AOP Orphan Pharmaceuticals AG Research Articles

AOP2014/P1101, a Novel Peg-Proline-Interferon Alpha (IFNa) 2b, Specifically Targets JAK2V617F-Positive Polycythemia Vera (PV) Cells

BackgroundPegylated Interferon alpha (PEG-IFNa) has proven clinical and molecular efficacy in the treatment of Bcr-Abl negative myeloproliferative neoplasms. Indeed PEG-IFNa induces complete hematological remissions but also molecular responses demonstrated by the reduction of the JAK2V617F (JAK2VF) allele burden. AOP2014/P1101 is a next generation long-acting PEG-IFNa-2b, recently shown to be safe and well tolerated in phase I-II studies in PV patients (pts) (Gisslinger at al, 2012). In addition, molecular responses (MR) were reported in these early phase trials with 50% of pts achieving partial MR at month 18. Furthermore, one pt with a baseline JAK2VF allelic burden of 22% achieved complete MR after 36 weeks of therapy suggesting a specific effect of AOP2014/P1101 on JAK2VF-positive cells. AimTo study the differential impact of AOP2014/P1101 on the proliferation and differentiation of wild type versus JAK2VF hematopoietic cells. Materials and methodsWe studied the effects of AOP2014/P1101 at different concentrations consistent with assumed exposure in patients (0.5 and 2µg/ml), compared with standard recombinant interferon alpha-2a (rIFNa-2a) at 700 U/ml in human cell lines in liquid suspension assay, and in normal and PV samples in methylcellulose assays. A) Two different human JAK2VF cell lines were studied: HEL characterized by the presence of multiple copies of JAK2VF, and UKE-1 which harbors 2 copies of JAK2VF. Cell lines were grown in presence or absence of drugs and living cells were counted each day during 3 days. B) Normal hematopoietic progenitors derived from cord blood and primary cells from 4 PV patients were studied in clonogenic assays (Methocult, Stemcell technologies©). In PV pts samples the presence of endogenous erythroid colonies (EECs) was determined in cultures without erythropoietin (EPO). Genotyping of the colonies was performed by picking the colonies, extracting the DNA and testing for the presence of JAK2VF using the JAK2 Mutascreen kit (Qiagen©). ResultsIn both HEL and UKE-1 JAK2 mutated cell lines AOP2014/P1101 exhibited a dose-dependent anti-proliferative effect which was comparable to that of rIFNa-2a. AOP2014/P1101 at 0.5µg/ml and 2µg/ml induced a 9%, and 41% inhibition of HEL cells proliferation, respectively (resp). Same doses induced an 18% and 35% inhibition of UKE-1 cells proliferation, resp. A similar antiproliferative effect was observed with rIFNa-2a with 38%, and 36% inhibition of HEL, and UKE-1 cells proliferation, resp.In normal CD34+ hematopoietic progenitors derived from cord blood, AOP2014/P1101 induced a small decrease in the number of erythroid colonies (median reduction by 7%, 15% and 14% with AOP2014/P1101 0.5 µg/ml, 2 µg/ml, and rIFNa-2a, resp). Myeloid colonies were almost unaffected by AOP2014/P1101 (no modification at 0.5µg/ml, and 9% reduction at 2µg/ml) while a reduction by 18% was obtained using rIFNa-2a, confirming the low level of toxicity of AOP2014/P1101 on normal hematopoietic progenitors.In contrast, AOP2014/P1101 drastically reduced the growth of JAK2VF erythroïd progenitors in all the PV samples tested. A 41%, and 62% median reduction of the number of EPO-stimulated colonies was observed with AOP2014/P1101 0.5µg/ml, and 2µg/ml, respectively. A more striking effect was observed on colonies grown in the absence of EPO: the number of EECs was reduced by 82% with AOP2014/P1101 2µg/ml compared to untreated cells. This result suggested that AOP2014/P1101 inhibited more efficiently JAK2-mutant hematopoietic progenitors. This hypothesis was confirmed by the study of the JAK2 genotype at the clonogenic level: a median 2-fold increase in the ratio of wild type to mutant colonies with 2µg/ml AOP2014/P1101 was observed, suggesting that AOP2014/P1101 does specifically target PV erythroid progenitors harboring the JAK2VF mutation. In addition, in one patient with both homozygous and heterozygous JAK2VF colonies, eradication of homozygous colonies was achieved with AOP2014/P1101, suggesting that JAK2VF homozygous progenitors are even more sensitive to AOP2014/P1101. ConclusionOur results show that AOP2014/P1101, a novel form of PEG-IFNa-2b, can specifically target PV JAK2VF hematopoietic progenitors while sparing wild type cells. These results are in line with the clinical efficacy with low hematologic toxicity reported in early phase trials with AOP2014/P1101. Disclosures:Cassinat:AOP Orphan: Research Funding. Klade:AOP Orphan Pharmaceuticals AG: Employment. Zahriychuk:AOP Orphan Pharmaceuticals AG: Employment. Kiladjian:AOP Orphan: Honoraria, Research Funding.

AOP2014, a Novel Peg-Proline-Interferon Alpha-2b with Improved Pharmacokinetic Properties, Is Safe and Well Tolerated and Shows Promising Efficacy in Patients with Polycythemia Vera (PV)

AbstractAbstract 175AOP2014 is a next generation long-acting pegylated IFNa-2b, consisting predominantly of only one isoform, as opposed to other commercially available pegylated interferons. AOP2014 has a distinct pharmacokinetic and pharmacodynamic profile which may potentially allow reduced dosing frequencies compared to other pegylated IFNs. This is being expected to result in improved tolerability, better compliance, and, finally, favorable long-term treatment outcomes. AOP2014 is a designated Orphan Drug in EU for treatment of patients with PV. The maximum tolerated dose (MTD), long term safety and efficacy of AOP2014, administered subcutaneously every 14 days, are the main objectives of the study. Patients with confirmed PV diagnosis, age equal or older 18 years, both naïve and cytoreduction pre-treated are eligible. After establishing the MTD, an extended cohort of 25 additional patients was planned to be recruited. European LeukemiaNet criteria were used for response assessment. 34 patients, treated by March 31, 2012 were included into this analysis: 25 in Phase I (dose-finding) and 9 in the Phase II (cohort extension). Median time from diagnosis was 24 months (range 0–180). 12 patients (35%) were HU pre-treated (mean past duration of HU pre-treatment 39 months, mean daily HU dose 950 mg). Median number of phlebotomies in the past 3 months prior to inclusion was 1 (range 0–8), a total of 21 patients (62%) were regularly phlebotomized at least once in three months prior to study entry. 11 patients (32%) had a history of thrombotic complications. Median Hct at baseline was 42% (range 36–51). Median WBC and platelet counts were 10.6*109/l (range 3.9–20.4) and 452*109/l (range 141–1019), respectively. 17 patients (50%) had splenomegaly at baseline. The median reported treatment duration was 41 weeks (range: 1 day – 80 weeks), 11 patients completed 1 year on treatment. Doses from 50 to 540 ug every two weeks were tested, 540 ug has been concluded as MTD as the highest tested dose, since no DLTs occurred in the study. The mean administered dose (both Phase I and II patients) was 287 ug. After 28 weeks of treatment (21 evaluable patients), 71% of patients had hematological response (7 CR, 33%; 8 PR, 38%), at week 36 (19 evaluable patients) 8 patients (42%) achieved a CR and 8 patients (42%) a PR, overall response rate (ORR, CR+PR) was 84%. At week 52 (1 year; 11 evaluable patients), 5 patients (46%) had CR and 5 (46%) PR, ORR was 91%; 8 (73%) patients presented with completely normalized blood values, all evaluable patients were phlebotomy free at this timepoint. 4 patients (of 12 evaluable for this measurement, 33%) had still enlarged spleen at week 52. At week 76, 2 evaluable patients were complete responders. At week 52, 1 patient (of 9 evaluable, 11%) developed partial molecular response, at week 68 3 patients (of 7 evaluable, 43%) had partial molecular response. One patient with allelic burden of 22% at baseline developed complete molecular response at week 36 (still ongoing). Mainly grade 1 and 2 adverse events were reported. A total of 358 adverse events occurred. 27 patients (79%) suffered from drug-related adverse events. 9 patients (26%) developed serious adverse events; 4 SAEs were considered to be treatment related. 5 patients (15%) discontinued their study participation prematurely, 3 of them due to adverse events (deterioration of underlying disease and two cases of depression). Acceptable tolerability and durable clinical benefits have been demonstrated in PV patients measured as overall response rate of above 90% with CRs of 46% at one year after treatment start. Phlebotomy independence and normalization of hematological parameters could be seen in most of the patients. The study continues to recruit and collect long term follow up information. Presented data support further development of AOP2014 in PV, a Phase III study is planned to start early 2013. Disclosures:Gisslinger:AOP Orphan Pharmaceuticals AG: Research Funding; Novartis: Speakers Bureau; Celgene Austria: Research Funding, Speakers Bureau. Kralovics:AOP Orphan Pharmaceuticals AG: Research Funding. Gisslinger:AOP Orphan Pharmaceuticals AG: Research Funding. Lechner:AOP Orphan Pharmaceuticals AG: Research Funding. Buxhofer-Ausch:AOP Orphan Pharmaceuticals AG: Research Funding. Strecker:AOP Orphan Pharmaceuticals AG: Research Funding. Gastl:AOP Orphan Pharmaceuticals AG: Research Funding. Willenbacher:AOP Orphan Pharmaceuticals AG: Research Funding. Greil:AOP Orphan Pharmaceuticals AG: Research Funding. Egle:AOP Orphan Pharmaceuticals AG: Research Funding. Melchardt:AOP Orphan Pharmaceuticals AG: Research Funding. Burgstaller:AOP Orphan Pharmaceuticals AG: Research Funding. Schloegl:AOP Orphan Pharmaceuticals AG: Research Funding. Tarmann:AOP Orphan Pharmaceuticals AG: Employment. Zoerer:AOP Orphan Pharmaceuticals AG: Employment. Klade:AOP Orphan Pharmaceuticals AG: Employment. Zahriychuk:AOP Orphan Pharmaceuticals AG: Employment. Thaler:AOP Orphan Pharmaceuticals AG: Research Funding.

An Individual Patient Supply Program for Ruxolitinib for the Treatment of Patients with Primary Myelofibrosis (PMF), Post-Polycythemia Vera Myelofibrosis (PPV-MF), or Post-Essential Thrombocythemia Myelofibrosis (PET-MF).

AbstractAbstract 2844 Background:Myeloproliferative neoplasms, including PMF, PET-MF, and PPV-MF, are a group of clonal stem cell–derived diseases characterized by bone marrow fibrosis, splenomegaly, and debilitating constitutional symptoms. Ruxolitinib (rux), a potent oral JAK1 & 2 inhibitor, demonstrated rapid and durable reductions in splenomegaly and improved MF-related symptoms and quality of life in 2 phase 3 studies (COMFORT-I and -II). Due to unmet medical need, rux has been made available through an individual patient supply program (IPSP) outside the US. Methods:Patients (pts) with PMF, PPV-MF, or PET-MF requiring treatment (as determined by their physician) and classified as high-, intermediate (int)-2–, or int-1–risk with an enlarged spleen were evaluated for eligibility on an individual basis by the sponsor, irrespective of JAK2 mutation status. The starting dose of rux was determined on the basis of baseline platelet count (15 or 20 mg twice daily for pts with platelet counts of 100–200 × 109/L and > 200 × 109/L, respectively) and can be adjusted for efficacy and safety. Dose changes during treatment, adverse events (AEs), and serious AEs (SAEs) are registered throughout the program. Results:To date, 1339 requests have been received from > 800 physicians in 48 countries, including locations in Europe, Latin America, the Middle East, and Asia. The baseline characteristics are shown in the Table for pts whose requests for access were approved (n = 1240). Drug resupply requests are received every ≈ 3 months. Follow-up information, based on the first resupply request, was available for 381/639 (60%) of the pts who were enrolled in the program prior to February 2012; 303 (80%) remain on rux therapy, 37 (10%) have discontinued, 11 (3%) died, and 30 (8%) did not initiate therapy. Spleen response was available for 247 pts (decreased, n = 201; unchanged, n = 39; increased, n = 7). Changes in constitutional symptoms were available for 203 pts (decreased, n = 151; unchanged, n = 49; increased, n = 3). In pts enrolled in the IPSP undergoing rux treatment, most pts who had a decrease in spleen length also had a decrease in symptoms. Dose-modification information was available for 259 pts, of whom 44 had dose increases and 89 had dose decreases. Reasons for dose modifications included efficacy (n = 28), safety (n = 69), and other reasons (n = 36). Safety information was available for 266 pts; 75 reported significant AEs or SAEs as determined by investigators. Enrolled pt characteristics are generally similar to those expected in the overall MF pt population. Thus far, the proportion of pts enrolled in the IPSP with the JAK2 V617F mutation (73%) is higher than that for the general MF population (50%-60%). This may reflect a misconception that JAK inhibition is primarily effective in pts who have the JAK2 V617F mutation, when in fact rux has demonstrated similar efficacy in both pt types in the phase 1/2 251 study and the two phase 3 COMFORT trials. This may also be reflected in the higher proportion of PPV-MF pts in the IPSP than in the general MF population (28% vs 10%-15%), of whom 95% are JAK2 V617 F–positive. Conclusions:Considerable requests for access to rux have been received through the IPSP, highlighting the need for an effective treatment in pts with a range of IPSS risk-assessment scores. The demographics of the IPSP pts are similar to those expected in the overall MF population. Responses and safety patterns observed in the IPSP appear to be comparable to those from the COMFORT trials. [Display omitted] Disclosures:Off Label Use: Jakafi™ (ruxolitinib) is indicated in the United States for the treatment of patients with intermediate or high-risk myelofibrosis, including primary myelofibrosis, post–polycythemia vera myelofibrosis and post–essential thrombocythemia myelofibrosis. In Canada, JAKAVI ® is indicated for the treatment of splenomegaly and/or its associated symptoms in adult patients with primary myelofibrosis (also known as chronic idiopathic myelofibrosis), post-polycythemia vera myelofibrosis or post-essential thrombocythemia myelofibrosis. This abstract reports on a clinical study conducted outside the US including patients of all risk categories. All patients have provided written informed consent. Zweegman:Novartis: Membership on an entity’s Board of Directors or advisory committees, Research Funding. Willenbacher:Novartis: Honoraria, Membership on an entity’s Board of Directors or advisory committees, Research Funding. Raymakers:Novartis: Consultancy. Cantoni:CSL Behring Switzerland: Research Funding; Robapharm/Pierre Fabre Oncology Switzerland: Research Funding; Janssen-Cilag Switzerland: Consultancy; Novartis Oncology Switzerland: Consultancy, Research Funding. Modi:Novartis Pharmaceuticals Corporation: Employment. Khan:Novartis: Employment. Perez:Novartis Pharmaceuticals Corporation: Employment, Equity Ownership. Gisslinger:AOP Orphan Pharmaceuticals AG: Consultancy, Speakers Bureau; Celgene: Consultancy, Research Funding, Speakers Bureau; Novartis: Consultancy, Research Funding, Speakers Bureau. Lavie:Novartis: Membership on an entity’s Board of Directors or advisory committees. Harrison:Sanofi Aventis: Honoraria; YM Bioscience: Consultancy, Honoraria; Novartis: Honoraria, Research Funding, Speakers Bureau; Shire: Honoraria, Research Funding.

Expand: a Phase 1b, Open-Label, Dose-Finding Study of Ruxolitinib in Patients with Myelofibrosis and Baseline Platelet Counts Between 50 × 109/L and 99 × 109/L

Abstract Abstract 177 Background: Ruxolitinib (rux) is a potent oral JAK1 and JAK2 inhibitor that has demonstrated superiority over traditional therapies for the treatment of myelofibrosis (MF). In the two phase 3 COMFORT studies, rux demonstrated rapid and durable reductions in splenomegaly and improved MF-related symptoms and quality of life. Although there has been considerable experience in patients (pts) who developed thrombocytopenia in the COMFORT studies, there has been limited experience in pts with baseline thrombocytopenia as those with platelet counts (PLTs) < 100 × 109/L were excluded. The aims of EXPAND are to evaluate the safety of rux and to establish the maximum safe starting dose (MSSD) in thrombocytopenic MF pts. Methods: Phase 1b, open-label, dose-finding study (NCT01317875) in pts with PMF, PPV-MF, or PET-MF and baseline PLTs 50–99 × 109/L. A Bayesian logistic regression model will be used to guide dose-escalation decisions; intra-pt dose modification is allowed during the study. The study consists of 2 phases: dose escalation and safety expansion. Starting dose of rux is 5 mg bid with a maximum of 15 mg bid. In the dose-escalation phase, cohorts will be: 5 mg bid, 5 mg AM/10 mg PM, 10 mg bid, 10 mg AM/15 mg PM, and 15 mg bid. Pts are assigned to 1 of 2 strata based on their baseline PLTs: stratum 1, 75–99 × 109/L; stratum 2, 50–74 × 109/L. Each dose level in the second stratum will be open only if both that dose and the following one are deemed safe in the first stratum. In the safety-expansion phase, 20 additional pts (10 in each stratum) will be treated at the respective MSSD for their stratum. Results: 14 pts (PMF, n = 10; PPV-MF, n = 3; PET-MF, n = 1) have been enrolled in 4 cohorts: 4 pts in stratum 1/cohort 1 (5 mg bid), 3 in stratum 1/cohort 2 (5 mg AM/10 mg PM), 4 in stratum 1/cohort 3 (10 mg bid), and 3 in stratum 2/cohort 1 (5 mg bid). At baseline, all pts had an ECOG performance status of 0–2, and spleen length ranged from 5–30 cm below the costal margin. 12 pts have completed > 28 days of treatment and are evaluable. 2 pts were nonevaluable: 1 pt discontinued at day 6 due to granulocytic sarcoma, and 1 pt took an incorrect dosage from day 1 to 7 but treatment is ongoing. Reported adverse events (AEs) were similar to those previously seen with rux. 7 pts experienced grade 3/4 AEs (only 2 anemia events were study-drug related), and 4 pts experienced serious AEs (Table). The majority of hemoglobin and absolute neutrophil count (ANC) abnormalities were grade 1 or 2. No pt had a grade 4 decrease in PLTs or ANC; 2 pts experienced a grade 4 decrease in hemoglobin. No pt discontinued due to anemia, neutropenia, or thrombocytopenia. No hemorrhagic events were observed. The lowest PLTs across all pts ranged from 29–96 × 109/L. No dose-limiting toxicities (DLTs) were observed. Reductions in spleen length were reported for all 12 evaluable pts and 1 ongoing nonevaluable pt. Splenomegaly completely resolved in 3 pts. Spleen length reductions were rapid and occurred within the first few weeks of therapy. Conclusions: In this study, no DLT has occurred with the first 3 dose levels in pts with PLTs 75–99 × 109/L or with the first dose level in pts with PLTs 50–74 × 109/L. Rux was generally well tolerated, similar to results reported in previous studies, and no pt has discontinued because of thrombocytopenia. The study is ongoing, and additional pts are being recruited for both strata. Pts are receiving dose levels approaching those approved for nonthrombocytopenic MF pts. Disclosures: Harrison: Novartis: Honoraria, Research Funding, Speakers Bureau; YM Bioscience: Consultancy, Honoraria; Sanofi Aventis: Honoraria; Shire: Honoraria, Research Funding. Gisslinger:Novartis: Consultancy, Research Funding, Speakers Bureau; Celgene: Consultancy, Research Funding, Speakers Bureau; AOP Orphan Pharmaceuticals AG: Consultancy, Speakers Bureau. Miller:Novartis: Consultancy, Research Funding, Speakers Bureau, development of educational presentations Other; Incyte: development of educational presentations, development of educational presentations Other. 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. Atienza:Novartis Pharmaceuticals Corporation: Employment. Stalbovskaya:Novartis Pharma AG: Employment, Equity Ownership. Sirulnik:Novartis Pharmaceuticals Corporation: Employment, Equity Ownership. Al-Ali:Sanofi Aventis: Consultancy, Honoraria; Celgene: Honoraria, Research Funding; Novartis: Consultancy, Honoraria. McMullin:Novartis: Honoraria; Bristol-Myers Squibb: Honoraria; Shire: Honoraria. Verstovsek:Incyte Corporation: Research Funding. Vannucchi:Novartis: Membership on an entity's Board of Directors or advisory committees.

Open-Label, Prospective, Multicentre, Phase I/II Study of AOP2014, a Novel PEG-Proline-Interferon Alpha-2b in Patients with Polycythemia Vera: Update from an Ongoing Study

Abstract 1747▪▪This icon denotes a clinically relevant abstractBackground. IFN-alpha (IFN) is reported to induce molecular response in patients with chronic myeloproliferative neoplasms and may therefore improve survival. However, the use of conventional and pegylated IFNs is limited by toxicity, leading to treatment withdrawals in a substantial proportion of patients. In polycythemia vera (PV), recently published phase II data indicate occurence of grade 3 and 4 toxicities in 20%, and toxicity-related discontinuations in 22–24% of patients administered once weekly with pegylated IFNs. Results from large-scale randomized studies of IFNs in PV are not available. AOP2014 is a next generation long-acting IFNa-2b, consisting predominantly of only one isoform as opposed to other commercially available pegylated interferons. AOP2014 is expected to have pharmacokinetic and pharmacodynamic profiles which may allow a reduced dosing frequency compared to other pegylated IFNs, potentially leading to improved tolerability, better compliance, and, finally, favourable long-term treatment outcomes.Study design. This is an open-label, prospective, multicentre, phase I/II dose escalation study of AOP2014 to determine the maximum tolerated dose (MTD), safety and efficacy in PV. Inclusion criteria are: age ≥18 years, confirmed diagnosis of PV (WHO, 2008, or the PSVG plus JAK2 positivity). Both newly diagnosed and pre-treated (cytoreduction) patients are eligible; hydroxyurea (HU) is allowed until the first application of AOP2014. If abnormally elevated prior to entry, sustained hematocrit (Hct) ≤45% is to be achieved by phlebotomy prior to the first administration. 3+3 dose escalation with cohort extension after MTD definition is being utilized. Intra-patient dose escalation to the dose level, previously established to be safe, is encouraged. MTD is defined as the highest dose level at which no more than 1 of 6 subjects experience a DLT during the first treatment period (2 weeks). Complete hematological response (CR) is defined by Hct <45%, platelet count ≤400*109/L, WBC count ≤10*109/L, normal spleen size, and absence of thromboembolic events. Partial response (PR) is defined as haematocrit <45% without phlebotomy but with persistent splenomegaly or elevated (>400*109/L) platelet count, or reduction of phlebotomy requirements by at least 50%. Evaluation of toxicities and JAK2 allele burden quantication will be performed.Results. 20 patients have been included to date, M/F ratio was 16/4, median age 58 years (range 44–83). Median time from diagnosis to inclusion was 19 months (range 0–170). 9 patients were pre-treated with HU prior to study entry. Median number of phlebotomies in the past 3 months prior to inclusion was 1 (range 0–4), a total of 13 patients were regularly phlebotomized at least once in three months prior to study entry. Six patients had a history of thrombotic complications. Median Hct at baseline was 46% in males (range 46–52) and 42% in females (range 41–43). Median WBC and platelet counts were 11.3*109/L (range 4.7–17.8) and 366*109/L (range 148–1016), respectively. Twelve patients (60%) had splenomegaly. Dose levels of 50, 100, 150, 225, 300, 360 and 450 microgramm once in two weeks were investigated. The median reported treatment duration is 24 weeks (range 0–33). After 10 weeks of treatment (14 evaluable patients), 64% of patients had hematological response (2 CR; 7 PR), one patient needed to be phlebotomized. At 18 weeks (9 evaluable patients), 1 patient had CR and 4 – PR, overall response (CR+PR) was 56%; at 28 weeks (8 evaluable patients), 1 patient had CR and 5 PR, overall response was 63%. The only evaluable patient at week 34 had CR. Starting from week 18, no patient required phlebotomy. Mainly grade 1 and 2 adverse events were reported. Administration site reactions developed in 11 patients, all of mild intensity and recovered within 72h. The most frequent adverse reactions were muscle and joint pain and gastrointestinal toxicities (12 and 6 patients, respectively). Fever and depression were observed in 5 and 2 patients, respectively. Drug-related adverse event (depression) was the reason of treatment discontinuation in one patient. Molecular response data are still undergoing evaluation.Conclusion. Response rate of above 60% at six month already observed in the phase I dose finding part suggests that AOP2014 has promising efficacy and good tolerability profile in PV. Updated results will be presented as the trial progresses. Disclosures:Gisslinger:AOP Orphan Pharmaceuticals AG: Research Funding, Speakers Bureau; Novartis: Speakers Bureau; Celgene Austria: Research Funding, Speakers Bureau. Kralovics:(7) AOP Orphan Pharmaceuticals AG: Research Funding. Schoder:AOP Orphan Pharmaceuticals AG: Research Funding. Gisslinger:AOP Orphan Pharmaceuticals AG: Research Funding. Buxhofer-Ausch:AOP Orphan Pharmaceuticals AG: Research Funding. Strecker:AOP Orphan Pharmaceuticals AG: Research Funding. Wolf:AOP Orphan Pharmaceuticals AG: Research Funding. Willenbacher:AOP Orphan Pharmaceuticals AG: Research Funding. Greil:AOP Orphan Pharmaceuticals AG: Research Funding. Egle:AOP Orphan Pharmaceuticals AG: Research Funding. Melchardt:AOP Orphan Pharmaceuticals AG: Research Funding. Burgstaller:AOP Orphan Pharmaceuticals AG: Research Funding. Tarmann:AOP Orphan Pharmaceuticals AG: Employment. Wachter:AOP Orphan Pharmaceuticals AG: Employment. Zahriychuk:AOP Orphan Pharmaceuticals AG: Employment. Thaler:AOP Orphan Pharmaceuticals AG: Research Funding.

Activity of Azacitidine in 26 Unselected, Consecutive CMML Patients Included in the Austrian Azacitidine Registry (AAR) of the AGMT-Study Group

Abstract 1715Twelve participating centers in Austria included 257 unselected, consecutive patients with MDS/CMML or AML, who received azacitidine (AZA) between 02/2007 and 07/2011, in the nationwide Austrian Azacitidine Registry (AAR) of the AGMT-study group. Approval by the national Ethics Committee was obtained. The AAR includes 26 patients with CMML (10 with CMML-1, 16 with CMML-2) and is currently the 2nd largest report on CMML patients treated with AZA, the largest comprising 36 evaluable patients (Costa R. et al., Cancer, June 2011, pp2690). Myeloproliferative CMML (MP-CMML), defined as WBC>13.000/μl at diagnosis, was present in 16/26 patients, whereas 10/26 had myelodysplastic CMML (MD-CMML). Thus, the AAR includes patients for whom AZA is currently not approved by the FDA/EMEA.The AAR includes a high proportion of very old CMML patients (31% 75–79a, 15% >80a). Median age was 75a for both males (n=15) and females (n=11). Patients with various levels of PS were included (ECOG-0 (n=6), ECOG-1 (n=14), ECOG-2 (n=8) and ECOG-3 (n=4)). CMML-patients of the AAR suffered from renal insufficiency (n=8), mild liver disease (n=8), coronary artery disease (n=5), diabetes mellitus (n=5), a prior/concomitant solid tumor (n=3), COPD (n=2) and/or venous thromboembolic disease (n=1), respectively. There was no relevant difference in RBC transfusion dependence (TD) for MP-CMML vs. MD-CMML. However, PLT-TD at diagnosis was lower for MP-CMML (23%) than for MD-CMML (67%). In the 19 patients in whom pretreatment cytogenetics were performed, 15, 4 and 0 could be grouped into IPSS good, intermediate and poor risk categories, respectively. Only 57% of all included CMML-patients were treatment-naïve, whereas the rest were pretreated with ICT (10%), ESA (14%), intensive chemotherapy (21%) and other substances (17%) (mainly hydroxyurea and anagrelide) (numbers add up to more than 100% as several patients were pretreated with more than 1 agent). Thus, this registry more accurately reflects a real-life treatment scenario, than most clinical trials that have strict inclusion/exclusion criteria.Most AZA-cycles were applied s.c. (98%), whereas 2% were applied i.v. Median and mean number of AZA-cycles was 5.5 and 9 (SD 10.61; range 1–43), respectively. The FDA-approved d1-7 schedule was used in 62% of all AZA cycles, whereas the non-approved alternative schedules d1-5, 5-2-2 and ‘others' were applied in 21%, 12% and 6% of all cycles, respectively. Concerning the number of patients however, 20/26 predominantly received the d1-7 schedule. The FDA-approved target dose (75mg/m2 over 7 days) was achieved in 52% of all cycles and in 17/26 of patients, respectively.Reasons for termination of treatment with AZA were death (33%), disease progression (22%), transformation to AML (11%), no response (6%), toxicity (6%) and other reasons (22%).Any kind of HI was noted in 12/26 (46%) of patients. When looking at each lineage separately, 8/26 had HI-ery, 7/26 HI-PLT and 9/26 HI-neutrophils. 6/14 patients who were RBC-TD and 3/7 patients who were PLT-TD prior to AZA-treatment achieved transfusion independence (TI). In patients, in whom (repetitive) bone marrow aspirations/biopsies were performed for response evaluation (n= 12), the following best marrow responses were observed: CR in 4/12 (33%), marrow CR 1/12 (8%), PR in 2/12 (16%), SD in 4/12 (33%) and primary PD in 1/12 (8%). The OR rate observed prior to 07/2011 was 44% (CR + marrow CR + PR + HI). At the time of writing, 9 patients had received <=2 cycles. When limiting response analysis to patients who received >2 AZA cycles, which is required for achievement of hematologic response by the IWG-criteria, ORR was 66%. These are amongst the highest response rates observed for CMML to date.The median OS was 12.7 months (95%CI 6.9; 19.4). Median OS for patients demonstrating HI was significantly higher than for those who did not (19.4 vs. 5.6 months, p<0.0001). Detailed OS analyses and statistical analyses of various factors known or thought to influence prognosis are currently being analyzed, including MP-CMML vs. MD-CMML, CMML-1 vs. CMML-2, comparison of IPSS cytogenetic risk groups, as well as treatment-naïve vs. pretreated patients.In conclusion, in this population of partly pretreated, comorbid, very old patients with CMML, AZA was well tolerated and yielded substantial clinical and hematological benefit. Disclosures:Pleyer:Celgene: Research Funding. Off Label Use: Azacitidine for treatment of CMML including CMML-1 with transfusion-dependence and MP-CMML. Melchardt:AOP Orphan Pharmaceuticals AG: Research Funding. Egle:AOP Orphan Pharmaceuticals AG: Research Funding. Fridrik:Cephalon: Research Funding. Greil:AOP Orphan Pharmaceuticals AG: Research Funding.

BCR-ABL Positive Chronic Myeloid Leukaemia (CML) with Del 11q22 and JAK 2 V617F Positive Chronic Myelomonocytic Leukaemia (CMML) in One Patient – a Rare Coincidence

Abstract 4891 Introduction:Coincidence of BCR-ABL positive CML and JAK2 V617F positive CMML in one patient is a rare phenomenon. Case report:We report on a 61 year old patient with a diagnosis of CML in August 2008. Peripheral blood count showed a WBC of 3.1 G/l and a mild thrombocytopenia with 139 G/l thrombocytes. Differential blood count revealed virtually all cells of the neutrophilic line with myelocytes, metamyelocytes and blasts, basophils were elevated with 3%. While bone marrow (BM) aspirate was not representative, histologic examination of the BM biopsy showed a hypercellular marrow with a pattern of cell maturation similar to peripheral blood. An increase in reticulin fibrosis and vascularity was demonstrated correlating with a diagnosis of CML. Cytogenetics confirmed diagnosis of CML with a t(9;22)(q34;q11) in 4 out of 21 metaphases, 11 metaphases showed a deletion 11q and 2 metaphases showed both, a del 11 q and a Philadelphia translocation. Four metaphases showed a normal karyotype. BCR-ABL and JAK2 V617F have been demonstrated on the molecular level.Imatinib was started with a standard dose of 400 mg daily. The patient achieved a complete cytogenetic response (CCR) and a complete molecular response (CMR – BCR-ABL transcripts not detectable with quantitative and nested PCR) after 3 and 7 months of therapy, respectively. Despite having achieved an excellent response on cytogenetic and molecular level a complete haematological response was not obtained. At that time bone marrow examination revealed a marked hypercellular marrow with 10% blasts and 15% monocytic forms consistent with the diagnosis of CMML. Philadelphia chromosome was absent. The deletion 11q and JAK2 V617F were still detectable. Beause of comorbidities allogeneic stem cell transplantation was no treatment option for this patient. In July 2009 therapy with azacitidine, a hypomethylating agent licensed for the use in CMML was initiated. Imatinib was administered intermittently on azacitidine free days dependent on the current haematological situation. BCR-ABL transcript levels varied between one log up/down reflecting the intermittent imatinib administration. CMR and MMR were lost after 4 and 9 months, respectively. Subsequently, an additional deletion 7q was detected in 20% of metaphases with a deletion 11q (no Ph+ or normal metaphases were present). Azacitidine was stopped because of disease progression and hydroxyurea was commenced with no significant response. Cutaneous infiltrations resistant to systemic therapy reflected further disease progression. WBC increased to 334 G/l and the patient died 25 months after diagnosis due to progression of CMML to acute leukaemia. Methods:Conventional karyotyping was done using Giemsa-Trysin banding. For FISH, BCR-ABL dual colour fusion probes and MLL dual colour break apart probes (both Abott Molecular) were used. JAK2V617F mutation was detected by melting curve analysis. BCR-ABL RNA monitoring was performed according to the Europe Against Cancer protocol (Gabert et al.). Conclusions:Coincidence of two distinct myeloproliferative disorders in one patient is relatively rare. Both, conventional cytogenetics and molecular biology provided important information for diagnosis, course and treatment. This case vignette illustrates the importance of repeated cytogenetic and molecular analyses demonstrating an unexpected turn of an apparently predetermined course. Disclosures:Burgstaller:AOP Orphan Pharmaceuticals AG: Research Funding. Thaler:AOP Orphan Pharmaceuticals AG: Research Funding.

Report on Response and Overall Survival of 128 Unselected, Consecutive AML Patients From the Austrian Azacitidine Registry (AAR) of the AGMT-Study Group

Abstract 4266Twelve participating centers in Austria included 257 unselected, consecutive patients with MDS, CMML or AML, who received azacitidine (AZA) between 02/2007 and 07/2011, in the nationwide Austrian Azacitidine Registry (AAR) of the AGMT-study group. This registry was approved by the national Ethics Committee and includes 128 patients with AML of all FAB-subtypes, as well as de novo AML (39%), t-AML, MDS-AML and post-CMPD-AML.This registry comprises a large number of patients with >30% bone marrow blasts (83/128) (currently off-label indication for AZA), as well as myeloproliferative AML (35/128), as defined by presence of >10.000 WBC/μ l at diagnosis. The AAR includes a high proportion of very old AML patients (median age 73a, 20% 75–79a, 24% >80a). Although the PS was generally low (22% ECOG-0, 47% ECOG-1), AML patients suffered from coronary artery disease (n=29), renal insufficiency (n=26), diabetes mellitus (n=21), a prior/concomitant solid tumor (n=17), COPD (n=14) and/or mild liver disease (n=13), respectively. Only 40% of all AML-patients included were treatment-naïve, whereas the rest was pretreated with G-CSF (12%), ESA (9%), ICT (3%) revlimid or thalidomide (6%), other agents (11%) and/or intensive chemotherapy (47%), respectively. Thus, this registry more accurately reflects a real-life treatment scenario, than most clinical trials that have strict inclusion/exclusion criteria.In the 93 patients in whom pre-AZA cytogenetics were performed, 56.9%, 25.8% and 17.2% could be grouped into IPSS good, intermediate and poor risk categories, respectively. Of these, 43 patients had MDS-specific cytogenetic aberrations (5q-, +8, -7, -7q, -Y and -20q). Most AZA-cycles were applied s.c. (89%), whereas 11% were applied i.v. Median and mean number of AZA-cycles was 4.0 and 5.6 (range 1–24), respectively. 60% of patients predominantly received the FDA-approved d1-7 schedule, whereas the non-approved alternative schedules 5-2-2, d1-5 and ‘others' were most often given in 17%, 16% and 7% of patients, respectively. The FDA-approved target dose (75mg/m2 over 7 days) was achieved in 58% of all cycles and in 61% of patients, respectively.Longitudinal repetitive analysis of serum GOT, GPT, bilirubin and creatinine over up to 24 cycles shows no relevant variation or worsening tendency of these parameters during treatment with AZA, including patients with reduced baseline renal and/or hepatic function.Reasons for termination of treatment were death for any reason (26%), disease progression or relapse (27%), no response (6%), toxicity (7%), recurrent infectious complications (2%) and other reasons (23%). Adverse events will be presented in detail (number, grade, duration, hospitalization rate, effects on AZA (dose reductions/treatment pause/termination)).Any kind of hematologic improvement (HI) was noted in 38% of patients. When looking at each lineage separately, 21/128 had HI-ery, 23/128 HI-PLT and 24/128 HI-neutrophils. 35/85 patients who were RBC-TD and 19/55 patients who were PLT-TD prior to AZA-treatment achieved transfusion independence (TI). In patients, in whom (repetitive) bone marrow analyses were performed for response evaluation (n= 56), the following best marrow responses were observed: CR (19.6%), marrow CR (7.1%), PR (33.9%), SD (30.4%) and primary PD (8.9%). At the time of writing, 35 patients had received ≤2 cycles. This number largely accounts for the patients in whom no bone marrow response evaluation was performed. The OR rate observed prior to 07/2011 was 38% (CR + marrow CR + PR + HI). When limiting response analysis to patients who received ≥2 AZA cycles, which is required for achievement of hematologic response by the IWG-criteria, ORR was 57%.The median OS was 9.5mo (95%CI 8.15–10.9). In univariate analyses, ECOG >=2 (p=.0026), circulating blasts (9.3 vs. 24.8mo; p=.0014), IPSS poor risk cytogenetics (p=.0037) and failure to achieve any HI (8.6 vs. 22.4mo; p=.0001), significantly negatively impacted OS. Prior treatment with G-CSF and/or ESA, age >80a, WBC >10G/l, BM blasts >30%, LDH >225U/l, number of cytopenic lineages as well as RBC-TD and/or PLT-TD at baseline, did not significantly impact OS (p>0.05) (detailed statistics will be presented).In conclusion, in this population of partly heavily pretreated very old patients with AML, AZA was well tolerated and yielded substantial clinical and hematological benefit, irrelevant of baseline BM blast or PB WBC count. Disclosures:Pleyer:Celgene: Research Funding. Off Label Use: Azacitidine for treatment of AML including patients with >30% bone marrow blasts. Egle:AOP Orphan Pharmaceuticals AG: Research Funding. Fridrik:Cephalon: Research Funding. Greil:AOP Orphan Pharmaceuticals AG: Research Funding.

Azacitidine Is Feasible and Safe in Patients with MDS and Co-Existing Plasma Cell Dysplasias (PCD) - Report on 9 Patients From the Austrian Azacitidine Registry (AAR)

Abstract 5056Azacitidine (AZA) has been approved for the treatment of higher-risk MDS and therefore marks a cornerstone in the development of hypomethylating agents. Recent clinical trials raise questions regarding optimal sequencing and also about combining hypomethylating agents with other classes of drugs targeting epigenetic processes. It has been postulated that unspecific demethylation of promotors may lead to the activation of oncogenes, and therefore result in an elevated rate of secondary malignancies.We report on 9 patients from the Austrian Azacitidine Registry (AAR) with co-excisting plasma cell dyscrasias (PCD) receiving treatment with AZA for MDS. Six male and 3 female patients had a median age of 73 years at time of diagnosis of MDS and 73 years at time of diagnosis of PCD. They were diagnosed with Waldenstrom macroglobulinemia (WMG) (n=3), multiple myeloma (n=2) and MGUS (IgG (n=2), IgM (n=1), IgA (n=1)). All PCD were diagnosed either before or at least at the same time as MDS. None occurred after diagnosis of MDS or after treatment initiation with AZA. However, one patient with multiple myeloma likely had treatment–related MDS due to prior treatment with MPT (melphalan, prednisone, thalidomide).At the time of writing, the mean number of AZA cycles given was 9 (range 1–27). Two patients were concomitantly treated with Rituximab (R) whilst on AZA treatment. Importantly, no additional toxicities occurred and there seemed to be no negative interaction between Rituximab and AZA. In all patients treated with AZA for MDS, M-gradient remained stable, and in some cases significant improvement was noted. One patient even achieved complete remission of WMG following AZA/R treatment (data will be shown; Weiss L et al, J Clin Oncol. 2011 Jul 25 [Epub ahead of print]). Importantly, no progression of PCD was seen in any of the 9 patients treated with AZA, and PCD did not contribute to death in any of these patients.In conclusion, AZA treatment of MDS in patients with co-existing PCD seems safe, combination with Rituximab seems feasible, no aggravation of PCD was seen and remarkably, one patient with WMG achieved CR following AZA/R. Disclosures:Pleyer:Celgene: Research Funding. Egle:AOP Orphan Pharmaceuticals AG: Research Funding. Greil:AOP Orphan Pharmaceuticals AG: Research Funding.

Bortezomib-Bendamustine-Dexamethasone in Patients with Relapsed/Refractory Multiple Myeloma (MM) Shows Marked Efficacy and Is Well Tolerated, but Assessment of PNP Symptoms Shows Significant Discrepancies Between Patients and Physicians

Abstract 2928 Introduction:Bendamustine, an alkylating drug with purine like activities may exert synergistic activity in combination with bortezomib. Here we analyze the efficacy and tolerance of bortezomib-bendamustine-dexamethasone with particular focus on possible discrepancies between patient and physician assessed neuropathic symptoms. Patients:45 patients with relapsed/refractory MM have been enrolled. Median age: 64 years (range 40–86), male/female: 17/28, ISS stage I/II/III: 14, 16, and 15 patients, respectively. ECOG status 0/I/II: 25, 22, and 2 patients, respectively. Previous treatment lines: 1–2: 25, 3–4: 16, >4: 4 patients, respectively. Full data documentation for response evaluation (≥ 2 cycles) is available for 33 patients. Treatment regimen: Bendamustine 70 mg/m2 day 1+4, Bortezomib 1.3 mg/m2 days 1, 4, 8 and 11, Dexamethasone 20 mg on days 1, 4, 8 and 11, repeated every 4 weeks. For assessment of neuropathic sides effects the FACT-GOG/NTX self assessment instrument was used. Efficacy:After a median follow up of 4.7 months, myeloma response (ORR: CR+VGPR+PR) was noted in 17 (51.5%) of the 33 evaluable patients. 5 (15% of) patients achieved CR, 2 (6%) VGPR, 10 (30%) PR; 10 (30%) MR, and 6 (18%) remained stable, while PD was noted in 6 (18% of) patients. Median time to response was 82 days. Responses were observed in 48.1% of patients previously exposed to bortezomib and in 47.1% pretreated with lenalidomide. Responses were seen in 53.8% of patients with high [ampl.1q21, del17p, t (4; 14)] and in 53.8% with standard risk (del13 or no aberration) cytogenetics. Median PFS is 9, 4 months; median overall survival is not reached at present (figure). Tolerance:The regimen was well tolerated with low incidence of infections and gastrointestinal toxicities. Hematological toxicity remained stable from baseline to cycle 4, with G4 anemia, leucopenia and thrombopenia being recorded in < 5%. Patient self reported neuropathic symptoms at baseline were recorded as G1–2 in 57% and as G3–4 in 17%, respectively. This pattern remained stable from cycle 1 to 4. In contrast, physician assessed neurotoxicity G1–2 was documented in only 18% of patients at baseline. During the following 4 cycles physician assessed PNP remained constant in almost all patients with only 3 patients developing G3 PNP. G4 PNP was not reported. Conclusions:The BBD regimen yielded a response rate of 52% and a PFS of 9.6 months in heavily pretreated myeloma patients. Substantial response rates were noted in patients pre-exposed to bortezomib (33.3%) and lenalidomide (36.4%) Patient self assessment of neuropathic symptoms revealed a much higher incidence of G1–2 and G3–4 symptoms than physician assessment. Physician assessment of neurotoxicity may underestimate neurologic symptoms associated with disease or neurotoxic treatment. [Display omitted] Disclosures:Ludwig:Mundipharma, Janssen-Cilag: Research Funding, Speakers Bureau. Greil:AOP Orphan Pharmaceuticals AG: Research Funding.

A PROGNOSTIC MODEL to PREDICT SURVIVAL In WHO-DEFINED ESSENTIAL THROMBOCYTHEMIA: A STUDY by the IWG-MRT (International Working Group for Myeloproliferative Neoplasms Research and Treatment)

Abstract 1746▪▪This icon denotes a clinically relevant abstractDiagnosis of essential thrombocythemia (ET) has been updated in the last World Health Organization (WHO) classification, that provides a guideline to distinguish ET from early/prefibrotic primary myelofibrosis. These two conditions differ in term of disease evolution and survival (Barbui et al, J. Clin. Oncol. 2011). To design a prognostic model for survival in WHO-defined ET (International Prognostic Score for Essential Thrombocythemia, IPSET), we studied 891 patients with strict WHO diagnostic criteria. Demographics have been presented elsewhere (Barbui et al, J. Clin. Oncol. 2011). We tested the prognostic impact on survival of age, prior thrombosis, leukocyte count, platelet count, hemoglobin level, JAK mutational status, splenomegaly. Harrell’s C concordance statistics were used to set the best cutoff levels of continuous variables in order to predict survival. Univariate Cox proportional hazard regression showed that age over 60 years (P<.0001), leukocyte count greater than 11 x109/L (P<.0001), anemia (P=.04), platelet count greater than 1000 x109/L (P<.004) and prior history of thrombosis (P< 0001) were significant risk factors for survival. Age over 60 years (hazard ratio-HR- 6.5, 95% CI: 3.9–10.7; P<.0001), leukocyte count greater than 11 × 109/L (HR: 3.1, 95% CI: 2–4.7; P<.0001) and prior history of thrombosis (HR: 2.9, 95% CI: 1.9–4.5; P< 0001) retained statistical significance on survival by multivariable analysis and were included in the new prognostic model. We assigned each factor an integer weight close to the corresponding HR in the multivariable Cox regression: weight 2 for age over 60 years; weight 1 for leukocyte count greater than 11 x109/L and for prior thrombosis. Finally, we defined the IPSET score by allocating patients into three risk categories with significantly different survival according to the sum of weights: low risk (sum of weights=0; n= 342; median survival not reached), intermediate risk (sum=1-2; N=374; median survival 24.5 years), and high risk (sum=3-4, n=158; median survival 13.8 years). Fisher exact test did not reveal a difference in the distribution of the causes of death among IPSET categories. We validated the model in two independent cohorts: one from Germany (132 WHO-defined ET) and another from France (234 ET patients not strictly diagnosed according to WHO). Log rank test and Cox regression showed significant differences in term of survival among IPSET categories in both series. Finally, we designed an age-specific IPSET model for patients younger than 60 years (IPSET-y). Using the same methodology, we found that age over 45 years (weight 2), leukocyte count greater than 11 × 109/L (weight 1) and prior history of thrombosis (weight 1) were independent risk factors for survival. IPSET-y defined three risk categories (LR, sum=0; IR, sum=1-2; HR, sum=3–4) with a median survival not reached in LR and IR, and of 22.3 years in HR. In conclusion, IPSET, based on age over 60 years, leukocyte count greater than 11 x109/L and history of thrombosis allows prognostic assessment of WHO-defined ET. The validation process makes IPSET applicable in all patients phenotypically appearing as ET. IPSET models may be useful for treatment decision-making. Disclosures:Vannucchi:Italfarmaco: Consultancy; Novartis: Honoraria. Gisslinger:AOP Orphan Pharmaceuticals AG: Research Funding.

Risk Factors for Thrombosis in WHO-Defined Early/Prefibrotic Myelofibrosis: An International Study of 264 Patients,

Abstract 3846▪▪This icon denotes a clinically relevant abstract INTRODUCTIONThere is strong evidence indicating that the clear-cut separation of prefibrotic primary myelofibrosis (PMF) from essential thrombocythemia (ET) by consequent application of the World Health Organization (WHO) 2008 criteria is reflected in different, well defined clinical pictures and divergent prognoses (Barbui et al, JCO 2011,Thiele et al, Blood 2011). Very recently the specific risk profile for arterial and venous thrombosis in WHO- diagnosed ET was published (Carobbio et al, Blood 2011). In PMF so far all published data on vascular events were exclusively based on overt disease manifestations until now there are no data available regarding prefibrotic stages. Consequently, we aimed to evaluate the corresponding risk profile of patients with WHO-diagnosed prefibrotic PMF. METHODSA total number of 264 patients with WHO-defined prefibrotic PMF derived from either the Medical University of Vienna or an International Database (Barbui et al, JCO 2011) were studied. Nonfatal thrombotic events considered in this study were reported as rates per 100 patient-years and included transient ischemic attacks, thrombotic cerebrovascular accidents, coronary artery disease, myocardial infarction, peripheral arterial disease, deep vein thrombosis of peripheral vasculature, pulmonary embolism, and abdominal large vein thrombosis. Cardiovascular risks factors considered, comprised of arterial hypertension, diabetes mellitus and tobacco use. To evaluate risk factors for total thrombosis and for arterial and venous events in particular multivariate Cox- regression analysis including the co-variables sex, age, previous thrombotic event, laboratory parameters measured at diagnosis and need for cytoreductive and/or antiplatelet therapy during follow-up was calculated. P values less than 0.05 were considered as statistically significant. RESULTSAfter a median follow- up of 5.8 years (range0.0 – 27.2), the total rate of non fatal thrombotic events was 2.1% patient-years (95% CI, 1.5–2.8); the incidence of arterial events was higher (1.7% patient- years) than of venous events (0.6% patient-years).Considering thrombosis in general a higher white blood cell (WBC) count enhances the risk significantly (p=0.005; HR 1.15). This is also true in arterial events in particular (p=0.047; HR 1.12). A lower platelet count is associated with a higher risk for thrombotic events; for thrombosis in general this association is of borderline significance (p=0.056; HR 0.99), for arterial thrombosis in particular of significance (p= 0.042; HR 0.99). A lower hemoglobin level is associated with a higher risk for venous thrombosis (p=0.007; HR 0.59). CONCLUSIONLeukocytosis appears as a risk factor for thrombosis in general and also for arterial thrombosis in particular in WHO-diagnosed prefibrotic PMF. Moreover, higher platelet counts seem to decrease significantly the risk for thrombotic events in general and arterial thrombosis in particular. Anemia is associated with a higher risk for venous thrombosis. These observations are partly in line with recently published findings in WHO-diagnosed ET (Carobbio et al,2011) and might indicate the existence of a specific risk profile for thrombotic events in prefibrotic PMF. This is the first study reporting data on the risk profile for thrombosis in WHO-diagnosed prefibrotic PMF. Certainly these findings ask for validation in a larger patient population. Disclosures:Gisslinger:Novartis: Speakers Bureau; Celgene Austria: Research Funding, Speakers Bureau; AOP-Orphan Pharmaceuticals AG: Speakers Bureau. Vannucchi:Novartis: Honoraria.