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Abstract Background Momelotinib (MMB, GS-0387, CYT387) is a JAK1 and JAK2 inhibitor under investigation for the treatment of myelofibrosis. Preliminary results of a phase I/II core study (n=166) were previously reported. Subjects who achieved at least stable disease in the core study could continue MMB treatment in an extension study (n=120). Final data from the phase I/II core study and updated data from the extension study are presented. Methods Subjects with myelofibrosis categorized as IPSS intermediate-2 or high risk, or intermediate-1 risk with symptomatic splenomegaly or hepatomegaly and/or unresponsive to available therapy, were enrolled. Following a dose escalation phase, subjects were treated on a dose expansion phase in the core study with MMB at either 150 mg or 300 mg once-daily, or 150 mg twice-daily for 9 months. In the extension study, MMB was at the same dose the subject tolerated and derived clinical benefit from in the core study. Clinical responses were adjudicated according to IWG-MRT criteria. Spleen Response was defined as ≥ 50% reduction in palpable splenomegaly that lasted ≥ 8 weeks (wks) for baseline splenomegaly ≥ 10 cm, plus resolution of palpable splenomegaly that lasted ≥ 8 wks for baseline splenomegaly > 5 to < 10 cm. Anemia Response was defined as transfusion-free interval of ≥ 12 wks for baseline transfusion dependence, plus ≥ 2 g/dL rise in hemoglobin (Hb) for baseline transfusion independence and Hb < 10 g/dL. Baseline transfusion dependence was defined as ≥ 2U RBC transfusion in the 30 days prior to first dose of MMB or identified as transfusion dependent in medical history. Results As of April 2013, 58 of 120 subjects remained on treatment in the open-label extension study, with median treatment duration of 507 days (range 23-1036) for both core and extension studies. Based on interim analysis, the most common reasons for discontinuation from the extension study were disease progression (n=13), investigator's decision (n=12), and consent withdrawal (n=10), with 2 drug-related adverse events (both peripheral neuropathy) that led to study discontinuation. Efficacy data for the core and extension studies are depicted in table below. Median time to onset of Spleen Response was not yet reached (range 6-693 days), median duration of Spleen Response was 324 days (range 56-936). Median duration of 12-week transfusion independence was not yet reached (91-987 days), median duration of Anemia Response was not yet reached (57-987). Constitutional symptoms assessment at 3 months for the core study showed ≥ 50% improvement in 72%, 46%, 77%, 100%, and 74% of subjects with pruritis, cough, bone pain, fever, and night sweats respectively. Most common Grade 3 or 4 treatment-related events were thrombocytopenia (29%), neutropenia (5%), and elevated lipase (4%) without clinical pancreatitis. Peripheral neuropathy was reported by 38% of subjects, all ≤ Grade 2, with 17 subjects experiencing neuropathy at baseline. Four subjects transformed into acute leukemia (1 in core study, 3 in extension study). There was no treatment-related death. Conclusion Prolonged administration of MMB for treatment of myelofibrosis is well tolerated and has an acceptable safety profile. MMB is efficacious in durably reducing myelofibrosis-related splenomegaly as well as improving transfusion requirement and disease-related symptoms. These data form the basis for the phase 3 randomized study of MMB in myelofibrosis. Disclosures: Gupta: Novartis: Lecture fee, Lecture fee Other; Novartis: Consultancy; Incyte: Consultancy; Novartis: Research Funding; Incyte: Research Funding. Bavisotto:YM Biosciences: Consultancy. Kawashima:Gilead Sciences: Employment. Lee:Gilead Sciences: Employment. Kowalski:Gilead Sciences: Employment. Deng:Gilead Sciences: Employment. Niforos:Gilead Sciences: Employment.

OBJECTIVE Phenotypic differences between moyamoya disease (MMD) and moyamoya syndrome (MMS) remain unclear. The purpose of this study was to evaluate whether such differences exist when presentation, procedure-related, and outcome variables are compared quantitatively. METHODS The study cohort included 185 patients with moyamoya presenting to the Johns Hopkins Medical Institutions between 1994 and 2015. Baseline demographic, angiographic, and clinical characteristics were compared between patients with MMS and MMD, in addition to procedure-related complications and length of stay (LOS) after surgery. Stroke-free survival was compared between both disease variants after diagnosis. Kaplan-Meier analysis and Cox proportional hazards regression were used to compare stroke-free survival between surgically treated and conservatively managed hemispheres in both types of disease, while evaluating interaction between disease variant and management. RESULTS The cohort consisted of 137 patients with MMD (74%) with a bimodal age distribution and 48 patients with MMS (26%) who were mostly under 18 years of age (75%). Underlying diseases included sickle cell disease (48%), trisomy 21 (12%), neurofibromatosis (23%), and other disorders (17%). Patients with MMS were younger (p < 0.001) and less likely to be female (p = 0.034). Otherwise, baseline characteristics were statistically comparable. The rate of surgical complications was 33% in patients with MMD and 16% in patients with MMS (p = 0.097). Both groups of patients had a similar LOS after surgery (p = 0.823). Survival analysis (n = 330 hemispheres) showed similar stroke-free survival after diagnosis (p = 0.856) and lower stroke hazard in surgically managed patients in both MMD (hazard ratio [HR] 0.29, p = 0.028) and MMS (HR 0.62, p = 0.586). The disease variant (MMD vs MMS) did not affect the relationship between management approach (surgery vs conservative) and stroke hazard (p = 0.787). CONCLUSIONS MMD and MMS have largely comparable clinical and angiographic phenotypes with analogously favorable responses to surgical revascularization.

Abstract Introduction Polycythemia vera (PV) is characterized by excessive production of erythroid cells and in most cases a point mutation (V617F) in the Jak2 cytokine signaling kinase. We investigated whether a selective JAK2 inhibitor decreased Jak2 V617F induced erythroid differentiation. Methods Wild-type and mutant Jak2 V617F genes were excised from the retroviral Jak2-mus-MSCV-neo vector (Levine et al), cloned into the lentiviral vector pLV CMV IRES2 GFP and their presence verified by DNA sequencing. Lentiviral vectors bearing the wild-type and mutant Jak2 genes or vector alone were used to transduce human peripheral blood CD34+ cells, which were then divided for plating into megacult medium for megakaryocytic colony growth and methylcellulose culture for enumeration of all other progenitor cell types. Normal cord blood HSC (CD34+/CD38−/CD90+) were clone sorted with the FACS Aria and transduced with no vector, backbone vector, wild-type JAK2 or mutant JAK2 vector in methocult media (Stem Cell Technologies Inc, GF+ H4435) +/− 300 nM of a selective JAK2 inhibitor, TG101348. Colonies were scored at day 14. RNA was isolated from the colonies (Qiagen RNeasy kit) and RT-PCR was performed with wild-type and mutant JAK2 allele specific primers. Results Transduction of cord blood HSC with the mutant Jak2 vector resulted in skewed erythroid colony formation compared to wild-type Jak2, vector alone and untransduced HSC (Figure 1; n=3). RT-PCR with murine Jak2 specific primers resulted in ~900 bp fragments corresponding to murine Jak2 from colonies transduced with the wild-type and mutant Jak2 and confirmed by sequencing, but not those from colonies transduced with the vector alone or the untransduced cells. Like the results in cord blood cells, adult peripheral blood CD34+ cells transduced with the mutant Jak2 developed a skewed developmental pattern, with far greater erythroid colony formation compared to wild-type Jak2 or vector alone. In megacult assays, CD34+ cells transduced with the mutant Jak2 had similar megakaryocytic potential as wild-type Jak2 or vector alone. Addition of TG101348 (300 nM), inhibited mutant kinase-induced erythroid colony formation (Figure 1) in 3 experiments while 100– 300 nM was inhibitory to PV (n=2 patients) HSC and progenitors. Current experiments focus on inhibition of Jak2 in a bioluminescent highly immunocompromised mouse model of Jak2V617F-induced myeloproliferation (Figure 2). Conclusion JAK2 V617F skews differentiation of HSC toward the erythroid lineage and may be inhibited with a selective JAK2 inhibitor - TG101348. Figure 1. In vitro JAK2 Inhibition. Figure 1. In vitro JAK2 Inhibition. Figure 2. Bioluminescent JAK2 V617F-induced Myeloproliferation Model. Figure 2. Bioluminescent JAK2 V617F-induced Myeloproliferation Model.

Abstract PRM-151 (PRM) is a recombinant form of Pentraxin-2, an endogenous human protein that acts at sites of tissue damage, inducing macrophage differentiation to prevent and reverse fibrosis. PRM has broad anti-fibrotic activity in multiple preclinical models of established fibrotic diseases and no dose limiting toxicities in phase 1 trials. Myelofibrosis (MF: primary (PMF), post-essential thrombocythemia (post-ET MF), and post polycythemia vera (Post PV MF)) is a myeloid malignancy characterized by progressive bone marrow (BM) fibrosis with resultant anemia, abnormal platelet and leukocyte counts, extramedullary hematopoiesis, and a well-defined symptom complex. This study investigated the potential of PRM in MF to reduce BM fibrosis and to improve key disease features including abnormal blood counts, symptoms, and splenomegaly. MF patients (pts) with Dynamic International Prognostic Scoring System (DIPSS) intermediate-1, intermediate-2, or high-risk disease and grade ≥ 2 BM fibrosis, either on no current therapy or on a stable dose of ruxolitinib (RUX) for ≥ 12 weeks and no improvement in spleen for ≥ 4 weeks, were eligible for stage 1 of this open-label adaptive trial. Assignment to one of the 4 treatment arms was per investigator and pt choice: PRM 10 mg/kg IV 1-hour infusion days 1, 3, 5, then weekly (QW) or every 4 weeks (Q4W), alone or with RUX, for 24 weeks. Primary endpoint was overall response rate by IWG-MRT (symptoms by MPN-SAF Total Symptom Score (TSS), spleen by palpation) and/or decrease in BM fibrosis by ≥ 1 grade with otherwise stable disease. BM biopsies were obtained at baseline, 3 and 6 months, and were evaluated centrally by two blinded hematopathologists. Pts with clinical benefit were allowed to continue treatment in an extension. At least one response in any arm was required for that regimen to be evaluated in Stage 2. Twenty seven pts were enrolled: 8 PRM QW, 7 PRM Q4W, 6 PRM QW + RUX, 6 PRM Q4W + RUX. Median age 67 years (52-85); 70% DIPSS Int-2 or High Risk; 52% PMF, 15% post-ET MF, 33% post-PV MF; 63% grade 3 BM fibrosis, Hemoglobin (Hgb) < 100 g/L in 56% and < 85 g/L in 26%, platelet count (PLT)< 100 x 109/L in 52% and < 25 x 109/L in 30%; 22% were JAK inhibitor-naive and 52% had received a prior JAK inhibitor (not including ongoing RUX). Twenty pts completed 24 weeks of therapy; 18 continued extension treatment. PRM-151 was well-tolerated alone and with RUX; most adverse events (AEs) were Grade 1/2 and unrelated, with 3 Grade 3 possibly related AEs and 5 possibly related serious AEs. Nine of 26 evaluable pts responded, for an overall response rate (ORR) of 35%, with 4 IWG symptom clinical improvements (CI) and 6 BM fibrosis responses (Table 1), with ≥ 1 response in each arm. One pt had a CI and BM response. Reduction in BM fibrosis was associated with normal erythroid microarchitecture, normal or decreased myeloid:erythroid ratio, and fewer paratrabecular megakaryocytes, all potential surrogates of improved bone marrow microenvironment. IWG stable disease was observed in 77% of pts, with trends of clinical benefit in Hgb, PLT, peripheral blood blasts, spleen, and symptoms (Table 2). In 14 patients (54%), all parameters were stable or improved. Conclusion: PRM-151 was well-tolerated in patients with advanced MF, with no evidence of drug-related myelosuppression and encouraging trends in both clinical and histologic aspects of the disease. Reduction in BM fibrosis, stable to improved hematologic parameters, symptom responses, and stable to reduced spleen size support further development of PRM-151 in MF. Table 1 Two additional subjects had decrease in bone marrow fibrosis but progressive disease. Number of Patients BM Fibrosis Grade at Last Study Timepoint 3 2 1 BM Fibrosis Grade at Baseline 3 8 3 1 2 1 4 2 Abstract 713. Table 2 Outcome Parameter Denominator (n) Clinical Benefit Pts with Improvement (n/%) ORR (primary endpoint) All evaluable pts (26) IWG-MRT CI AND/OR reduction in BM fibrosis by ≥ 1 grade 9 (35%) Hgb Hgb < 100 g/L (15) ≥10 g/L increase from baseline AND no transfusions or 50% reduction in transfusions if transfusion dependent 6 (40%) PLT PLT < 100 x 109/L (13) > 100 x 109/L AND increase of ≥20 x 109/L ; increase of ≥20 x 109/L if baseline < 50, AND/OR increase of ≥ 10 x 109/L with discontinuation of transfusions 8 (62%) Blasts ≥ 1% peripheral blasts (14) No peripheral blasts 3 (21%) Symptoms All evaluable pts (26) ≥ 25% reduction in TSS ≥ 12 weeks 10 (38%) Spleen Palpable spleen (19) ≥ 25% decrease ≥ 4 weeks AND any decrease ≥ 12 weeks 5 (26%) Disclosures Verstovsek: Incyte: Research Funding; Astrazeneca: Research Funding; Lilly Oncology: Research Funding; Roche: Research Funding; Geron: Research Funding; NS Pharma: Research Funding; Bristol Myers Squibb: Research Funding; Novartis: Research Funding; Celgene: Research Funding; Gilead: Research Funding; Seattle Genetics: Research Funding; Promedior: Research Funding; Cell Therapeutics: Research Funding. Mesa:Incyte, CTI, NS pharma, Gilead, Celgene: Research Funding; Promedior: Research Funding. Foltz:Janssen: Consultancy; Promedior: Research Funding; Gilead: Research Funding; Incyte: Research Funding; Novartis: Consultancy, Honoraria, Research Funding. Gupta:Incyte Corporation: Consultancy, Research Funding; Novartis: Consultancy, Honoraria, Research Funding; Promedior: Research Funding. Mascarenhas:Novartis Pharmaceuticals Corporation: Research Funding; Incyte Corporation: Consultancy, Research Funding; Promedior: Research Funding. Ritchie:Celgene, Incyte: Speakers Bureau; Promedior: Research Funding. Hoffman:Geron: Consultancy, Membership on an entity's Board of Directors or advisory committees; All Cells LLC: Consultancy, Membership on an entity's Board of Directors or advisory committees; Promedior: Research Funding. Pozdnyakova:Sanofi: Consultancy; Incyte: Consultancy; Promedior: Consultancy. Hasserjian:Sanofi: Consultancy; Incyte: Consultancy; Promedior: Consultancy. Trehu:Promedior: Employment, Equity Ownership. Kantarjian:ARIAD, Pfizer, Amgen: Research Funding. Gotlib:Novartis: Research Funding, Travel Reimbursement, Travel Reimbursement Other; Sanofi: Research Funding; Gilead: Research Funding; Incyte: Consultancy, Honoraria, Research Funding, Travel Reimbursement Other; Promedior: Research Funding.

Abstract Abstract 1733 Background: Patients with myelofibrosis (MF) suffer from cytopenias, debilitating symptoms, and splenomegaly, all of which may contribute to shortened life expectancy. Cachexia is a common manifestation of MF. Its causes are multifactorial and include elevated inflammatory cytokines and mechanical effects of splenomegaly. It is a predictor of poor survival in patients with MF. Cachexia manifests as weight loss with low body-mass index (BMI; <20–21 kg/m2) (Strasser F. Sixth Research Congress of the European Association of Palliative Care; Wagner PD. Eur Respir J. 2008;31:492–501) and with metabolic indicators of poor nutritional status including hypocholesterolemia (total cholesterol <150 mg/dL or <3.89 mmol/L), which has been linked to poor prognosis in MF (Mesa et al. Blood 2007;110:abstract 2548). In the phase III, placebo-controlled, COMFORT-I study, ruxolitinib treatment significantly reduced spleen volume, improved MF-related symptoms, and exhibited a survival advantage compared with placebo in patients with MF. In this post hoc analysis, we investigated the effects of ruxolitinib treatment on weight and total cholesterol and the association of these changes with survival in COMFORT-I. Methods: Eligible patients in COMFORT-I were randomized to receive placebo (n=154) or ruxolitinib (n=155) at starting doses of 15 and 20 mg PO BID depending on baseline platelet count. Body weight was measured at baseline, and weeks 4, 8, 12, 16, and 24 and then every 12 weeks thereafter. Total serum cholesterol was measured at baseline and weeks 4, 12, 24, and then every 24 weeks thereafter. All patients receiving PBO completed crossover or discontinued within 3 months of the primary data analysis (when all patients completed 24 weeks and when half the patients remaining on study completed 36 weeks of treatment); thus, data for these patients were available for up to week 36 for weight and week 24 for total cholesterol. Kaplan-Meier analyses of overall survival were conducted in patients randomized to ruxolitinib stratified into 2 groups based on the median values separately for maximum weight gain and for maximum increase in total cholesterol during randomized treatment. Results: At baseline, mean body weight was similar between the treatment groups (72 kg, both) and mean total cholesterol was low (<150 mg/dL) in both treatment groups (ruxolitinib: 118 mg/dL; placebo: 115 mg/dL). The proportion of patients with BMI <22 were similar between the treatment groups (ruxolitinib: 23%; placebo: 28%) as was the proportion with total cholesterol <150 mg/dL (82%, both). Patients randomized to ruxolitinib experienced a gradual increase in body weight that stabilized by week 36 of treatment whereas patients receiving placebo experienced decreases in body weight over time (Figure 1). Similarly, total cholesterol increased in patients randomized to ruxolitinib and decreased in patients receiving placebo (Figure 2). Although total cholesterol increased over time in ruxolitinib-treated patients, increases did not exceed the upper limit of normal (199 mg/dL or 5.15 mmol/L). Nearly all patients randomized to ruxolitinib experienced weight gain (96% of patients) or an increase in total cholesterol (97% of patients). In patients randomized to ruxolitinib, weight gain above the median was associated with prolonged survival relative to lesser degrees of weight gain (HR=0.40; 95% CI: 0.18, 0.90; P=0.022; Figure 3). Similarly, increase in total cholesterol above the median was also associated with prolonged survival relative to a lesser degree of total cholesterol increase (HR=0.46; 95% CI: 0.21, 1.01; P=0.048; Figure 4). Meaningful comparisons with the placebo group based on the same stratification criteria could not be conducted as the majority of such patients experienced weight loss and decreases in total cholesterol while on the study; however, overall survival favored both ruxolitinib groups relative to all patients randomized to placebo even for ruxolitinib-treated patients with lower than median levels of weight gain or increase in total cholesterol. Conclusions: Ruxolitinib therapy promotes weight gain and improves total cholesterol in MF patients. These results suggest that the survival advantage exhibited by ruxolitinib over placebo in MF patients may be partly explained by reversal of the catabolic state and cachexia. Disclosures: Mesa: Incyte: Research Funding; Lilly: Research Funding; Sanofi: Research Funding; NS Pharma: Research Funding; YM Bioscience: Research Funding. Verstovsek:Incyte Corporation: Research Funding. Gupta:Incyte: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene: Research Funding; YM Biosciences: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Sanofi#x2610;#x0025; Aventis: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding. Mascarenhas:Incyte Corporation: Consultancy; Novartis: Clinical Trial Support, Clinical Trial Support Other. Atallah:Incyte: Consultancy, Research Funding. Sun:Incyte Corporation: Employment, Equity Ownership. Sandor:Incyte Corporation: Employment, Equity Ownership. Gotlib:Incyte Corporation: Consultancy, Honoraria, Support for travel to meeting for the study or other purposes from Incyte Other.

Abstract Abstract 1732 Background: In addition to chronic myelogenous leukemia (CML), the classic myeloproliferative neoplasms (MPNs) include polycythemia vera (PV), essential thrombocythemia (ET), and primary myelofibrosis (PMF). The JAK2 V617F mutation (V617F) can be detected through genomic analysis of peripheral blood in 95% of PV and 50–60% of ET and MF patients (pts). These MPNs are often associated with debilitating symptoms and decreased quality of life (QOL). Systemic mastocytosis (SM) is an uncommon MPN in which proliferation of mast cells can result in mediator symptoms, as well as organ damage in advanced disease. We sought to compare the symptom burden of individuals with CML and SM to pts with classic MPNs in a more quantitative manner using a web-based recruitment design. Methods: Individuals with MPN were recruited through a web-based outreach effort. Participants gave IRB-approved consent, and completed on-line surveys of demographic information and questions based on the validated MPN-symptom assessment form (MPN-SAF). In addition, pts submitted saliva samples which were genotyped with SNP arrays based on the Illumina OmniExpress BeadChip, including probes for V617F. Regression analysis was used to evaluate the correlation between symptom responses and genotype data for 495 pts (118 PV, 121 ET, 97 MF, 85 SM, and 74 CML). For each MPN diagnosis, mean scores were calculated based on six fatigue-focused questions (Fatigue-6) and for six other symptoms (Symptom-6): early satiety, abdominal pain/discomfort, inactivity, night sweats, pruritis, and bone pain (ranked from 0–10; 10 = worst). ET pts' scores were used as the reference in the regression analysis based on prior data showing that ET pts have the lowest symptom burden among the classic MPNs. Individual symptoms, Fatigue-6, Symptom-6, and QOL (ranked 0–10; 10=worst) were analyzed using regression analysis against age, gender, diagnosis and V617F status. Results: Median age was 56 years (7–87), with 70% women. V617F was detected in 63% of classic MPN pts (87% PV, 46% ET, 56% MF). Analysis of Fatigue-6 scores revealed that age in years was negatively correlated with reported fatigue (β=-0.007 per year, P=0.032), while female gender and SM diagnosis were positively correlated with fatigue (female: β=0.33, P=2.4×10−4; SM: β=0.46, P=7.6×10−4). This trend was also seen for the Symptom-6: age (β=-0.025, P=5.8×10−4), female gender (β=0.73, P=1.4×10−4), and SM (β=1.8, P=5.0×10−10). Both Fatigue-6 and Symptom-6 were positively correlated with QOL, but Fatigue-6 had a much stronger association with QOL than did Symptom-6 (β=1.3, P=1.5×10−28 vs. β=0.36, P=1.2×10−11). When analyzed individually, abdominal pain/discomfort, pruritis, and bone pain were significantly correlated with V617F (β=0.676, P=0.0371; β=0.768, P=0.0241; β=0.791, P=0.0341, respectively), though these associations were not significant when all six symptoms were evaluated together (Symptom-6: β=0.315, P=0.171). There was no statistically significant correlation between V617F and Symptom-6. In addition, there was no correlation between any symptom and a germline variant in telomerase reverse transcriptase (TERT) rs2853677, identified as a novel predisposition allele for MPNs using a genome-wide association study of this cohort. Conclusion: Using a novel, web-based recruitment design combining MPN symptom assessment and genotyping of saliva samples, we identified significant correlations between 3 specific symptoms (pruritis, abdominal pain/discomfort, and bone pain) with V617F. Fatigue was also more strongly associated than other symptoms with QOL. There was no association between symptoms and TERT. This design is a powerful tool for future studies seeking to correlate symptoms with genotyping analysis. Disclosures: Hinds: 23andMe: Employment, Equity Ownership, Patents & Royalties. Barnholt:23andMe, Inc.: Employment. Kiefer:23andMe, Inc.: Employment. Do:23andMe, Inc.: Employment, Equity Ownership, Patents & Royalties. Eriksson:23andMe, Inc.: Employment, Equity Ownership, Patents & Royalties. Mountain:23andMe, Inc.: Consultancy, Employment, Honoraria, Patents & Royalties, Research Funding. Francke:23andMe, Inc.: Employment, Honoraria, Research Funding; Locus Development: Consultancy, Membership on an entity's Board of Directors or advisory committees. Tung:23andMe, Inc.: Employment. Zehnder:23andMe, Inc.: Unpaid advisor and collaborator Other. Gotlib:23andMe, Inc.: Unpaid advisor and collaborator Other. Mesa:23andMe, Inc: Unpaid advisor and collaborator Other.

Abstract Abstract 2847 Background and Purpose: Myelofibrosis (MF) is a progressive Philadelphia-negative myeloproliferative neoplasm characterized by debilitating symptoms, massive splenomegaly, and anemia, which severely impairs quality of life. When medical therapy is not effective or tolerated, splenectomy may be required to ease symptoms in patients with symptomatic portal hypertension, massive splenomegaly, and/or frequent red blood cell transfusions (Barbui et al. J Clin Oncol. 2011;29:761–770). In a recent study (Tefferi et al. Mayo Clin Proc. 2012;87:25–33) up to 27% of patients diagnosed with MF eventually underwent splenectomy. However, splenectomy is associated with limited duration of symptom response, high rates of perioperative morbidity and mortality, and acceleration of hepatomegaly. Clinical studies in patients with MF have demonstrated that ruxolitinib, an oral JAK1/JAK2 inhibitor, provides significant and durable reductions in splenomegaly, the burden of MF-associated symptoms, and also improved quality of life. In this post hoc analysis of pooled data from these studies, we determined the incidence of splenectomy in patients treated with ruxolitinib and those who received placebo or best available therapy (BAT) to evaluate whether ruxolitinib therapy may affect the need for splenectomy. Methods: This analysis included patients who participated in the ruxolitinib phase I/II trial (N=153; Verstovsek et al. N Engl J Med. 2010;363:1117–1127); COMFORT-I, a phase III, 24-month placebo-controlled trial of ruxolitinib (N=309; Verstovsek et al. N Engl J Med. 2012;366:799–807); and COMFORT-II, a phase III, 48-month randomized trial comparing the effects of ruxolitinib and BAT (N=219; Harrison et al. N Engl J Med. 2012;366:787–798). Incidence of splenectomy while on treatment or during the protocol-specified follow-up period, adjusted for differences in the duration of follow up, was calculated for patients on ruxolitinib, placebo, or BAT. Results: As a result of the crossover rules and a higher discontinuation rate on the comparator arms in the phase III studies, mean follow-up duration for placebo (0.67 years) or BAT (0.95 years) overall was substantially shorter than mean follow-up duration for ruxolitinib (1.78 years). Baseline characteristics of the 14 patients who underwent splenectomy were as follows: median age=63 years; median time since initial diagnosis=7.8 years; median spleen length (n=13): 17.0 cm (range: 0–28.0 cm); median spleen volume (in those with measurement, n=11)=2924 cm3 (range: 1203–6807 cm3); IPSS high risk=50%, intermediate-2 risk=43%, intermediate-1=7%. Among patients originally randomized and treated with ruxolitinib, the incidence of splenectomy was 1.1 events per 100 patient years (Table). For patients treated with placebo or BAT in the phase III studies, the incidence of splenectomy was approximately three times higher at 2.9 events per 100 patient years, despite the fact that patients on placebo or BAT were allowed to crossover to ruxolitinib if they had worsening symptomatic splenomegaly. Conclusions: Although limited by small numbers, results of this analysis suggest that ruxolitinib reduces the need for splenectomy in patients with MF. Because of crossover to ruxolitinib and higher discontinuation rates in placebo and BAT, follow-up duration was shorter in these treatment arms compared with ruxolitinib. Further, ruxolitinib treatment in crossover patients may have prevented progression of symptomatic splenomegaly in some patients who may have otherwise become candidates for splenectomy. Our analysis may underestimate the true incidence of splenectomy among patients not receiving ruxolitinib therapy and therefore, the relative reduction in splenectomy rate in patients receiving this therapy. Longer-term follow up will better define the splenectomy rate in ruxolitinib-treated patients. Disclosures: Verstovsek: Incyte Corporation: Research Funding. Kiladjian:Novartis: Membership on an entity's Board of Directors or advisory committees, Research Funding; Shire: Membership on an entity's Board of Directors or advisory committees; Incyte: Membership on an entity's Board of Directors or advisory committees; Celgene: Research Funding. Mesa:Incyte: Research Funding; Lilly: Research Funding; Sanofi: Research Funding; NS Pharma: Research Funding; YM Bioscience: Research Funding. Vannucchi:Novartis: Membership on an entity's Board of Directors or advisory committees. Gotlib:Incyte Corporation: Consultancy, Honoraria, Support for travel to meeting for the study or other purposes from Incyte Other. Kantarjian:Incyte: grant support Other. Sirulnik:Novartis: Employment, Equity Ownership. Peng:Incyte Corporation: Employment, Equity Ownership. Sandor:Incyte Corporation: An employee of Incyte and receiving stock options as part of his compensation Other, Employment. Harrison:Novartis: Honoraria, Research Funding, Speakers Bureau; YM Bioscience: Consultancy, Honoraria; Sanofi Aventis: Honoraria; Shire: Honoraria, Research Funding.

Abstract Abstract 1727 Background: Myelofibrosis (MF) is characterized by cytopenias, splenomegaly, and burdensome symptoms that may worsen over time. Ruxolitinib (RUX) has been shown to reduce splenomegaly and improve MF-associated symptoms in 2 phase III studies, including COMFORT-I, a randomized, double-blind, placebo (PBO)-controlled trial, which also showed prolonged survival in favor of RUX. Purpose: In this post hoc analysis of COMFORT-I, the efficacy of RUX in patients with varying degrees of splenomegaly and symptom severity at baseline was evaluated to assess the potential effects of earlier versus later intervention in this progressive disease. Methods: COMFORT-I participants randomized to RUX (n=155) or PBO (n=154) had MF with an International Prognostic Scoring System (IPSS) score ≥2 and a platelet count of ≥100 × 109/L. Patients with protocol-defined worsening splenomegaly were permitted to cross over from PBO to RUX. The primary endpoint was the percentage of patients with ≥35% reduction in spleen volume (SV) at week (wk) 24. Change in Total Symptom Score (TSS) was a secondary endpoint. TSS was the sum of 6 symptom scores (night sweats, itching, abdominal discomfort, pain under ribs on left side, early satiety, muscle/bone pain) assessed with the modified MF Symptom Assessment Form (MFSAF) v2.0 on a scale of 0 (“absent”) to 10 (“worst imaginable”). Patients were stratified by palpable spleen length (SL) (≤ 10 cm, <10 to 20 cm, >20 cm) and TSS tertile (≤11.1, >11.1 to 22.0, >22.0) at baseline. SV and TSS stratified by baseline values as described were summarized over time. To account for PBO crossover, modeling was performed to predict SV after crossover using a nonlinear mixed model that best predicted individual patient data. Last observation carried forward was used to impute missing TSS data. Results: Mean absolute SV and TSS worsened over time in the PBO group regardless of baseline SL and TSS, demonstrating the progressive nature of MF. In patients treated with RUX, mean absolute SV and TSS at wk 24 were lower for patients with smaller SL and less severe TSS at baseline, respectively (Table); absolute differences with PBO were significant within each subgroup. Therefore, patients who initiated RUX therapy with more advanced MF were less likely to achieve the same clinical status experienced by patients initiating therapy with less advanced MF. Notably, even after 24 wks of RUX treatment, SV and TSS reductions in the cohorts with larger SL or greater TSS at baseline did not achieve levels equivalent to baseline of the next lesser baseline severity group (Table; Figure). Although the severity of splenomegaly and symptoms at baseline influenced the absolute SV and TSS achieved at wk 24, RUX treatment resulted in similar percent reductions in SV and improvements TSS across all subgroups, with the exception of the lower TSS tertile (where there is less room for improvement). In contrast, PBO treatment resulted in increases in SV and worsening of symptoms and patients with less severe SV and TSS at baseline experienced the greatest percent increases in SV and TSS at wk 24. Conclusions: RUX therapy was associated with SV reduction and symptom improvement regardless of spleen size or symptom severity at baseline, whereas patients on PBO experienced disease progression across all subgroups. Patients receiving RUX with less advanced disease achieved an overall better clinical status, as defined by lower absolute SV and symptom scores. This analysis suggests that initiation of RUX in patients with less severe splenomegaly and symptoms may contribute to improved patient outcomes. Disclosures: Mesa: Incyte: Research Funding; Lilly: Research Funding; Sanofi: Research Funding; NS Pharma: Research Funding; YM Bioscience: Research Funding. Gotlib:Incyte: Consultancy. Kantarjian:Incyte: grant support Other. Sun:Incyte: Employment. Verstovsek:Incyte Corporation: Research Funding.

Abstract Abstract 178 Background: CYT387 is a potent and selective small molecule inhibitor of JAK 1 and JAK 2 which is in clinical development for the treatment of myelofibrosis. Previously reported preliminary results from a phase I/II multicenter study demonstrated improvements in splenomegaly and constitutional symptoms as well as in RBC transfusion requirements. Enrollment has been completed and all subjects have now reached a minimum of 9 months on study. Updated safety and efficacy results are presented. Methods: Subjects with high or intermediate-risk primary myelofibrosis (PMF) and post-polycythemia vera (post-PV) or post-essential thrombocythemia (ET) myelofibrosis were enrolled. Following an initial dose expansion phase, subjects were treated in a 9 month core study at an initial dose of 150 mg QD, 300 mg QD or 150 mg BID. Continued treatment with CYT387 was permitted in an extension phase for subjects who maintained at least stable disease. Responses were assessed by International Working Group (IWG) criteria with transfusion independence response defined as achieving a minimum 12 week transfusion-free period. Results: Enrollment of 166 subjects was completed at 6 study sites. Initial doses included 52 subjects at 150 mg QD, 60 subjects at 300 mg QD and 42 subjects at 150 mg BID. An additional 12 subjects were enrolled in other dose groups (100 mg QD, 200 mg QD, 400 mg QD) during the initial dose escalation phase. The median duration (range) of follow-up is 16.1 months (0.7 to 31.0 months). Durable transfusion independence responses were observed in more than half of the RBC transfusion dependent subjects with a maximal transfusion-free period exceeding 2 years and ongoing. In addition, the percentage of all subjects requiring RBC transfusions substantially decreased over the treatment period. Treatment with CYT387 resulted in rapid and sustained reductions in splenomegaly with a maximal response duration approaching 2 years. The majority of subjects reporting constitutional symptoms at baseline experienced complete resolution or marked improvement by 6 months with measurable improvement within the first month of therapy. Higher transfusion independence and spleen response rates were seen in the 300 mg dose group compared to the 150 mg QD or 150 mg BID dose groups. For the first 60 consecutively enrolled subjects for whom the most mature data is available, the median follow-up period (range) is 21.5 months (2.9–31.0 months). The anemia and spleen response rates in these subjects, per IWG-MRT, were 59% and 48%, respectively; among 33 of these subjects who were RBC transfusion dependent by IWG-MRT criteria, 70% achieved a minimum 12-week period without transfusions with a maximal transfusion-free period of greater than 2 years and ongoing. While 90% of subjects reported at least one treatment-related AE, the majority were reported as Grade 1. The most common treatment-related AEs were thrombocytopenia, peripheral neuropathy, dizziness, diarrhea, nausea, and headache. Treatment-related peripheral neuropathy was sensory, with almost all events reported as Grade 1. The most common Grade 3–4 treatment-related AEs included thrombocytopenia and hyperlipasemia. Only 5% of subjects reported treatment-related AEs resulting in study drug discontinuation. There were no treatment-related deaths. Conclusions: CYT387 has proven safe and well tolerated even with prolonged administration for over 2.5 years. Treatment with CYT387 results in clinical improvement by effecting a rapid, meaningful and durable reduction of splenomegaly and the achievement of sustained RBC transfusion independence in a substantial number of subjects. CYT387 is also effective in improving constitutional symptoms. These results support the development of CYT387 at a dose of 300 mg QD for the treatment of myelofibrosis. Final analyses of safety and efficacy will be available at the time of the meeting. Disclosures: Pardanani: Bristol-Myers Squibb: Clinical trial support, Clinical trial support Other; YM BioSciences: Clinical trial support, Clinical trial support Other; Sanofi-Aventis: Clinical trial support Other. Off Label Use: Data from the ongoing Phase-1/2 study of CYT387 use in myelofibrosis treatment will be described. Gotlib:YM Biosciences: Research Funding. Gupta:Celgene: Research Funding; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; YM Biosciences: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Sanofi-Aventis: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Incyte: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding. Roberts:YM BioSciences: clinical trial support Other. Wadleigh:Incyte: Membership on an entity's Board of Directors or advisory committees. Sirhan:Novartis: Consultancy, Honoraria. Bavisotto:YM BioSciences: Consultancy. Kawashima:YM BioSciences: Employment. Kowalski:YM BioSciences: Employment.

Abstract Abstract 1737 Background: The somatic JAK2 V617F (V617F) mutation is found in approximately 95% of polycythemia vera (PV) and 50–60% of essential thrombocythemia (ET) and primary myelofibrosis (PMF) patients. Detection of this mutation occurs primarily through genomic analysis of peripheral blood samples of myeloproliferative neoplasm (MPN) patients. This study demonstrates a novel broad screening mechanism for detection of V617F from myeloid cells in saliva samples from an online cohort of MPN patients and from a broader database of genotyped individuals. Methods: MPN patients were recruited primarily through social media and patient-mediated outreach efforts. Patients gave IRB-approved consent and completed surveys through an online 23andMe account. Participation in the MPN research initiative was free. In collaboration with an uncompensated panel of academic experts, online surveys were developed to collect patient-reported data on diagnosis and results of genetic testing for the V617F mutation. Participants were genotyped on SNP arrays based on the Illumina Omni Express, with additional custom content, including four probes for the V617F mutation. We estimated V617F mutation burden as the median across the four probes of B/(A+B) where A and B were normalized intensities for the reference and mutated alleles, respectively. We estimated sensitivity and specificity of our estimated V617F allele ratio, using the self-reported V617F-positive individuals to approximate the distribution of true positives, and 23andMe members from the broad database (outside of the MPN research cohort) and younger than 40 as likely true negatives. Results: Web-based recruitment efforts led to the accrual of over 900 MPN patients of different subtypes over 12 months. Of these participants, 745 patients have been genotyped and provided MPN-related health history and outcomes through online surveys. The cohort is disproportionately female (71%), with an average age of 53.1 ± 14.9 years. More than 57% of patients indicated a classic MPN diagnosis (PV, ET, PMF, or post PV/ET MF), 19.2% reported an atypical MPN diagnosis (systemic mastocytosis or hypereosinophilic syndrome), 14.5% indicated chronic myelogenous leukemia, and 9.3% of the cohort reported other diagnoses. From this MPN cohort, a total of 345 participants reported mutation test results. Consistent with expectations, the V617F variant was reported by patients in nearly all PV cases (105 of 110 patients with a self-reported diagnosis of PV), and at a lower rate in ET and MF cases (59 of 95 patients and 48 of 61 patients, respectively). In addition to self-reported data, we were specifically able to detect the V617F mutation using SNP array data. We determined a detection threshold for the V617F variant at which 86% of self-reported V617F carriers were scored as positive (i.e. test sensitivity), and 99.975% of young 23andMe customers were scored as negative (i.e. test specificity). Participants with a classic diagnosis in the MPN cohort who carry the V617F variant tended to be older (mean age=59.5 versus 54.6 years) and were less likely to be female (62.5% versus 72.0%) than non-carriers. At this threshold, we detected 133 individuals who likely carry the V617F mutation among a broader set of 23andMe participants (n= 99,700) who were not specifically recruited for the MPN study, corresponding to a prevalence of 0.14%. We estimated the positive predictive value of the test in this cohort, or the expected proportion of positive test results that are true, as 81%. Within the general 23andMe cohort, the frequency of the V617F variant increases with participant age, from a rate of 0.017% for age 20 to 30, to 1.1% for age 80 to 90. We also observed that patients with a high allele burden of V617F frequently had acquired uniparental disomy of chromosome 9p, as determined from calculated heterozygosity scores and no-call rates for this chromosomal arm. Conclusion: We can detect V617F with high specificity and sensitivity from myeloid cells in saliva. This non-invasive source for DNA extraction offers new possibilities for detecting genomic alterations and for finding novel genetic associations in MPN patients as well as the general population. This study demonstrates the feasibility of online technology to significantly accelerate recruitment and research progress in MPNs and other rare diseases. Disclosures: Barnholt: 23andMe, Inc.: Employment. Hinds:23andMe: Employment, Equity Ownership, Patents & Royalties. Kiefer:23andMe, Inc.: Employment. Do:23andMe, Inc.: Employment, Equity Ownership, Patents & Royalties. Eriksson:23andMe, Inc.: Employment, Equity Ownership, Patents & Royalties. Mountain:23andMe, Inc.: Consultancy, Employment, Honoraria, Patents & Royalties. Francke:23andMe, Inc.: Employment, Honoraria, Research Funding; Locus Development: Consultancy, Membership on an entity's Board of Directors or advisory committees. Tung:23andMe, Inc.: Employment. Mesa:23andMe, Inc.: Unpaid advisor and collaborator Other. Gotlib:23andMe, Inc.: Unpaid advisor and collaborator Other. Zehnder:23andMe, Inc.: Unpaid advisor and collaborator Other.