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Abstract Background: Patients with polycythemia vera (PV) have an increased symptom burden (eg, fatigue, pruritus, and splenomegaly-related symptoms) and an increased risk of mortality compared with the general population, often resulting from thrombotic events, disease transformation to myelofibrosis, or secondary malignancies. There are limited data regarding PV burden and treatment patterns in a contemporary, real-world US setting. REVEAL is an ongoing observational study being conducted to describe contemporary demographics, burden of disease, clinical management, patient-reported outcomes, and healthcare resource utilization among patients with PV in the US. The objective of this assessment is to describe the clinical characteristics at enrollment among patients currently enrolled in REVEAL (enrollment from July 22, 2014 to June 9, 2015). Methods: REVEAL is a multicenter, noninterventional, nonrandomized, prospective, observational study. Eligible patients are ≥18 years of age with a PV diagnosis and currently under active management by a physician in the US. Data regarding disease and clinical characteristics, patient-reported outcomes, and health resource utilization are being collected at usual-care visits over a planned 36-month observation period. Analyses of these preliminary data were descriptive. Results: At data cutoff, 865 patients were enrolled (total planned enrollment, n=2000) from 174 sites (academic, n=27; community, n=147). Median (range) age at enrollment was 67 (22-95) years, 55.5% were male, 89.5% were white, and 45.4% had a history of smoking. Most patients (99.4%) had health insurance, including Medicare (56.0%), PPO (24.3%), or HMO (11.6%). Fifty-two percent were retired, 29.6% were employed, and 4.5% were unable to work or disabled. A total of 40.2% of patients completed a college/graduate degree, 19.9% had some college, and 32.5% completed high school or the equivalent. Documented major World Health Organization diagnostic criteria included JAK2V617F mutation in 50.9% of patients, elevated hemoglobin in 52.3%, and red cell mass in 5.5%. A bone marrow biopsy was conducted in 24.0% of patients, approximately half of whom (52.4% of the 24.0%) had trilineage myeloproliferation. Erythropoietin levels were abnormal in 19.7% of patients. Approximately half (46.6%) of patients had physician-reported PV-related symptoms at diagnosis, most frequently fatigue (25.2%) and pruritus (14.0%). At enrollment, median disease duration was 52.6 months; 42.3% of patients were diagnosed ≥5 years before enrollment. The most common comorbidities were hypertension (51.3%), obesity (14.2%), dyspnea (13.4%), myalgia (11.2%), and diabetes mellitus (11.1%). Mean hematocrit was 44.9%, hemoglobin was 14.5 g/dL, white blood cell count was 11.4×109/L, platelet count was 363.7×109/L, and absolute neutrophil count was 363.7×109/L. Twenty-one percent of patients had a history of thrombotic events, with 13.1% and 8.6% of patients experiencing ≥1 venous or arterial thromboembolic event, respectively. Of the 261 reported thrombotic events, 43.7% occurred after diagnosis of PV. The most common PV symptoms recorded at enrollment (using the Myeloproliferative Neoplasm Symptom Assessment Form) were fatigue (37.1%), pruritus (24.0%), headache (18.6%), insomnia (17.0%), dizziness (13.2%), bone pain (10.5%), and blurred vision (7.9%); 19.7% of 518 evaluable patients had palpable splenomegaly. Fewer than half of patients were receiving aspirin at enrollment (47.7%). The most common PV treatments ± aspirin were phlebotomy (PBT; 63.5%), hydroxyurea (HU; 42.2%), watchful waiting (5.3%), and ruxolitinib (3.1%); 23.0% of patients received PBT + HU. Conclusion: The REVEAL study is unique in that it captures data from both academic and community centers, and therefore includes a broader segment of the PV population typically not described in the literature. REVEAL can provide novel insights into questions related to the contemporary demographics of PV, practice patterns regarding diagnosis and therapy, and the real-world burden of PV and its impact on patients' quality of life and work productivity. Preliminary descriptive data from this early subset of patients suggest that a high proportion of patients report having PV-related symptoms at diagnosis, fewer patients are treated with aspirin than expected, and that thromboembolic event rates remain high after diagnosis. Disclosures Stein: Incyte Corporation: Consultancy, Membership on an entity's Board of Directors or advisory committees. Moliterno:Incyte Corporation: Membership on an entity's Board of Directors or advisory committees. Boccia:Incyte Corporation: Honoraria. Naim:Incyte Corporation: Employment, Equity Ownership. Cordaro:Incyte Corporation: Employment, Equity Ownership. Peng:Incyte Corporation: Employment, Equity Ownership. Sun:Incyte Corporation: Employment, Equity Ownership. Parasuraman:Incyte Corporation: Employment, Equity Ownership. Mesa:Promedior: Research Funding; Novartis Pharmaceuticals Corporation: Consultancy; NS Pharma: Research Funding; CTI Biopharma: Research Funding; Gilead: Research Funding; Pfizer: Research Funding; Incyte Corporation: Research Funding; Genentech: Research Funding.

Abstract Abstract 230 The prognosis for patients (pts) with acute myeloid leukemia (AML) who are aged 60 years or older at the time of initial diagnosis is poor. Even for pts achieving a first complete remission (CR1), prospects for long-term survival are poor due to the very high risk of relapse. Conventional myeloablative conditioning followed by allogeneic blood or marrow transplantation is associated with significantly less relapse compared with conventional chemotherapy when performed in younger pts with AML in CR1. However, the toxicity of this approach in older pts is prohibitive. A reduced intensity conditioning (RIC) regimen may mitigate the risk of early toxicity and while early results in older AML pts have been encouraging and suggest disease free survival (DFS) rates above 30% at 3 yrs (Farag et al, Biol Blood Marrow Transplant 2011), most data are retrospective and pts have not been treated uniformly. We therefore sought to determine the effectiveness of a uniform RIC regimen given to older pts with AML in CR1 on a prospective multi-center phase II trial conducted by the Alliance (formerly Cancer and Leukemia Group B (CALGB)) and the Blood and Marrow Transplant Clinical Trials Network (BMT CTN). The study, activated in 2004, was initially limited to recipients of a matched related donor (MRD) graft but was amended in 2006 to include matched unrelated donor grafts (URD). The primary endpoint of the study was 2-year DFS. We hypothesized that DFS at 2-years would exceed 20% and powered the study to detect a 2-year DFS probability of 35% for URD recipients. We focused the primary analysis on URD recipients since the majority of older pts require an URD graft. Eligible pts were from 60–74 years old inclusive, had AML in CR1 following induction chemotherapy, availability of a 6/6 MRD or 8/8 URD, and absence of significant end-organ damage prior to transplantation. Adverse events (AE) were initially recorded according to NCI-CTCAE v3.0, amended to v4.0 in 10/2010. Accrual was completed in 12/2011. 132 pts were registered at 21 centers and 123 transplanted (MRD (47%); URD (53%). All donor grafts were mobilized and collected following G-CSF (PBSC). The median age of pts was 65 (range 60–74) and 76 pts (62%) were male. At diagnosis, 67% had an intermediate risk karyotype, 20% adverse risk, <1% favorable, and in 11% data were missing. More than 90% achieved CR following standard “7+3” based induction. CR1 was achieved after 1 (59%) or 2 (41%) induction cycles. Consolidation therapy was administered for one (50%) or two (24%) cycles and 17% received no consolidation with data missing in 9%. All but the initial 8 MRD recipients (who received fludarabine and busulfan alone) were conditioned with the same regimen containing fludarabine (30mg/m2/day × 5), busulfan (6.4mg/kg IV total dose), and antithymocyte globulin (ATG; thymoglobulin) (7.5mg/kg total dose). Only one case of primary graft failure was reported. With a median follow-up of 3.3 yrs, the results in the 123 transplanted pts are depicted below: Event Cumulative incidence at 100 days* or 2yrs† 95% CI Acute GVHD 2-4 9.4%* 4.1–15% Acute GVHD 3-4 3.4%* 1.2–6.7% Chronic GVHD 26%† 17–34% Relapse 47%† 37–57% Treatment related mortality (TRM) 14%† 7.2–21% Event Probability at 2 yrs 95% CI DFS 39% 30–50% DFS URD only 38% 26–55% Overall survival (all pts) 46% 36–57% The rates of both acute and chronic GVHD as well as TRM were relatively low. There were 81 grade 3–5 non-hematologic AE recorded, including 7 grade 5 (4 infections, 1 each cardiac, pulmonary, and second malignancy). Relapse was the most common cause of death. In conclusion, the results of this first prospective US cooperative group trial conducted in a homogeneously treated group of older AML patients in CR1 demonstrate the feasibility and effectiveness of RIC allografting using MRD or URD PBSC grafts. DFS appears better following a RIC allograft compared to results achieved historically after conventional therapies, warranting prospective comparison in pts with contemporary cytogenetic and molecular disease characterization. Future research should also focus on preventing disease relapse after RIC allografting in this population. Disclosures: Devine: Sanofi: Honoraria, Research Funding. Off Label Use: Antithymocyte globulin for GVHD prophylaxis is included in the abstract. Vij:Millennium: Speakers Bureau. Shea:Otsuka: Research Funding.

Abstract Abstract 2910 Poster Board II-886 Background: Polycythemia vera (PV) and primary myelofibrosis (PMF) are stem cell-derived myeloproliferative neoplasms characterized clinically by increased red cell volume and bone marrow fibrosis, respectively. Phlebotomy is the cornerstone of treatment in PV whereas hydroxyurea has been the traditional drug of choice in both PV and PMF. Over the last 20 years, several new treatment approaches have been introduced and promoted (e.g. interferon-alpha, anagrelide, thalidomide, allogeneic stem cell transplantation) but their benefit in terms of survival has not been confirmed in controlled studies. Methods: Study patients were recruited form the Mayo Clinic database for myeloproliferative neoplasms. Diagnosis was based on 2001 WHO criteria. Follow-up information was updated in July, 2009. In order to assess changes in survival over time, patients were stratified into two groups by year-of-diagnosis: 1970-1990 and 1991-2005. Survival analysis was performed by the Kaplan-Meier method and comparisons made by the log-rank test. Cox regression model was used for multivariable analysis. Results: 652 patients were studied, including 314 with PMF (median age 57 years, range 18-88; 193 males) and 338 with PV (median age 63 years, range 18-93; 183 males). Overall median survivals were 6.5 years for PMF and 12.2 years for PV (p<0.0001); ten- and twenty-year survival rates were 37% and 13% in PMF and 60% and 18% in PV (Figure). Both the International Prognostic Scoring System for PMF (IPSS; Cervantes et al. Blood 2009;113:2895) and the age/leukocyte count-based PSS for PV (Gangat et al. BJH 2007;138:354) were validated in the current series of patients. Considering all patients, there was no significant difference in survival when either PMF (p=0.91) or PV (p=0.73) patients were stratified according to year-of-diagnosis (Figure); median survivals were 4.7 and 6.6 years in PMF patients diagnosed 1970-1990 (n=54) and 1991-2005 (n=260), respectively; the corresponding median survival figures for PV were 11.8 (n=170) and 12.2 (n=168) years. These results did not change when adjusted for age and sex and, in PV, for age/leukocyte count-based PSS. In PMF, however, borderline significance (p=0.05) was noted when IPSS scores were introduced into the Cox model with further analysis showing improved survival in Int-2/high risk patients with PMF diagnosed after 1990 (p=0.01). Conclusion: The current study provides mature survival data in PMF and PV using large cohorts of consecutive patients seen at a single institution. Although median survival is significantly better in PV compared to PMF, their survival curves converge after 20 years of follow-up, underscoring the poor long-term prognosis in PV patients. The study also suggests improved survival for high/intermediate-2 risk PMF in recent years. Disclosures: Off Label Use: hydroxyurea use in myelofibrosis.

Abstract Introduction Erlotinib is an epidermal growth factor receptor small-molecule inhibitor and is FDA approved for the treatment of lung and pancreatic cancers. In preclinical study, in vitro colony culture assays revealed that erlotinib at micro-molar concentrations effectively suppressed the growth and expansion of Polycythemia Vera (PV) hematopoietic progenitor cells while having little effect on normal cells. Several JAK inhibitors are being studied for the management of PV, one of which has been approved for the treatment of myelofibrosis (ruxolitinib). Aim To study the clinical effect of erlotinib in pts diagnosed with JAK2V617F + PV. Methods We conducted a single arm, prospective phase II study at the University of Oklahoma and the Oklahoma City VA hospitals in pts with WHO defined JAK-2 V617F positive PV from June 2010 to August 2012. Appropriate IRB approval was obtained in accordance with Hilsinki declaration. Pts had to be requiring phlebotomy. Toxicity was assessed by treating physicians using NCI version 4. Dose modification for erlotinib was done using label recommendations. Results Five Caucasian pts were enrolled (3 (60%) males, with median age at enrollment of 63 years, range 26-79). Pts had pretreatment median hemoglobin14.4 g/dL (10.4 -19.2 g/dL), median platelet count 511 x109 (424-681 x109), median white blood cell (WBC) 14.4 x109(7.8- 18.3 x109). Three pts had splenomegaly prior to treatment. Median number of prior pharmacologic treatments (hydroxyurea, anagralide or interferon) was 1, range 0-2. Pts were given erlotinib 150 mg orally daily for 16 weeks: responders (phlebotomy free or decrease in spleen size) were allowed to continue a total of 1 year of treatment, while non-responders were taken off the study. Three (60%) patients received therapy for 16 weeks and did not achieve hematological response or improvement in spleen size. Two (40%) pts were taken off the study after 2 doses secondary to severe toxicities (grade 3 colitis in 1 case, and grade 3 facial rash in 1case). No therapy continued beyond 16 weeks (due to toxicity or lack of response). All pts in the study developed rash (grade 1 – 3) and diarrhea (grade 1 – 2). Three pts developed mucositis (see Table 1). No death was observed during the study and follow up period (median follow up was 23 months, range 12-37 months). Study was closed due to lack of efficacy. Conclusions Despite in vitro efficacy of erlotinib as potent inhibitor of JAK-2 activity, erlotinib is not effective in pts with JAK-2 V617F positive PV with poor toxicity profile. Poor accrual was related to potential toxicity of erlotinib compared to alternative treatments in view of lack of clinical efficacy. Disclosures: No relevant conflicts of interest to declare.

Abstract Introduction Patients with masked polycythemia vera (mPV) present with hemoglobin (HB) values borderline inferior to those required by the World Health Organization (WHO) diagnostic criteria (HB >16.5g% and >18.5 g% in female and male respectively) but are suspected to have PV for presenting clinico-hematological features. The diagnostic HB values required by the WHO guidelines have been considered surrogate of increased red cell mass (RCM). However, in both males and females HB values are not always equal to an absolute erythrocytosis and conversely a HB concentration below the required cut off level could be associated with an increased red cell mass. We believe that bone marrow (BM) morphology may play an important role in differentiating PV from other MPN entities and reactive changes. In this study we investigated JAK2V617/Exon12-positive patients showing BM features characteristic for PV and classified as mPV or overt PV according to their hemoglobin levels and evaluated their respective outcomes including thrombosis, progression to myelofibrosis (MF), acute leukemia (AL) and overall survival with the purpose to support the diagnosis of PV also in patients presenting with lower HB levels than required by WHO criteria. Materials and Methods A clinicopathological database of patients who were diagnosed and treated for PV was created by clinicians and hematopathologists from seven international centers of excellence for MPNs. Eligibility criteria for entry included the presence of JAK2V617F (or Exon12) mutation, EPO measurement, no evidence of subnormal ferritin levels and the availability of representative, treatment-naive BM biopsies (hematoxylin-eosin staining and silver impregnation after Gomori or Gordon-Sweet). All BM biopsies were centrally re-reviewed by one of the authors (J.T.) who was completely blinded to outcome data. In both mPV and overt PV patients, phlebotomy and cytoreductive therapy were used with the same frequency (p=0.101). Results and Discussion Among 397 mutated patients, with PV BM morphology as defined by WHO, 257 (65%) met the full WHO-2008 criteria. The remaining 140 patients (35%) were classified as mPV for levels of HB at diagnosis, ranging from 16.5 to 18.5 g/dL in men and from 15.0 to 16.5 g/dL in women, and frequent presence of subnormal EPO levels (65%). At baseline, mPV patients were more males, had more previous arterial thrombosis and presented more frequently with platelet counts exceeding the required level of WHO-defined ET (450 x 109/L), often mimicking clinically this entity at onset. After a median follow-up of 3.8 (0-29.8) and 4.5 (0-21.1) years in mPV and overt PV, respectively, time to the first thrombotic event was superimposable in the two groups while time to progression to MF and AL was significantly different .These combined events were recorded in 10% of mPV and 5.8% of overt PV, corresponding to an annual rate of 1.60 % pts/year in mPV and 0.97 % pts/year in overt PV, respectively (p=0.010). In addition, an inferior overall survival was documented in mPV patients in comparison with overt PV (p=0.011). The annual rate of death in mPV was almost twice that of overt PV, mainly due to an excess of hematological transformation (overt MF and AL). Multivariable analysis identified age older than 65 years (hazard ratio (HR) 6.63, P<.0001), WBC >10 x109/L (HR 2.99, P=.005) and diagnosis of mPV (HR 2.38, P=.036) as independent risk factors for survival in these patients. These results show that in JAK2 mutated patients with borderline HB levels, BM features may be a valid support to confirm the suspicion of PV diagnosis. Of interest, recent data demonstrated that all patients with increased RCM also had BM morphology typical of PV. It is tempting to speculate that the clinico-hematologic phenotype of mPV may represent an early stage of a JAK2 mutated MPN, presenting as a variant of PV, with a more rapid progression to MF and AL. The recognition of these early PV patients has an important clinical impact since, in spite of not meeting the full WHO criteria, mPV share the same vascular risk as overt PV. In conclusion, these data suggest that mPV is not necessarily only an early form of classical PV but a distinct entity with disease outcomes akin to primary myelofibrosis. Disclosures: No relevant conflicts of interest to declare.

Abstract Background : Polycythemia vera (PV) is a myeloproliferative neoplasm driven by JAK/STAT activation and is associated with erythrocytosis and a broad symptom burden that may negatively impact patient quality of life (QoL). Hydroxyurea (HU) is often used as first-line therapy for high-risk patients but may not effectively control or reduce symptom burden. RESPONSE is a phase III trial comparing ruxolitinib (RUX) with best available therapy (BAT) in patients with PV who were intolerant of or resistant to HU according to modified European LeukemiaNet (ELN) criteria. The primary study endpoint (a composite of hematocrit control and ≥35% spleen volume reduction at Week 32) was achieved by 21% of patients in the RUX arm vs 1% in the BAT arm (P<0.0001); 77% of patients in the RUX arm achieved at least one component of the primary endpoint. The current analysis was conducted to evaluate the effect of RUX on PV-related symptoms and QoL measures in the RESPONSE trial. Methods : Patients with PV aged ≥18 years, resistant to or intolerant of HU (modified ELN criteria) with splenomegaly, and who required phlebotomy for hematocrit control were randomized 1:1 to receive open-label RUX 10 mg twice daily (BID) or BAT (administered based on investigator judgment). Dose adjustments were permitted (RUX, 5-mg BID increments [25 mg BID max]; BAT was adjusted per investigator judgment). Objectives of this analysis included assessment of improvement in symptom burden as assessed by patient-reported outcomes using the 14-item modified Myeloproliferative Neoplasm Symptom Assessment Form (MPN-SAF), the Pruritus Symptom Impact Scale (PSIS), the European Organization for the Research and Treatment of Cancer Quality of Life Questionnaire-Core 30 (EORTC QLQ-C30), and the Patient Global Impression of Change. The 14-item MPN-SAF (graded from 0 [absent] to 10 [worst imaginable]) comprised symptoms related to cytokines (tiredness, itching, muscle ache, night sweats, and sweats while awake), hyperviscosity (vision problems, dizziness, concentration problems, headache, numbness/tingling, ringing in ears, and skin redness), and splenomegaly (abdominal discomfort and early satiety). Changes in total symptom score (TSS; maximum score = 140) and individual symptom scores from baseline to Week 32 were summarized by treatment group. For the EORTC QLQ-C30 Global Health Status/QOL score, the percentage of patients with a minimally important difference (MID) from baseline (10-point change) at Week 32 was summarized. Results : Overall, 222 patients were randomized (RUX, 110; BAT, 112). Median age (range) was similar between arms (RUX, 62.0 [34.0–90.0]; BAT, 60.0 [33.0–84.0]); the RUX and BAT arms were 60% and 71% male, respectively. At Week 32, a higher proportion of patients in the RUX vs the BAT arms had a ≥50% improvement in MPN-SAF TSS (49% vs 5%, respectively) and MPN-SAF symptom cluster scores (cytokine, 64% vs 11%; hyperviscosity, 37% vs 13%; splenomegaly, 62% vs 17%). Median percentage changes in individual symptom scores are presented in the Table. Mean changes from baseline at Week 32 on the 5 items of the PSIS indicated that the severity of pruritus and its interference on daily life improved with RUX (range, −1.5 to −2.2) and was unchanged/worsened with BAT (range, −0.1 to 0.3). Treatment with RUX vs BAT was associated with improved mean changes from baseline at Week 32 on EORTC QLQ-C30 symptom subscales, functional subscales, and Global Health Status/QOL (Table); 46% of RUX patients versus 10% of BAT patients achieved an MID in Global Health Status/QOL (Figure). At Week 32, RUX patients were more likely to rate their global impression of symptom changes as “very much improved” or “much improved” (67%) vs BAT patients (13%). Conclusion : In patients with PV who were resistant to or intolerant of HU, treatment with RUX was associated with greater and clinically meaningful improvements in PV-related symptom burden and QoL measures compared with BAT. Figure 1 Figure 1. Figure 2 Figure 2. Disclosures Mesa: Incyte Corporation: Research Funding; CTI: Research Funding; Gilead: Research Funding; Genentech: Research Funding; Eli Lilly: Research Funding; Promedior: Research Funding; NS Pharma: Research Funding; Sanofi: Research Funding; Celgene: Research Funding. Off Label Use: Ruxolitinib is a JAK1/JAK2 inhibitor approved for the treatment of patients with intermediate or high-risk myelofibrosis, including primary myelofibrosis, post polycythemia vera myelofibrosis, and post-essential thrombocythemia myelofibrosis. Verstovsek:Incyte Corporation: Research Funding. Kiladjian:Novartis Pharmaceuticals: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding. Masszi:Novartis Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees. Durrant:Novartis Pharmaceuticals: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding. Harrison:Novartis Pharmaceuticals: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding. He:Incyte Corporation: Employment, Equity Ownership. Jones:Incyte Corporation: Employment, Equity Ownership. Parasuraman:Incyte Corporation: Employment, Equity Ownership. Li:Novartis Pharmaceuticals: Employment, Equity Ownership. Côté:Novartis Pharmaceuticals: Employment, Equity Ownership. Habr:Novartis Pharmaceuticals: Employment, Equity Ownership. Vannucchi:Novartis Pharmaceuticals: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding.

Abstract Abstract 1750 Background: Polycythemia vera (PV) and chronic idiopathic myelofibrosis (CIMF) are both clonal disorders of CD34+ hematopoietic stem and progenitor cells (HSPC) that undergo inappropriate expansion. The pathological CD34+ clones from both disorders are found at increased levels in the peripheral blood of patients, indicating that the interactions between these CD34+ cells and tissue HSPC niches are different from normal HSPC. Other studies have implicated deficiencies in the CXCR4 signaling axis as a possible reason for the abnormal trafficking of HSPCs in PV and CIMF. We set out to functionally test the importance of CXCR4 for the interactions of HSPCs collected from peripheral blood of patients with PV and CIMF with the bone marrow and other tissue microenvironments. Methods: We purified CD34+ cells from peripheral blood of patients with PV or CIMF, labeled them with fluorescent trackers, and engrafted them into unmanipulated SCID mice. Using video rate, scanning confocal microscopy we tracked CD34+ cell interactions with bone marrow, spleen and liver. To functionally test the role of CXCR4 in the homing of patient CD34+ cells to different microenvironments, we treated CD34+ cells with a blocking antibody prior to engraftment. Results: Flow cytometry revealed that PV CD34+ cells had significantly lower surface expression of CXCR4 than control HSPCs (PV mean: 32.93% positive, range: 14.8–55.1; Control mean: 58.85% positive, range: 33.5–78.7; p value = 0.018) while CIMF samples had scattered CXCR4 expression (mean 61.2% positive range: 0.6–95.4) PV CD34+ cells migrated toward SDF-1 in migration assays, demonstrating that although they had lower surface CXCR4 expression, they were still able to respond to signals from the environment through this receptor. In vivo imaging of mice after engraftment revealed that PV and CIMF CD34+ cells had decreased BM homing compared to control HSPCs. However, CD34+ cells from PV and CIMF patients homed to similar areas of bone marrow vasculature as control cells. Treating CD34+ cells with a blocking antibody against CXCR4 before engraftment significantly reduced the number of PV and CIMF cells that homed to the bone marrow, indicating that their bone marrow homing still relied on CXCR4. Interestingly, there were an increased number of PV and CMF cells that homed to the spleen at baseline compared to control HSPC, suggesting that a distinct homing mechanism favored PV and CMF cell trafficking to the spleen over the BM. The number of cells that homed to the spleen increased upon antibody blockade of CXCR4, indicating that splenic homing of CD34+ cells did not depend on CXCR4/SDF-1 interactions. Conclusion: CD34+ HSPC from PV and CIMF patients and controls homed to similar areas of the BM, although PV and CIMF cells had significantly decreased BM homing. Conversely, PV and CIMF CD34+ cells homed to the spleen in significantly higher numbers than control cells. PV, CIMF and control CD34+ cells were all dependent on CXCR4 for maximal BM homing. Splenic homing was not CXCR4 dependent, however, and PV and CIMF cells homed to the spleen in higher numbers when BM homing was inhibited by CXCR4 blockade. Taken together, we conclude that unique signaling mechanisms regulate trafficking of CD34+ cells to the BM vs. the splenic microenvironments. PV and CIMF CD34+ cells have an abnormal response to these tissue signals, resulting in their preferential homing to the spleen. Molecularly targeted therapies with the Jak2 inhibitors significantly decrease splenomegaly in CIMF patients, although they do not reverse the BM disease process. Recent evidence in a mouse model suggests that the BM is in fact a sanctuary site for disease during treatment with these agents. Whether PV and CIMF CD34+ cells in patients can escape apoptosis during treatment by trafficking to more favorable microenvironments is unknown. Our study suggests that an increased understanding of the mechanisms that these cells use to engage different tissue niches could aid the treatment of these diseases. Disclosures: No relevant conflicts of interest to declare.

Abstract Abstract 2849 Background We have previously reported on the natural history of polycythemia vera (PV), focusing primarily on overall and leukemia-free survival (ASH Annual Meeting Abstracts. 2011;118(21):277-). In the current study, we present, on behalf of the International Working Group for Myeloproliferative neoplasms Resarch and Treatment (IWG-MRT), our analysis regarding risk factors for thrombosis. Methods Under the auspices of IWG-MRT, seven international centers of excellence for myeloproliferative neoplasms participated in the current study. The two principle investigators (AT and TB) reviewed all the cases and selected 1,545 patients who met the 2008 WHO criteria for PV, were age 18 years or older, diagnosed after 1970, and whose submitted data included diagnostically essential information. Results I: Presenting Features Median age was 61 years (range, 18–95; 51% females). Arterial and venous thrombosis history before or at diagnosis was documented in 246 (16%) patients and 114 (7.4%) patients, respectively. Major hemorrhage hemorrhage before or at diagnosis was documented in 17 (4.5%) patients. Other features at diagnosis included pruritus (36%), microvascular disturbances (28.5%), palpable splenomegaly (36%), abnormal karyotype (12%), leukoerythroblastosis (6%), increased LDH (50%), thrombocytosis (53%), extreme thrombocytosis (platelets >1 million mm3; 4%) leukocytosis (49%), JAK2 V617F (95%), other JAK2 mutations (3%), subnormal serum erythropoietin (Epo) level (81%), and endogenous erythroid colonies (EEC; 73%). History of hypertension (46%), hyperlipidemia (18.3%), diabetes (8.4%), and tobacco use (16%) was also obtained. Results II: Clinical Course To date, 347 (23%) deaths, 50 (3%) leukemic progressions, and 138 (9%) fibrotic transformations have been recorded. Overall, cytoreductive treatment was not used in 416 (27%) patients and the remaining were exposed to different agents based on physician discretion. Post-diagnosis arterial or venous thrombosis occurred in 184 (12%) and 137 (9%) patients, respectively. Results III: Risk Factors for thrombosis Arterial and venous thrombosis-free survival, from time of diagnosis, were separately analyzed using the occurrence of thrombosis as the endpoint (uncensored variable) and last follow-up or death before thrombosis as the censored variable. In univariate analysis, the following were significantly associated with post-diagnosis arterial thrombosis: advanced age, leukocyte count, presence of a leukoerythroblastic smear (LES), history of hypertension and history of arterial thrombosis before or at diagnosis; multivariable analysis using all these five parameters identified arterial thrombosis history (RR 2.5, 95% CI 1.6–4.0; p<0.0001), LES (RR 2.3, 95% CI 1.3–4.2; p=0.005) and history of hypertension (RR 1.6, 95% CI 1.1–2.4; p=0.02) as independent predictors of post-diagnosis arterial thrombosis. Only two parameters predicted post-diagnosis venous thrombosis, in univariate analysis, and both remained significant during multivariable analysis: abnormal karyotype (RR 3.1, 95% CI 1.7–5.4; p=0.0001) and history of venous thrombosis (RR 2.4, 95% CI 1.2–4.9). Of note, the type of JAK2 mutation or presence of either subnormal Epo or EEC did not influence either arterial or venous thrombosis. Results IV: Risk Stratification for arterial and venous thrombosis The figures below illustrated arterial or venous thrombosis-free survival of patients stratified by the absence of all risk factors or presence of one or ≥2 risk factors. For arterial thrombosis, the presence of ≥2 risk factors clearly delineated a high risk group (RR 3.1, 95% CI 1.9–5.0) whereas the presence of one (RR 2.4, 95% CI 1.4–4.2) or two risk factors (RR 10.1, 95% CI 3.6–28.2) for venous thrombosis delineated an intermediate and high risk group, respectively. Conclusions: History of arterial thrombosis and venous thrombosis are key risk factors, respectively, for recurrent arterial and venous thrombosis in PV. In addition, abnormal karyotype is a strong independent risk factor for venous thrombosis and the presence of leukoerythroblastosis and hypertension, for arterial thrombosis. This information allows for a simple and practical risk stratification and raises interesting pathogenetic implications that require further clarification. Disclosures: Vannucchi: Novartis: Membership on an entity's Board of Directors or advisory committees. Gisslinger:Novartis: Consultancy, Research Funding, Speakers Bureau; Celgene: Consultancy, Research Funding, Speakers Bureau. Passamonti:Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees; Sanofi-Aventis: Honoraria, Membership on an entity's Board of Directors or advisory committees.

Abstract Background Increased bone marrow (BM) reticulin fibrosis in polycythemia vera (PV) has been reported in 20% (Ann Hematol. 1999;78:495) to 51% (Eur J Haematol. 2011;86:148) of patients at diagnosis. In a previous report by the international working group for myeloproliferative neoplasms (MPN) research and treatment (IWG-MRT), the presence of BM fibrosis (≥ grade 1) at diagnosis was associated with a lower incidence of thrombosis during the clinical course and a higher risk of fibrotic progression while it did not affect overall (OS) or leukemia-free (LFS) survival (Blood. 2012;119:2239). The objectives for the current single center study of 262 PV patients were to validate the observations from the IWG-MRT and also identify other risk factors for myelofibrosis-free survival (MFFS) in PV. Methods Study patients were selected from our institutional database of MPN and fulfilled the 2016 World Health Organization (WHO) criteria for the diagnosis of PV (Blood. 2016;127:2391). Cytogenetic analysis and reporting was done according to the International System for Human Cytogenetic Nomenclature (Cytogenetic and Genome Research 2013;141:1-6). The degree of BM reticulin fibrosis was based on "real life" BM reports from Mayo Clinic hematopathologists and often in accordance with the European consensus scoring system (Haematologica 2005;90:1128). Statistical analyses considered clinical and laboratory parameters obtained at time of diagnosis. Results Patient characteristics: Analysis was conducted on 262 patients (median age 62 years; 50% males) who met 2016 WHO criteria for diagnosis of PV. Median (range) values were: hemoglobin 18 g/dl (14.8-24), leukocyte count 11.7 x109/L (4.3-59.3) and platelet count 454 x109/L (44-2747). Among informative cases, palpable splenomegaly was present in 27%, pruritus in 33% and erythromelalgia in 6%. Thrombosis history at diagnosis was documented in 28% of the patients and 23% experienced thrombotic events after diagnosis. Information on cytogenetics was available in 142 patients and karyotype was abnormal in 19%. BM reticulin fibrosis was reported to be absent in 135 patients (MF-0, 52%), grade 1 (MF-1) in 101 (39%), grade 2 (MF-2) in 22 (8%) and grade 3 (MF-3) in 4 (2%) patients. After a median follow up of 85 months, 107(41%) deaths, 30 (11%) fibrotic progression and 5 (2%) leukemic transformations were documented. Comparison of patients with and without bone marrow fibrosis A number of clinical and laboratory parameters were evaluated for possible association with the presence of ≥ grade 1 BM reticulin fibrosis and none, including age, sex, complete blood count, palpable splenomegaly, pruritus or erythromelalgia displayed a significant association. In univariate analysis, the presence of BM fibrosis (MF-0 versus MF-1 or greater) did not affect OS (p=0.5), LFS (p=0.2) or thrombosis-free survival (p=0.97) whereas a significant association was noted for MFFS (p=0.009; HR 2.9, 95% CI 1.3-6.7). Others risk factors for MFFS, in a univariate analysis, were leukocytosis ≥15 x 109/L (p=0.02; HR 2.7, 95% CI 1.17-6.48), presence of splenomegaly (p=0.02; HR 2.6, 95% CI 1.16-6) and abnormal karyotype (p=0.0005; HR 4.6, 95% CI 1.9-11). During multivariable analysis, not including karyotype, leukocytosis ≥15 x 109/L (p=0.04), presence of splenomegaly (p=0.04) and presence of BM reticulin fibrosis (p=0.01) remained significant; however, this significance for leukocytosis ≥15 x 109/L, presence of splenomegaly and BM reticulin fibrosis was lost when abnormal karyotype was added as covariate to each risk factor individually (p=0.4, p=0.1 and p=0.9, respectively). Conclusion We report a not infrequent (48% incidence) occurrence of ≥ grade 1 BM reticulin fibrosis at time of initial diagnosis of PV. In the current study, we did not find a prognostic impact for the presence of BM reticulin fibrosis, in terms of OS, LFS or thrombosis-free survival; however, a significant association was confirmed for MFFS that was independent of other non-genetic risk factors. The preliminary observation on the adverse prognostic impact of abnormal karyotype on MFFS requires additional studies. Disclosures No relevant conflicts of interest to declare.

Abstract Abstract 1726 Background: We previously reported that symptom burden among persons with ET and PV can be severe and adversely affect QOL. The presence of severe symptoms is linked to poor prognosis. There is considerable inter-subject heterogeneity regarding which symptoms are present in which subjects. No studies have empirically evaluated whether disease characteristics can be grouped in related symptom clusters. Using our previously validated 18 item Myeloproliferative Neoplasm Assessment Form (MPN-SAF) (Blood 2011;118:401–408) given in conjunction with the 9 item Brief Fatigue Inventory (BFI) (Cancer 1999;85:1186–1196), we sought to evaluate symptom burden by means of cluster analysis. Methods: Data was collected from an international cohort of subjects with MPNs including demographics, disease features and the completed BFI and MPN-SAF instruments. Surveyed symptoms included fatigue, early satiety, abdominal pain and discomfort, inactivity, headaches, concentration, dizziness, extremity tingling, insomnia, sexual difficulties, mood changes, cough, night sweats, pruritus, bone pain and fever on a 0 (absent) to 10 (worst-imaginable) scale. Development of symptom clusters was based on consideration of r-squared in hierarchical clustering using Ward linkage. Final cluster assignment was based on the nonhierarchical k-means method. Comparisons between symptom clusters were based on ANOVA and chi-squared tests. Results: Subject Demographic and Disease Characteristics: Data from 1,141 subjects with PV (N=519) and ET (N=622) was prospectively collected (Chinese 236, French 305, German 45, Italian 114, Dutch 191, English 56, Spanish 109, Swedish 85. Age (mean 59, range, 26–87) and gender (54% F) were typical. Five clusters were selected (Figure 1). Frequencies of prior bleeding, spleen size, anemia, presence of any lab abnormality, language, gender, and MPN type varied significantly between clusters (P<0.05). Cluster 1: The “Reduced Symptom” Profile (n=421 (37%; 60% ET, 40% PV) The largest cluster, subjects had increased complaints of sexual difficulties and fatigue. There was a slightly higher proportion of subjects with ET (60%) versus PV. There were fewer lab abnormalities (28% prevalence) and less prior bleeding (3%) compared to other clusters. Spleen size was smallest of the cluster (1 cm below costal margin). Cluster 2: The “Fatigue-dominant” Group (n=286 (25%; 56% ET, 44% PV)). Subjects in this cluster were predominantly female and had relatively few laboratory abnormalities (19%) than other cohorts. They are characterized by high severity of fatigue compared to end-organ symptoms. Symptom profiles emphasize fatigue, QOL and insomnia with some end-organ complaints. The cohor 63% of the cohort. Cluster 3: The “End-Organ Complaints” Group (n=210 (18%; 49% ET, 51% PV)). Male predominant (56%), subjects had mainly macro-vascular symptom complaints including sexual difficulties, insomnia, and overall QOL, with few microvascular related symptoms (low itching/night sweats). Cluster 4: “Cognitive Complaints” Cluster (n=110 (10%; 53% ET, 47% PV)). The smallest cluster and female predominant (64%), main complaints include fatigue, insomnia, loss of concentration, numbness, and sad mood. Cluster 5: The “Highly Symptomatic” Cluster (n=114 (10%; 44% ET, 56% PV)). Subjects had many cognitive complaints and symptoms correlated with severe micro-vascular abnormalities (pruritus) and or splenomegaly. This cluster had the largest spleen sizes (mean 3 cm), the highest prevalence of prior thrombosis (29%), and highest frequency of lab abnormalities (43%). Cognitive and end-organ complaints were rated as most severe. Conclusion: This analysis offers new means of evaluating persons with PV and ET utilizing symptom clusters. Laboratory and physical abnormalities differed significantly between symptom clusters indicating that our groupings likely result from biological alterations present in specific disease phenotypes. Future studies should investigate correlations between clusters and prognosis and genotype. Disclosures: Kiladjian: Celgene: Research Funding; Novartis: Honoraria, Research Funding; Shire: Honoraria. Roy:Novartis, BMS: Speakers Bureau. Harrison:Novartis: Honoraria, Research Funding, Speakers Bureau; YM Bioscience: Consultancy, Honoraria; Sanofi Aventis: Honoraria; Shire: Honoraria, Research Funding. Vannucchi:Novartis: Membership on an entity's Board of Directors or advisory committees. Passamonti:Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees; Sanofi: Honoraria, Membership on an entity's Board of Directors or advisory committees. Mesa:Incyte: Research Funding; Lilly: Research Funding; Sanofi: Research Funding; NS Pharma: Research Funding; YM Bioscience: Research Funding.