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Abstract Abstract 2850 Myelofibrosis (MF), both primary myelofibrosis (PMF) and post essential thrombocytosis/polycythemia vera myelofibrosis (post ET/PV-MF), are chronic myeloproliferative neoplasms characterized by a progressive clinical course that leads to shortened survival. The heterogeneous nature of MF lends itself to a variable clinical course that commonly includes hepatosplenomegaly, constitutional symptoms, and progressive cytopenias. Medical therapy for myelofibrosis has been effective in palliation of common symptoms related to anemia, splenomegaly but allogeneic stem cell transplantation (ASCT) remains the only potentially curative therapeutic modality. The timing of ASCT, choice of conditioning regimen, patient selection and the impact of co-morbidities are critical to optimal use of this modality. We have retrospectively analyzed our experience for patients undergoing ASCT for primary and post ET/PV myelofibrosis at Mayo Clinic across all 3 sites: Scottsdale Arizona; Rochester, Minnesota; and Jacksonville, Florida. Methods: We conducted a retrospective review of all patients from 1992 to 2012 with PMF or post ET/PV-MF who underwent an ASCT at Mayo Clinic. This retrospective review included a waiver of informed consent and was approved by the Mayo Clinic Institutional Review Board. Patients that transformed to the MPN blast phase and individuals who underwent a second transplant for either relapse or graft failure were also included. Overall survival was estimated using Kaplan-Meier. Associations between prognostic factors and overall survival were assessed using Cox regression. Results: Baseline Patient Characteristics: Forty-eight patients (29 male) with a median age of 57 yrs (range 31–73) underwent ASCT. DIPSS-plus risk score was low in 2, intermediate 1 in 2, intermediate 2 in 9 and high in 35 patients. Disease type was PMF in 24, PV-MF in 10, ET-MF in 10, and MPN/MDS overlap in 4 pts. Eight patients evolved to the MPN-blast phase prior to transplant. JAK-2 mutation was positive in 27 patients and negative in 12 patients with JAK-2 status unknown in 9 patients. The median time from PV/ET to MF was 136 months (83–189 months) and from MF diagnosis to transplant was 59 months (3–144 months). All but 2 patients were red cell transfusion dependent prior to transplant (96%). Eight patients underwent splenectomy prior to transplant. Transplantation Characteristics: Patients who underwent ASCT received either myeloablative (MA, 13 pts) or reduced-intensity conditioning (RIC, 35 pts) regimen. The graft was from an unrelated donor in 22 pts and related donor in 26 pts with 44 being matched and 4 being mismatched. The myeloablative regimens included Bu/Cy, TBI/Cy, and Bu/Flu. The RIC regimens included flu/mel, Bu/Flu, FBM, and TBI/Flu. GVHD prophylaxis was with tacrolimus/MTX, CSA/MTX, and tacrolimus/MMF. Nineteen patients received ATG. Infectious disease prophylaxis, CMV monitoring, and additional supportive care measures were according to institutional guidelines. A majority of patients received peripheral blood stem cells with only 1 patient receiving bone marrow as the source of stem cells. Outcomes: The median time to neutrophil engraftment was 17.2 days. Two patients received a second transplant for relapsed disease. The incidence of graft failure was 10%. Graft versus host disease both acute and chronic occurred in 33 patients and 15 patients respectively. Day 100 overall survival was 92% and 2 year survival was 62% (95% CI 45–75%). There were no statistically significant associations between individual prognostic factors (DIPSS-plus classification, age, and HLA match) and survival. Conclusions: The Mayo Clinic national experience of ASCT for MF across our geographically diverse Cancer Center is encouraging. Our centers have transplanted 48 patients over the past 10 years with very favorable outcomes. Our results from a multi center practice are consistent with regards to survival, graft versus host disease, and types of transplants being performed compared to currently available published data from large single location transplant centers. This data helps confirm the prevailing knowledge that ASCT is a useful treatment. Disclosures: Mesa: Incyte: Research Funding; Lilly: Research Funding; Sanofi: Research Funding; NS Pharma: Research Funding; YM Bioscience: Research Funding.

Background: Hematopoietic stem cell transplantation (HCT) remains the most effective postremission therapy for high-risk acute myeloid leukemia (AML). FMS-like tyrosine kinase3 (FLT3) mutations occur in about 30% of patients with cytogenetically normal AML. FLT3-ITD (internal tandem duplications) mutations are associated with short-lived remissions and poor outcomes. These adverse effects can be offset by allogeneic HCT in first complete remission (CR1). We carried out this study to get a real world perspective on feasibility of allogeneic HCT in CR1 for FLT3-ITD mutant AML patients. Methods: The Mayo Clinic AML database was queried for all patients that had tested positive for the FLT3 ITD, from January 2003 to December 2014. 75 patients were identified, of which 28 (37%) underwent allogeneic HCT in CR1. 12 were excluded as they were transplant ineligible from an age standpoint, 6 patients actually had MDS and 2 were excluded for primary induction failure. Clinical and outcomes data were abstracted retrospectively. Results: 29 patients were included in the final analysis, with a median age of 57 years (range 21-68), 38% males. Median time from diagnosis to last follow up was 339 days. 24(83%) had normal cytogenetics. 26(90%) received treatment with anthracycline + cytarabine based therapy, 3(10%) were enrolled on a clinical trial. 25(87%) patients went on to receive consolidation therapy. 22 (75%) of the patients relapsed after achieving a CR1, with a median time to relapse of 134 days (range 27-1710 days). Only 8 (26%) of the 22 patients were able to achieve a CR2 with salvage chemotherapy, of which 6 (75 %) successfully underwent allogeneic HCT.2 (25%) out of 8 patients received FLT3 inhibitor in 1st relapse. We then assessed the reasons why relapsed patients did not undergo HCT in CR1. The most common being; relapse during evaluation/work up for HCT in 8(27%) patients, 5 (17%) had comorbidities that precluded HCT, 3 (10%) were never referred for HCT due to personal preferences. At last follow up 19(65%) patients were dead. Conclusion: While allogeneic HCT is an effective consolidative strategy for FLT3 ITD mutant AML patients, in the real world, a large number are not transplanted in CR1 due to delays in donor search and transplant scheduling strategies resulting in disease relapse. Effective strategies to avoid delays in scheduling, rapid donor searches and the use of alternative donor sources are much needed for these patients. Figure 1 Figure 1. Figure 2 Figure 2. Disclosures No relevant conflicts of interest to declare.

Abstract Background: Donor cell chimerisms are tested at frequent intervals after allogeneic hematopoietic stem cell transplantation (alloHSCT). However, the predictive value of this testing in patients with myelofibrosis (MF) is not well-defined. In this study, our primary objective is to evaluate the correlation of day 30 and day 100 donor cell chimerism and overall survival (OS) in patients (pts) who undergo alloHSCT for MF. Methods: Charts were reviewed for pts who underwent alloHSCT for MF at Mayo Clinic in Arizona, Minnesota and Florida between January 2005 and December 2015. Patients who died within 30 days of alloHSCT were excluded. Chimerism studies were evaluated in the peripheral blood for CD3 and CD33 fractions at day +30 (D30) and day +100 (D100). Cut-off value of 100% and less than 100% was used because of limited variability below 100%. Standard statistical methods were used to compare continuous and categorical variables. The Kaplan-Meier method was used to provide survival curves. Results: Baseline characteristics: Sixty three consecutive patients who underwent alloHSCT for MF since January 2005 until December 2015, and had D30 and/or D100 chimerism studies available were included in the study. Of these, 24 (38%) were female. Median age at diagnosis was 56 years (range, 19 - 73 years) and median age at AHSCT was 58 years (range, 19 - 73 years). Dynamic International Prognostic Scoring System-Plus (DIPSS-Plus) risk category at the time of alloHSCT was high in 31 (49%), intermediate-2 in 30 (48%) and intermediate-1 in 2 (3%) pts. JAK2 V617F mutation status was available in 61 pts and was positive in 35 (57%) pts. Nineteen (30%) pts had been treated with a JAK2 inhibitor prior to alloHSCT. Fifty-two (83%) pts had at least grade-2 fibrosis in bone marrow at the time of HCT. Transplantation: Median time from diagnosis to AHSCT was 12.9 months (range, 2.3 - 248.2 months). Fifty-five (87%) received a reduced intensity conditioning (RIC) regimen while 8 (13%) received myeloablative conditioning regimen. Of these 55 pts, RIC regimens used were busulfan fludarabine based regimen in 15 (27%), fludarabine melphalan based regimen in 18 (33%) and fludarabine melphalan carmustine in 22 (40%) pts. Donor source was matched related in 30 (48 %), matched unrelated in 28 (44%), single-antigen mismatched related in 4 (6%) and mismatched unrelated in 1 (2%). Peripheral blood stem cells were used in all AHSCTs. Outcomes: Median follow-up was 24.4 months (range, 1.5 - 83.6 months). Amongst pts who had <100% donor chimerism at D30 in CD33 fraction, 2 had 90%, 1 had 80% and 2 had zero% donor chimerism. At D100, 1 pt had 95%, 1 had 90%, 1 had 60%, 2 had 5% and 1 had zero% donor chimerism. Eighteen out of 57 (32%) pts who had 100% donor chimerism in CD33 fraction at D30 had died at the time of analysis compared to 4 out of 5 (80%) patients with less than 100% (p=0.03). Eight out of 38 pts (21%) who had 100% donor chimerism in CD33 fraction at D100 died versus 3 out of 6 (50%) with less than 100% (p=0.12). There was no significant survival effect of CD3 chimerism (p values=0.68, 0.59). Of the 23 deaths that had occurred at the time of analysis, cause of death was disease progression or relapse in 8 (35%), graft versus host disease in 6 (26%), transplant related (sepsis / engraftment failure) in 5 (22%) and unrelated causes in 4 (17%). Survival analysis: As depicted in the Kaplan Meier curve (figure 1), median overall survival (OS) for pts with 100% donor chimerism in CD33 fraction at day 30 was not reached while for <100% donor chimerism was 16 months (p=0.04). Survival at 3 years for patients with 100% CD33 donor chimerism at D30 was 65% while it was 40% for pts with less than 100%. Also, survival at 3 years for patients with 100% CD33 donor chimerism at day 100 was 75% compared to 50% for patients with less than 100%. Conclusions: In our study, 100% donor chimerism in CD33 fraction is associated with improved survival after alloHSCT for MF compared to pts with less than 100%. Further understanding regarding the reason for this relationship is critical. Larger studies to replicate these results would be imperative to validate these findings. Disclosures Mesa: Incyte: Research Funding; Ariad: Consultancy; Promedior: Research Funding; Novartis: Consultancy; Celgene: Research Funding; Gilead: Research Funding; CTI Biopharma: Research Funding; Galena: Consultancy.

Abstract Background: Acute graft versus host disease (aGVHD) is the leading cause of morbidity and mortality following allogenic hematopoietic cell transplantation (HCT). Corticosteroids are the first line treatment although <50% of patients with severe aGVHD (grades III-IV) achieve durable remissions. Monoclonal antibodies (mAb) are often used as second line agents for steroid refractory aGVHD (SR-aGVHD) (Patriarca et. al.; 2004). However, data regarding their tolerability and efficacy is retrospective and limited. We carried out this study to assess the clinical outcomes related to mAb therapy (Infliximab and Tocilizumab) for SR-aGVHD. Methods: Patients with SR-aGVHD that received therapy with either Infliximab or Tocilizumab between January 2003 and May 2016 were retrospectively identified. Clinical grading of aGVHD was per the Glucksberg criteria (Glucksberg et. al.; 1974). SR-aGVHD was defined as any grade progression within 3 days or failure to achieve at least one grade improvement within 7 days of initiation of systemic steroids. Infliximab and Tocilizumab were administered intravenously at 10mg/kg and 8mg/kg weekly for a total of 4 doses, respectively. Clinical response was evaluated at 4 weeks and 12 weeks post mAb treatment. Complete response (CR) was defined as sustained resolution of all clinical signs of aGVHD; partial response (PR) was defined as overall improvement of 1 or more grades; no response (NR) was defined as neither improvement nor worsening of the overall aGVHD grade. Overall response (OR) was defined as either CR or PR. Overall survival (OS) was calculated from the first day of mAb treatment until death or last available follow up. Results: Forty-three patients (median age 54, range 29-74 years; male 67%) with severe SR- aGVHD were included in the study. Of these, 35 (81%) received Infliximab for a median of 4 (range 1-6) cycles and 8 (19%) received Tocilizumab for a median of 3 (range 1-4) cycles. Both groups were comparable with regards to age, gender, conditioning regimen, graft source, degree of HLA match, ABO blood group, CMV incompatibility, and GVHD prophylaxis regimens. Only differences seen were a higher proportion of unrelated donor (p = 0.004) and cord blood HCT (p = 0.031) in the Tocilizumab group. Twenty (57%) of 35 patients treated with Infliximab and 6 (75%) of 8 patients treated with Tocilizumab had an overall aGVHD grade of IV prior to initiation of mAb therapy (p = 0.44). Organ specific distribution and severity of aGVHD are described in table 1. At 4 weeks post mAb therapy, 17 (40%) patients had an OR, 7 (16%) had no response, and 19 (44%) had died. Twenty-six (60%) patients died at 12 weeks, with OR and no response observed in 9 (21%) and 8 (19%) patients, respectively (table 2). Overall response for Tocilizumab versus Infliximab was comparable at 4 weeks (38% vs. 40%; p = 1.0) and at 12 weeks (38% vs. 17%; p = 0.33). Outcomes per aGVHD grade and gastrointestinal-specific stage at 4 weeks and 12 weeks are shown in figures 1-A and 1-B, with organ specific responses shown in figures 1-C and 1-D, respectively. The estimated median OS was 41 (range 4-3837) days for patients treated with Infliximab and 60 (range 10-756) days for those treated with Tocilizumab (p = 0.48). Disease relapse occurred in 5 (11%) patients treated with Infliximab and in none (0%) treated with Tocilizumab (p = 0.56). Thirty-four (79%) patients had infectious complications during and up to one month after mAb therapy. These included 31 (72%) patients with bacterial blood stream infection and 10 (23%) with invasive fungal infections. Overall, infectious complications were comparable (Infliximab - 83% vs. Tocilizumab - 63%; p = 0.33). CMV reactivation occurred in 11 (31%) and in 2 (25%) patients who were treated with Infliximab and Tocilizumab, respectively (p = 1.0). Given the retrospective nature of the study and the concomitant presence of aGVHD, it was difficult to attribute and grade gastrointestinal and hepatobiliary side effects. Conclusions: The use of anti-inflammatory monoclonal antibody therapy in patients with steroid refractory acute GVHD is associated with significant infectious complications (~80%) and poor response rates (~20% at 12 weeks). Current data, limited by a small sample size, does not show any advantages of using Tocilizumab over Infliximab or vice versa. Prospective clinical trials addressing this question are needed. Disclosures No relevant conflicts of interest to declare.

Abstract Abstract 3138 Background: Several recent reports have suggested that doxycycline can inhibit amyloid fibril formation in different in vitro and in vivo model systems. Doxycycline is the antibiotic of choice for infectious disease prophylaxis in patients with penicillin allergy, following autologous peripheral blood stem cell transplantation for various hematological malignancies. We examined the outcome of patients with light chain amyloidosis (AL) undergoing autologous stem cell transplantation to study the impact of doxycycline used as antibacterial prophylaxis. Patients and methods: We studied 455 patients who underwent autologous stem cell transplant (ASCT) for AL between March 1996 and December 2011. We excluded 44 patients who died of transplant related complications or did not survive beyond 100 days after transplant. Patient records were reviewed to ascertain the prophylactic antibiotic used. Survival was estimated using Kaplan Meier method and the survival curves were compared using log-rank test. Cox proportional hazard model was used to estimate the prognostic impact of different variables. Results: The median age of the patients was 58 years (range, 26–74); 290 (67%) were male. The median estimated follow up for the entire cohort was 73 months (95% CI; 66, 79) and 314 (69%) were alive at last follow up. Doxycycline was used a prophylaxis in 106 (23%) of the patients, with most of the remaining receiving penicillin. The usual reason for using doxycycline was a history of penicillin allergy. Hematological response to transplant occurred in 377 (87%) patients, and there was no significant difference between patients receiving doxycycline prophylaxis compared with the rest. The median OS for the entire cohort was 161 months (95% CI; 101, NR). The median OS for those receiving doxycycline prophylaxis was not reached compared with 113 months for the rest (P=0.09). Looking specifically at those patients with a hematological response, the median OS was not reached for the doxycycline group compared with 161 months for the rest (P=0.04, figure). There was no difference in the OS between the groups among those with no hematological response. The impact of the prophylaxis was independent of the number of organs involved as well as organ response to SCT. Conclusions: The results of the current study appear to demonstrate a survival advantage for patients with AL who receives doxycycline prophylaxis, in the setting of hematological response from SCT. The results are consistent with the data regarding the effect of doxycycline on amyloid fibril formation. These initial findings should form the basis of clinical exploration of doxycycline as an adjunctive therapy in patients receiving other standard therapies for AL. Such a study can further clarify if use of doxycycline for longer duration can be of additional benefit. Disclosures: Kumar: Cephalon: Research Funding; Novartis: Research Funding; Millennium: Research Funding; Celgene: Research Funding; Merck: Consultancy, Honoraria; Genzyme: Research Funding.

Abstract Abstract 1476 Background: Monosomal Karyotype (MK) is defined as the presence of two or more autosomal monosomies or one autosomal monosomy and one structural abnormality. MK has been found to be an independent poor prognostic factor in myeloid diseases (Patnaik et al, Leukemia 2011, Haferlach et al, Blood 2012) even in the setting of allogeneic stem cell transplantation (Fang et al, Blood 2011). The prognostic relevance of MK in Acute Lymphoblastic Leukemia (ALL) is unknown. Absolute lymphocyte count (ALC) at diagnosis, on the other hand, has been shown to be prognostic in a variety of lymphoproliferative disorders (Porrata et al, Leukemia 2010). However, the prognosis of ALC at diagnosis in ALL is undetermined Methods: This is a retrospective analysis of the Mayo Clinic leukemia database (1998–2010). The study was approved by the Institutional Review Board. Outcomes analyzed included overall survival (OS), leukemia free survival (LFS) and relapse rate. Clinical characteristics, cytogenetics, therapy and outcomes of patients with Philadelphia negative ALL (Ph-negative ALL) were analyzed. Cytogenetics were classified as follows: standard risk [hyperdiploidy], intermediate risk [Normal, del(11q)-not MLL, del(6q), del(17p), del(9p), del(12p), del(13q), t(14q32), t(10;14), low hyperdiploidy, others], high risk [-7, del(7p), +8, MLL translocations, t(1;19), t(17;19), t(5;14)], and very high [t(4;11), t(8;14), complex (≥5 abnormalities), hypodiploidy, triploidy] (Pullarkat et, Blood 2008). Multivariate analysis was performed using Cox Regression Model. Results: Between 1998 and 2010, a total of 175 consecutive patients with ALL were identified. Of these, 112 (64%) had Ph-negative ALL. The median age was 39.5 (16–88) years and 74 were male (66%). The majority of cases were B-ALL (78 patients, 69%). At presentation, the median hemoglobin was 10 (4.1–18.5) g/dL, platelet count was 61 (3–523) ×10(9)/L, WBC was 7.2 (0.8–377) ×10(9)/L and ALC was 1.9 (0–69.0) ×10(9)/L. The ALC was > 1000 in 75 (71%) patients. Cytogenetics risk categories were as follows: standard risk in 5 (4.4%), intermediate risk in 70 (62.5%), high risk in 8 (7.1%) and very high risk in 29 (25.9%) patients. Twenty-two patients (20.9%) presented with extranodal disease (CNS disease in 13 patients, 11.6%). Six patients (5.4%) had prior exposure to chemotherapy. Treatment involved allogeneic stem cell transplantation (SCT) in 34 (30.4%) patients. The median OS for the whole cohort was 24 (0–206) months and LFS was 18 (0–193) months. Forty four patients (39.3%) relapsed after achieving initial remission with a median time to relapse of 15 (2–73) months In a univariate analysis, low platelet count at diagnosis, poor ECOG performance status (PS), and high or very high risk cytogenetics risk categories were associated with inferior OS. ALC at diagnosis did not impact OS or LFS. On a multivariate analysis, high/very high risk cytogenetics, low platelet counts and poor ECOG PS were independent predictors of inferior outcomes. Nineteen patients (16.9%) had a MK. Of these, 16 (84.2%) fell in the very high risk cytogenetics category regardless of MK status. Three patients (1.6%) presented with extramedullary disease and six (3.2%) underwent SCT. The median OS of these 19 patients was 15 (1–73) months. While MK was associated with inferior LFS and a trend towards worse OS, this was not significant on a multivariate model that included cytogenetic risk categories, thrombocytopenia and the ECOG PS. Conclusions: Our study demonstrates that cytogenetics risk stratification, thrombocytopenia and ECOG performance status are independent prognostic factors in ALL. MK and ALC at diagnosis had no prognostic significance. Disclosures: No relevant conflicts of interest to declare.

Abstract Graft-versus-host disease (GVHD), the primary cause of non-relapse mortality (NRM) following allogeneic hematopoietic stem cell transplantation, does not always respond to treatment with high dose systemic corticosteroids. We have recently shown that a combination of three biomarkers (TNFR1, ST2, and REG3α) measured at onset of GVHD can predict day 28 response to treatment and 6-month NRM (Levine, Lancet Haem, 2015). Our goal in the current study was to determine if the same biomarker-based Ann Arbor GVHD algorithm can alsopredict treatment response andmortality whenapplied after one week of systemic corticosteroid treatment. The study population consisted of 378 patients (pts) with acute GVHD from 11 centers in the Mount Sinai Acute GVHD International Consortium. All pts were treated with systemic steroids and provided a plasma or serum sample obtained after one week of treatment (±3 days). The median starting dose of systemic steroids for Grade II-IV GVHD was 2.0 mg/kg/day and for Grade I was 1.0 mg/kg/day, after which treatment varied. Patients were divided into test (n=236) and validation (n=142) cohorts. We applied the Ann Arbor GVHD algorithm to concentrations of TNFR1, ST2, and REG3α measured after one week of treatment to generate a predicted probability of 6-month NRM, which we term the treatment score (TS). We employed unsupervised k-medoidclustering to partition TS values from the test cohort into two groups (high and low). This unbiased approach identified a high score group made up of 25% of pts (n=58) in the test cohort. We observed that the day 28 response rate (complete, CR + partial, PR) was significantly lower in pts with high scores compared to low scores in the test cohort (24% vs 65%, p<0.0001) (Fig 1A). Analysis of the validation cohort using the same TS definitions showed similar differences in response rates (22% vs 61%, p<0.0001) (Fig 1B). Further, nearly four times as many pts with high scores in both cohorts died within 6 months from non-relapse causes compared to pts with low scores (test: 57% vs 17%, p<0.0001; validation: 57% vs 14%, p<0.0001) (Fig 1C/D). As expected, the majority of non-relapse deaths in pts treated for GVHD were directly attributable to GVHD (test: 95%; validation: 89%). Relapse rates for high and low score pts were similar (data not shown), and thus pts with a high TS experienced significantly worse overall survival in both cohorts (test: 37% vs 72%, p<0.0001; validation: 38% vs 79%, p<0.0001) (Fig 1E/F). Approximately half of the pts in each cohort (test: 48%; validation: 44%) responded (CR+PR) to the first week of steroids and these ptshad significantly lower 6-month NRM than non-responders (NR) (test: 17% vs 36%, p=0.0002; validation: 13% vs 36%, p=0.0014). Yet the TS continued to stratify mortality risk independently of clinical response. In the test cohort, pts with a high score comprised 16% of all early responders and experienced more than twice the NRM of early responders with a low score (33% vs 13%, p=0.022) (Fig 2A). Conversely, test cohort pts who did not respond by day 7, but had a low score, fared much better than non-responders with a high score (NRM 21% vs 68%, p<0.0001) (Fig 2B). Two thirds of early non-responders comprised this more favorable group. These highly significant results reproduced in the independent validation cohort in similar proportions (CR+PR: 45% vs 6%, p=0.0003; NR: 61% vs 22%, p=0.0001) (Fig 2C/D). Finally, a subset analysis revealed that pts classified as NR after one week of steroids due to isolated, yet persistent, grade I skin GVHD (24/378, 6%) overwhelmingly had low treatment scores (22/24, 92%) and experienced rates of NRM (9%) comparable to responders with low scores, thus forming a distinct, albeit small, subset of pts with non-responsive GVHD that fares particularly well (Fig 3). In conclusion, a treatment score based on three GVHD biomarkers measured after one week of steroids stratifies pts into two groups with distinct risks for treatment failure and 6-month NRM. It is particularly noteworthy that the TS identifies two subsets of pts with steroid refractory (SR) GVHD who have highly different outcomes (Fig 2B/D). The much larger group, approximately two thirds of all SR pts, may not need the same degree of treatment escalation as is traditional for clinical non-response, and thus overtreatment might be avoided. Because the TSis measured at a common decision making time point, it may prove useful to guide risk-adapted therapy. Disclosures Mielke: Novartis: Consultancy; MSD: Consultancy, Other: Travel grants; Celgene: Other: Travel grants, Speakers Bureau; Gilead: Other: Travel grants; JAZZ Pharma: Speakers Bureau. Kroeger:Novartis: Honoraria, Research Funding. Chen:Incyte Corporation: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Research Funding. Jagasia:Therakos: Consultancy. Kitko:Therakos: Honoraria, Speakers Bureau. Ferrara:Viracor: Patents & Royalties: GVHD biomarker patent. Levine:Viracor: Patents & Royalties: GVHD biomarker patent.

Abstract Background: The presence of circulating plasma cells (CPCs) is associated with an adverse prognosis in multiple myeloma along the entire spectrum of disease. However, the impact of CPCs prior to autologous stem cell transplantation (ASCT) has not been defined in the era of novel agents. The objective of this study is to assess the impact of the presence and number of CPCs before transplant using 6-color multiparameter flow cytometry (MFC). We also explored the additional prognostic implications of CPCs over the current paradigm for risk stratification at transplant, including high-risk (HR) cytogenetics and disease status at transplant by the IMWG criteria. Methods: A total of 1113 consecutive patients transplanted between 2007 and 2015 in Mayo Clinic were included in the study. Flow-cytometry of peripheral blood to identify clonal CPCs is routinely performed in all patients before ASCT in Mayo Clinic, Rochester. The mononuclear cells from peripheral blood samples are isolated by Ficoll gradient and subsequently stained with antibodies to CD19, CD38, CD45, CD138 and cytoplasmic kappa (κ) and lambda (λ) immunoglobulin light chains. Clonality is assessed by light chain restriction (κ:λ expression ratio of 4:1 [κ restricted] or <1:2 [λ restricted]). The target for collection is >150,000 cellular events. For samples where less than 150,000 clonal events are examined, the number of final clonal events is adjusted to 150,000 events. HR cytogenetics by fluorescence in situ hybridization (FISH) on bone marrow (BM) plasma cells was defined by one of the following abnormalities: t(4;14), del(17p), t(14;16), t(14;20) or +1q, detected at any time point from diagnosis to transplant. Patients who had insufficient plasma cells for FISH analysis in BM specimens were not included in the denominator to calculate the percentage of patients with HR cytogenetics. The primary end-points of this study were post-transplant response, PFS and OS. Result: CPCs were detected in 238 out of 1113 (21.4%) patients, with the median number of CPCs being 82 (range, 1-102381) per 150,000 events. The median age of patients at transplant was 62 years. A total of 1097 (99%) patients had received novel agent based induction therapy with PIs and IMiDs, including 458 (41%) patients who had received both PIs and IMiDs. 401 (36%) patients had received post-transplant maintenance or consolidation therapy. The frequency of t(4;14) in BMPCs was significantly higher in patients with CPCs compared to those without [15.2 vs 7.0% for t(4;14); P<0.001]. The median follow-up from transplant for survivors was 45 months. The 5-year OS rate in patients with and without CPCs was 34% (95% CI, 27-42) and 70% (95% CI, 66-74) respectively (P<0.001). After exploring several cut-offs for the number of CPCs per 150,000 events, we chose a simple pre-transplant risk stratification model: No CPCs (n=874; 78.5%), 0<CPCs≤400 (n=188; 16.9%) and CPCs>400 (n=51; 4.6%). The number of patients achieving stringent complete response post-transplant in groups with no CPCs, 0<CPCs≤400 and CPCs>400 was 310 (36%), 31 (16%) and 3 (6%) respectively (P<0.001). The median PFS in the 3 groups was 27 months (95% CI, 25-30), 15 months (95% CI, 13-18) and 6 months (95% CI, 4-10) respectively (P<0.001) and 5-year OS rates were 70% (95% CI, 66-74), 42% (95% CI, 34-51) and 12% (95% CI, 5-26) respectively (P<0.001). Kaplan-Meier curves for PFS and OS are depicted in Figure I (A and B). In a multivariate model (Table I), the groups with 0<CPCs≤400 and CPCs>400 had an increased risk of death, independent of the presence of HR cytogenetics and disease status at transplant. Conclusion: Our study shows the strong negative prognostic impact of CPCs prior to transplant on post-transplant response and survival in MM in the era of novel agents. The proposed risk stratification model can be easily employed with simple equipment and should be routinely incorporated in the pre-transplant workup. Detailed epigenomic, genomic and transcriptomic analysis of CPCs is urgently needed to uncover the biological basis of resistance to both high-dose cytotoxic therapy and novel agents and identify potential avenues of targeted therapy against CPCs. Disclosures Kumar: Onyx: Consultancy, Research Funding; Kesios: Consultancy; Celgene: Consultancy, Research Funding; Glycomimetics: Consultancy; AbbVie: Research Funding; BMS: Consultancy; Sanofi: Consultancy, Research Funding; Skyline: Honoraria, Membership on an entity's Board of Directors or advisory committees; Millennium: Consultancy, Research Funding; Janssen: Consultancy, Research Funding; Array BioPharma: Consultancy, Research Funding; Noxxon Pharma: Consultancy, Research Funding. Dispenzieri:Takeda: Membership on an entity's Board of Directors or advisory committees, Research Funding; Alnylam: Research Funding; GSK: Membership on an entity's Board of Directors or advisory committees; pfizer: Research Funding; Prothena: Membership on an entity's Board of Directors or advisory committees; Celgene: Research Funding; Jannsen: Research Funding. Kapoor:Celgene: Research Funding; Amgen: Research Funding; Takeda: Research Funding. Gertz:Sandoz Inc: Honoraria; NCI Frederick: Honoraria; Celgene: Honoraria; Alnylam Pharmaceuticals: Research Funding; GSK: Honoraria; Novartis: Research Funding; Research to Practice: Honoraria, Speakers Bureau; Med Learning Group: Honoraria, Speakers Bureau; Ionis: Research Funding; Prothena Therapeutics: Research Funding; Annexon Biosciences: Research Funding.

Abstract Background: Autologous stem cell transplantation is an integral part of myeloma therapy for patients who are able to undergo the treatment. While high dose melphalan has remained the typical conditioning regimen for ASCT in MM, recently there have been efforts to enhance the conditioning therapy by adding newer drugs to melphalan. Addition of bortezomib as well as carfilzomib have been attempted in phase 2 trials. Previous studies have shown that the combination of melphalan and total body irradiation (TBI) is an effective conditioning regimen. Pre-clinical studies have shown that bortezomib can sensitize MM cells to radiation, and based on this finding, we designed a clinical trial to examine the feasibility of combining low dose TBI with a combination of melphalan and bortezomib. Patients and Methods: The primary goal of the phase 1 study was to determine the maximally tolerated dose (MTD) of bortezomib that can be added to high dose melphalan and low dose TBI as part of conditioning chemotherapy in patients undergoing an ASCT for MM. The secondary goals were to examine the toxicities associated with addition of bortezomib to high dose melphalan and TBI in patients with MM and to determine the progression free rate at 1 and 2 years. Patients eligible to receive full dose melphalan conditioning regimen for ASCT were included as long as they had no more than 2 prior regimens and had not received a prior transplant. An accelerated design that was later converted to a standard 3+3 cohort design was used for dose escalation. Three patients were treated at a given dose level combination and observed for at least 36 days to assess toxicity. Melphalan 80 mg/m2 was given days -4, -3, with bortezomib at increasing doses given on day -5, -2 along with TBI of 200 cGY given on the same days of bortezomib, timed after bortezomib administration. Stem cells were infused day 0. Results: Eleven patients were enrolled; 6 were males, and the median age was 60 years. Median time from diagnosis was 5.4 months (range 3.4-7.0). Four dose levels were explored with increasing doses of bortezomib (0.7 mg/m2 to 1.6 mg/m2). No dose limiting toxicities were observed. The dose levels and the best response after ASCT are as shown in the Table. The overall response rate was 100%, including 7/11 with a CR or sCR. With a median follow-up of 12.5 months, two patients have progressed; median OS was not reached. Toxicity was mostly hematologic, with other AEs being grade 3 or less and attributable to the conditioning therapy. All patients engrafted their counts adequately. Conclusion: The combination of melphalan, bortezomib, and low dose TBI is a safe conditioning regimen in patients with MM with good efficacy. The regimen should be further examined in the phase 2 setting. Table Table. Disclosures Kapoor: Celgene: Research Funding; Amgen: Research Funding; Takeda: Research Funding. Kumar:Noxxon: Consultancy, Honoraria; Celgene: Consultancy, Research Funding; Sanofi: Consultancy, Research Funding; Takeda: Consultancy, Research Funding; Amgen: Consultancy, Research Funding; BMS: Consultancy; AbbVie: Research Funding; Janssen: Research Funding; Skyline: Consultancy, Honoraria.

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.