Tefferi, Ayalew

Abstract Abstract 3917 Poster Board III-853 Background Patients with Myelofibrosis (MF) suffer from significant fatigue, constitutional symptoms and splenomegaly (Mesa et. al. Cancer 2007) not improved by current therapy. The MF-SAF is a 19 item self administered instrument specific to MF associated symptoms previously validated for use at a single time point (Mesa et. al. Leukemia Research 2009). We sought to assess the performance characteristics of the MF-SAF when administered sequentially in the context of a prospective clinical trial. Methods Sequential MF patients enrolled in the prospective, uncontrolled Phase II, trial were given a 15 item modified MF-SAF to complete at enrollment, and after 15 days, 1 month, 2 months, 3 months and every 3 months thereafter. The MF-SAF was scored as previously published on a 0 (absent) to 10 (maximal) scale. Cross validation of serial change in MF-SAF scores was undertaken by comparison to objective measurements made as part of the therapeutic drug trial. Results Patients Eighty six MF patients were enrolled and had 2 or more MF-SAF instruments completed to allow for sequential analysis. Patients were of a median age (65 years), gender distribution (35 % females), and disease subtype (53 % PMF) typical for a clinical trial in MF. Baseline MF-SAF Responses: Baseline assessment of the most frequent MF abnormalities reported by patients completing the MF-SAF (see Table 1) confirmed the wide prevalence of MF associated symptoms, and their significant severity. General fatigue was the most frequent symptom cited (91%), while cough was the least frequently observed symptom (44%). 95% of patients had at least 2 symptoms present on the MF-SAF. Serial MF-SAF Changes in Response to Therapy Therapy with INCB018424 resulted in a significant and rapid reduction in MF associated symptoms with 46% to 85% of patients experiencing improvement in a given symptom. The greatest improvements in MFSAF score improvements were reported by patients experiencing abdominal discomfort, night sweats, pruritus and fever (see Table 1), and corresponded to significant improvements in the individual MF symptom scales as well as the patient's overall assessment of quality of life (QOL). Correlation of MF-SAF to Objective Changes during INCB018424 Therapy Objective measurements obtained on the INCB018424 trial included MRI measurements of splenic reduction, the six minute walk test (6MWT) for inactivity, and serial weights. Reduction in spleen size (by ≥ 35% by volume or ≥ 50% by palpable length) corresponded to improvement in MF-SAF scores of abdominal discomfort and fatigue (50% of patients, median score decrease of -1.2, and -1.8, respectively). Improvement in the 6MWT by > 50 meters was associated with a 2-fold greater improvement in inactivity score on the MF-SAF compared to subjects who improved 6MWT performance by <50 meters. Finally, improvements in weight loss and fever were corroborated by objective measurements made at physician visits on the trial. Conclusions The MF-SAF is a brief, easily self administered, MF specific instrument which was successfully administered sequentially in the conduct of a large Phase II clinical trial. The significant symptomatic improvements reported by patients in the open label trial of INCB018424 corresponded to both improvements in symptom specific scores on the MF-SAF and objective measurements. Further validation of the MF-SAF will be possible by inclusion in upcoming randomized placebo controlled trials in MF patients. Parallel trials performed in MF patients should consider use of this instrument to allow for comparisons. Disclosures: Levy: Incyte Corporation: Employment, Equity Ownership. Vaddi:Incyte Corporation: Employment, Equity Ownership. Erickson-Viitanen:Incyte Corporation: Employment, Equity Ownership. Verstovsek:Incyte: Research Funding.

Abstract Prompted by the activity of lenalidomide (Revlimid®) in pts with chronic idiopathic myelofibrosis (CIMF), we sought to evaluate the safety and efficacy of the combination of lenalidomide and prednisone in a phase II study for pts with CIMF. The rationale for this combination is that the anti-angiogenic and anti-TNFa effects of lenalidomide may be potentiated by the effects of prednisone to reduce marrow fibrosis and improve hematopoiesis in CIMF. Initial therapy consisted of lenalidomide 10 mg/d (dose level [DL] 0) on days 1–21 of a 28–day cycle for 6 cycles, in combination with prednisone 30 mg/d orally during cycle 1, 15 mg/d orally during cycle 2, and 15 mg/d every other day during cycle 3. The lenalidomide dose could be reduced to 5 mg/d (DL -1) or to 5 mg/d every other day (DL -2), or increased to 15 mg/d (DL +1) or 20 mg/d (DL +2) depending upon toxicity or lack of response, respectively. A total of 40 pts (23 male, 17 female) have been enrolled. The median age was 62 years (range, 41–86), time from CIMF diagnosis to the study treatment 10 months (range, 0–269), WBC count 87x109/L (range, 1.1–89), hemoglobin 9.8 g/dL (range, 7.8–17.3), platelets 137x109/L (range, 8–1183). Pts had received a median of 1 prior therapy (range 0–4): hydroxyurea (HU; n=14), anagrelide (AG; n=4), azacitidine (n=6), steroids (n=5), thalidomide (n=4), and interferon (n=3). Ten (25%) pts had not received any prior therapy. JAK2 V617F mutation was detected in 18 (50%) of 36 tested pts and 20 (50%) of 40 had abnormal cytogenetics. A total of 260 cycles have been administered. All 40 pts are evaluable for response and toxicity. Responses have been observed in 12 (30%) pts, including complete response (CR) in 2 (normal blood counts and <5% bone marrow blasts, off HU, AG, growth factors, and no transfusions); partial response (PR) in 7 (at least 2 of the following: Hb increase by ≥2 g/dL, 50% increase in platelets, decrease of bone marrow blasts or organomegaly by ≥50%, normalization of WBC count without blasts, or reduction in bone marrow fibrosis; off HU, AG, growth factors, and transfusion independence); and hematologic improvement (HI) in 3 (at least 2 of the following: decrease by ≥25% of pretreatment leukocytosis, splenomegaly, or marrow blasts, or increase of Hb by ≥1g/dl without growth factor or transfusion support or platelets by ≥25%; off HU, AG, growth factors). Median time to response was 12 weeks (range, 2–32). Responses have been sustained for a median of 15 wks (range, 5–36) and are ongoing in all 12 responders. Overall, 21 (53%) pts experienced grade 3–4 toxicity, being the most frequent neutropenia, anemia, musculoskeletal pain, and fatigue. Twenty-four (60%) pts have required dose reduction to DL -1, of which 5 (12.5%) further reduced to DL -2. One (2.5%) pt dose-escalated to DL +1, while 15 (25%) remained at DL 0. Twenty-one (53%) pts discontinued lenalidomide due to: lack of response (n=8), pt’s decision (n=7), grade 3–4 toxicity (n=5), and poor compliance (n=1). No deaths or transformation to acute myeloid leukemia occurred. In summary, the combination of lenalidomide and prednisone is an active and generally well-tolerated regimen for pts with CIMF. Longer follow-up is warranted to evaluate the durability of ongoing responses. Updated results will be presented at the meeting.

Abstract Background: Previously established adverse prognostic factors in myelofibrosis with myeloid metaplasia (MMM) include anemia (hemoglobin < 10 g/dL), leukocytosis or leukopenia, presence of circulating blasts, and hypercatabolic symptoms (Dupriez et al. 1996;88:1013, Cervantes et al. BJH1998;102:684). Measurement of peripheral blood (PB) CD34 count has been shown to have diagnostic as well as possible prognostic value in MMM (Barosi et al. Blood2001;98:3249). Methods: A concurrent evaluation of PB CD34 count, bone marrow histology, and other clinical and laboratory parameters was conducted in a consecutive cohort of both newly and previously diagnosed patients with MMM. The study patients were prospectively followed for a minimum of 3 years in order to determine the prognostic value of PB CD34 count on survival, leukemic transformation, and disease progression from the time of PB CD34 analysis. Results: i. Patient cohort: A total of 94 patients (median age 61 years, range 26–81; 61 males) were accrued between January 2000 and August 2001 and subsequently followed through July 2004. MMM subtypes included agnogenic myeloid metaplasia (AMM; 58 patients), post-polycythemic myeloid metaplasia (PPMM; 12 patients), post-thrombocythemic myeloid metaplasia (PTMM; 12 patients), cellular phase MMM (8 patients) and hypocellular variant MMM (4 patients). At the time of study entry, 19 patients (20%) were newly diagnosed and 75 were established cases (median of 36 months from initial diagnosis, range 4–221). The Dupriez prognostic scores were 0 in 37 (39%), 1 in 37 (39%), and 2 in 20 patients (21%). ii) Clinical correlates of PB CD34 count: The median PB CD34 count for the entire study cohort was 54.7 x 106/L (range 0–5345) with 85% patients having increased values (> 5 x 106/L). Cellular phase MMM and PPMM had significantly lower PB CD34 counts compared to the other MMM subtypes. On univariate analysis, PB CD34 count significantly correlated with Dupriez prognostic score, leukocyte count, circulating blast or immature myeloid cell percentage, and presence of hypercatabolic symptoms but not with age, gender, anemia (hemoglobin < 10 g/dL), abnormal cytogenetics, disease duration, treatment history, splenectomy status, nucleated RBC count (NRBC), platelet count, or bone marrow histology including fibrosis, osteosclerosis, and angiogenesis. On multivariate analysis, only leukocyte count and PB blast or immature myeloid cell percentage retained their significance. iii) Prognostic evaluation of PB CD34 count : As of July 16, 2004, 43 patients (46%) have died and median duration of follow up in the surviving patients was 41 months (range 36–54). The projected overall survival at 5 years was 50%. On Cox proportional regression analysis, individual variables that correlated with inferior survival included anemia (hemoglobin < 10 g/dL), advanced age, presence of hypercatabolic symptoms, abnormal cytogenetics, and increased leukocyte count, circulating blast percentage, Dupriez prognostic score, and NRBC. PB CD34 count displayed borderline significance (p=0.06). However, on multivariate analysis, only anemia, leukocytosis, and age retained prognostic significance. Similarly, PB CD34 count did not predict either subsequent leukemic transformation or disease progression. Conclusion: PB CD34 count is often but not always increased in MMM and correlates significantly with leukocytosis and degree of PB myeloid immaturity. The current prospective study does not support an independent prognostic value for PB CD34 count in MMM.

Abstract Peripheral blood infused total autograft absolute lymphocyte count (A-ALC) correlates with day 15 absolute lymphocyte count and is an independent prognostic factor for survival after autologous stem cell transplantation (ASCT) for non-Hodgkin lymphoma (NHL). Factors to enhance A-ALC collections are not well defined. We hypothesize that the number of peripheral blood apheresis collections (PBAC) directly correlates with A-ALC. 190 consecutive NHL patients who underwent ASCT at the Mayo Clinic between 1993 and 2001 were analyzed. The primary end point of the study was to assess the correlation between the number of PBAC and A-ALC. The secondary end point was to determine if the number of PBAC affected survival post-ASCT. Of the 190 patients, 18 patients underwent 1 PBAC, 23 patients 2 PBAC, 50 patients 3 PBAC, 37 patients 4 PBAC, 50 patients 5 PBAC, and 12 patients had ≥ 6 PBAC. There was no association between the number of PBAC and the number of CD34+ stem cells collected (p= 0.25). A strong association between number of PBAC and A-ALC (Kruskall Wallis test, p <0.0001)(Figure 1) was identified. Using a cut-off of 4 PBAC, superior overall survival (OS) and progression-free survival (PFS) were observed for patients that underwent 4 PBAC or more compared to patients that underwent less than 4 PBAC (86 months vs 18 months, p <0.0001; 76 months vs 10 months, p <0.0001, respectively). Multivariate analysis demonstrated PBAC ≥ 4 is an independent prognostic factor for OS (RR = 0.654, 95%CI: 0.529–0.804, p< 0.0001) and for PFS (RR = 0.682, 95%CI: 0.561–0.826, p< 0.0001) when compared with other significant factors including performance status, lactate dehydrogenase and extra nodal disease. These data suggest that increasing the number of PBAC beyond the minimum number required to meet CD34+ collection targets may result in improved overall and progression-free survival mediated by an increase in autograft absolute lymphocyte count.

Abstract Introduction: Several groups are developing orally bioavailable small molecule JAK2 inhibitors as an approach to targeted therapy of myeloproliferative disorders. We previously reported that one such inhibitor (TG101209) potently inhibits JAK2V617F in vitro, and was effective in reducing tumor growth in a mouse xenograft model (Leukemia, 2007 Aug;21(8):1658–68). Here, we expand our analysis using TG101348, a highly selective JAK2 inhibitor currently in preclinical development, using cell lines and primary cells harboring JAK2V617F, MPLW515L/K, or JAK2 exon 12 mutations. Methods: Cell proliferation was assessed using the XTT assay. For primary cell experiments, PBMCs were plated in methylcellulose medium at 0, 300nM, 600nM, and 1200nM TG101348, both with and without erythropoietin (Epo). Hematopoietic colonies were scored after 12–16 days culture, and harvested for genotyping. Results: TG101348 inhibits growth of human erythroleukemia (HEL) and Ba/F3-V617F cells (IC50=300nM and 580nM, respectively), as well as Ba/F3-(MPL)W515L cells (IC50=620nM). JAK2:JAK3 selectivity of TG101348 was demonstrated by its 10-fold more potent inhibition of CHRF (JAK2T875N) as compared to CMK (JAK3A572V) cell proliferation. TG101348’s inhibitory effect on ex vivo hematopoietic colony growth was studied in 12 MPD patients (JAK2V617F=9, MPLW515L/K=1, JAK2 exon 12 mutation [N542-E543del]=1, no mutation=1), and 2 healthy controls (Table). Conclusions: (1) TG101348 inhibits colony growth from MPD patients more potently than healthy controls, reflecting its potential therapeutic window. (2) Endogenous colony growth is inhibited at nanomolar concentrations in all cases, with some alleles showing greater sensitivity than others (MPLW515K = exon 12 mutation > JAK2V617F). The corresponding Epo-supported erythroid colonies are less potently inhibited, reflecting the generally lower prevalence of JAK2 mutations in such colonies. (3) EEC growth in the absence of known JAK2 or MPLW515 mutations is also inhibited, indicating a similar dependence on dysregulated JAK-STAT signaling in such cases. (4) The ability of TG101348 to selectively suppress mutation-positive hematopoietic colonies will be discussed. Inhibitor effect on ex vivo hematopoietic colony growth Paient Mutation IC50 (nM) % Mutation-positive colonies Epo No Epo Epo No Epo (EEC) Normal 1 None >1200 n/a n/a n/a Normal 2 None >1200 n/a n/a n.a PV1 V617F 600 <300 5 40 PV2 V617F 600 300 33 50 PV3 V617F 600–1200 300–600 9 70 PV4 V617F 300–600 600 0 15 PV5 V617F 600–1200 300 80 100 PV6 V617F 600 300–600 7 19 PV7 V617F 600–1200 600 32 36 PV8 V617F 600–1200 <300 45 37 PV9 V617F 600 600–1200 20 12 PV10 Exon 12 (N542–E543del) 900 <300 9 60 PMF1 W515K 300–600 <300 100 33 PMF2 None >1200 300 n/a n/a

Abstract Abstract 3915 Poster Board III-851 Background Thromboembolic disease (TE) is a major cause of morbidity and mortality in polycythemia vera (PV) and essential thrombocythemia (ET). There is limited information on the prevalence of TE in primary myelofibrosis (PMF) and associated prognostic factors. Methods Study patients were recruited form the Mayo Clinic database for PMF. Diagnosis was according to the 2001 WHO criteria. Clinical and laboratory information was collected at time of diagnosis and correlated with the occurrence of TE in general and arterial (AT) or venous (VT) thrombosis in particular. Leukocytosis was defined as a leukocyte count of > 10 × 109/L. Qualitative JAK2V617F analysis was done according to previously published PCR-based methods. In addition, a subset of the study patients underwent quantitative PCR for JAK2V617F and rs12343867 SNP genotyping (performed by a commercially available Taqman assay). All molecular studies were performed on stored bone marrow. Standard statistical methods were used to test significance of associations between thrombosis and other variables. Results 207 patients with PMF were studied (median age 62, range 28-87; 132 males). At presentation, the median (range) of hemoglobin (Hb), leukocytes (WBC) and platelets (plt) were 11 g/dl (6.4-15.4), 8.6 × 109/L (0.8-156.7) and 273 × 109/L (13-1916), respectively. Dupriez prognostic scores at diagnosis were low, intermediate and high in 57%, 33% and 10% of the patients, respectively. 130 (63%) patients were JAK2V617F positive. Among 73 patients in whom quantitative JAK2V617F analysis was performed, the mutation was not detected in 30 (41%) patients and the median mutant allele burden in the 43 mutation-positive patients was 28% (range 1-85). The same 73 patients had rs12343867 SNP genotyping performed that revealed C/C genotype in 14 (19%) patients, C/T in 34 (47%) and T/T in 25 (34%). At or before diagnosis, a total of 29 patients (14 %) had TE: 23 (11%) AT and 9 (4%) VT. The AT included acute coronary syndromes (ACS; n=19), transient ischemic attack/ cerebrovascular accidents (TIA/CVA; n=6) and peripheral arterial thrombosis (PAT; n=1). The VT included abdominal vein thrombosis (AVT; n=4), deep vein thrombosis/pulmonary embolism (DVT/PE; n=6) and dural sinus thrombosis (n=1). Several patients had more than one event and some both AT and VT. During follow-up, 22 (11%) patients experienced TE: 17 (8%) VT and 8 (4%) AT. The post-diagnosis VT included AVT (n=8), DVT/PE (n=13) and both DVT/PE and AVT (n=4). Post-diagnosis AT included CVA (n=4), TIA (n=1), ACS (n=2) and PAT (n=1). AT at or before diagnosis was associated with advanced age (p=0.003) but not with sex, leukocytosis, hemoglobin level, platelet count, JAK2 mutational status, JAK2 mutant allele burden or rs12343867 SNP genotype. VT at or before diagnosis also did not correlate with all these variables or age. These variables were also evaluated regarding their relationship with post-diagnosis AT, which showed significant associations with hemoglobin level (p=0.006), platelet count (p=0.04) and high JAK2V617F allele burden (0.03). The corresponding significant variables for post-diagnosis VT were leukocytosis (p=0.02) and high JAK2V617F allele burden (p=0.01). Of note, AT or VT at or before diagnosis did not predict post-diagnosis events. During multivariable analysis, only higher hemoglobin level predicted post-diagnosis AT. Conclusion The current study provides an accurate description of both arterial and venous thrombotic events in PMF. The association between higher hemoglobin and leukocyte counts at diagnosis and post-diagnosis occurrence, respectively, of arterial and venous thrombosis is similar to observations in patients with PV or ET and suggests a potential benefit from early institution of cytoreductive therapy for the appropriate patient groups. Disclosures: No relevant conflicts of interest to declare.

Abstract Background: Almost all cases of polycythemia vera (PV) and more than half of those with either essential thrombocythemia (ET) or primary myelofibrosis (PMF) harbor JAK2V617F. It has been previously shown that V617F-positive ET patients, as opposed to their mutation-negative counterparts, require lower doses of hydroxyurea (HU) for control of their platelet count. In the current study we looked for a similar scenario in PMF and PV. Methods: Study patients were identified by database inquiry based on the presence of treatment history with HU and adequate follow-up. Qualitative (PMF) and quantitative (PV) analysis of JAK2V617F was performed according to previously published allele specific PCR-based methods. Mutation analysis was performed on bone marrow samples collected at time of initial diagnosis or within one year of diagnosis. HU treatment response assignment was according to criteria set by the International Working Group for Myelofibrosis Research and Treatment. In PV, a complete response (CR) required normalization of blood counts associated with a more than 50% benefit in both phlebotomy requirement and splenomegaly. Partial response (PR) required either becoming phlebotomy independent or normalization of blood counts or a greater than 50% improvement in splenomegaly. Results: The study cohort consisted of 69 patients with PMF (median age 62 years; 36% females) and 56 patients with PV (median age 67 years; 45% females). In PMF, by univariate analysis, HU response was associated with a shorter disease duration (p=0.008), absence of previous therapy (p=0.01), older age at diagnosis (p=0.009), and presence of V617F (p=0.02). On multivariable analysis, only the latter retained its significance; HU response rate was 48% in V617F-positive patients (11/21 patients) and 8% in mutation-negative cases (1/12 patients). In PV, V617F allele burden correlated directly with HU response (p=0.05) and, in responding patients, inversely with HU dose (p=0.01; Figure). All 9 patients with upper quartile V617F allele burden responded (8 with CR) whereas 6 of the 11 (55%) HU non-responders displayed V617F allele burden in the lower quartile range. Among the 45 HU responders, the maximum daily dose of HU employed in all 9 patients in the upper quartile allele burden range and 4 of the 5 in the middle quartiles range was below 1500 mg. In contrast, 8 of the 31 patients (26%) in the lower allele burden quartile range required doses at 1.5 gm or more per day. Conclusion: The current study suggests that response to HU therapy in both PMF and PV is more robust in the presence of JAK2V617F; the particular information is useful in identifying PMF patients who are likely to benefit from HU therapy and in individualizing HU starting dose in PV patients. Figure Figure

Abstract Background: JAK2V617F is a recurring mutation in patients with polycythemia vera (PV) (95%) and essential thrombocythemia (ET) (50%), diseases that are frequently complicated by arterial and/or venous thrombosis. JAK2V617F is also frequently identified in patients with splanchnic vein thrombosis, including in those with occult myeloproliferative disorder (MPD). We previously reported a low prevalence of JAK2V617F in thrombosis patients - only 2% of 210 patients with non-splanchnic vein thrombosis (Leukemia, 2007 Aug;21(8):1828–9), and <1% of 136 patients with arterial stroke (J Thromb Haemost. 2007 Aug;5(8):1784–5). Here, we expanded the analysis to 664 thrombosis patients to describe: JAK2V617F prevalence, and clinical course of patients harboring this mutation. Methods: In Phase I, we screened 439 consecutive patients who underwent thrombophilia testing at our institution in early 2005 - patients with splanchnic vein thrombosis or overt MPD were excluded. In Phase II, we identified 228 additional patients considered to be at high risk for harboring JAK2V617F, who were seen at our institution from 2004 to 2006. JAK2V617F screening (assay sensitivity <1%) was performed as described in the aforementioned references. Results: In the initial cohort of 439 patients (median age=56 years; range 17–93 years; 222 female), 136 (31%) presented with stroke, 114 (26%) with deep venous thrombosis (DVT), 95 (22%) with pulmonary embolism (PE), 50 (11%) with DVT and PE, 10 (2%) with central retinal vein occlusion (CRVO), 7 (2%) with cerebral vein thrombosis, and the remaining 27 (6%) with other thromboses. Five patients (MC1-MC5; median age=78 years) were found to harbor JAK2V617F (prevalence=1%) - none had overt clinical features of MPD and all harbored a low level of JAK2V617F in peripheral blood (median=5–2%; range=2.2–7.5%) (Table). One patient (MC2) carried the Prothrombin G20210A mutation In the subsequent cohort, we studied 197 patients (median age=39 years; range=16–84 years) with recurrent DVT and/or PE, and 28 patients (median age=27 years; range=31–49 years) with acute myocardial infarction at a young age (<50 years). One patient (MC6) who presented with recurrent idiopathic DVT was found to harbor JAK2V617F (prevalence <0.5%) (Table) - this patient had no features of underlying MPD and the mutation burden was low (9%). After a median follow up of 27 months (range=4–66 months), none of the 6 patients harboring JAK2V617F has developed overt MPD. Conclusions: In patients with thrombosis, JAK2V617F is infrequently detected in the absence of overt MPD and/or involvement of splanchnic veins. Thus, JAK2V617F screening cannot be recommended as part of the hypercoagulable workup in routine clinical practice in this setting. The risk of developing overt MPD may be quite low for patients harboring a low JAK2V617F burden at the time of thrombosis although longer follow up is needed in this regard. Furthermore, the thrombosis risk may be well controlled with standard warfarin therapy, and the role of myelosuppressive agents (eg. hydroxyurea) is unclear in these patients. Characteristics of patients harboring JAK2V617F Patient Age Sex Thrombosis JAK2V617F allele burden MPD Follow up (months) Status MC1 84 M PE, DVT 5.3% No 66 Alive MC2 82 F PE, cerebral vein 5% No 38 Alive MC3 74 F PE 2.2% No 4 Dead MC4 78 F Central retinal vein 5.2% No 22 Alive MC5 63 M Stroke 7.5% No 30 Alive MC6 69 M Recurrent DVT No No 24 Alive

Abstract Abstract 3903 Poster Board III-839 Background A peripheral blood (PB) absolute eosinophil count (AEC) of ≥ 1.5 × 109/L is operationally referred to as “hypereosinophilia”. In general, one can classify hypereosinophilia into 3 major categories: i) secondary, ii) clonal, and iii) idiopathic. The 2008 WHO proposal provides a modern-era framework for the classification of clonal eosinophilia and subcategories include (i) myeloid/lymphoid neoplasms associated with eosinophilia and PDGFRA-, PDGFRB-, or FGFR1-rearrangement; (ii) clonal eosinophilia associated with an otherwise WHO-defined myeloid malignancy such as systemic mastocytosis (MN-eo), and (iii) chronic eosinophilic leukemia, otherwise not specified (CEL-NOS). Idiopathic hypereosinophilia (IH) with organ damage and without clonal/abnormal lymphocytes is referred to as hypereosinophilic syndrome (HES). In the current study, we define the spectrum of disease phenotypes and survival in 357 consecutive patients with hypereosinophilia seen at a single institution. Methods Mayo Clinic patient records from January 1994 to October 2008 were reviewed, and those with persistent eosinophilia ≥1.5 × 109/L identified. Clinical data and bone marrow (BM) histology were reviewed, and the eosinophilic disorder classified as above. The aims of the current study were to: (i) study the spectrum of eosinophilic disorders within the context of the WHO proposal; (ii) describe the clinical, laboratory, and molecular/cytogenetic characteristics of patients with primary eosinophilia (i.e. clonal and idiopathic); and (iii) assess the prognostic relevance of the WHO proposal from the standpoint of life expectancy and risk of leukemic transformation. Results (i) Disease spectrum and clinical characteristics: A total of 357 cases (median age=52 years) were identified: (i) secondary eosinophilia 165 (46%; male ∼52%) (autoimmune 33%, non-myeloid malignancy 19%, drugs 12%, allergies 10%, parasitosis 2%, others 24%); (ii) PDGFRA- or PDGFRB-rearranged myeloid neoplasm 17 (5%; male 100%); (iii) CEL-NOS 6 (2%; male 67%); (iv) MN/eo 36 (10%; male 69%) (systemic mastocytosis 50%, chronic myeloproliferative neoplasm 33%, AML 6%, others 11%); (v) IH 115 (32%; male 58%); and (vi) eosinophilia associated with clonal/abnormal lymphocytes 14 (4%; male 57%). Of the 115 patients with IH, 72 (63%) had evidence of end-organ damage, and could be classified as having HES: 36 patients had 1 organ involved, 21 had 2, and 15 had 3-4. In HES patients, the major organs involved were: lung 23%, skin/mucosa 22%, cardiac 14%, nervous system 10%, and thrombosis 9%. (ii) Molecular and cytogenetic abnormalities: Complete karyotype information was available for 144 (77%) patients; 21 (15%) patients had an abnormal karyotype; MN/eo 12 (35%), PDGFRA- or PDGFRB-rearranged myeloid neoplasm 4 (31%), CEL-NOS 5 (83%), IH and eosinophilia associated with clonal/abnormal lymphocytes 0 (p<0.01). Of the 126 (67%) patients screened for FIP1L1-PDGFRA, 16 (13%) tested positive. Two patients (1%) harbored t(5;12). Of the 108 (57%) patients screened for presence of an occult T-cell clone (PCR for TCR gene rearrangement), 14 (13%) tested positive. (iii) Survival and risk of disease transformation: At a median follow of 21 months (range <1-174), 56 (30%) deaths were recorded; MN/eo 23 (64%), IH 25 (22%), PDGFRA- or PDGFRB-rearranged myeloid neoplasm 3 (18%), CEL-NOS 3 (50%), and T-cell/eo 2 (14%). The combined median survival was 95 months: MN/eo 34 months, CEL-NOS 13 months, IH 151 months, PDGFRA- or PDGFRB-rearranged myeloid neoplasm and eosinophilia associated with an abnormal lymphocyte clone (not reached) (p<0.01; Figure). Transformation to acute leukemia was seen in 4 patients (2 with PDGFRA- or PDGFRB-rearranged myeloid neoplasm, and 1 each with CEL-NOS and IH) (p<0.01). Conclusions In a major tertiary center in the United States, the two major causes of hypereosinophilia were secondary (46%) and idiopathic (32%). Regarding the former, autoimmune diseases and parasitic infections were the most and least frequent causes, respectively. Cases with clonal eosinophilia were predominantly male while the sex ratio was more balanced in the other subcategories. Among primary hypereosinophilia, survival was the worst in clonal eosinophilia not associated with the imatinib-sensitive PDGFR mutations. Additional data regarding clinical characteristics, laboratory findings, and treatment outcome of idiopathic hypereosinophilia patients will be presented at the meeting. Disclosures: Pardanani: TargeGen: Research Funding; Cytopia: Research Funding.