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Introduction: The Philadelphia-negative chronic myeloproliferative neoplasms (MPNs) are associated with a high risk of arterial and venous thrombosis, which are attributed to several mechanisms, including elevated blood cell counts per se, in vivo leukocyte and platelet activation with increased adhesion of granulocytes, monocytes and platelets to each other and to a dysfunctional endothelium. In recent years, evidence has accumulated that chronic inflammation is an important pathogenetic mechanism for MPN-disease development and disease progression, inducing increasing genomic instability in hematopoietic cells and thereby emergence of additional mutations of significance for myelofibrotic and leukemic transformation. Recent studies have shown several thrombo-inflammatory genes to be upregulated in patients with MPNs, likely contributing to the increased risk of thrombosis. Several studies have documented that long term treatment with interferon-alpha2 (IFN) is able to normalize elevated cell counts in concert with induction of a remarkable decrease in the JAK2V617F allele burden and accordingly impacting important thrombosis promoting factors in MPNs. Herein, using whole blood gene expression profiling we for the first time report that treatment with IFN is able to normoregulate or significantly downregulate upregulated thrombo-inflammatory genes in patients with MPNs. Methods: Eight patients with ET, 21 patients with PV, and 4 patients with PMF participated in the study. All patients received treatment with IFN, in the large majority in a dosage ranging from 45-90 ug x 1 sc/week. Gene expression microarray analysis of whole blood was performed before and after 3 months of treatment. Total RNA was purified from whole blood, amplified to biotin-labeled RNA, and hybridized to Affymetrix HG-U133 2.0 Plus chips. Results: We identified 6261, 10,008, and 2828 probe sets to be significantly differentially expressed in ET, PV, and PMF, respectively, in response to treatment with IFN (pvalue < 0.05). Six thrombo-inflammatory genes were investigated: F3, PADI4, SELP, SERPINE1, SLC2A1, and THBS1. In all patients groups, the 6 genes were significantly upregulated at baseline and either normoregulated or significantly downregulated during treatment with IFN (Figure 1). Discussion and Conclusions: Thrombosis contributes significantly to morbidity and mortality in MPNs. Despite treatment with conventional drugs (hydroxyurea, anagrelide) - the most used cytoreductive therapies worldwide - patients with MPNs are still suffering potentially life-threatening or life-invalidating thrombotic complications in the brain, heart, lungs and elsewhere. Therefore, there is an urgent need for studies that explore the pathogenetic mechanisms eliciting the thrombotic state and the impact of novel therapies, such as IFN, upon the thrombogenic factors which might be operative. Herein, we have for the first time shown that IFN significantly downregulates several thrombo-inflammatory genes, known to be the upregulated in patients with concurrent or previous thrombosis. Highly intriguing, we found that IFN significantly downregulated the PADI4 gene, which is required for neutrophil extracellular trap (NET) formation and thrombosis development. A most recent study has shown neutrophils from patients with MPNs to be associated with an increase in NET formation, which was blunted by ruxolitinib. This study also showed that JAK2V617F-driven MPN mouse models have a NET-rich, prothrombotic phenotype, highlighting NETosis to be yet another important thrombosis mechanism in MPNs. In conclusion, we have for the first time shown 3 months IFN-treatment to be associated with a significant downregulation of upregulated thrombo-inflammatory genes, including significant downregulation of the NETosis associated gene - PADI4. In the context of a significantly increased risk of thrombosis after the MPN-diagnosis with a particular increased risk at 3 months, our results of significant downregulation of these thrombo-inflammatory genes during IFN-therapy are of paramount importance and may signal an advantage of IFN over conventional cytoreductive therapies. Further studies are required to decipher the impact of IFN upon upregulated thrombo-inflammatory genes and if combination therapy with ruxolitinib may be even more efficacious. Figure 1 Disclosures Hasselbalch: Novartis: Research Funding; AOP Orphan Pharmaceuticals: Other: Data monitoring board. OffLabel Disclosure: Interferon-alpha for treatment of myeloproliferative neoplasms

Background: To investigate the role of genomics in determining response and resistance to front line treatment in MPN, we performed somatic mutational profiling of the DALIAH trial, a randomized controlled phase III trial of interferon versus hydroxyurea in newly diagnosed MPN patients. Methods: We performed genomic analyses on 202 pre-treatment primary MPN samples obtained from patients enrolled on the DALIAH trial (NCT01387763) and 135 samples obtained after 24 months of treatment. Genomic profiling comprised targeted next generation sequencing (NGS) of 100 genes, selected on the basis of their known or suspected involvement in the pathogenesis of myeloid malignancies, and 1609 informative single nucleotide polymorphisms (SNPs) on chromosome 9p. Clinicohematological response was determined by central review using ELN 2009 (ET, PV and pre-MF) and EUMNET 2005 (PMF) criteria. We evaluated the association of somatic mutations with clinical parameters and with attainment of clinicohematological complete response (CR) at 24 months. Results: Prior to treatment, 191 of 202 (95%) patients had somatic mutations, including 93% with canonical MPN phenotypic drivers: JAK2 (74%), CALR (14%), and MPL (5%). Among those with JAK2 mutations 37% had JAK2 copy-neutral loss of heterozygosity (JAK2 CN-LOH). Patients with PV were more likely to have JAK2 CN-LOH (p = 0.0001) as compared with patients with other MPN subtypes. At baseline, patients with JAK2 CN-LOH had significantly higher hemoglobin (p = 0.0001), higher white blood cell count (WBC, p = 0.002) and lower platelet count (p=0.0001) than patients without JAK2 CN-LOH. Mutations in TET2 (24%), DNMT3A (16%), and ASXL1 (10%) were the most frequent co-occurring non-MPN phenotypic driver mutations and they occurred across all MPN subtypes. In addition, 5% of patients had spliceosome gene mutations, and 6% had mutations in genes involved in RAS/MAPK signaling. Patients with TET2, DNMT3A or ASXL1 mutations were significantly older than patients without these mutations (p= 0.0001) and there was a significant association between the presence of a TET2, DNMT3A or ASXL1 mutation and prior stroke (p = 0.004). There were no other significant associations between somatic mutation status and baseline clinical characteristics. The probability of attaining clinicohematological CR at 24 months was independent of baseline somatic mutations. Among patients with JAK2 mutations who remained on interferon treatment at 24 months, those with CR had a greater reduction in mean variant allele fraction (VAF) (28% to 8%, p Among patients who remained on treatment for 2 years, 44 mutations in 35 patients were newly detected or expanded on serial sampling. DNMT3A mutations were the most frequently acquired, accounting for 41% of new mutations. ASXL1, TET2, PPM1D, TP53, IDH2, and CBL mutations were also recurrently acquired. 97% of patients who acquired new mutations were JAK2-mutant. Among those with acquired DNMT3A mutations, 85% were treated with interferon, and 23% had CR at 24 months. Among those that acquired non-DNMT3A mutations, 38% were treated with interferon and 47% had CR at 24 months. The VAF of newly detected mutations was low (median 1.5%), and half of the patients with newly acquired mutations had at least 50% reduction in JAK2V617F VAF, suggesting that new mutations could either have arisen independently or be subclonal to the dominant JAK2-mutant clone. Conclusions: Using sequential genomic analyses of a phase III clinical trial of interferon versus hydroxyurea in MPN patients, we found mutation-specific and treatment-specific patterns of response. We uncovered distinct patterns of response to interferon in JAK2-mutant MPN as compared with CALR-mutant MPN. We found that DNMT3A mutations were the most frequent acquired mutations at 24 months and that these were enriched in patients treated with interferon. In aggregate, these results provide insights into molecular response and resistance to interferon and inform the clinical use of interferon in MPN patients. Disclosures Hansen: Alexion: Research Funding. Neuberg:Pharmacyclics: Research Funding; Madrigal Pharmaceuticals: Equity Ownership; Celgene: Research Funding. Hasselbalch:Novartis: Research Funding; AOP Orphan Pharmaceuticals: Other: Data monitoring board. Lindsley:Jazz Pharmaceuticals: Research Funding; Takeda Pharmaceuticals: Consultancy; Medlmmune: Research Funding. Mullally:Janssen: Research Funding.

Introduction: The Philadelphia-negative myeloproliferative neoplasms are associated with deregulation of inflammation and immune genes implying a gene signature of a chronic inflammatory state and immune deregulation. Several studies have demonstrated interferon-alpha2 (IFN) to be highly efficacious in normalizing elevated blood cell counts and in inducing molecular remissions as well. Using whole blood gene expression, we herein for the first time show that IFN profoundly influences the deregulated inflammation- and immune genes giving rise to a gene signature indicative of decreased inflammation and improved regulation of immune genes during IFN treatment. Material and Methods: Gene expression microarray studies have been performed on eight patients with ET, 21 patients with PV, and 4 patients with PMF. All patients received treatment with IFN, in the large majority in a dosage ranging from 45-90 ug x 1 sc/week. Gene expression profiles were generated using Affymetrix HG-U133 2.0 Plus microarrays recognizing 54.675 probe sets (38.500 genes). Total RNA was purified from whole-blood and amplified to biotin-labeled aRNA and hybridized to microarray chips. Results: We identified 6261, 10,008, and 2828 probe sets to be significantly differentially expressed in ET, PV, and PMF, respectively, during treatment with IFN (pvalue Discussion and Conclusion: Interferon-alpha2 is increasingly been recognized as a highly efficacious and promising agent in the treatment of MPNs. During recent years several studies have shown that chronic inflammation and immunoderegulation is likely involved in the pathogenesis of MPNs. Thus, elevated blood levels of circulating inflammatory cytokines have been recorded, some even having a prognostic impact and predicting imminent leukemic transformation. Chronic inflammation impairs IFN-signaling and likely therefore the efficacy of IFN in MPNs, although this notion has to be confirmed in MPNs. Immunoderegulation with defective immune surveillance may contribute to the increased risk of second cancers both before and after the MPN-diagnosis. Accordingly, there is an urgent need to explore if IFN might be able to restore deregulated inflammation and immune genes in MPNs. In this study, we have convincingly shown that several genes of significance for inflammation and immune surveillance are positively influenced by IFN treatment implying a significant downregulation of upregulated inflammation genes (e.g. BCL6, IL1R1, MAPK1, ORM1,) and a significant upregulation of downregulated immune genes (e.g. ABCF1, CCR2, CCR5, CCR7, CD3D, CD3E, CD3G, CD4, CD40LG, CXCR1, HLA-G, IL10RA, IL8, TFGB1, TNFAIP3, and TP53). Recently, we have shown significant downregulation of CCR9, CREB1, FAS, LSP1, LTB, NFKB1, SCYE1, SELPG, STAT3, and TNFAIP8L1, and significant upregulation of CCL25, CCL7, CSF3, CXCL9, FOXP3, IL17A, IL17C, IL1F10, IL1F6, IL22, IL4, IL5, ITGB3, in ET, PV, and PMF compared to controls. These genes were no longer significantly deregulated during IFN-treatment. In conclusion, our results have added highly important information on the impact of IFN upon deregulated inflammation and immune genes in MPNs, thereby substantiating the beneficial effects of IFN and its major role as the cornerstone in the future treatment of MPNs. Our study opens the avenue for larger studies exploring the genomic landscape during treatment of patients with MPNs. Disclosures Hasselbalch: Novartis: Research Funding.

Introduction: Human endogenous retroviruses (HERVs) are genomic sequences that result from ancestral germ-line infections by exogenous RVs and therefore are transmitted in a Mendelian fashion. Several lines of genetic evidence suggest the involvement of HERVs in the etiology of autoimmune diseases and cancer. Here, by means of genetic epidemiology, we describe a case-control association study of SNPs located in the proximity of HERVs elements in patients with myeloproliferative neoplasms (MPNs). Methods: Genomic DNA from two cohorts recruited from 4 university hospitals, in total 376 patients with MPN and 527 control subjects, was isolated from whole blood. 148 SNPs related to 49 HERV loci were tested using the Sequenom platform. To quantify genomic DNA copy number variation, real-time PCR was performed using the LightCycler system. Data was analyzed using the χ2-test. For synergy, we recoded controls and cases as 0 and 1, respectively, and used ANOVA with type III sum of squares. Adjustment for multiple hypothesis testing was done using the Bonferroni correction (pB Results: In cohort 1, analysis of 148 SNPs in 188 MPN patients and 453 controls demonstrated a significant association in MPNs of the two SNPs rs219077 and rs5993426 belonging to HERV-K and HERV-9, respectively. The two SNPs were validated in an additional cohort of 188 MPNs and were again highly significant, rs219077 (OR 1.97 (1.43 - 2.7), combined pB = 0.005) and rs5993426 (OR 3.94 (2.72 - 5.71), combined pB = 9x10-11). Additionally, we report that in patients carrying the SNP risk allele (G), rs219077, qPCR analysis results in significantly higher copy numbers compared to patients not carrying the risk allele. Discussion and conclusion: About 30 years ago HERV-K particles were reported in megakaryocytes cultured from patients with ET. Surprisingly, since then no studies have focused upon a potential link between virus infection and the development of MPNs. In the present study, we revive the HERV-story in MPNs. Thus, we show that two SNPs, rs5993426 and rs219077, close to HERVs correlate with risk of MPNs supporting a role of these genetics elements in MPN pathogenesis. In our study, rs219077, located on the chromosome 2, associates with the disease and maps in the proximity of the HERV-9 sequence. Additionally, the SNP risk allele (G) in rs219077 results in significantly higher copy numbers. There are two possible explanations for the amplification of rs219077 in MPNs. First, it might be an amplification of a part of chromosome 2, as genomic features of MPNs often include clonal, non-random chromosomal amplifications. Second, it might be due to the formation of a transducing virus from the right LTR of HERV-9, possibly now (after a few rounds of replication) with HERV-K LTRs. The observed amplification of risk allele (G) in MPN may indicate that the recombinant virus pathogenic copy can retrotranspose in PBMCs with an active viral reverse transcriptase and, eventually, integrate through recombination/integration events. rs219077 is also located in genetic proximity to MIR3 SINE elements. Thus, one fascinating possibility is that the putative transducing ERV-9 virus could encode or regulate microRNA. The second marker showing significant association with MPN risk was rs5993426. This marker in the proximity of HERV-K encoding Gag, Pol has been reported to be associated with rheumatoid arthritis. Our genetic data are currently exclusively based on genetic association and cannot as such predict any functional relationship beyond presence or absence of SNPs. Nevertheless, statistical associations are most easily explained by functional relations and it is therefore pertinent to pursue the potential molecular mechanisms mediated by HERVs in MPNs. As an example, the induction and progression of rodent erythroleukemias by Friend spleen-forming virus are mainly due to the ability of proviruses to activate cellular oncogenes or inactivate tumor suppressor genes. In this regard, we have most recently shown downregulation of TP53 in MPNs to be significantly upregulated during treatment with interferon-alpha2. In conclusion, we have for the first time demonstrated a genetic association of MPNs with HERV elements. The association supports a pathogenetic role of these loci in MPNs. Our observations stimulate to further studies on HERVs in the pathogenesis of MPNs and our results need to be confirmed in larger cohorts of patients. Disclosures Hasselbalch: Novartis: Research Funding.

Background: The Philadelphia-negative, chronic myeloproliferative neoplasms (MPN) include essential thrombocythemia (ET), polycythemia vera (PV) and primary myelofibrosis (MF) (PMF). Chronic inflammation and a deregulated immune system are considered important for clonal evolution and disease progression. Ruxolitinib is a potent anti-inflammatory agent and has shown great benefit in MPN patients (pts), reducing spleen size and inflammation-mediated symptoms, thereby improving quality of life (QoL). Interferon-alpha2 (IFNa2) has been used successfully for decades in the treatment of MPN. However, 10-20% of pts are intolerant to IFNa2, yet others show limited response. Since concurrent inflammation might attenuate the efficacy of IFNa2 therapy, a combination therapy (CT) with the two agents may be more efficacious than monotherapy, likely reducing the inflammation-mediated adverse effects of IFNa2 as well. The purpose of this COMBI-trial is to evaluate the safety and efficacy of CT with IFNa2 and ruxolitinib. Patients and Methods: At the time of data cutoff, a total of 30 pts ≥18 years with prefibrotic or hyperproliferative PMF (n=7), PV (n=20) or post-PV MF (PPV-MF) (n=3) with or without prior treatment with IFNa2 and without serious comorbidity were enrolled. Evidence of active disease was required. Initial therapy was IFNa2 45 μg x 1 sc/week (Pegasys®) or 35 μg x 1 sc/week (PegIntron®) + ruxolitinib (Jakavi®) 20 mg x 2/day. Efficacy was evaluated by internationally accepted clinicohematological response criteria, with the modification that splenomegaly was assessed by palpation instead of imaging, by week 2 and 1, 3, 6 and 9 months. In addition, JAK2V617F-allele burden was monitored. Adverse events (AE) including serious AE (SAE) were recorded. Results: Median treatment duration was 24.4 weeks (range, 3.4 weeks-43.3 weeks). Twenty-seven pts were previously treated with IFNa2 (n=18 intolerant, n=5 unresponsive, n=4 both). Three pts were treatment-naïve. Twenty-seven pts (90%) remained on CT; 3 pts discontinued treatment due to an AE. One patient died from transformation to AML shortly after initiation of CT and was not included in this interim analysis. Marked improvements in pruritus, night sweats, and fatigue were recorded within the first 2-3 days in the large majority of pts and in all within 4 weeks. Palpable splenomegaly in 7 pts at baseline was significantly reduced by week 2. Hct control without phlebotomy was achieved by week 4 in 78 % of pts (7 of 9), who at baseline had an elevated hct. Only 3 pts required a total of 3 phlebotomies after initiation of CT. In Figure 1 median hct levels at 0, 1, 3, 6 months are shown. Overall, complete response (CR) was achieved as best response in 19 pts (63.3%) and partial response (PR) or major response in 8 pts (26.7%). Only 3 pts (10%) had no response (NR) to treatment. Among PV pts, 15 (75%) achieved CR (week 2, n=6; 1 month, n=6; 3 months, n=3). The other 5 PV pts achieved PR (week 2, n=3; 1 month, n=2). In PMF pts, CR (n=2) or major response (n=2) was achieved in 4 pts (57.1%) by week 2 or 1 month, and NR in 3 pts (42.8%). Among PPV-MF pts, 2 pts (66.7%) achieved CR and 1 patient (33,3%) PR by week 2. Furthermore, JAK2V617F% declined significantly as depicted in Figure 2 (JAK2V617F% over time for each patient) and 3 (median JAK2V617F% at 0, 3, 6 months). Anemia (n=15, 2 grade 3), granulocytopenia (n=13, 2 grade 3) or thrombocytopenia (n=6, 1 grade 3) were the most common AEs and were managed by dose reduction. One patient with PPV-MF (leuko- and thrombocytosis) developed pancytopenia within the first 2 weeks on CT, necessitating pausing medication for > 2 weeks. Eleven SAEs requiring hospitalization were recorded in 9 pts: pneumonia (n=3), fever (n=2), lipotymia, hematemesis, phlebitis, herpes zoster, angina pectoris and arterial hypertension, 1 patient each. Conclusion: CT with IFNa2 and ruxolitinib is highly efficacious and safein pts with PV or hyperproliferative MF,who were unresponsive or intolerant to monotherapy with IFNa2. Complete clinicohematological responses were achieved in the majority of pts in concert with a reduction in the JAK2V617F-allele burden. In general, the treatment was well tolerated. The preliminary results from this study are highly promising, encouraging a prospective study with CT in newly diagnosed pts. Additional follow-up data will be presented including QoL assessment and the impact of concurrent treatment with statins. Figure 1. Figure 1. Figure 2. Figure 2. Figure 3. Figure 3. Disclosures Off Label Use: The combination therapy with ruxolitinib (JAK1-2 inhibitor) and interferon-alpha is off-label in MPNs. The concept is dual myelosuppressive action and dual clonal suppression in addition to the anti-inflammatory properties of ruxolitinib.. Bjørn:Novartis Oncology: Research Funding. Bjerrum:Bristoll Myers Squibb, Novartis and Pfizer: Other: educational activities. El Fassi:Novartis Denmark: Honoraria, Other: Have conducted an educational session for Novartis Denmark, regarding MPNs and ruxolitinib, for this a honorarium was received.. Nielsen:Novartis: Research Funding. Pallisgaard:Roche: Other: travel grant; Amgen: Membership on an entity's Board of Directors or advisory committees, Other: travel grant, Speakers Bureau; Novartis: Other: travel grant, Research Funding, Speakers Bureau; Qiagen: Membership on an entity's Board of Directors or advisory committees; Bristol Meyer Squibb: Speakers Bureau. Hasselbalch:Novartis: Research Funding.

Abstract 4117 Introduction: The proteasome is an ubiquituous enzyme complex that plays a critical role in the degradation of many proteins involved in cell cycle regulation, apoptosis, and angiogenesis. Since these pathways and functions are often deregulated in cancer cells, inhibition of the proteasome is an attractive potential anticancer therapy. Bortezomib (Velcade, formerly PS-341) is an extremely potent and selective proteasome inhibitor that shows strong activity against many solid and hematologic tumor types. Moreover, bortezomib, mainly by inhibition of the NF-kappaB pathway, has a chemosensitizing effect when administered together with other antitumoral drugs. Bortezomib is a well-established treatment in multiple myeloma and studies are focusing in the potential benefit of bortezomib in other haematological malignancies, including malignant lymphomas. Since the NF-kappaB pathway is considered to be implicated in the abnormal release of cytokines in primary myelofibrosis (PMF), the proteasome inhibitor bortezomib might be a potential therapy. In a murine model, bortezomib has been demonstrated to inhibit thrombopoietin (TPO)-induced NF-kappaB activation in megakaryocytes and to reduce myeloproliferation induced by high TPO levels. Accordingly, from in vitro studies it was concluded that bortezomib might be a promising therapy for future treatment of PMF patients. Surprisingly, however, these encouraging results have not been achieved in clinical trials testing bortezomib in patients with myelofibrosis. We have performed gene expression profiling of patients with PMF and in patients with other chronic myeloproliferative neoplasms (CMPNs) in order to describe aberrant genes in the proteasome pathway in PMF. Materials and methods: The HG-U133 Plus 2.0 microarray from Affymetrix was used to profile expression of 38500 genes in whole blood from 70 patients with CMPNs, including 9 patients with PMF and 61 patients with other CMPNs. All patients were diagnosed according to the WHO criteria of a CMPN (ET=19, PV=41, PMF=9). The patients were diagnosed and followed in two institutions. Most patients were studied on cytoreductive therapy, which for the large majority included hydroxyurea. Total RNA was purified from whole blood and amplified to biotin-labeled aRNA and hybridized to microarray chips. Differences in gene expression between the two groups were calculated for each gene in the dataset by using Welch two sample t test, and the Benjamini Hochberg method was applied to control for multiple hypothesis testing (false discovery rate (FDR) < 0.05). Data were integrated with biological pathways and networks using Gene Microarray Pathway Profiler (GenMAPP 2.1) and Cytoscape 2.6.3, respectively. Hypothesis driven discovery was used to find significantly differentially expressed genes and pathways associated with PMF. Results: Single gene analysis demonstrated significantly elevated expression of seventeen proteasomal subunit genes in patients with PMF (PSMA1, PSMA2, PSMA6, PSMA7, PSMB4, PSMB5, PSMB6, PSMB7, PSMC2, PSMC3, PSMD10, PSMD14, PSMD4, PSMD8, PSMD9, PSMG1, and PSMG3 (FDR < 0.05). Only one gene, PSMB4, was significantly downregulated (FDR < 0.05). Global pathway analysis showed a significant upregulation of the proteasome degradation pathway (adjusted P < 0.03), and the network analysis revealed a significant subnetwork only composed of upregulated genes (CDC25A, CDC6, CDT1, GMNN, ORC1L, PSMA6, PSMA7, PSMB5, PSMB6, PSMB7, PSMC3, PSMD5, PSMD8, PSMD9, PSMD14) of which 10 were proteasomal genes (Z=2.6). Conclusion: In this study, we have for the first time described the gene signature of the proteasome in peripheral blood cells from patients with myelofibrosis and patients with ET and PV. Using single gene analysis, global pathway and network analysis, we found significant upregulation of the proteasomal transcriptome in patients with PMF as compared to patients with ET and PV as a group. This study has added new important information of the genes involved in the upregulation of the proteasome degradation pathway in these patients. Disclosures: No relevant conflicts of interest to declare.

Abstract 4116 Introduction: Carcinoembryonic antigen-related cell adhesion molecule (CEACAM) 6, also known as non-specific cross-reacting antigen (NCA) or CD66c is a glycosylphosphoinositol (GPI)-linked cell surface protein and a member of the CEA family of proteins. Structurally, this protein shares close homology with CEACAM1, CEACAM7 and CEACAM8. Functionally, CEACAM6 has been implicated in cell adhesion, cellular invasiveness and metastatic behaviour of tumour cells. Expression of CEACAM6 protein has been found in a variety of normal human tissues, including myeloid cells. A key pathophysiological feature of primary myelofibrosis (PMF) is changes in the bone marrow micromilieu, progressive accumulation of connective tissue, pronounced neovascularisation and altered stromal cell adhesion. Consequently, CD34+ cells escape the bone marrow and seed extramedullarily. Being involved in cell adhesion, cellular invasiveness, angiogenesis, and inflammation – all key processes in the pathophysiology of PMF – we hypothesized that CEACAM6 might play an important role in these processes in patients with myelofibrosis. We have assessed gene expression of several CEA genes in patients with PMF and related neoplasms in order to elucidate the significance of CEACAM6 and other members of the CEA family of proteins in these disorders. Patients and Methods: Gene expression microarray studies have been performed on whole blood from control subjects (n=21) and patients with ET (n =19), PV (n=41), and PMF (n=9). Gene expression profiles were generated using Affymetrix HG-U133 2.0 Plus microarrays recognizing 54.675 probe sets (38.500 genes). Total RNA was purified from whole-blood and amplified to biotin-labeled aRNA and hybridized to microarray chips. Results: 20.439, 25.307, 17.417, and 25.421 probe sets were identified to be differentially expressed between controls and patients with ET, PV, PMF, and CPMNs as a whole, respectively (false discovery rate (FDR) adjusted p values < 0.05). Several CEACAM-genes were significantly deregulated. In PMF patients, the CEACAM genes 1, 6 and 8 were significantly upregulated with the highest upregulation of CEACAM6 and CEACAM8 (fold change (FC) 12.5 and 14.0, respectively and FDR adjusted p values 7.71 × 10-7 and 1.48 × 10-5, respectively). Only the CEACAM21 gene was significantly downregulated (FC -1.3 and FDR adjusted p-value 4.14 × 10-7) whereas the other CEACAM-genes tested (3, 4, 5, 7, 19) displayed no significant changes as compared to controls. In ET patients, the CEACAM genes 3, 6, and 7 were significantly upregulated (FC 1.2, 1.8, and 1.1, respectively) and FDR adjusted p values < 0.03). The CEACAM21 gene was significantly downregulated (FC -1.3 and FDR adjusted p-value 0.0004). In PV patients, the CEACAM genes 1, 3, 6 and 7 were significantly upregulated (FC 1.7, 1.2, 1.7, and 1.1, respectively) and FDR adjusted p values 0.0002, 0.0009, 0.0002, and 0.03, respectively. The CEACAM21 gene was significantly downregulated (FC -1.3 and FDR adjusted p-value 4.14×10-5) All other CEACAM-genes showed no significant changes in either ET or PV as compared to controls.When comparing controls with non-PMF-patients, a significant upregulation of the CEACAM genes 1, 3, 6, and 7 were recorded in non-PMF patients (FC 1.5, 1.2, 1.7, and 1.1, respectively; FDR adjusted p values 0.001, 0.0002, 0.002, and 0.02, respectively). The CEACAM19 and CEACAM21 genes were significantly downregulated (FC - 1.1 and -1.4, respectively; adjusted p-values 0.008 and 3.46 × 10-8). Discussion and Conclusions: Using global gene expression profiling, we have found a pronounced deregulation of CEACAM genes, involving highly significant upregulation of the CEACAM genes 6 and 8 in PMF (FCs 12.0 and 14.0, respectively). Upregulation of CEACAM6 was seen in both ET, PV and PMF by far the highest levels being recorded in PMF-patients. Of note, significant upregulation of CEACAM8 (FC 14) was only seen in patients with myelofibrosis. The elevated expression of CEACAMs genes in ET, PV, and PMF may solely reflect neutrophil activation being most exaggerated in patients with PMF in whom the highest CEACAM6 and 8 expression patterns were recorded. Alternatively, the highly elevated gene expression of CEACAM6 and 8 in PMF are molecular markers of clonal expansion and myelofibrotic transformation, implying enhanced proteolytic activity and egress of CD34+ cells into the circulation. Disclosures: No relevant conflicts of interest to declare.

Abstract 4118 Introduction: The polycomb repressive complex (PRC) 2 contains 3 core proteins, EZH2 (enhancer of zeste homolog 2), SUZ12, and EED, in which the SET (suppressor of vaegation-enhancer of zeste-trithorax) domain of EZH2 mediates the histone methyltransferase activity. This induces trimethylation of lysine 27 on histone H3, regulates the expression of HOX genes, and promotes proliferation and aggressiveness of neoplastic cells. EZH2, a known repressor of gene transcription, has been reported to be overexpressed in many cancers and correlates with poor prognosis. EZH2 may also be involved in disease progression in patients with the classical Philadelphia-negative chronic myeloproliferative neoplasms (CMPNs) encompassing essential thrombocythemia (ET), polycythemia vera (PV), and primary myelofibrosis (PMF). Since the potential oncogenic role of EZH2 in CMPNs has never been investigated, we have assessed gene expression of EZH2 in a cohort of patients with CMPNs. Patients and Methods: Using Affymetrix HG-U133 2.0 Plus microarrays, recognizing 54675 probe sets (38500 genes), gene expression profiling has been performed on control subjects (n=21) and patients with ET (n =19), PV (n=41), and PMF (n=9). All patients were diagnosed according to the WHO criteria of a CMPN. Total RNA was purified from whole blood and amplified to biotin-labeled RNA and hybridized to microarray chips. Results: We identified 20439, 25307, 17417, and 25421 probe sets which were differentially expressed between controls and patients with ET, PV, PMF, and CPMNs as a whole, respectively (false discovery rate (FDR) adjusted p values < 0.05). These genes included EZH2, which was highly significantly upregulated in patients with PMF as compared to controls (2.3 fold upregulated; uncorrected p-value=1.09×10-8 and FDR=1.75×10-6, and between PMF and non-PMF patients (fold change=2.0, FDR < 0.0005). No significant differences in EZH2 gene expression were recorded between controls and ET patients, controls and PV patients, or controls and the CMPN group as a whole. Within patients, the EZH2 gene was also differentially expressed with the highest levels being recorded in patients with PMF compared to PV patients (fold change=2.4, FDR < 7.5 ×10-6). Discussion and Conclusions: Using global gene expression profiling we have found the EZH2 gene to be significantly upregulated in CMPN patients, with the highest expression levels being found in PMF. We hypothesize that an altered expression of EZH2 may be involved in the transformation of ET and PV into myelofibrosis. It remains to be clarified if deregulation of EZH2 occurs consequent to mutations in the EZH2-gene. Enhanced EZH2 expression may also be associated with silencing of differentiation genes during myelofibrotic and leukemic transformation. An increased expression of EZH2 may provide a proliferative advantage of the malignant clone through interaction with the pathways of key elements controlling cell growth arrest and differentiation, (e.g. nuclear factor kappa beta and - the proteasome pathway). Studies are in progress to elucidate if genomic loss of distinct microRNAs (microRNA 101 leads to overexpression of EZH2 in cancer is associated with overexpression of EZH2 in CMPNs. Highly expressed EZH2 may be a new marker of an aggressive clinical phenotype which might imply EZH2 as a novel biomarker for predicting prognosis. If so, EZH2-blockade might be a novel approach to be incorporated in the strategies for developing epigenetic therapies in patients with CMPNs. Disclosures: No relevant conflicts of interest to declare.