Najfeld, Vesna

Introduction TP53 alterations (TP53+) are seen in <5% of patients (pts) with chronic myeloproliferative neoplasms (MPNs) but are more common in accelerated/blast phase (MPN-AP/BP) [Luque Paz D, et al 2020]. While pts with low-burden TP53+ (Variant allele frequency (VAF) <5%) may remain stable for years [Kubesova et al, 2018]; biallelic loss of TP53 is thought to confer higher risk for progression [Li et al, 2022] and worse overall survival (OS) than non-TP53+ pts [Rolles et al, 2023]. However, TP53 abnormalities have not been incorporated into currently utilized molecular based prediction models (MIPSS or MIPSS70) or compared with currently validated high molecular-risk (HMR) mutations (mut). We report the outcomes of the largest cohort of TP53+ MPN pts to date in comparison with HMR mut, and identify a VAF cut-off associated with highest risk of progression to MPN-AP/BP. Methods We retrospectively reviewed 2583 MPN pts from Mount Sinai Hospital (MSH) and Memorial Sloan Kettering Cancer Center (MSK) with at least one next generation sequencing (NGS) performed. Deidentified data from an additional cohort of 8 TP53+ MPN pts was received from University of Miami Sylvester Cancer Center (UMiami). Patient characteristics such as MPN subtype, gender, age at MPN diagnosis, driver mutation, thrombosis history were recorded. We also recorded date of transformation to MPN-AP/BP, dates of NGS testing, mutational and cytogenetic data, and survival status. We defined multi-hit TP53 as presence of =/>2 TP53mut, VAF > 50% or TP53 mutation + 17p deletion. Additional cohorts of pts with HMR mut (ASXL1, EZH2, IDH1/2, U2AF1, SRSF2 as per MIPSS70v.2) from MSH and non-TP53+ pts from the MPN-Research Consortium Tissue Bank were used as comparator arms. Patient characteristics were compared between TP53 single-hit and multi-hit using Chi-Sq test for categorical variables and Kruskal-Wallis test for continuous variables. Cumulative incidence function and Kaplan-Meier method were used to compare leukemic transformation and OS, respectively, between groups. Successive VAF levels with minimum groups of 25% of the total cohort were used to identify an optimal VAF cut-off. Results Of the 2583 MPN pts from MSH and MSK, 66 pts (2.6%) were found to have a TP53 mutation. Including 8 additional pts from UMiami, we analyzed a total of 74 TP53+ MPN pts; 40 single-hit and 34 multi-hit. Median age at MPN diagnosis was 61 years with a male predominance (60%). Distribution of driver mut was similar in single-hit vs multi-hit cohort with JAK2V617F being the most common (58%), whereas 11% of pts had triple negative disease . Thrombotic history was available for 45 TP53+ pts, with a high frequency of venous/arterial thrombosis (21/45 or 46.7%) in the TP53+ group as compared to 18.5% in the non-TP53+ MPN cohort (p= 0.0001). A significantly higher number of multi-hit TP53+ pts had a concurrent complex karyotype (79% vs 24% in single-hit; p<.001). MPN diagnosis at the time of detection of TP53+ was ET/PV (25.7%), MF (44.6%), MDS/MPN overlap syndrome (6.8%), MPN-U (2.7%) and MPN-AP/BP (20.3%), respectively. One or more genetic samples with TP53+ was available prior to transformation to MPN-AP/BP in 77% of pts (21/34 multi-hit; 36/40 single-hit) while a TP53+ was detected at the time of MPN-AP/BP diagnosis in the rest. Multi-hit TP53+ was associated with a significantly higher incidence of transformation to MPN-AP/BP as compared to single-hit; [65% vs 17.5%; HR=4.08 (1.71-9.71), p=0.0015]. Compared with HMR mut, multi-hit (HR=2.41; p=0.004) but not single-hit (HR=0.53; p=.277) TP53+ MPN pts were found to have a significantly increased risk of MPN-AP/BP transformation. One-year OS from the time of mutation detection was significantly inferior for both multi-hit (53.3%) and single-hit (75%) TP53+ pts as compared to HMR mut (98.8%, p=<.001). Cut-point analysis identified VAF >36% to be associated with the highest risk of transformation (HR=3.08) with lowest p-value (0.002). Conclusions Multi-hit TP53 alterations are associated with a significantly increased risk of leukemic evolution as compared to previously validated HMR mut, whereas both multi and single-hit TP53 mut are associated with worse OS highlighting the importance of TP53 in MPN disease progression.

Abstract Purpose: Myelofibrosis (MF) is a clonal myeloproliferative neoplasm characterized by systemic symptoms, cytopenias, organomegaly, and bone marrow fibrosis. JAK2 inhibitors afford symptom and spleen burden reduction but do not alter the disease course and frequently lead to thrombocytopenia. TGFβ, a pleiotropic cytokine elaborated by the MF clone, negatively regulates normal hematopoiesis, downregulates antitumor immunity, and promotes bone marrow fibrosis. Our group previously showed that AVID200, a potent and selective TGFβ 1/3 trap, reduced TGFβ1-induced proliferation of human mesenchymal stromal cells, phosphorylation of SMAD2, and collagen expression. Moreover, treatment of MF mononuclear cells with AVID200 led to increased numbers of progenitor cells (PC) with wild-type JAK2 rather than JAK2V617F. Patients and Methods: We conducted an investigator-initiated, multicenter, phase Ib trial of AVID200 monotherapy in 21 patients with advanced MF. Results: No dose-limiting toxicity was identified at the three dose levels tested, and grade 3/4 anemia and thrombocytopenia occurred in 28.6% and 19.0% of treated patients, respectively. After six cycles of therapy, two patients attained a clinical benefit by IWG-MRT criteria. Spleen and symptom benefits were observed across treatment cycles. Unlike other MF-directed therapies, increases in platelet counts were noted in 81% of treated patients with three patients achieving normalization. Treatment with AVID200 resulted in potent suppression of plasma TGFβ1 levels and pSMAD2 in MF cells. Conclusions: AVID200 is a well-tolerated, rational, therapeutic agent for the treatment of patients with MF and should be evaluated further in patients with thrombocytopenic MF in combination with agents that target aberrant MF intracellular signaling pathways.

Abstract The goal of therapy for patients with essential thrombocythemia (ET) and polycythemia vera (PV) is to reduce thrombotic events by normalizing blood counts. Hydroxyurea (HU) and interferon-α (IFN-α) are the most frequently used cytoreductive options for patients with ET and PV at high risk for vascular complications. Myeloproliferative Disorders Research Consortium 112 was an investigator-initiated, phase 3 trial comparing HU to pegylated IFN-α (PEG) in treatment-naïve, high-risk patients with ET/PV. The primary endpoint was complete response (CR) rate at 12 months. A total of 168 patients were treated for a median of 81.0 weeks. CR for HU was 37% and 35% for PEG (P = .80) at 12 months. At 24 to 36 months, CR was 20% to 17% for HU and 29% to 33% for PEG. PEG led to a greater reduction in JAK2V617F at 24 months, but histopathologic responses were more frequent with HU. Thrombotic events and disease progression were infrequent in both arms, whereas grade 3/4 adverse events were more frequent with PEG (46% vs 28%). At 12 months of treatment, there was no significant difference in CR rates between HU and PEG. This study indicates that PEG and HU are both effective treatments for PV and ET. With longer treatment, PEG was more effective in normalizing blood counts and reducing driver mutation burden, whereas HU produced more histopathologic responses. Despite these differences, both agents did not differ in limiting thrombotic events and disease progression in high-risk patients with ET/PV. This trial was registered at www.clinicaltrials.gov as #NCT01259856.

Abstract TGFβ plays a pivotal role in the pathobiology of myelofibrosis (MF) by not only promoting bone marrow fibrosis (BMF) but also by enhancing the dormancy of normal but not MF hematopoietic stem cells (HSCs). TGFβ has also previously been reported to inhibit normal megakaryocyte (MK) production (Bruno et al Blood 1998). TGFβ1 promotes the synthesis of collagen by normal human mesenchymal stromal cells (MSCs). Treatment of MSCs with AVID200, a potent TGFβ1/3 protein trap, significantly decreased MSC proliferation, phosphorylation of SMAD2, and collagen expression. Robust expression of pSMAD2 was observed in the absence of exogenous TGFβ in normal donor or MF-MKs, Addition of AVID200 to MKs decreased pSMAD2 without affecting total SMAD2/3 and led to increased numbers of MKs. Treatment of MF MNCs with AVID200 also led to increased numbers of progenitor cells with wild type JAK2 and a reduction of mutated colonies. A phase 1b trial of AVID200 (NCT03895112) was performed and completed in INT-2/high risk MF patients resistant/intolerant to ruxolitinib (rux); baseline platelet count of ≥ 25 x 10 9/L, and grade 2/3 BMF. Subjects received AVID200 intravenously on Day 1 of a 21 day cycle. Response was assessed by IWG/ELN criteria after 6 cycles of AVID200. Subjects attaining at least a CI or SD with a decrease in BMF by ≥1 grade, continued AVID200. We previously presented the results of the dose escalation study (Mascarenhas ASH 2020) demonstrating that AVID200 was well tolerated without dose limiting toxicities at 3 tested dose levels (Lots A and B) in dose cohorts of 180 mg (A), 550 mg (A)/70 mg (B), and 180 mg (B). Here we report updated safety and efficacy results of the phase 1b dose expansion stage at the two highest doses tested (70 mg (B) and 180 mg (B). Twenty-two subjects were enrolled (1 withdrew before receiving treatment) and 9 were treated with AVID200 in the dose escalation phase and 12 in the dose expansion phase [Table1]. Median time after rux discontinuation was 7.4 months (0.5-59.9). The most common mutations observed at baseline in this cohort included JAK2V617F (71%), TET2 (29%) ASXL1 (24%) and CALR (19%). (Fig 1) No DLTs were observed and Grade 3/4 AEs were observed in 16 (76.2%) subjects. Grade 3/4 non-hematologic AEs were observed in 8 (38.1%) subjects and included one subject in each case (epistaxis, mucositis, extraocular muscle paresis, fatigue, rash, duodenal hemorrhage, gastric hemorrhage, urinary tract infection, and syncope). Grade 3/4 hematologic AEs were anemia (6; 28.3%) and thrombocytopenia (2; 14.3%) [Table 2]. No fatal events were observed. The median number of cycles received was 5 (range 2 - 13) and 7 (33%) patients received more than 6 cycles. For dose levels 2-3 at cycle 7, a CI was attained in one subject at dose level 2 [anemia, spleen and TSS], 5 subjects had SD, 3 subjects had PD and two subjects with 10% and 15% blasts at screening developed MPN-BP while on study based on central review. Reasons for discontinuation by local PI included PD (n=8), lack of response (n=5), study completed (n=2), other (n=2), patient decision (n=1). Median % change in palpable spleen length was +10% (range -70% to +150%) and TSS change was -50% (-100% to +185.7%) The median platelet count at baseline was 114 x 10 9/L (range: 28-695) and 215 x 10 9/L (range: 66-263) after cycle 6 in 7 evaluable subjects (Fig 2A). Notably, 17 subjects had an increase in platelets from baseline during treatment and two subjects normalized their platelet counts. Maximum changes in platelets from baseline across all cycles was +63.8% [range -15.7%, +505.5%] (Fig 2B). Paired bone marrow biopsy pathology samples for 12 subjects were available for central review and showed no significant changes in BMF score or MK histo topography at end of treatment compared to baseline. All patients had elevated plasma levels of TGF β1, but not TGFβ2/β3 levels as detected by ELISA, which were dramatically reduced 21 days after the last dose of AVID200. AVID200 a TGFβ1/3 protein trap is well tolerated and clinical responses at cycle 7 of therapy in this advanced MF patient population were limited as judged by IWG/MRT response criteria. However, AVID200 therapy resulted in significant reduction in serum TGFβ levels and improvements in platelet counts indicating that TGF β1 plays a pivotal role in MF leading to thrombocytopenia which can be reversed with AVID200 therapy. We conclude that AVID200 may best be employed in combination therapy approaches in thrombocytopenic MF patients. Figure 1 Figure 1. Disclosures Mascarenhas: Constellation: Consultancy, Membership on an entity's Board of Directors or advisory committees; Promedior: Consultancy, Membership on an entity's Board of Directors or advisory committees; Incyte: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Geron: Consultancy, Research Funding; Forbius: Research Funding; Genentech/Roche: Consultancy, Membership on an entity's Board of Directors or advisory committees; Sierra Oncology: Consultancy, Membership on an entity's Board of Directors or advisory committees; Celgene/BMS: Consultancy, Membership on an entity's Board of Directors or advisory committees; PharmaEssentia: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Roche: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Galecto: Consultancy; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Prelude: Consultancy; Kartos: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; CTI Biopharm: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Geron: Consultancy; Merck: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; AbbVie: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Gilead: Consultancy, Membership on an entity's Board of Directors or advisory committees; Merus: Research Funding. Palmer: PharmaEssentia: Research Funding; Sierra Oncology: Consultancy, Research Funding; Incyte: Research Funding; CTI BioPharma: Consultancy, Research Funding; Protagonist: Consultancy, Research Funding. Kuykendall: Celgene/BMS: Honoraria; Pharmaessentia: Honoraria; Novartis: Honoraria, Speakers Bureau; Protagonist: Consultancy, Research Funding; Incyte: Consultancy; Abbvie: Honoraria; Blueprint: Honoraria. Mesa: Genentech: Research Funding; Promedior: Research Funding; Samus: Research Funding; Gilead: Research Funding; CTI: Research Funding; Abbvie: Research Funding; Sierra Oncology: Consultancy, Research Funding; Celgene: Research Funding; Novartis: Consultancy; Pharma: Consultancy; CTI: Research Funding; Constellation Pharmaceuticals: Consultancy, Research Funding; AOP: Consultancy; La Jolla Pharma: Consultancy; Incyte Corporation: Consultancy, Research Funding. Rampal: Stemline: Consultancy, Research Funding; Memorial Sloan Kettering: Current Employment; BMS/Celgene: Consultancy; Abbvie: Consultancy; CTI: Consultancy; Novartis: Consultancy; Disc Medicine: Consultancy; Blueprint: Consultancy; Pharmaessentia: Consultancy; Incyte: Consultancy, Research Funding; Jazz Pharmaceuticals: Consultancy; Constellation: Research Funding; Kartos: Consultancy; Sierra Oncology: Consultancy. Gerds: PharmaEssentia Corporation: Consultancy; Sierra Oncology: Consultancy; CTI BioPharma: Research Funding; Constellation: Consultancy; Celgene/Bristol Myers Squibb: Consultancy; AbbVie: Consultancy; Novartis: Consultancy. Yacoub: Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; CTI Biopharma: Membership on an entity's Board of Directors or advisory committees; ACCELERON PHARMA: Membership on an entity's Board of Directors or advisory committees; Agios: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Dynavex: Current equity holder in publicly-traded company; Cara: Current equity holder in publicly-traded company; Ardelyx: Current equity holder in publicly-traded company; Seattle Genetics: Honoraria, Speakers Bureau; Incyte: Consultancy, Honoraria, Speakers Bureau; Hylapharm: Current equity holder in publicly-traded company. Talpaz: Imago: Consultancy; Constellation: Membership on an entity's Board of Directors or advisory committees; Bristol Myers Squibb: Membership on an entity's Board of Directors or advisory committees; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Takeda: Other: Grant/research support ; Celgene: Consultancy. Komrokji: Acceleron: Consultancy; Taiho Oncology: Membership on an entity's Board of Directors or advisory committees; AbbVie: Consultancy; BMSCelgene: Consultancy, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; PharmaEssentia: Membership on an entity's Board of Directors or advisory committees; Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Geron: Consultancy; Jazz: Consultancy, Speakers Bureau. Kremyanskaya: Astellas: Research Funding; Astex: Research Funding; Chimerix: Research Funding; Bristol Myers Squibb: Research Funding; Constellation: Research Funding; Protagonist Therapeutics: Consultancy, Research Funding; Incyte: Research Funding. Salama: Mayo Clinic: Current Employment, Other: Mayo Clinic had the contractual work for the central pathology review for this study and I was one of the reviewing pathologists; Constellation Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees. Hoffman: Kartos Therapeutics, Inc.: Research Funding; Protagonist Therapeutics, Inc.: Consultancy; Novartis: Other: Data Safety Monitoring Board, Research Funding; AbbVie Inc.: Other: Data Safety Monitoring Board, Research Funding. OffLabel Disclosure: AVID200 is a TGFb trap and is in clinical testing for fibrotic diseases. It does not have an approved indication at this time.

Abstract Myeloproliferative neoplasms (MPN) that have evolved into accelerated or blast phase disease (MPN-AP/BP) have poor outcomes with limited treatment options and therefore represent an urgent unmet need. We have previously demonstrated in a multicenter, phase 1 trial conducted through the Myeloproliferative Neoplasms Research Consortium that the combination of ruxolitinib and decitabine is safe and tolerable and is associated with a favorable overall survival (OS). In this phase 2 trial, 25 patients with MPN-AP/BP were treated at the recommended phase 2 dose of ruxolitinib 25 mg twice daily for the induction cycle followed by 10 mg twice daily for subsequent cycles in combination with decitabine 20 mg/m2 for 5 consecutive days in a 28-day cycle. Nineteen patients died during the study follow-up. The median OS for all patients on study was 9.5 months (95% confidence interval, 4.3-12.0). Overall response rate (complete remission + incomplete platelet recovery + partial remission) was 11/25 (44%) and response was not associated with improved survival. We conclude that the combination of decitabine and ruxolitinib was well tolerated, demonstrated favorable OS, and represents a therapeutic option for this high-risk patient population. This trial was registered at www.clinicaltrials.gov as #NCT02076191.

The TP53 pathway has been shown to be dysregulated in myeloproliferative neoplasms (MPN) through several different mechanisms, including TP53 mutations, TP53 deletions and Murine Double Minute 2 (MDM2) overexpression. Downregulation of the TP53 pathway likely plays a role in MPN progression as evidenced by the association of TP53 loss of heterozygosity with transformation to acute leukemia and the presence of inactivating mutations of TP53 found in a proportion of MPN-blast phase (MPN-BP) cases (Kubesova et al, Leukemia. 2018;32(2):450-61). Furthermore, MDM2 inhibition induces TP53 pathway upregulation and consequent targeting of hematopoietic stem and progenitor cells in polycythemia vera (PV) and myelofibrosis (MF). The MDM2 inhibitor, idasanutlin, has shown activity in a Phase I trial of high-risk PV patients (Mascarenhas et al. Blood. 2019 Jun 5). An additional regulator of TP53 is protein phosphatase, Mg2+/Mn2+ dependent 1D (PPM1D) which by dephosphorylating TP53 and stabilizing MDM2 regulates the DNA damage response pathway and apoptosis. Somatic activating mutations of PPM1D are present in both solid and hematologic malignancies and are specifically associated with therapy-related myeloid disorders (Hsu et al. Cell Stem Cell. 2018 Nov 1;23(5):700-13). Grinfeld et al. (N Engl J Med. 2018 Oct 11;379(15):1416-30) recently reported that in their genomic analysis of 2035 MPN patients, PPM1D was the eighth most common mutated gene in MPNs at 1.9% frequency. To determine whether there was an association of PPM1D mutations with MPNs we analyzed the genomic data of patients who participated in several clinical trials executed by the Myeloproliferative Neoplasm Research Consortium (MPN-RC). Of 89 MPN-BP patients, 5 patients harbored a PPM1D mutation with a median variant allele frequency (VAF) of 17%. In comparison, 4 out of 135 high risk PV and ET patients harbored a PPM1D mutation with a median VAF of 24%. All mutations were truncating which is consistent with previous reports of PPMID mutations in malignancies. The PPM1D gene is located on the long arm of chromosome 17 (17q23.2) and we hypothesized that cytogenetic aberrations involving this gene locus might also contribute to abnormalities of PPM1D function. Through analysis of our cytogenetic database, 16/1,124 (1.4%) MPN patients were found to have cytogenomic abnormalities involving the region containing the PPM1D gene. Eight of these patients had karyotypic abnormalities, including 3 pts with isochromosome 17q resulting in a gain of 17q and a loss of 17p, including the TP53 gene. The other 4 patients had structural variations of 17q which might lead to aberrant expression of PPM1D. One patient by FISH analysis had gain of 17q. Ten patients had cytogenomic aberrations of 17q detected through analysis of array comparative genomic hybridization and single nucleotide polymorphism (aCGH+SNP), 2 of which had concurrent karyotypic abnormalities of 17q. All patients had a gain or copy neutral loss of heterozygosity (cnLOH) of the 17q22-24.2 region. CnLOH of this region could lead to aberrant overexpression of the PPM1D gene. One of the 8 patients with cnLOH of 17q harbored a PPM1D mutation. Of the 16 patients with 17q cytogenomic abnormalities, 7 (44%) had MPN-BP and 7 (44%) patients had ET or ET that progressed to myelofibrosis (MF) or MPN-BP indicating an association of these abnormalities with advanced disease. By quantitative real time-PCR we determined the PPM1D transcript levels in mononuclear cells from 31 MPN patients without known PPM1D mutations (7 polycythemia vera (PV), 6 ET, 14 MF, 4 MPN-BP) and compared the transcript levels to mononuclear cells from healthy control patients. Forty-two percent (13/31) patients had overexpression of PPM1D (>1.5 fold increase range). Fold increase ranged from 1.5-8 and overexpression was present in the following diagnoses: 4/7 PV, 1/6 ET, 8/14 MF and 0/4 MPN-BP. We have provided evidence that a number of abnormalities of PPM1D including activating mutations, cytogenetic aberrations and transcript overexpression are present in a significant proportion of MPN patients. These abnormalities in PPM1D can be additional events that lead to the downregulation of TP53 and contribute to MPN disease progression. We propose that inhibitors of PPM1D may be used in combination with other drugs that upregulate TP53 to treat MPN patients. Disclosures Rampal: Constellation, Incyte, and Stemline Therapeutics: Research Funding; Agios, Apexx, Blueprint Medicines, Celgene, Constellation, and Jazz: Consultancy. Mascarenhas:CTI Biopharma: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Merck: Research Funding; Roche: Consultancy, Research Funding; Incyte: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Research Funding; Pharmaessentia: Consultancy, Membership on an entity's Board of Directors or advisory committees; Janssen: Research Funding; Promedior: Research Funding; Merus: Research Funding. Hoffman:Merus: Research Funding.

Abstract Background: Patients (pts) with polycythemia vera (PV) and essential thrombocythemia (ET) suffer from difficult MPN associated symptoms which impact quality of life (QoL). The impact of initial cytoreduction on ET/PV symptoms, resulting toxicity and QoL have not been prospectively studied. Methods: MPD-RC 112 trial (NCT01258856) randomized 168 therapy-naive (hydroxyurea [HU] <3 mo) high risk ET/PV pts (<5 years of disease) to response adjusted pegylated interferon alpha 2a (PEG) or HU. MPN symptoms, in depth toxicity assessment, and QoL were measured by two symptom instruments (MPN-SAF, EORTC QLQ-C30: baseline,3, 6, 9, and 12 mo) and toxicity questions. Blinded response review by European Leukemia Net (ELN) hematological responses (HR) was conducted at 12 months. Individual time point and longitudinal group comparisons were based on mixed models adjusting for age. Results: Patients: Of 168 randomized pts (86 HU, 82 PEG), 164 (98%) completed the survey package at baseline and 151 (HU 83%; PEG 98%) completed at least 1 survey during treatment. Median age was 61 (range 18-87) with 70 (42%) females; 81 (48%) / 87 (52%) with ET / PV; 46 (27%) had a history of a thrombosis. 119 (71%) received prior HU (up to 3 months). Baseline characteristics were balanced between arms with the exception of age (median HU 63 vs. PEG 60 yrs; p=0.02). Baseline Symptom Burden /QoL: Mean MPN-SAF Total Symptom Score (TSS), scale 0 [absent]-100 [worst imaginable] was 15.8 (SD 12.6; range 0-62.0) with means of 15.1 (SD 12.6) / 16.5 (SD 12.6) for ET / PV which were slightly lower than reported means of a previous cohort receiving any line of treatment (Scherber RM, JCO 2012). Median number of moderate (defined as score >=3) symptoms in ET patients was 3.0 and PV 4.0. Most common moderate symptoms were fatigue (65.9%), insomnia (37.2%), numbness (33.5%) , itching (29.9%), dizziness (27.4%), early satiety (26.8%) , headache (23.2%), sad mood (23.2%), inactivity (22%), concentration (20.7%). 50.6% of patients had one or more symptom with a score >=6. Mean QLQ-C30 global health status/QoL (GHS/QoL) was 70.8 (SD 21.9) - comparable to a general population (mean 71.2, SD 22.4) and better than a general cancer population (mean 61.3, SD 24.2; QLQ-C30 Reference Manual 2008). At baseline, TSS, symptoms, and QoL were similar between treatment arms. In patients with TSS >20 at baseline (highly symptomatic, n=50; ET:20, PV:30), median TSS was 28.0 (range 20.0 to 62.0); the highest scored symptom was fatigue (median=7.0), itching (median=4.5) and insomnia (median=4.0). Impact of Therapy on Symptom Burden/QoL: On HU, pts experienced worsening QoL (physical, cognitive functioning, HRQoL) and some persistent or transient worsened symptoms (inactivity, concentration (p<0.05) (Table 1)). On PEG, pts experienced worsening of fever, dyspnea, appetite loss and PEG-related symptoms including flu-like symptoms, injection site irritation, blurry vision, and visual changes (all p<0.05), but not sad mood (not corrected for antidepressants). In comparing arms, change in TSS significantly differed (p=0.01) between arms with increasing symptoms on HU vs PEG at 3 and 6 mo, but lower symptom burden at 9 and 12 mos (Figure 1). In highly symptomatic pts (with a baseline TSS > 20, n=50), improvements in weight loss, abdominal discomfort, fatigue, itching, fever, early satiety (12 m.) were observed in pts on HU. For PEG, in highly symptomatic pts, improvements were observed for overall TSS score, fatigue, inactivity, night sweats, and itching (with similar toxicities to all PEG patients). ELN Response and Symptom Burden/QoL: Among the 133 pts with 12-mo symptom data, complete hematologic response (CHR) rate was 43%. Inactivity and sad mood were worse in those patient achieving a CHR (inactivity: CHR worsening 0.68 vs PHR/NR better 0.26; p=0.03; sad mood: CHR worsening 0.67 vs PHR/NR better 0.67, p=0.002)). These latter changes were not related to higher doses utilized (in either arm), suggesting obtaining CHR may have negative effects on patient symptoms. Conclusions:In pts with a significant baseline MPN symptom burden, cytoreductive therapy has both a beneficial impact on baseline MPN symptom burden but also leads to therapy associated toxicity, although different patterns of efficacy and toxicity between HU and PEG. Achievement of a CHR in PV/ET may be associated with higher rates of drug related toxicities, and the value of achieving CHR may need further validation. Disclosures Mesa: Incyte Corporation: Research Funding; CTI Biopharma: Research Funding; Gilead: Research Funding; NS Pharma: Research Funding; Promedior: Research Funding; Novartis: Consultancy; Celgene: Research Funding; UT Health San Antonio - Mays Cancer Center: Employment; Genentech: Research Funding; Pfizer: Research Funding. Mascarenhas:Merck: Research Funding; CTI Biopharma: Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene: Membership on an entity's Board of Directors or advisory committees; Roche: Research Funding; Promedior: Research Funding; Incyte: Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Research Funding; Janssen: Research Funding. Rambaldi:Omeros: Consultancy; Roche: Consultancy; Celgene: Consultancy; Pfizer: Consultancy; Novartis: Consultancy; Italfarmaco: Consultancy; Amgen Inc.: Consultancy. Yacoub:Novartis: Honoraria, Speakers Bureau; Cara Therapeutics: Equity Ownership; Ardelyx, INC.: Equity Ownership; Inycte: Honoraria, Speakers Bureau; Seattle Genetics: Honoraria, Speakers Bureau; Dynavax: Equity Ownership. Harrison:Gilead: Honoraria, Speakers Bureau; CTI BioPharma: Consultancy, Honoraria; Roche: Consultancy, Honoraria; Novartis: Consultancy, Honoraria, Research Funding, Speakers Bureau; Celgene: Consultancy, Honoraria, Speakers Bureau. Kiladjian:AOP Orphan: Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene: Membership on an entity's Board of Directors or advisory committees. Mead:Elstar: Research Funding; Celgene: Research Funding; ARIAD: Consultancy; Cell Therapeutics: Consultancy; Evotek: Research Funding; Novartis: Consultancy, Honoraria, Research Funding, Speakers Bureau; Bristol-Myers Squibb: Consultancy. Kessler:Sangamo: Research Funding; Octapharma: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Pfizer: Honoraria, Membership on an entity's Board of Directors or advisory committees; Novo Nordisk: Honoraria, Research Funding; Dimension Advisory boards: Membership on an entity's Board of Directors or advisory committees; Bayer: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; DSMB: Membership on an entity's Board of Directors or advisory committees; Genentech: Research Funding; Biomarin: Research Funding. Kremyanskaya:Incyte: Research Funding. Rampal:Incyte: Honoraria, Research Funding; Constellation: Research Funding; Jazz: Consultancy, Honoraria; Stemline: Research Funding; Celgene: Honoraria. Hoffman:Incyte: Research Funding; Janssen: Research Funding; Merus: Research Funding; Formation Biologics: Research Funding; Summer Road: Research Funding. Dueck:Pfizer: Honoraria; Bayer: Employment; Phytogine: Employment.

Abstract Background: The Philadelphia chromosome negative myeloproliferative neoplasms (MPN), including polycythemia vera (PV), essential thrombocythemia (ET) and primary myelofibrosis (PMF), carry a propensity to evolve into an accelerated phase (MPN-AP, 10-19% blasts in the blood or marrow) and blast phase (MPN-BP, ≥20% in the blood or marrow). Such disease evolution carries a dismal prognosis with a median survival of 3-5 months, and thus the development of innovative treatment strategies represents an urgent unmet clinical need. Responses in patients with MPN-AP/BP to both hypomethylating agents and single-agent ruxolitinib (RUX) have been reported. In vitro, the combination of RUX and decitabine (DEC) are synergistically active in cells derived from patients with MPN-BP and from a murine model of MPN-BP. These observations led us to explore the safety of the combination in MPN-AP/BP in a phase I study. An MTD for RUX in combination with DEC 20mg/m2/d x 5 days was not reached in this study and the recommended Phase II dose of RUX was selected as 25mg BID for the first cycle of therapy followed by 10mg BID in subsequent cycles with a goal to minimize myelosuppression and maintain ambulatory administration (Rampal et al ASH 2016). Here we report the final results of the phase 2 combination of RUX + DEC in patients with MPN-AP/BP (NCT02076191). Methods: We conducted a multicenter, open label, phase II trial in patients with MPN-AP/BP, following a previous diagnosis of ET, PV or PMF. Patients enrolled were treated with the RPTD dose of RUX + DEC on a 28-day cycle until progression of disease, unacceptable toxicity or patient/physician withdrawal. Adverse events (AEs) were assessed using the NCI CTCAE v4.0. The primary endpoint was response rate by cycle 6 using modified Cheson criteria: CR required 0% peripheral blood blasts, ANC >1000/uL, hemoglobin ≥10g/L, and platelets ≥100x109/L; CRi required 0% peripheral blood blasts with incomplete count recovery; and PR required ≥50% decrease in peripheral blood blasts regardless of blood counts. Results: A total of 25 patients were accrued to study. The median age was 71 years (46.7-85.6). 10 patients (40%) had MPN-AP and 15 patients (60%) had MPN-BP. 6 patients (24%) had been previously been treated with single-agent RUX, and 2 patients (8%) had been treated with single-agent DEC. Median palpable spleen size was 7cm (range 0 - 20cm). The median number of cycles of treatment received on study was 4 (range 1 - 20). The most common grade 3/4 non-hematologic AEs observed were pneumonia (16%), febrile neutropenia (16%) and infection (8%). The most common grade 3/4 hematologic AEs were anemia (16%), neutropenia (12%) and leukopenia (8%). The most common reasons for study discontinuation were AEs in 9 patients (36%), disease progression in 5 (20%) patients and hematopoietic cell transplantation in 2 (8%) patients. Eighteen (72%) patients were evaluable for response. The overall response rate (CR+CRi+PR) was 61% (11/18 patients). CRi was observed in 2 patients (11%), PR in 9 patients (50%) and no response in 7 patients (39%). The median time to CR/PR was 3.4 mos (95% CI: 2.1 - not estimated). The median peripheral blood blast count reduction was 80.1% (range 71.4-100%) (Figure 1A). The median reduction in spleen size by palpation was 70.5% (range 0-100%) (Figure 1B). Median overall survival for all patients was 7.6 months (95% CI: 4.3 - Not estimated); 9.7 months (95% CI: 4.3 - Not estimated) for MPN-BP and 5.8 months (95% CI: 3.6 - Not estimated) for MPN-AP (Figure 2). Three patients (17%) were able to proceed to HCT. The results of ongoing genomic, histopathologic and cytokine profiling studies will be available for presentation at the meeting. Conclusions: The combination of RUX+DEC has activity in patients with MPN-AP/BP. The drug combination is generally well tolerated and can be administered as an outpatient, a distinct advantage over intensive induction therapies that have not shown significant benefit in these patients. Additional work is ongoing to assess the genomic and clinical variables predictive of response with this combination therapy approach. Given the tolerability and efficacy, this regimen may be of particular benefit to patients who are not candidates for intensive therapies. Disclosures Rampal: Constellation: Research Funding; Celgene: Honoraria; Stemline: Research Funding; Incyte: Honoraria, Research Funding; Jazz: Consultancy, Honoraria. Mascarenhas:Celgene: Membership on an entity's Board of Directors or advisory committees; Merck: Research Funding; CTI Biopharma: Membership on an entity's Board of Directors or advisory committees, Research Funding; Janssen: Research Funding; Novartis: Research Funding; Incyte: Membership on an entity's Board of Directors or advisory committees, Research Funding; Roche: Research Funding; Promedior: Research Funding. Wang:Jazz: Speakers Bureau; Abbvie: Consultancy, Membership on an entity's Board of Directors or advisory committees; Amgen: Consultancy; Abbvie: Consultancy, Membership on an entity's Board of Directors or advisory committees; Amgen: Consultancy; Pfizer: Consultancy, Membership on an entity's Board of Directors or advisory committees; Pfizer: Consultancy, Membership on an entity's Board of Directors or advisory committees; Novartis: Speakers Bureau; Jazz: Speakers Bureau; Novartis: Speakers Bureau. Gerds:Celgene: Consultancy; Apexx Oncology: Consultancy; Incyte: Consultancy; CTI Biopharma: Consultancy. Heaney:Roche: Consultancy, Research Funding; Incyte: Research Funding; Blueprint: Research Funding; Novartis: Research Funding; Decipheral: Research Funding. Abboud:Agios: Honoraria; Jazz: Honoraria, Speakers Bureau. Kremyanskaya:Incyte: Research Funding. Odenike:ABBVIE: Honoraria, Research Funding; Pfizer: Consultancy, Membership on an entity's Board of Directors or advisory committees; Celgene: Consultancy, Membership on an entity's Board of Directors or advisory committees; CTI/Baxalta: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Dava Oncology: Consultancy, Membership on an entity's Board of Directors or advisory committees; Incyte: Consultancy, Membership on an entity's Board of Directors or advisory committees; Jazz Pharmaceuticals: Consultancy, Membership on an entity's Board of Directors or advisory committees; Oncotherapy Science: Research Funding; Agios: Research Funding; Celgene: Research Funding; NS Pharma: Research Funding; Janssen: Research Funding; Astex: Research Funding; Gilead Sciences: Research Funding. Levine:Roche: Consultancy, Research Funding; C4 Therapeutics: Equity Ownership; Janssen: Consultancy, Honoraria; Gilead: Honoraria; Epizyme: Patents & Royalties; Prelude: Research Funding; Qiagen: Equity Ownership, Membership on an entity's Board of Directors or advisory committees; Celgene: Consultancy, Research Funding; Loxo: Consultancy, Equity Ownership; Imago: Equity Ownership; Novartis: Consultancy; Isoplexis: Equity Ownership. Mesa:Novartis: Consultancy; NS Pharma: Research Funding; Genentech: Research Funding; UT Health San Antonio - Mays Cancer Center: Employment; CTI Biopharma: Research Funding; Gilead: Research Funding; Pfizer: Research Funding; Celgene: Research Funding; Incyte Corporation: Research Funding; Promedior: Research Funding. Dueck:Phytogine: Employment; Bayer: Employment; Pfizer: Honoraria. Hoffman:Incyte: Research Funding; Formation Biologics: Research Funding; Janssen: Research Funding; Merus: Research Funding; Summer Road: Research Funding.

Abstract Introduction HU is the treatment of choice for patients (pts) with high risk ET/PV, however, PEG has been proposed as an alternative option due to its proposed potential to modify disease course. An interim analysis of MPN-RC 112 (Blood 2016 128:479;) did not reveal a difference in PR/CR rates between HU and PEG therapy after 12 months in the first evaluable 75 pts treated. Here we present the results and long-term follow-up of all pts participating in this pivotal study [NCT01259856]. Methods MPN-RC 112 was a randomized, open label, phase 3 clinical trial comparing HU and PEG in pts with high risk ET/PV. Pts were treated for up to 12 months to achieve PR or CR (ELN/IWG-MRT response criteria). Pts who achieved a PR/CR continued therapy for up to a maximum of 6 years. Minimum follow up was 1 year from the time the last pt was randomized. The primary objective was to compare the CR rate following HU vs. PEG at 12 months with 3 month confirmation. Secondary objectives included a comparison of toxicity and tolerability; PR rates; incidence of specific pre-defined toxicities and tolerance to therapy; impact of therapy on key biomarkers; survival and incidence of myelodysplastic syndrome, myelofibrosis, or leukemic transformation; and incidence of major cardiovascular events. Bone marrow pathologic responses were evaluated by central blinded expert review at baseline, 12, 24 months and end of study. Results The study accrued 168 pts; 86 were randomized to HU and 82 to PEG. A summary of pt baseline characteristics by treatment arm is shown in Table 1 and were well balanced between the treatment arms except for median age which was higher in the HU arm (p=0.02). Median duration of follow up was 89.9 weeks (range, 0 to 292.3) and the median treatment duration was 86.0 weeks (range, 0 to 287.3). At 12 months, the overall response rate (ORR= PR+CR) was 69.8% and 78% for HU and PEG, respectively (p=0.22). Figure 1 shows the distribution of responses stratified by disease type. At 24 months, 59 pts were on treatment with an ORR of 22/25 (88%) for HU and 31/34 (91%) for PEG. When considering all 106 pts who were eligible to receive treatment for 24 months (due to study closure), the ORR was 22/54 (40.7%, PR: 11 (20.4%), CR: 11 (20.4%)) for HU and 31/52 (59.6%, (PR: 15 (28.9%), CR: 16 (30.8%)) for PEG, p=0.04. Best ORR at any time on study was seen in 70.9% and 81.7% of HU and PEG treated pts, respectively, p=0.10. The median maximum change from baseline spleen volume was -6% (-100.0 - +53.8) in 112 evaluable pts and was similar between arms, p=0.99. Bone marrow morphologic responses are shown in Table 2 and the best response (CR) seen at any time on study for ET treated with HU was 52% (12/23) vs PEG 32% (8/25) and for PV treated with HU 19% (6/31) vs PEG 6% (2/34). Cytogenetic analyses at diagnosis were available in 86% (144/168). An abnormal karyotype was seen in 15% (22/144). Five PV and one ET pt lost their chromosomal abnormalities: 3 after one year (HU=1, PEG=2) and three after two years of therapy (HU=2, PEG=1). AE information is available for 162 pts (HU: 80; PEG: 82) (Table 3). Six pts randomized to HU never received treatment due to study withdrawal prior to initiation of treatment. Sixty pts had a grade 3 or higher event [HU: 22 (27.5%) and PEG: 38 (46.3%)]. 28 PV pts had a grade 3/4 [HU: 10 (24.4%) and PEG: 18 (41.9%)]. Four pts had a grade 4/5 event [HU: 3 (7.3%) and PEG: 1 (2.3%)]. 32 ET pts had a grade 3/4 [HU:12 (30.8%) and PEG:20 (51.3%)]. Two pts had a grade 4/5 event [HU:1 (2.6%), PEG:1 (2.6%)]. Additional outcomes of interest on study include one death attributed to new diagnosis of lung cancer (HU:1), progression to myelofibrosis (HU:1), vertebral artery occlusion (HU:1), and cerebral vascular accident (PEG:1). Reasons for study discontinuation are shown in Table 4. The effect of therapy on symptom burden and quality of life will be presented in a companion abstract (Mesa et al). The impact of mutation status on therapeutic outcome as well as the molecular responses will be presented at the meeting. Conclusion The final analysis of MPN-RC 112 revealed that the CR rates in pts with high risk ET/PV treated with PEG and HU at 12 and 24 months were similar. PEG was associated with a higher rate of grade 3/4 toxicity. Each drug appeared equally capable of modifying the natural history of high risk ET/PV based upon their effects on spleen size, karyotypic abnormalities, histopathological parameters and the low incidence of thrombotic complications and disease evolution in both arms. Disclosures Mascarenhas: Novartis: Research Funding; Promedior: Research Funding; Celgene: Membership on an entity's Board of Directors or advisory committees; Janssen: Research Funding; Merck: Research Funding; CTI Biopharma: Membership on an entity's Board of Directors or advisory committees, Research Funding; Roche: Research Funding; Incyte: Membership on an entity's Board of Directors or advisory committees, Research Funding. Rambaldi:Amgen Inc.: Consultancy; Pfizer: Consultancy; Novartis: Consultancy; Italfarmaco: Consultancy; Omeros: Consultancy; Roche: Consultancy; Celgene: Consultancy. Harrison:Novartis: Consultancy, Honoraria, Research Funding, Speakers Bureau; CTI BioPharma: Consultancy, Honoraria; Roche: Consultancy, Honoraria; Gilead: Honoraria, Speakers Bureau; Celgene: Consultancy, Honoraria, Speakers Bureau. Kiladjian:AOP Orphan: Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene: Membership on an entity's Board of Directors or advisory committees. Mead:Bristol-Myers Squibb: Consultancy; Elstar: Research Funding; Celgene: Research Funding; ARIAD: Consultancy; Evotek: Research Funding; Novartis: Consultancy, Honoraria, Research Funding, Speakers Bureau; Cell Therapeutics: Consultancy. Kessler:Genentech: Research Funding; Sangamo: Research Funding; Bayer: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Pfizer: Honoraria, Membership on an entity's Board of Directors or advisory committees; Biomarin: Research Funding; Octapharma: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; DSMB: Membership on an entity's Board of Directors or advisory committees; Novo Nordisk: Honoraria, Research Funding; Dimension Advisory boards: Membership on an entity's Board of Directors or advisory committees. Kremyanskaya:Incyte: Research Funding. Rampal:Stemline: Research Funding; Incyte: Honoraria, Research Funding; Constellation: Research Funding; Jazz: Consultancy, Honoraria; Celgene: Honoraria. Mesa:CTI Biopharma: Research Funding; Novartis: Consultancy; Genentech: Research Funding; Promedior: Research Funding; UT Health San Antonio - Mays Cancer Center: Employment; Pfizer: Research Funding; Celgene: Research Funding; Incyte Corporation: Research Funding; Gilead: Research Funding; NS Pharma: Research Funding. Dueck:Pfizer: Honoraria; Bayer: Employment; Phytogine: Employment. Hoffman:Incyte: Research Funding; Formation Biologics: Research Funding; Merus: Research Funding; Janssen: Research Funding; Summer Road: Research Funding.

Yacoub et al report excellent responses to pegylated interferon alfa-2a in patients with hydroxyurea-resistant/intolerant polycythemia vera or essential thrombocythemia.