoraria, Speakers Bureau. Verstovsek:Italfarmaco: Membership on an entity's Board of Directors or advisory committees; Incyte: Consultancy; Celgene: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau. Scherber:Gilead: Honoraria.

Abstract Introduction: Allogeneic hematopoietic stem cell transplantation (HCT) is the only curative therapy for myelofibrosis (MF). Consideration of HCT is recommended by international working groups and national guidelines for MF patients (pts) age <70 with intermediate-1 with adverse indicators, intermediate-2 or high-risk disease by the Dynamic International Prognostic Scoring System (DIPSS) for MF- a recommendation made in the absence of clear data indicating the optimal timing of HCT for MF. In this large multicenter retrospective study, we analyze overall survival in MF pts treated with and without HCT. Methods: Disease characteristics, treatments, and outcome data from MF pts receiving non-transplant therapy at 14 US academic medical centers between 2000-2014 were retrospectively collected. MF pts who underwent HCT were identified from the Center for International Blood and Marrow Transplant Research (CIBMTR). The Cox proportional hazards model was used. The reference time point (time zero) was time of referral for the non-transplant (non-HCT) arm and the time of transplant for the HCT arm. The main effect variable (HCT vs. non-HCT) violated the proportionality assumption where comparing to non-HCT, mortality was higher with HCT in early time period from time zero but then was lower in late time period; therefore, the comparison is presented as early time period and late time period. The Cox model identified 14 months from time zero as the ideal cut point to define early and late time periods. The proportionality assumption is satisfied within each of these two periods. Results: A total of 1377 and 551 pts were included in the non-HCT and HCT arms, respectively (Table 1). In the overall cohort, survival was higher with non-HCT vs. HCT in early time period (relative risk [RR]: 0.34, P< .0001, Figure 1D), but in late time period survival was lower with non-HCT vs. HCT (RR: 2.37, P< 0.001) (Table 2). In the DIPSS low-risk MF group, while survival was higher with non-HCT vs. HCT in the early time period (RR: 0.19, P=0.007, Figure 1A), survival was lower with non-HCT in the late time period, but the latter did not reach statistical significance (RR: 1.45, P=0.39). In the DIPSS intermediate-1 risk group, a survival advantage was present with non-HCT treatments vs. HCT in the early time period (RR: 0.27, P < .0001, Figure 1B), however survival was lower with non-HCT in the late time period (RR: 3.13, P < .0001). Similarly, in those with DIPSS intermediate-2 and high-risk MF, survival advantage was observed with non-HCT in the early time period (RR: 0.41, P< .0001, Figure IC), but survival was lower with non-HCT in the late time period (RR: 2.82, P < .0001). Conclusion: A long-term survival advantage with transplant was observed for pts with intermediate-1 or higher risk MF, but at the cost of potential early mortality. The magnitude of benefit increased as DIPSS risk score increased. Although this retrospective study has limitations, the results have an impact on clinical practice by suggesting that transplantation could be considered earlier in the disease course and supports the recommendation for consideration of HCT in the setting of intermediate-1 risk MF. Disclosures Gowin: Incyte: Consultancy, Other: Scientific Advisory Board, Speakers Bureau. Verstovsek:Celgene: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Incyte: Consultancy; Italfarmaco: Membership on an entity's Board of Directors or advisory committees. Ali:Incyte Corporation: Membership on an entity's Board of Directors or advisory committees. Gupta:Novartis: Consultancy, Honoraria, Research Funding; Incyte: Research Funding. Gerds:Celgene: Consultancy; Apexx Oncology: Consultancy; CTI Biopharma: Consultancy; Incyte: Consultancy.

Abstract Systemic mastocytosis (SM) is a rare hematologic neoplasm characterized by abnormal growth and accumulation of tissue mast cells (MC) in various organ systems, including bone marrow (BM). Indolent and advanced forms of SM have been described. Whereas patients with ISM have a normal or near normal life-expectancy, patients with advanced SM, including those suffering from mast cell leukemia (MCL) have a poor prognosis. In these patients, neoplastic MC are usually resistant against conventional drugs and various targeted drugs. In rapidly progressive aggressive SM (ASM) and MCL, polychemotherapy followed by allogeneic hematopoietic stem cell transplantation (alloHCT) has been proposed. However, outcome of alloHCT in advanced SM is unknown, and it also remains uncertain whether clinically relevant graft-versus-SM (GVSM) effects may occur in these patients, as only sporadic case reports have been published. We performed a retrospective multi-center analysis to evaluate the outcome of alloHCT in patients with advanced SM. Fifty-four advanced SM patients receiving SCT in 32 transplantation centers in Europe and America were identified between 1990 and 2013. The median patient age was 45 years. Donors were: HLA identical siblings (31), unrelated donors (URD) (15), umbilical cord blood donors (UCB) (2), and haploidentical donors (1). In 5 patients, stem cell source was not defined (5). Thirty-four patients received myeloablative conditioning (MAC) and 18 received reduced intensity conditioning regimens (RIC). In 2 patients, conditioning regimen was not specified. Indications for alloHCT were SM with an associated clonal hematologic non-mast cell lineage disease (SM-AHNMD) (n=32), MCL (n=13, including one with MCL-AHNMD), 8 with ASM and 1 with myelomastocytic leukemia (MML). The most prevalent AHNMD was acute myeloid leukemia (AML, n=16). With follow-up of 35-6180 (median 365) days, SM responses (defined as ≥50% decrease in BM mast cells ± decrease in serum tryptase ± regression of other organ manifestations) were observed in 39 patients (72%), including complete responses (CR) documented in 12 patients (22%). Eleven patients had stable disease, whereas 4 patients (7%) progressed immediately after alloHCT (primary resistance). In addition, 10 patients progressed (5 of them within 100 days) after an initial response. Progression was most frequently seen in MCL patients (n=6, 50%). In the AHNMD group, only 8 patients relapsed/progressed (25%). The overall survival (OS) and SM progression-free survival (PFS) at 1 year were 63% and 50% for all patients, 77% and 68% for SM-AHNMD, 63% and 50% for ASM, and 25% and 17% for MCL, respectively. The strongest predictive variable associated with inferior survival was a diagnosis of MCL. Other factors associated with poor outcome were: Karnofsky performance status ≤70%, ≥2 SM regimens given before alloHCT (e.g., steroids, cladribine, chemotherapy, tyrosine kinase inhibitor), donor source (alternative donors-UCB and haploidentical compared to sibling or URD), SM progression within the first 100 days, normal cytogenetics (compared to t(8;21) (q22;q22), and RIC (compared to MAC). The following variables were not associated with poor outcome: patient and donor age, recipient-donor sex match status, graft source (BM vs. peripheral stem cells), BM mast cell percentage at time of alloHCT, and CR status of AML or SM response at time of alloHCT. This largest multi-center analysis of results in advanced SM provides evidence for clinical efficacy of alloHCT, presumably because of a GVSM effect of alloHCT (achieving CR, and response to donor-lymphocyte infusions and RIC alloHCT). However, responses varied among different SM categories: while patients with SM-AHNMD enjoyed excellent outcomes, the OS for MCL patients in general, was poor. Nevertheless it is remarkable that 3 of 13 patients with MCL – an otherwise fatal disease with a median survival of &lt;12 months – became long-term survivors after alloHCT. In summary, our results support development of a prospective alloHCT study, with the aim to optimize therapy and to improve overall outcome in advanced SM. Based on our pilot study, alloHCT should also be considered in practice for eligible and fit patients with SM-AHNMD (if treatment of AHNMD component needs alloHCT or SM component is aggressive), rapidly progressing ASM, MCL and MML when a suitable HLA-matched sibling donor or URD is available. Disclosures: Vercellotti: Sangart Inc.: Research Funding; Seattle Genetics: Research Funding. Akin:Novartis: Consultancy. Valent:Novartis: Consultancy, Honoraria, Research Funding.