Knapper, Steven

Progression of myeloproliferative neoplasms to blast phase (BPMPN) is associated with lack of response to conventional therapies and dire clinical outcomes. Consequently, there is a major unmet need to develop new therapies for BPMPN. Chromothripsis, the process of catastrophic shattering and haphazard repair of chromosomes, is a key contributor to somatic variation in cancer, but this phenomenon has not yet been described in BPMPN. More broadly, whether chromothripsis might result in actionable molecular events that are amenable to targeting remains an open question. To characterise the contribution of structural variants to BPMPN, we first performed integrated copy number and mutation profiling in 64 BPMPN patients by SNP karyotyping and targeted next generation sequencing. We observed a recurrent pattern of chromothripsis that involved chromosome 21, which together with other structural variants led to amplification of a common region of chromosome 21 (‘chr21amp‘) in ~25% of patients (GISTIC q-val<0.01, Fig 1A). Chr21amp was associated with TP53 mutations and a higher number of copy number alterations. Patients with chr21amp had a particularly aggressive and treatment-resistant phenotype, with 0% surviving 12 months compared to 46% in the non-chr21amp pts ( p=0.0007), retaining significance in multivariate analysis including after correction for TP53 mutation status. Whole genome sequencing confirmed that the chromosomal rearrangements resulting in chr21amp occurred by different mechanisms, ranging from simple amplification to highly complex chromothriptic events involving multiple chromosomes. There were no recurrent translocation partners or mutations. The minimally amplified region (MAR) spanned 2.7Mb and contained 24 genes, with a median copy number of 3.5 (range 2.7-8.3) Single-cell transcriptomics combined with allelic resolution genotyping revealed that chr21amp was present in the dominant subclone and occurred subsequent to JAK2V617F and mut TP53 acquisition. Chr21amp was detectable in phenotypic HSCs and throughout early stages of hematopoiesis, but not in mature erythroid cells, consistent with a differentiation block. Of the 24 genes in the minimally amplified region, only one gene, DYRK1A, a serine threonine kinase linked to cell proliferation and survival, was both differentially expressed (single-cell and bulk RNAseq) and differentially accessible (ATACseq). To explore the functional role of DYRK1A in BPMPN we performed shRNA and CRISPR-mediated DYRK1A-knockdown and knockout (KO) in BPMPN cell lines (HEL and SET-2), which led to impaired cell proliferation. The DYRK1A inhibitors EHT1610 and GNF2133 also led to dose-dependent growth inhibition. DYRK1A-KO BPMPN HEL or SET2 cell clones showed a reduced ability to propagate leukemia in vivo with a significant survival advantage vs. wild type control mice. BPMPN chr21amp+ primary patient CD34+ cells were highly sensitive toDYRK1A inhibitors, while healthy control CD34+ cells were unaffected Prior studies have shown that DYRK1A activates the DREAM complex, a transcriptional repressor of DNA-repair pathways. In chr21amp patient cells, the DREAM DNA repair gene signature was significantly downregulated (NES -1.74, q-val <0.001), while conversely in CRISPR DYRK1A KO SET2 cells the transcriptional DNA repair signature was upregulated (NES 1.76, q-val <0.001). In functional assays, CRISPR DYRK1A KO was protective against DNA damage, with a reduction in γ-H2AX foci after etoposide treatment or irradiation ( p<0.01 for both). A second mechanism of leukemogenesis emerged from geneset enrichment analyses, which suggested enhanced JAK-STAT signaling in chr21amp BPMPN cells and downregulation in the CRISPR DYRK1A KO context. We validated this by showing that DYRK1A overexpression activates and potentiates STAT5B transcriptional activity in a luciferase reporter assay. Finally, we noted that the STAT target BCL2 was selectively upregulated in chr21amp cells. BCL2 inhibition showed strong synergy with DYRK1A inhibitors for induction of BPMPN cell apoptosis (Bliss synergy score 15). Collectively, these findings define the chr21amp event as a novel prognostic biomarker in BPMPN. We pinpoint DYRK1A amplification as a central driver of genomic instability and exacerbated JAK-STAT signalling, for the first time linking chromothripsis to a specific druggable target ( Fig 1B).

7019 Background: High-risk essential thrombocythemia (HR ET) is characterized by thrombocytosis, thrombohemorrhagic events and systemic symptoms. Pts can experience intolerance, inadequate response or loss of response to first-line cytoreductive therapies (hydroxyurea [HU] or interferon alfa-2a). BET protein inhibition is a novel therapeutic strategy that downregulates inflammatory cytokines and may inhibit differentiation and proliferation of abnormal megakaryocytes involved in ET pathogenesis. Results from the Phase 2 MANIFEST study (NCT02158858) suggested potentially encouraging clinical efficacy in pts with myelofibrosis treated with Pelabresib (PELA), an oral, small-molecule, investigational BET inhibitor. Here we present preliminary results from MANIFEST Arm 4 investigating PELA monotherapy in HR ET refractory or intolerant to HU. Methods: Eligible pts had platelets > 600 x 109/L and ≥ 2 symptoms (average score ≥3/ TSS≥15). Pts received PELA monotherapy 225 mg QD. The primary endpoint was complete hematologic response (CHR; normalization of platelet count (≤400 x 109/L), WBC count (≤10 x 109/L) confirmed after one cycle [after 3 weeks]) and normal spleen size. Secondary endpoints included partial HR (PHR; platelets 400–600 x 109/L and WBC ≤10 x 109/L), symptom improvement (≥50% TSS reduction) and safety. Results: As of July 2022, 20 pts with HR ET were treated: median age 64 yrs (42–83), median Hgb 13 (10–16) g/dL, median platelet count 772 (418–1255) x 109/L and median TSS 32.7 (6.9–123). The majority of pts had a hematologic response (90% [18/20] unconfirmed CHR or PHR); confirmed CHR was observed in 40% (8/20) (Table). Median platelet and WBC count at Wk 12 was 446 x109/L and 8.2 x 109/L, respectively. TSS reduction was reported in 86% (12/14 pts); median TSS reduction at Wk 12 was –31%. Hgb levels remained stable through Wk 24. The most common nonhematologic AEs were nausea (60%; 10% Gr 3), diarrhea (35%; 5% Gr 3) and dysgeusia (35%; no Gr 3). Hemorrhagic or thromboembolic events were reported in 30% pts (15% Gr 3). No events of thrombocytopenia and no Gr 4 events or higher were reported. Conclusions: Preliminary results from Arm 4 of the MANIFEST study suggest potential clinical benefit with PELA monotherapy in pts with HR ET refractory or intolerant to HU as supported by hematologic responses and symptom improvement. Safety results are consistent with the known safety profile of PELA and as expected in the underlying study population. Clinical trial information: NCT02158858 . [Table: see text]

PURPOSE Polycythemia vera (PV) is characterized by JAK/STAT activation, thrombotic/hemorrhagic events, systemic symptoms, and disease transformation. In high-risk PV, ruxolitinib controls blood counts and improves symptoms. PATIENTS AND METHODS MAJIC-PV is a randomized phase II trial of ruxolitinib versus best available therapy (BAT) in patients resistant/intolerant to hydroxycarbamide (HC-INT/RES). Primary outcome was complete response (CR) within 1 year. Secondary outcomes included duration of response, event-free survival (EFS), symptom, and molecular response. RESULTS One hundred eighty patients were randomly assigned. CR was achieved in 40 (43%) patients on ruxolitinib versus 23 (26%) on BAT (odds ratio, 2.12; 90% CI, 1.25 to 3.60; P = .02). Duration of CR was superior for ruxolitinib (hazard ratio [HR], 0.38; 95% CI, 0.24 to 0.61; P < .001). Symptom responses were better with ruxolitinib and durable. EFS (major thrombosis, hemorrhage, transformation, and death) was superior for patients attaining CR within 1 year (HR, 0.41; 95% CI, 0.21 to 0.78; P = .01); and those on ruxolitinib (HR, 0.58; 95% CI, 0.35 to 0.94; P = .03). Serial analysis of JAK2V617F variant allele fraction revealed molecular response was more frequent with ruxolitinib and was associated with improved outcomes (progression-free survival [PFS] P = .001, EFS P = .001, overall survival P = .01) and clearance of JAK2V617F stem/progenitor cells. ASXL1 mutations predicted for adverse EFS (HR, 3.02; 95% CI, 1.47 to 6.17; P = .003). The safety profile of ruxolitinib was as previously reported. CONCLUSION The MAJIC-PV study demonstrates ruxolitinib treatment benefits HC-INT/RES PV patients with superior CR, and EFS as well as molecular response; importantly also demonstrating for the first time, to our knowledge, that molecular response is linked to EFS, PFS, and OS.

Abstract MAJIC is a phase II trial of Ruxolitinib (RUX) vs Best Available Therapy (BAT) in polycythemia vera (PV) patients with resistance/intolerance to Hydroxycarbamide (HC). This analysis involved a primary comparison between the RUX and BAT arms for quality of life (QOL) durability over 60 months, with secondary comparisons of best QOL response within first year in complete hematologic responders (CR) vs a group of partial or no response (NR/PR). This is a unique analysis due to cross-over nature of prior studies. Patients were stratified by treatment arm with either RUX or BAT. QOL was assessed over 0-60 months using the Myeloproliferative Neoplasms Symptom Assessment Form (MPN-SAF). MPN-SAF Total Symptom Score (TSS) was computed as the average of all completed items multiplied by 10 (scale 0-100, higher score represents higher symptom burden). Estimates of change from baseline and between arm differences in change by timepoint were made using a linear mixed model with compound symmetry covariance structure, which included covariates for categorical time point, treatment arm, and the interaction between time point and treatment arm. The difference between arms in proportion of patients with best post-baseline TSS response of 50% or greater was testing using a Chi-square test. In this study, 147 of the 190 trial patients had started treatment and completed at least their baseline assessment and were included in the analysis with 39 patients completing through 60 months. Groups were comprised of 76 patients in the RUX group (31 females, 45 males, mean age 64.2 [SD 11.4]) and 71 patients in the BAT group (29 females, 42 males, mean age 64.6 [SD 11.5]). Symptom scores at baseline were similar between arms, with MPN-SAF weight loss the only statistically significant difference (BAT 0.7 [SD 1.71] vs RUX 1.7 [SD 2.83], p=0.02). Significant, durable improvements in TSS were noted in RUX patients with symptom improvements lasting a mean of 52 months. BAT patients experienced a worsening of their symptom burden with improvements back to baseline notable at 56 months (Figure 1). MPN-SAF TSS there were significant differences between treatment arms in change from baseline to months 2-32, 44, and 48 (all p&lt;0.05). In all months the trend was in the direction of larger improvement in the RUX arm, with the point estimate for difference ranging from 2.1 (at month 56) to 11.3 (at month 4) with most prominent changes occurring between months 2 and 32. Of the 80 patients with MPN-SAF TSS scores at baseline and at least one post-baseline timepoint, 13/41 (31.7%) BAT and 24/39 (61.5%) RUX patients had TSS reduction of 50% or greater in at least one time point, which was statistically significant (p=0.008). In regard to specific symptoms, there was a statistically significant between arm difference seen in over 5 timepoints for fatigue, early satiety, night-sweats, itching, bone pain, and weight loss. Comparing MPN-SAF TSS in Complete Response (CR n=51) vs Non-Responder/Partial Responders (NR/PR) (n=96) there was no difference at baseline in any of the measures at any time point. A possible limitation of this study is the potential for bias in which the patients who were lost to follow up could be different then the patients who remained in the study through all 60 months which would affect generalization, particularly at time points at the later years. The novel findings of this investigation demonstrate that Ruxolitinib ameliorates the PV symptom burden in patients resistant or intolerant to HC in a robust durable manner over at least four years, while patients receiving BAT have worsening of their symptom burden over this same time period. Figure 1 Figure 1. Disclosures Mead: Novartis: Consultancy, Honoraria, Speakers Bureau; Celgene/BMS: Consultancy, Honoraria, Research Funding; Abbvie: Consultancy, Honoraria. Yap: Celgene: Honoraria; Faron Pharmaceuticals: Honoraria. Scherber: Incyte Corporation: Current Employment, Current holder of stock options in a privately-held company. Knapper: Novartis: Consultancy, Research Funding, Speakers Bureau; Astellas: Ended employment in the past 24 months, Speakers Bureau; Pfizer: Consultancy, Speakers Bureau; Jazz: Consultancy, Speakers Bureau. Drummond: Novartis: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; BMS: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; CTI: Membership on an entity's Board of Directors or advisory committees. McMullin: Novartis: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Celgene: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Bristol Myers Squibb: Membership on an entity's Board of Directors or advisory committees, Other: clinical trial support, Research Funding; AbbVie: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; AOP Orphan: Research Funding, Speakers Bureau. Mesa: CTI: Research Funding; AOP: Consultancy; Celgene: Research Funding; Novartis: Consultancy; Gilead: Research Funding; Pharma: Consultancy; Promedior: Research Funding; Constellation Pharmaceuticals: Consultancy, Research Funding; CTI: Research Funding; Samus: Research Funding; Sierra Oncology: Consultancy, Research Funding; Genentech: Research Funding; Incyte Corporation: Consultancy, Research Funding; Abbvie: Research Funding; La Jolla Pharma: Consultancy. Harrison: CTI BioPharma: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Gilead Sciences: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Shire: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; BMS: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Geron: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Janssen: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Constellation Pharmaceuticals: Research Funding; Galacteo: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Roche: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Abbvie: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Incyte Corporation: Speakers Bureau; Sierra Oncology: Honoraria; Promedior: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; AOP Orphan Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Keros: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Novartis: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau.

Abstract The myeloproliferative neoplasms (MPN) polycythaemia vera (PV) and essential thrombocythaemia (ET) are associated with significant symptom burden with impaired quality of life (QoL). In the MAJIC study patients refractory/intolerant to hydroxycarbamide (HC), were randomised to treatment with ruxolitinib (Rux) or best available therapy (BAT). In this unique and comprehensive analysis we explore quality of life (QoL) outcomes in the MAJIC study using the MPN10 Self-Assessment Form (SAF) in particular using this unique dataset to explore for the first time differences between JAK2 ET vs PV, and JAK2 ET vs CALR ET at baseline and 12 months of therapy with Rux or BAT. Methods 306 patients were randomised, (190, PV and 116 ET arm) and followed for 5 years, no cross over was permitted. MPN10 SAF was assessed at baseline, 2, 4, 8 and 12 months in both arms. Equal variance two sample t-tests were used to test differences between diagnosis groups (JAK2 ET vs PV & JAK2 ET vs CALR ET) in baseline scores and 12-month change from baseline scores, here negative change from baseline indicates improvement. QoL data was also collected using MD Anderson Symptoms Inventory (MDASI) and 5 level EQ5D at the same time points as the MPN10 SAF. Results JAK2 ET vs PV 110 participants with JAK2 mutation were included in the analysis for JAK2 ET vs PV. 81 (74%) had PV and 29 (26%) had JAK2 ET; 44 patients (54.3%) with PV and 18 (62.1%) patients with ET were randomised to Rux, and 37 (45.6%) patients with PV and 11 (37.9%) with ET to BAT. Baseline mean total symptom score (TSS) was similar (JAK2 ET: 18.9. SD 18.4 and PV: 23.7, SD 17.81 (p=0.27). Mean for pruritus was 1.9 (SD 2.47) in JAK2 ET and 3.5 (SD 2.99) in PV (p=0.03). Other baseline scores were comparable: mean scores for fatigue was 3.3 (SD 3.07) for JAK2 ET vs 4.7 (SD 2.68) for PV, for early satiety was 2.6 (SD 2.78) for JAK2 ET vs 2.1 (SD 2.40) for PV, for abdominal discomfort 3.0 (SD 3.34) for JAK2 ET vs 2.0 (SD 2.78) for PV, for inactivity was 2.4 (SD 2.86) for JAK2 ET vs 3.2 (SD 2.72) for PV; for concentration problems was 2.2 (SD 2.51) for JAK2 ET vs 2.9 (SD 3.11) for PV, for night sweats was 1.6 (SD 2.20) for JAK2 ET vs 2.1 (SD 2.66) for PV, for bone pain was 1.8 (SD 2.97) for JAK2 ET vs 2.0 (SD 2.86) for PV, for fever was 0.5 (SD 1.46) for JAK2 ET vs 0.5 (SD 1.70) for PV and for weight loss was 0.3 (SD 0.73) for JAK2 ET vs 1.0 (SD 2.15) for PV (p&gt;0.05 for all). Concerning change at 12 months, mean (SD) change in TSS was -0.5 (SD 10.86) for JAK2 ET (n=21) vs -0.8 (SD 13.32) for PV (n=66) (P=0.93). Mean for individual symptom scores at 12 months were also not significantly different between the two phenotypic disease group (P&gt;0.05 for all parameters). (Fig 1, top panels). CALR vs JAK2 ET Exploring symptoms for CALR vs JAK2 ET: 45 patients were included; 9/16 (56.3%) CALR and 18/29 (62.1%) JAK2 patients were assigned to Rux (p=0.70). 10/16 (62.5%) CALR ET and 19/29 (65.5%) JAK2 ET. Baseline mean total symptom score (TSS) was similar (JAK2 ET: 18.9, SD 18.4 and CALR ET: 18.8, SD 16.99 (p=0. 0.98). All other baseline scores were comparable in this intolerant/ refractory population (p&gt;0.05 for all. Concerning change at 12 months, mean (SD) change in TSS was -0.5 (SD 10.86) for JAK2 ET vs -2.8 (SD 9.96) for CALR ET (P=0.56). Mean for individual symptom scores at 12 months were also not significantly different between the two phenotypic disease group (P&gt;0.05 for all parameters); the mean change in night sweats approached but did not reach significance similar (JAK2 ET: 0.2 (SD 1.89) and CALR ET: 1.8 (SD 3.07) (p=0. 0.06). (Fig 1, lower panels). Preliminary analysis of the MDASI and EQ5D-5L data at baseline and at 12 months shows similar results and will be presented. Conclusion This first analysis of its kind compared the symptom burden and other parameters of QoL of patients with PV and ET, resistant/intolerant to HC shows that with the exception of pruritus at baseline there were no substantial differences between JAK2 ET or PV. Equally changes in symptom burden across 12 months did not substantially differ between JAK2 ET or PV. A second analysis of JAK2 vs CALR ET also failed to show substantial differences. This data should be expanded in a larger cohort but supports a symptom continuum of JAK2 ET and PV and also JAK2 vs CALR ET. Figure 1 Figure 1. Disclosures Mead: Abbvie: Consultancy, Honoraria; Celgene/BMS: Consultancy, Honoraria, Research Funding; Novartis: Consultancy, Honoraria, Speakers Bureau. Yap: Faron Pharmaceuticals: Honoraria; Celgene: Honoraria. Knapper: Novartis: Consultancy, Research Funding, Speakers Bureau; Astellas: Consultancy, Speakers Bureau; Jazz Pharmaceuticals: Consultancy, Speakers Bureau; Pfizer: Consultancy, Speakers Bureau. Drummond: CTI: Membership on an entity's Board of Directors or advisory committees; BMS: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Novartis: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Mesa: Pharma: Consultancy; CTI: Research Funding; Abbvie: Research Funding; Genentech: Research Funding; Gilead: Research Funding; AOP: Consultancy; Incyte Corporation: Consultancy, Research Funding; Sierra Oncology: Consultancy, Research Funding; Novartis: Consultancy; La Jolla Pharma: Consultancy; Samus: Research Funding; Promedior: Research Funding; Constellation Pharmaceuticals: Consultancy, Research Funding; Celgene: Research Funding; CTI: Research Funding. Scherber: Incyte Corporation: Current Employment, Current holder of stock options in a privately-held company. McMullin: Celgene: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Novartis: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; AbbVie: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; AOP Orphan: Research Funding, Speakers Bureau; Bristol Myers Squibb: Membership on an entity's Board of Directors or advisory committees, Other: clinical trial support, Research Funding. Harrison: CTI BioPharma: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Roche: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Novartis: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Promedior: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Abbvie: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Gilead Sciences: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Keros: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; BMS: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; AOP Orphan Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Janssen: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Shire: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Sierra Oncology: Honoraria; Constellation Pharmaceuticals: Research Funding; Incyte Corporation: Speakers Bureau; Geron: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Galacteo: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau.

Abstract Introduction Individuals with the Philadelphia chromosome negative myeloproliferative neoplasms (MPNs) have previously been shown to experience symptoms in excess to age and comorbidity matched peers. Although numerous assessments of symptom burden and quality of life have been utilized among MPN populations, including the European Organisation for Research and Treatment of Cancer Quality of Life Questionnaire-Core 30 (EORTC QLQ-C30), Patient Reported Outcomes Measurement Information System (PROMIS¨) fatigue scale, and Functional Assessment of Cancer Therapy-Lymphoma (FACT-Lym) and the Myeloproliferative Neoplasm Symptom Assessment Form Total Symptom Score (MPN-10), there are currently no validated assessments of overall health. Developed by the EuroQol Group to assess heath status, the EQ-5D is an internationally validated self-assessment which may be useful in the assessment of health state among MPN patients (Annals of Medicine, 2001. 33:337-43). Methods The EQ-5D evaluates five dimensions of mobility, self-care, usual activities, pain/discomfort and anxiety/depression, on a scale from no problems to extreme problems and assesses patient reported health state via a numerical visual analogue scale (VAS) ranging from 0 to 100. The health state score is a composite score of these items ranging from 0 to 1.0, with higher scores indicating an improved health state. EQ-5D survey participants were essential thrombocythemia (ET) and polycythemia (PV) patients participating in the MAJIC United Kingdom (UK) trial. The MAJIC trial is a randomized, phase II study of best available therapy versus JAK inhibition in individuals with PV or ET who have been resistant or intolerant of cytoreduction with hydroxyurea /hydroxycarbamide. This study was one of the first Trials Acceleration Programme (TAP) trials and is funded by Leukaemia Lymphoma Research, with drug supplied by Novartis. Only baseline EQ-5D assessments taken at study enrollment were included in this analysis. Comparative analysis was preformed using the MPN-10 (J Clin Oncol.2012. 30:4098-103). Results: Participant Demographics: Sixty six patients with ET and 55 patients with PV completed the EQ-5D questionnaire. Median respondent age was 65 years old and half of respondents were female (54%). Average MPN duration was 10 years for ET and 9.2 years for PV. EQ-5D Scoring: Severe to extreme difficulties in the items of mobility, self-care, usual activities, pain/discomfort and anxiety/depression were common (Table 1).Patients with PV tended to have higher proportion of patients with severe to extreme difficulties in individual disease dimensions, higher VAS score, and worsened health state compared to their essential thrombocythemia counterparts, although these effects were not significant. Average VAS health score was 70.4 (+21.2) for ET and 66.5 (+19.6). When evaluating the health state composite score, the mean ET score was 0.74 (+0.32) and mean PV score was 0.66 (+0.28). EQ-5D Validation: The EQ-5D had excellent internal consistency (CronbachÕs alpha=0.87) and strong internal correlation. When evaluating external validity, strong correlations existed between the EQ-5D and the MPN-SAF TSS scales for dimensions of mobility, usual activities, pain and overall health state (many items with r >0.5 and p<0.001). Conclusions: The EQ-5D is a valid and accurate instrument for the brief assessment of health state among MPN patients. This instrument demonstrates excellent clinical utility in a large clinical study cohort and can be used in both clinical practice and trial settings. When comparing EQ-5D health state scores, ET and PV patients had worsened health than the general UK population age 60 to 69 (0.774; Med Decis Making. 2011.31(6)800-4), but similar health to individuals with other malignancies including breast cancer (0.760), prostate cancer (0.743), and lung cancer (0.689). Disclosures Mesa: NS Pharma: Research Funding; Novartis Pharmaceuticals Corporation: Consultancy; Incyte Corporation: Research Funding; Pfizer: Research Funding; Promedior: Research Funding; CTI Biopharma: Research Funding; Gilead: Research Funding; Genentech: Research Funding; Pfizer: Research Funding. Harrison:CTI Biopharma: Consultancy, Honoraria, Speakers Bureau; Sanofi: Honoraria, Speakers Bureau; Shire: Speakers Bureau; Gilead: Honoraria; Novartis: Honoraria, Research Funding, Speakers Bureau.

Abstract Introduction: There are few effective treatment options available for patients (pts) with myelofibrosis (MF). Pts with thrombocytopenia, a risk factor for shorter overall survival, have poorer prognosis (Gangat, J Clin Oncol 2010). Pacritinib is a kinase inhibitor with specificity for JAK2, FLT3, IRAK1, and CFSR1 and has demonstrated minimal myelosuppression in clinical trials (Hart, Leukemia 2011; Komrokji, Blood 2015; Mesa, ASCO 2015). In the phase III open-label PERSIST-1 trial, a significantly greater proportion of pts treated with pacritinib achieved spleen volume reductions (SVR) ≥35% vs BAT (ITT: 19.1% vs 4.7%, p=0.0003; pts evaluable at baseline and Week 24: 25.0% vs 5.9%, p=0.0001; Mesa, ASCO 2015). This analysis examines pt responses across subgroups. Methods: Pts naive to treatment with JAK inhibitors were randomized 2:1 to receive oral pacritinib 400 mg once daily or BAT. Stratification factors included DIPSS risk status and baseline platelet count. Pts were eligible who had DIPSS Intermediate (Int)-1, Int-2, or High risk disease; absolute neutrophil count >500/µL; palpable splenomegaly ≥5 cm; and baseline Total Symptom Score (TSS) ≥13 using the Modified MPN Symptom Assessment Form Total Symptom Score (MPN-SAF TSS and TSS 2.0). There was no restriction on baseline platelets or hemoglobin (Hgb) levels. The primary endpoint was the proportion of pts achieving SVR ≥35% at Week 24 by centrally-reviewed MRI or CT and the secondary endpoint was the proportion of pts achieving ≥50% reduction in TSS from baseline at Week 24 using 6 symptoms from the MPN-SAF TSS. Pt responses were analyzed by baseline risk factors for MF including platelet counts (<50,000/µL vs ≥ 50,000/µL and <100,000/µL vs ≥100,000/µL), sex, age (≥65 y vs <65 y), JAK2V617F mutation status (positive vs negative), baseline MF diagnosis (primary MF [PMF] vs secondary MF), reticulin and collagen fibrosis staging (> 1 vs ≤1), TSS (≥20 vs <20), white blood cell count (>25×109/L vs ≤25×109/L), peripheral blasts (≥5% vs <5%), Hgb (<10 g/dL vs ≥10 g/dL), transfusion dependency by Gale criteria (Y vs N), time from diagnosis (<12 mos vs ≥12 mos), ECOG PS (2-3 vs 0-1), and bone pain (>3 vs ≤3). In multivariate logistic regressions, the odds of SVR ≥35% and TSS reduction ≥50% at Week 24 were modeled as a function of prognostic factors for MF and adjusted for treatment (pacritinib vs BAT). Results for the 6 symptoms common to both TSS versions are reported. Results: 327 pts were enrolled and randomized (pacritinib: 220, BAT: 107). Overall, 62% of pts had PMF; 32% had baseline platelets <100,000/µL and 16% had <50,000/µL; 75% were positive for JAK2V617F. After a median follow-up of 8.4 months, treatment with pacritinib resulted in consistent rates of SVR across subgroups (Figure 1). When comparing vs BAT, the greatest differences in SVR ≥35% rates between treatment arms were observed in pts with baseline platelets <50,000/μL (+22.9% vs BAT), JAK2V617F-negative pts (+23.0% vs BAT) and those aged <65 y (+21.2% vs BAT). Improvements in TSS (TSS and TSS 2.0 reduction ≥50%) were also consistent for pts receiving pacritinib (Figure 2). By multivariate analysis, SVR ≥35% was significantly correlated only with ECOG PS ≥2 (odds ratio [OR]=2.97, p=0.030) and TSS reduction ≥50% was significantly correlated only with bone pain >3 (OR=0.35, p=0.004). Conclusions: Treatment with pacritinib resulted in consistent rates of SVR ≥35% and TSS reduction ≥50% irrespective of baseline characteristics. Comparisons vs BAT were favorable for all patient subpopulations examined for both endpoints. These results support the use of pacritinib across all intermediate- or high risk MF pt subgroups analyzed. Figure 1. Proportion of Patients Receiving PAC who Achieved ≥35% SVR from baseline to Week 24 (95% CI) Figure 1. Proportion of Patients Receiving PAC who Achieved ≥35% SVR from baseline to Week 24 (95% CI) Figure 2. Proportion of Patients Receiving PAC who Achieved ≥50% TSS reduction (6 common symptoms in MPN-SAF TSS and MPN-SAF TSS 2.0) from baseline to Week 24 (95% CI) Figure 2. Proportion of Patients Receiving PAC who Achieved ≥50% TSS reduction (6 common symptoms in MPN-SAF TSS and MPN-SAF TSS 2.0) from baseline to Week 24 (95% CI) Disclosures Vannucchi: Shire: Speakers Bureau; Novartis Pharmaceuticals Corporation: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Baxalta: Membership on an entity's Board of Directors or advisory committees. Off Label Use: This abstract discusses off-label use of pacritinib. Mesa:Gilead: Research Funding; NS Pharma: Research Funding; Incyte Corporation: Research Funding; Genentech: Research Funding; Novartis Pharmaceuticals Corporation: Consultancy; Promedior: Research Funding; Pfizer: Research Funding; CTI Biopharma: Research Funding. Cervantes:Novartis: Consultancy, Speakers Bureau; Sanofi-Aventis: Consultancy; CTI-Baxter: Consultancy, Speakers Bureau. Prasad:BIOGEN IDEC: Consultancy, Membership on an entity's Board of Directors or advisory committees; BMS: Speakers Bureau. Elinder:Celgene: Consultancy. Recher:Sunesis: Consultancy, Membership on an entity's Board of Directors or advisory committees; Amgen: Research Funding; Chugai: Research Funding; Celgene: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding. te Boekhorst:CTI Biopharma: Consultancy; Novartis: Consultancy. Somervaille:Novartis Pharmaceuticals Corporation: Consultancy, Membership on an entity's Board of Directors or advisory committees. Dean:CTI Biopharma: Employment, Equity Ownership. Harrison:Shire: Speakers Bureau; Gilead: Honoraria; CTI Biopharma: Consultancy, Honoraria, Speakers Bureau; Sanofi: Honoraria, Speakers Bureau; Novartis: Honoraria, Research Funding, Speakers Bureau.

Abstract Abstract 1736 Background: Histone deacetylase inhibition (HDACi) has shown a potent inhibitory activity on the autonomous proliferation of hematopoietic cells of PV and ET patients carrying the JAK2V617F mutation (Leukemia. 2008;22(4):740–7). Hematological responses have been recorded during treatment with the HDACi givinostat in patients with PV and myelofibrosis (Blood. 2011; 118:a1748). Additionally, combinational use of givinostat and hydroxyurea (HU) have shown encouraging clinical response in PV (Br J Haematol. 2010;150:446–55). Recent laboratory studies of vorinstat-treated JAK2V617F knock-in mice have observed normalization of peripheral blood counts, markedly reduced splenomegaly and decreased mutant allele burden (Blood 2012; 119, 3779–89). Despite this evidence of hematologic response, to date no studies have evaluated specific changes in symptom burden among PV and ET patients treated with HDACi. METHODS ET and PV patients from the UK were enrolled in a non-randomized, open-label phase II multicenter study of the HDACi vorinostat (Haematologica 2011;96(s2):a1023). Patients were asked to complete the 18 item Myeloproliferative Neoplasm Assessment Form (MPN-SAF) (Blood 2011;118:401–408), 9 item Brief Fatigue Inventory (BFI) (Cancer 1999;85:1186–1196) and 30 item EORTC QLQ-C30 (J Natl Cancer Inst 1993; 85(5):365-76) at enrollment, week 12, week 24, and week 36. From weeks 1 through 24, participants were given 400mg of vorinostat daily and were observed from weeks 24 to 36. RESULTS Participant Demographics and Mutational Status: 15 PV and 10 ET patients were enrolled in the study. Median age of participants was 65 and 48% of participants were female. JAK2 mutations were present in 5/10 (50%) of ET and 14/15 (93%) of PV patients. Change in Symptom Severity with Vorinostat: Although most symptom severity changes did not reach statistical significance likely due to the small sample size, individual symptoms of headache (mean 1.6 baseline to 0.5 wk 36, mean maximum improvement 0.5 from baseline), dizziness (mean 1.6 baseline to 0.9 wk 36, mean maximum improvement 0.6 from baseline), sad mood (mean 2.6 baseline to 1.9 wk 36, mean max improvement 0.2 from baseline), and bone pain (mean 2.7 baseline to 0.8 wk 36, mean max improvement 0.7 from baseline) indicated consistent reductions in severity. Change in Symptom Incidence with Vorinostat: Non-sustained reductions in symptom incidence were seen with initiation of therapy for items of dizziness (50% baseline, 43% wk12, 55% wk 24, and 38% wk 36), numbness (65% baseline, 38% wk 12, 36% wk 24, 63% wk 36), sad mood (55% baseline, 47% wk 12, 40% wk 24, 50% wk 36), and itching (65% baseline, 50% wk 12, 40% wk 24, 75% wk 36). Change in MPN-SAF TSS Score with Vorinostat: Overall, MPN-SAF TSS did not vary significantly for the cohort over the course of the study (score change −.4 week 12, −0.5 week 24, −1.2 week 36, Figure 1). However, 9/17 participants who had a TSS of at least 6 at baseline had an overall improvement of at least 6 points (a moderate improvement) on at least one assessment after baseline. Of these, 5 of those 9 participants had an improvement of at least 10 points, which constitutes a large improvement in symptom burden based on a distributional definition of clinical significance using the standard deviation from a previous cohort. CONCLUSION This study represents the first analysis of symptom burden among PV and ET patients receiving vorinostat to date. In addition to previously identified changes in clinical and hematologic response, reductions in symptom burden including QOL and fatigue were observed in patients receiving vorinostat therapy which was most noticeable in patients with high baseline burden. The toxicity profile of vorinostat also suggests that better results might have observed if individualized assessment of clinicohematological responses including an integrated a marker for response into daily clinical practice and tailoring pharmacotherapy based on side effect profile (Leukemia. 2012;26(5):1148–9). Although further investigation among larger cohorts is needed, preliminary data is encouraging for successful therapeutic use of vorinostat in a clinical setting and with possible combinational therapy to reduce symptom burden among PV and ET patients. Disclosures: Harrison: Novartis: Honoraria, Research Funding, Speakers Bureau; YM Bioscience: Consultancy, Honoraria; Sanofi Aventis: Honoraria; Shire: Honoraria, Research Funding. Mesa:Incyte: Research Funding; Lilly: Research Funding; Sanofi: Research Funding; NS Pharma: Research Funding; YM Bioscience: Research Funding.