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Abstract Background: Current drug therapy in primary myelofibrosis (PMF) offers palliative value only, including alleviation of splenomegaly, constitutional symptoms and anemia; hydroxyurea (HU), JAK2 inhibitors and interferon (IFN)-α are used for splenomegaly; JAK2 inhibitors for constitutional symptoms; and immunomodulatory drugs (IMiDs), erythropoiesis-stimulating agents (ESAs) and androgens for anemia. The current study constitutes a retrospective evaluation of specific drug response in anemia or splenomegaly in PMF. Methods : Study patients were recruited from the Mayo Clinic, Rochester, MN, USA. Diagnoses were according to the 2016 World Health Organization criteria (Blood. 2016;127:2391). For the purposes of the current study, conventional response criteria were modified to reflect clinical benefit assessment without strict adherence to criteria designed for clinical trials; accordingly, spleen response was evaluated only in patients with palpable splenomegaly and was defined as a minimum 50% reduction in palpable spleen size, regardless of response duration; anemia response was evaluated only in patients with hemoglobin level <10 g/dl and was defined as achieving transfusion-indpendence lasting for at least one month or an increase in hemoglobin of 2 g/dl, regardless of response duration. The JMP® Pro 13.0.0 software from SAS Institute, Cary, NC, USA, was used for all statistical calculations. Results: 432 cytogenetically- and molecularly-annotated patients with PMF were accessed in order to identify 333 patients who received first-line treatment with HU (n=97), JAK2 inhibitors (n=41), IFN-α (n=22), IMiDs (n=58), androgens (n=19), ESAs (n=54) and various other drugs (n=42), and were evaluable for response; driver mutational status was JAK2 59%, CALR type 1/like 20%, CALR type 2/like 4%, MPL 7% and triple-negative 10%; karyotype included very high risk (VHR) 6%, unfavorable 18% and favorable 76%; 60% of the patients harbored high molecular risk (HMR) mutations including ASXL1 (45%), SRSF2 (18%), U2AF1Q157 (10%), EZH2 (4%), IDH2 (4%) and IDH1 (2%). MIPSS70+ version 2.0 risk distribution was very high 17%, high 46%, intermediate 21%, low 14% and very low 2%. Overall, 249 patients were evaluable for spleen response, including 218 that were treated with the specific drugs analyzed in the current study. Anemia response was evaluated in 222 patients, including 194 (105 transfusion-dependent) that were treated with the specific drugs analyzed in the current study. Predictors of response to HU: Spleen response to HU was more likely in the presence of HMR mutations (37% vs 11%; p=0.02); however, responses were mixed and limited to presence of ASXL1 (40% vs 17%; p=0.06) or SRSF2 (47% vs 22%; p=0.1) mutations while none of 8 patients with either U2AF1Q157 or IDH2 mutations responded. None of 5 patients with VHR karyotype and only 1 (9%) of 11 patients with platelet count <100 x 109/l responded. Anemia responses to HU were infrequent. Overall response rate to HU was predicted by the absence of U2AF1Q157 mutations (64% vs 0%; p=0.007). Predictors of response to JAK2 inhibitors: Spleen response to JAK2 inhibitors was more likely in female patients (87% vs 50%; p=0.01) and in the presence of CALR type 1/like mutations (90% vs 57%; p=0.06). Anemia responses to JAK2 inhibitors were largely unpredictable. In order to further verify the aforementioned observed associations, we accessed data from a previous formal clinical trial of momelotinib (JAK2 inhibitor); among 91 evaluable patients, spleen response was higher in the presence of CALR mutations (73% vs 37%; p=0.009) and female sex (49% vs 39%, p=NS). Predictors of response to other agents: Spleen response to IFN-α was unlikely in the presence of ≥2% circulating blasts (0/6 responded) or presence of ASXL1 mutations (0/7 responded). IFN-α was ineffective for the treatment of anemia. Spleen responses to treatment with IMiDs, androgens or ESAs were unusual while anemia response to all three agents was not predicted by either genetic or clinical markers. Conclusions: Our observations, which require additional examination in a prospective setting, suggest limited value of genetic and clinical markers in predicting response to currently available drugs for PMF; this is consistent with the non-specific mechanism of action for these drugs. CALR (JAK inhibitors) and U2AF1Q157 (HU) mutations respectively predict favorable or unfavorable spleen response. Disclosures No relevant conflicts of interest to declare.

Abstract Background: Type 1 calreticulin (CALR) variants comprise ~70% of all CALR mutations in primary myelofibrosis (PMF) and form a distinct phenotypic and prognostic disease subset (Leukemia. 2014;28:1568). Determinants of long-term outcome have not, however, been systematically appraised in this population. The current study documents the natural history, molecular correlates, and independent predictors of overall (OS), leukemia-free (LFS), and thrombosis-free (TFS) survival in CALR type 1/like-mutated myelofibrosis. Methods: Patients were recruited from the Mayo Clinic, Rochester, MN, USA. Diagnoses were consistent with World Health Organization (PMF, fibrotic/leukemic transformations) (Blood. 2016;127:2391) and International Working Group for Myeloproliferative Neoplasms Research and Treatment criteria (post-essential thrombocythemia (ET) MF) (Leukemia. 2008;22:437). Laboratory and clinical data were retrospectively abstracted corresponding to time of referral (PMF) or myelofibrotic transformation (post-ET MF). Conventional prognostic scoring was as previously outlined (Blood. 2010;115:1703; J Clin Oncol. 2018;36:1769). Recipients of allogeneic stem cell transplant were censored at the time of transplant. Standard statistical methods were used for all analyses using the JMP® Pro 13.0.0 software package (SAS Institute, Cary, NC, USA). Results: A total of 162 consecutive patients with CALR type 1/like-mutated myelofibrosis were identified: 139 (86%) with PMF and 23 (14%) with post-ET MF with median age 55 years (range 23-85), 62% male. The PMF and post-ET MF cohorts displayed similar phenotypic features with the exception of higher platelet counts (median 443 vs 340 x 109/l; P=0.02) in post-ET MF (Table 1). The most frequent co-existing mutations were ASXL1 (n=47; 37%) and SRSF2 (n=4; 3%), with ASXL1 seen more frequently in PMF (39% vs 11% post-ET MF; P=0.07). Over a median follow-up of 6 years (range 0-25 years), a total of 20 (12%) leukemic transformations and 66 (41%) deaths were recorded, with no significant differences between the PMF and post-ET MF cohorts (P=0.16 and 0.11, respectively). Kaplan-Meier survival estimates revealed comparably favorable median OS in both CALR type 1/like-mutated variants: not yet reached and 13 years in post-ET MF vs PMF, respectively (P=0.7) (Figure 1A). Multivariable analysis disclosed moderate to severe sex-adjusted anemia (P<0.001), ≥2% circulating blasts (P<0.001), very high risk (VHR) karyotype (P<0.001), age >70 years (P=0.006), and constitutional symptoms (P=0.008) to be independent predictors of inferior OS in CALR type 1/like-mutated PMF (Table 2). LFS was significantly shortened in the presence of IDH1 mutations (P=0.01) and platelets <100 x 109/l (P=0.02) while IDH2 mutations (P=0.02), leukocytosis ≥11 x 109/l (P=0.03) and history of arterial thrombosis (P=0.04) were independent predictors of shortened TFS. Importantly, myelofibrosis variant (primary vs post-ET) did not influence survival (P=0.7) or complication rates (P=0.8 for LFS, P=0.09 for TFS) (Table 2). The karyotype- and mutation-enhanced international prognostic scoring system (MIPSS70+ version 2.0), was effective in risk stratifying type 1/like CALR-mutated PMF (P-values 0.01 to <0.0001), with the exception of low vs intermediate (P=0.22) and intermediate vs high risk (P=0.49) (Figure 1C). The detrimental influences of unfavorable/VHR karyotype and ASXL1 mutations were confirmed (Figure 2A-B) while borderline adverse and prognostically neutral effects were seen on OS for U2AF1 (n=116; P=0.05) and SRSF2 (n=120; P=0.98) respectively (Figure 2C-D). Conclusions: The current study documents analogous disease patterns in primary and post-ET CALR type 1/like-mutated MF and provides information on determinants of long-term survival. Disclosures No relevant conflicts of interest to declare.

Abstract Background : Chronic myelomonocytic leukemia (CMML), a myeloid neoplasm with overlapping features of myelodysplastic syndromes and myeloproliferative neoplasms (MPN), is characterized by peripheral blood (PB) monocytosis and a risk for leukemic transformation (LT). Gene mutations commonly seen in CMML include, TET2 (~60%), SRSF2 (~50%) and ASXL1 (~40%). MPN associated-driver mutations such as JAK2V617F (~10%), MPL (<1%) and CALR (<1%) are uncommon, and in fact, the 2016 World Health Organization (WHO) guidelines state that the presence of these mutations tends to support a diagnosis of MPN with monocytosis. We carried out this study to assess the i) clinical correlates and ii) survival outcomes of MPN associated-driver mutations in CMML. Methods : 323 molecularly annotated patients with WHO-defined CMML were included in the study. All patients had bone marrow (BM) biopsies and cytogenetics performed at diagnosis. Targeted capture assays were carried out on BM DNA specimens obtained at diagnosis for 30 myeloid relevant genes, by previously described methods. Results: Among the 323 study patients, 67% were males and median age was 71 years (range, 18-95). Twenty five (8%) patients had CMML with MPN associated-driver mutations; 24 (96%) with JAK2V617F and 1(4%) with a MPLW515L mutation. There were no patients with CALR or JAK2 exon 12 mutations. Additional signal-pathway mutations included NRAS (15%), KRAS (4%), CBL (14%), PTPN11 (3%), CSF3R (1%), and SH2B3 (<1%). i) Phenotypic correlates: The median age of CMML patients with MPN-associated driver mutations was 71 years and 66% were male. The WHO morphological subtypes included CMML-0 60%, CMML-1 24% and CMML-2 16%; while 91% of patients had a normal karyotype. The distribution of mutations included TET2 75%, SRSF2 54%, ASXL1 48%, RUNX1 20%, NRAS and EZH2 12% each, SETBP1 8%, SF3B1, U2AF1, CBL, PTPN11, FLT3-TKD, & Tp53 4% each, respectively. Risk stratification by the Mayo Molecular Model included high 16%, intermediate-2 32%, intermediate-1 36% and low risk 16%, respectively. In comparison to CMML patients without MPN associated-driver mutations, those with, had a higher hemoglobin (HB, p=0.001) and hematocrit (p=0.001), were more likely to have leukocytosis (p=0.02) and elevated LDH levels (p=0.0002), less likely to have thrombocytopenia (p=0.003), more likely to have a "proliferative" CMML phenotype (p=0.01) with palpable splenomegaly (p=0.0007), and more likely to have mutations involving TET2 (p=0.02). Six (2%) thrombotic events were documented in the cohort; 2 (8%) in patients with MPN-driver mutations and 4 (1%) in those without (p=0.07). There were no differences between the two groups with regards to the degree of monocytosis, PB and BM blasts, BM cellularity, BM megakaryocytic atypia, and BM fibrosis. ii) Survival outcomes: At last follow up 219 (68%) deaths and 55 (17%) LT were documented, of which 14 (56%) deaths and 2 (8%) LT occurred in the MPN-driver mutation group. The median OS for the entire cohort was 28 months (22-32); 31 months for CMML patients with MPN associated-driver mutations and 24 months for those without (p=0.4). On a univariate analysis, survival was adversely impacted by low HB (p<0.0001), high white blood count (p=0.0009) and absolute monocyte count (p=0.0004), circulating immature myeloid cells (p=0.02) and blasts (p=0.005), BM blasts (p=0.02), palpable splenomegaly (p=0.03), abnormal karyotype (p=0.001), presence of DNMT3A (p=0.006), ASXL1 (p=0.009), EZH2 (p=0.03) and Tp53 (p=0.02) mutations and the absence of TET2 (p=0.0009) mutations. Survival was not affected by the presence of JAK2V617F (p=0.4) or MPL (p=0.46) mutations. On a multivariable analysis that included the aforementioned significant variables, only HB <10 gm/dl (p=0.0016), presence of PB blasts (p=0.01), presence of DNMT3A (p=0.003) and the absence of TET2 mutations (p=0.02) retained significance. The presence of MPN associated-driver mutations did not impact LFS (p=0.36). Conclusions: The occurrence of MPN associated-driver mutations in CMML is infrequent (~8%) and is largely restricted to JAK2V617F. CMML patients with MPN-associated driver mutations have a higher HB/hematocrit, are more likely to have proliferative features and palpable splenomegaly, and are less likely to be thrombocytopenic. There was a trend towards an increased thrombotic risk, with no impact of these mutations on overall and leukemia free survival. Disclosures No relevant conflicts of interest to declare.

Abstract Background: Current prognostic models in primary myelofibrosis (PMF) target overall survival (OS) and utilize MIPSS70 (mutation-enhanced international prognostic scoring system for transplant-age patients), MIPSS70+ version 2.0 (karyotype-enhanced MIPSS70) and GIPSS (genetically-inspired prognostic scoring system, which is based on mutations and karyotype) (JCO 2018;36:310; JCO doi: 10.1200/JCO.2018.78.9867; Leukemia. 2018;doi:10.1038/s41375-018-0107). In the current study, we used logistic regression statistics to identify risk factors for leukemic transformation (LT) within 5 years of diagnosis/referral (i.e. early events) and also performed Cox regression analysis of overall leukemia-free survival (LFS). Methods : Study patients were recruited from the Mayo Clinic, Rochester, MN, USA. Diagnoses of LT and chronic phase PMF were confirmed by both clinical and bone marrow examinations, in line with the 2016 World Health Organization criteria (Blood. 2016;127:2391); specifically, LT required presence of ≥20% blasts in the peripheral blood (PB) or bone marrow (BM) (Blood 2016;127:2391). Statistical analyses considered clinical and laboratory data collected at the time of initial PMF diagnosis or Mayo Clinic referral point. Logistic regression statistics was used to identify predictors of LT at 5 years from initial diagnosis/referral; in the particular method, patients with documented LT within 5 years were "uncensored" while those followed up for at least 5 years, without developing LT, were "censored"; the analysis excluded patients without LT and not followed for at least 5 years. In addition, Cox regression analysis was performed to identify risk factors for overall LFS. The JMP® Pro 13.0.0 software from SAS Institute, Cary, NC, USA, was used for all calculations. Results: 1,306 patients with PMF (median age 65 years; 63% males) were included in the current study; MIPSS70+ version 2.0 risk distribution was 20% very high risk, 41% high risk, 19% intermediate risk, 16% low risk and 4% very low risk. 149 (11%) patients were documented to experience LT, and compared to the remaining patients (n=1157), they were more likely to be males (p=0.02) and mutated for ASXL1 (p=0.01), SRSF2 (0.001) and IDH1 (0.02) and present with higher risk MIPSS70+ version 2.0 (p=0.02). Multivariable logistic regression identified the following as predictors of LT in the first 5 years of disease: IDH1 mutation (odds ratio; OR 78.4), very high risk (VHR) karyotype (OR 57.6), ASXL1 mutation (OR 15.1), age >70 years (OR 13.3), SRSF2 mutation (OR 8.5), male sex (OR 6.9), PB blasts ≥3% (OR 5.4), presence of moderate or severe anemia, adjusted for sex (OR 3.6) and constitutional symptoms (OR 3.1). On Cox regression analysis, the following were associated with inferior LFS: IDH1 mutation (HR 4.3), PB blasts ≥3% (HR 3.3), SRSF2 mutation (HR 3.0), age >70 years (HR 2.1), ASXL1 mutation (HR 2.0) and presence of moderate or severe anemia, adjusted for sex (HR 1.9). Subsequently, HR-based risk point allocation resulted in highly discriminating LT predictive model with HR (95% CI) of 39.4 (10.8-114) for high risk and 4.1 (2.4-7.3) for intermediate risk (Figure 1). Conclusions: The current study identifies IDH1 mutation as a main predictor of LT in PMF. Our study also implicates SRSF2 and ASXL1 mutations and VHR karyotype as other genetic markers of early LT. Other independent contributors of early LT and inferior LFS, overall, included PB blasts ≥3%, moderate to severe anemia and older age. We provide LT prediction model, based on these variables, with leukemia risk ranging from 8% to 57%. Disclosures No relevant conflicts of interest to declare.

Abstract Background: The 2016 World Health Organization (WHO) system lists five morphological categories of systemic mastocytosis (SM): indolent (ISM), smoldering (SSM), SM with an associated hematological neoplasm (SM-AHN), aggressive (ASM) and mast cell leukemia (MCL) (Blood. 2016;127:2391). In the current study, we capitalized on the large number of accumulated cases of SM seen at the Mayo Clinic, between 1968 and 2015 (n=580), in order to devise two separate but complementary prognostic models that are based on either clinically-derived variables, or a combination of both clinical and molecular information. Methods : Study patients (n=580) were recruited from the Mayo Clinic, Rochester, MN, USA. Diagnoses of SM and its morphological subcategories were confirmed by both clinical and bone marrow examinations, in line with the 2016 WHO criteria (Blood. 2016;127:2391). Next-generation sequencing (NGS) was performed in a subset of the study population (n=150). Statistical analyses considered clinical and laboratory data collected at the time of initial diagnosis at the Mayo Clinic. Conventional statistics was used for calculation and of overall survival and determination of inter-independent risk factors. Receiver operating characteristic (ROC) curves were used to determine the prognostically most discriminative platelet threshold. The JMP® Pro 13.0.0 software from SAS Institute, Cary, NC, USA, was used for all calculations. Results: 580 patients with SM (median age 55 years; range 18-88 years; 52% males) were included in the current study; 291 (50%) constituted indolent and 289 (50%) advanced variants; the latter included 85 (15%) ASM, 199 (34%) SM-AHN and 5 MCL cases. At presentation, anemia defined by hemoglobin level below the lower limit of the sex-adjusted reference range, was present in 41% of the patients, hemoglobin <10 g/dl in 16%, red cell transfusion-dependency in 9%, platelet count below the ROC-determined limit of 150 x 109/l in 26%, serum albumin below the lower normal limit (LNL) of the reference range in 22%, serum alkaline phosphatase (ALP) above the upper normal limit (UNL) of the reference range in 54%, urticaria pigmentosa in 41%, mast cell mediator symptoms in 46%, palpable hepatomegaly in 21%, palpable splenomegaly in 31%, "C" findings in 23% and "B" findings in 42%. Median follow-up was 34 months with 239 (41%) deaths and 9 (1.5%) leukemic transformations documented. Cytogenetic information was available in 342 cases, including 51 (15%) with abnormal karyotype and 27 (8%) with unfavorable karyotype. NGS-derived mutation information was available in 150 cases and most frequent mutations were KIT (75%), TET2 (29%), ASXL1 (17%) and CBL (11%). Age-adjusted multivariable analysis of clinical variables, which did not include mutation or cytogenetic information, identified age >60 years (HR 2.5, 95% CI 1.8-3.4), advanced vs ISM (HR 2.3, 95% CI 1.5-3.7), thrombocytopenia <150 x 109/l (HR 2.4, 95% CI 1.8-3.4), anemia (HR 2.1, 95% CI 1.5-3.0), ALP above UNL (HR 2.1, 95% CI 1.5-3.1) and albumin below LNL (HR 1.4, 95% CI 1.0-1.9). A similar age-adjusted multivariable analysis for mutations identified ASXL1 (HR 3.3, 95% CI 1.9-5.5), RUNX1 (HR 4.1, 95% CI 1.2-10.2) and NRAS (HR 5.7, 95% CI 1.7-14.9) as independent molecular risk factors; these mutations were henceforth labelled as "adverse". The addition of "adverse" mutations (HR 2.7, 95% CI 1.6-4.7) to the list of the aforementioned clinical risk factors resulted in loss of significance for age and anemia while platelets below 150 x 109/l (HR 2.9, 95% CI 1.8-4.8), ALP above UNL (HR 3.2, 95% CI 1.8-6.1), albumin below LNL (HR 2.5, 95% CI 1.6-4.0) and advanced vs ISM (HR4.2, 95% CI 1.9-10.7) remained significant. Subsequently, based on the number of risk factors present, a "clinical" (figure 1a; n=380 informative cases) and "clinical-molecular" (figure 1b; n=129 informative cases) risk models were prepared; both risk models performed effectively for advanced and indolent SM, when analyzed separately (data not shown). Conclusions: The current study advances two separate but complimentary risk models for SM and illustrates the additional prognostic contribution of mutations and underlines the importance of thrombocytopenia and serum ALP and albumin levels in both risk models. Furthermore, we show effective application of both risk models in advanced and indolent SM. Disclosures No relevant conflicts of interest to declare.

Abstract Background While unfavorable karyotype at referral is associated with significantly inferior overall and leukemia-free survival in myelofibrosis (MF) patients (Blood. 2011 Oct 27;118(17):4595), the incidence of clonal evolution during JAK inhibitor (JAKi) treatment and its clinical significance are not currently known. We conducted a sponsor-independent, single-center retrospective analysis examining the phenotypic correlates and prognostic impact of clonal evolution during JAKi treatment. Methods Clinical, cytogenetic and molecular data were collected on MF patients treated with one or more JAKi on a clinical trial at the Mayo Clinic, Rochester, MN. Baseline data pertained to the onset of treatment with first JAKi. Karyotype risk categories were as previously defined (Blood. 2011 Oct 27;118(17):4595). Serial bone marrow biopsies were obtained at varying frequencies based on individual JAKi protocol requirements. Mutation screening was performed as previously described (Leukemia. 2013 Apr 26. doi: 10.1038/leu.2013.119). Information on survival and leukemic transformation was updated in July 2013. Results A total of 157 MF patients were studied (60% male; median age 65 years, range 34-89 years). The DIPSS-plus distribution was: Low/Int-1 20 (13%), Int-2 66 (42%), and High 71 (45%). The first JAKi was momelotinib (CYT387) in 79 patients (50%), ruxolitinib in 51 (33%) and fedratinib (SAR302503) in 27 (17%). Median follow up from first JAKi treatment was 30 months (range 1-67 months); during this period, 72 deaths (46%) and 14 (9%) leukemic transformations were documented. Eighty nine patients (57%) had a median total 3 (range 2-8) bone marrow biopsies with karyotype analysis during JAKi treatment. Of these, 21 patients (24%) showed clonal evolution (ie, acquisition or loss of one or more chromosome abnormalities when comparing last observed karyotype during JAKi treatment to baseline). Overall, 13 patients (15%) had upstaging of karyotype risk category (eg, normal to unfavorable), 9 (10%) had downstaging (eg, favorable to normal) and 67 (75%) had no change. Acquisition of worse-than-baseline karyotype was significantly higher in DIPSS-plus high-risk patients (26%) versus non-high risk patients (6%) (p=0.03). There was no association between acquisition of a worse karyotype category and baseline karyotype risk category or ASXL1 or SRSF2 mutation status. There was borderline association with RBC transfusion-dependence and constitutional symptoms at baseline (p=0.06). There was no relationship between clonal evolution and achievement of spleen or anemia response during JAKi treatment (p>0.05). The median overall survival of the entire cohort was 41 months. On univariate analysis, overall survival was significantly worse in patients who acquired a worse-than-baseline karyotype risk category during JAKi treatment (n=13, 77% deaths, median survival=31 months) versus those who did not (n=76, 43% deaths, median survival=52 months) (p=0.01) (Figure). On multivariate analysis, the prognostic significance of acquiring a worse karyotype risk category was maintained against all individual DIPSS-plus prognostic variables, including baseline karyotype risk category, except age >65 years. On univariate analysis, leukemia-free survival was significantly worse in patients who acquired a worse-than-baseline karyotype risk category during JAKi treatment (n=13, 31% leukemic transformation, median leukemia-free survival=32 months) versus those who did not (n=76, 8% leukemic transformation, median leukemia-free survival not reached) (p=0.0006) (Figure). On multivariate analysis against known predictors of leukemic risk in PMF patients (ie, baseline unfavorable karyotype, SRSF1 mutated status and platelet count <100 x 109/L), only acquisition of a worse-than-baseline karyotype risk category maintained its prognostic value (HR 5.3, p=0.03) Conclusions This is the first study to examine the incidence of clonal evolution during JAKi treatment in MF patients. Approximately 25% of patients exhibited clonal evolution; acquisition of a worse-than-baseline karyotype risk category had a strong and independent association with inferior leukemia-free survival. A similar association was also observed for inferior overall survival, albeit not independent of older age. In contrast, there was no association with spleen or anemia response during JAKi treatment. Disclosures: Pardanani: Bristol Myers Squibb: Clinical trial support Other; Sanofi: Clinical trial support. Publication support service., Clinical trial support. Publication support service. Other; PharmaMar: Clinical trial support, Clinical trial support Other; JW Pharmaceutical Corp.: Clinical trial support, Clinical trial support Other.

Abstract Background Therapy-related myeloid neoplasm (tMN) includes t-myelodysplasia (tMDS) and t-acute myeloid leukemia (tAML) and are serious late effects of the treatment of cancer. Prognosis of tMN is poor, related to the increased frequency of adverse cytogenetics and other clinical features which predict poor response to conventional treatment. Over the last years, azacitidine (AZA) has become the standard of treatment for high risk MDS (Silverman, JCO 2002; Fenaux, Lancet Oncol 2009) and has shown efficacy in AML. AZA represents an interesting option for patients with tMN considering its safety profile and its efficacy in poor prognosis subgroups of apparently de novo MDS patients including those with monosomy 7. Most prospective trials of AZA have excluded patients with tMN. Most tMN data are retrospective or registry studies (Bally, Leuk Res 2013). This abstract presents the results of 47 t-MN patients prospectively enrolled as a specific cohort in the E1905 study. Methods E1905 study is a randomized phase 2 study from the North American Leukemia Intergroup (NCT00313586, Prebet , ASH 2010) testing 10 days of AZA (50mg/m2/d s.c.) vs. 10 days of AZA + the histone deacetylase inhibitor entinostat (4 mg/m2/d PO days 3 and day 10). 6 cycles of treatment were planned; responding patients could receive up to 24 cycles. MDS, CMML, and AML with myelodysplasia-related changes were included. Patients with tMN were subsequently accrued as a separate cohort after amendment of the protocol. Response was assessed using IWG 2000 criteria (Cheson et al, Blood 2000); the primary endpoint of the overall trial was achievement of a normal hemogram in 25% of treated patients in either treatment arm. Results A total of 47 patients were included. Median age was 70 years (39y-83y), 45% male, and 94% of patients had ECOG PS 0-1. 29 patients could be subclassified as t-MDS and 18 as t-AML. At inclusion, median peripheral blood counts were: neutrophils 1.0 G/l, Platelets 35 G/L, Hemoglobin 9.2 g/l, peripheral blood blasts 0%, marrow blasts 14.0%. 68% of patients were RBC transfusion dependent and 40% platelet transfusion dependent. As expected, the cytogenetic evaluation showed a high frequency of unfavorable risk cytogenetics (74%) as compared to normal or intermediate risk cytogenetics (26%). Baseline characteristics were not statistically different between the 2 arms. 24 patients were treated with AZA monotherapy and 23 with AZA+entinostat. The median number of administered cycles was 4 and was significantly higher in patients treated with AZA monotherapy (6 cycles vs.3 cycles, p=0.008). 8 patients in the combination arm and 1 patient in the AZA monotherapy arm died of infection or hemorrhage before cycle 3. In an intent to treat analysis, overall response rates (CR, PR, or trilineage Hematologic improvement) were 11/24 (46%) in AZA monotherapy (95% CI 26 – 67%) and 4/23 (17%) in the combination arm (95% CI 5 – 39%, p=0.06 comparing the two arms). Median overall survival in the two arms were 12.8 months and 5.7 months (p=0.008). Conclusions In this group of very high risk patients with therapy-related myeloid neoplasms, the use of the novel 50 * 10 schedule of azacitidine monotherapy appears effective, with response rates comparable to those for patients with de novo MDS/AML treated on the same protocol (74 pts, 40% with unfavorable cytogenetics, ORR=32%, median OS=18 months). Because there are no prospective data examining the approved dose schedule of AZA (75 mg/m2/day * 7 days), it is not clear if this surprisingly high response rate derives from the current extended schedule of lower dose AZA, or would be true with standard dose AZA as well. This high response may enable many of these patients to proceed to allogeneic stem cell transplant. Entinostat combined with azacitidine at the dose and schedule applied in E1905 does not appear to be effective and tolerable as compared to azacitidine alone. Disclosures: Prebet: CELGENE: Honoraria. Off Label Use: Use of azacitidine in acute myeloid leukemia. Gore:CELGENE: Equity Ownership, Research Funding.

Abstract Background Peripheral T-cell lymphomas (PTCLs) are aggressive non-Hodgkin lymphomas with poor overall survival rates. The genetics of PTCLs are poorly understood. We have described t(6;14)(p25.3;q11.2) translocations in PTCLs involving the T-cell receptor-alpha (TRA@) and interferon regulatory factor-4 (IRF4) genes and overexpressing IRF4 protein (also called MUM1). IRF4/MUM1 is a lymphoid transcription factor involved in differentiation and growth, the expression of which is tightly regulated in normal T cells. However, nearly half of PTCLs constitutively express IRF4/MUM1 and this expression is associated with adverse overall survival in several PTCL subtypes. Because IRF4/TRA@ translocations are rare among PTCLs (<1%), we investigated the presence of other genetic abnormalities of IRF4 in PTCLs and examined their association with IRF4/MUM1 protein expression. Methods Studies were performed on paraffin tissue sections of PTCL specimens diagnosed by standard WHO criteria. IRF4/MUM1 immunohistochemical staining (IHC) was performed using the MUM1p antibody and considered positive if nuclear staining was present in >30% of tumor cell nuclei. Fluorescence in situ hybridization (FISH) was performed using breakapart probes constructed from bacterial artificial chromosome DNA that hybridized to loci flanking the IRF4 locus on 6p25.3. Cases with 3 or more fusion signals were considered to have extra copies of the IRF4 gene. In a subset of cases, PCR and Sanger sequencing was performed on DNA extracted from frozen PTCL tumor tissue with primer sets that amplified exons 1 to 10 of the IRF4 gene. Data were analyzed using the chi-square test or t test. Results PTCLs from 277 patients (175 M:102 F; median age, 61 y) were examined by both IHC and FISH. The subtype distribution was: PTCL, not otherwise specified (NOS), 93; anaplastic large cell lymphoma (ALCL), 89; angioimmunoblastic T-cell lymphoma (AITL), 27; cutaneous T-cell lymphoma (CTCL), 43; and cytotoxic PTCL, 25. IRF4/MUM1 was positive in 116 cases (42%). Extra copies of IRF4 were identified in 18 PTCLs (7%), 83% of which were IRF4/MUM1 protein-positive. In contrast, 39% of cases without extra copies of IRF4 were IRF4/MUM1 protein-positive (p=0.0002). The mean percentage of tumor cells with IRF4/MUM1 staining was 69% in cases with extra copies of IRF4, compared to 30% in cases without extra copies (p=0.0001). Extra copies of IRF4 were seen in 13% of ALCLs, 4% each of PTCLs, NOS and cytotoxic PTCLs, 2% of CTCLs, and 0% of AITLs (p=0.02). Two IRF4/MUM1-positive cases had an IRF4/TRA@ translocation (1%). We selected 30 IRF4/MUM1-positive PTCLs for Sanger sequencing. In this subset, we identified a previously undescribed non-synonymous variant in exon 5 (S309R) in 1 case (3%) without an extra copy of IRF4. Conclusions Extra copies of IRF4 are seen in ∼7% of PTCLs, are significantly associated with IRF4/MUM1 expression, and are preferentially observed in ALCLs. Both IRF4/TRA@ translocations and IRF4 mutations are rare in PTCLs. These data suggest that genetic abnormalities of the IRF4 gene – specifically extra copies of IRF4 – may contribute to IRF4/MUM1 expression in some PTCLs. Since IRF4/MUM1 expression is seen in ∼42% of PTCLs, these data also imply the existence of other regulatory mechanisms. Characterizing these mechanisms may be important clinically, since IRF4/MUM1 has been proposed as a therapeutic target in human cancers but drugs that directly inhibit its function are currently not available. Disclosures: No relevant conflicts of interest to declare.

Abstract Background : Pre-treatment determinants of survival in adult acute myeloid leukemia (AML) include performance status, age, karyotype, the distinction between primary and non-primary AML and FLT3-ITD/NPM1 mutational status. Current literature on AML natural history and risk factors is often based on information derived from stringent protocol studies. In the current series of 1,123 adult patients seen at the Mayo Clinic between 2004 and 2017, we examined long-term survival specified by a number of primarily established risk factors. Methods: Diagnosis of AML and its sub-classification was according to World Health Organization criteria. Study subjects were recruited from the Mayo Clinic AML database. Conventional response criteria were used for CR and CRi assignment; the latter met all criteria for CR with the exception of platelet count <100 x 109/l or absolute neutrophil cunt <1 x 109/l. Standard statistical methods were used for analysis of overall survival, calculated from the initial diagnosis of AML to date of death or last follow-up; analyses were performed both in the absence and in the presence of censoring of survival at time of allogenic stem cell transplant (ASCT). The JMP® Pro 13.0.0 software from SAS Institute, Cary, NC, USA, was used for all calculations. Results: 1,123 adult patients (median age 65 years, range 18-94; 61% males) with non-APL AML were considered; 61% were age >60 years. 351 (31%) patients were seen between 2004 and 2009 and 772 (69%) between 2010 and 2017. AML subcategories were primary (56%), post-myelodysplastic syndromes (post-MDS; 24%), therapy-related (10%), post-myeloproliferative neoplasm (post-MPN; 8%) and post-MDS/MPN (3%). Cytogenetic risk distribution, according to the European LeukemiaNet classification, was favorable in 47 (4%), intermediate in 650 (58%) and adverse risk in 426 (38%) patients. FLT3, NPM1 and CEBPA mutation information was available in 462 (24% mutated), 393 (27% mutated) and 228 (11% mutated) patients, respectively. Treatment included intensive chemotherapy (IC) in 766 (68%) patients, less aggressive chemotherapy, including the use of hypomethylating agents in 144 (13%) and supportive care alone in 213 (19%) patients. ASCT was utilized in 258 (23%) cases, almost all performed after achieving CR/CRi. Complete remission (CR) and CR with incomplete count recovery (CRi) were listed in 333 (30%) and 248 (22%) patients, respectively; the corresponding rates in IC-treated patients were 43% and 32%. Almost all cases of CR/CRi occurred in IC-treated patients; 2 (1.4%) CRs were listed for less aggressive chemotherapy. After a median follow-up of 11 months, 798 (71%) deaths were recorded. Median survival for all 1,123 patients was 14 months with 1-, 3- and 5-year survival rates of 54%, 29% and 23%, respectively; a slight but significant (p=0.01) improvement in survival was apparent in more recent years (Figure 1a). Figures 1b, 1c and 1d depict analysis stratified by AML subcategories, treatment received and response obtained, respectively. Similarly, figures 2a, 2b and 2c depict analysis stratified by karyotype, use of ASCT and age. Multivariable analysis of pre-treatment parameters evaluable in all 1,123 patients identified age >60 years (HR 2.2, 1.9-2.6), adverse karyotype (HR 2.9, 1.9-4.9), intermediate-risk karyotype (HR 1.6, 1.02-2.6), post-MPN AML (HR 1.9, 1.5-2.4) and other secondary AML (HR 1.3 (1.1-1.6), as risk factors for shortened survival; the inclusion in the model of FLT3/NPM1 mutational status in 392 informative cases confirmed the adverse prognostic effect of age >60 years (HR 1.8, 1.4-2.5), adverse karyotype (HR 3.7, 1.4-15.3), post-MPN AML (HR 2.8, 1.6-4.6), other secondary AML (HR 1.4, 1.0-1.9) and FLT3+NPM1- (HR 2.8, 1.6-4.9) and FLT3-NPM1- (HR 1.7, 1.2-2.7) profile. Results were unchanged when survival was censored at time of ASCT. Additional prognostic interaction with treatment strategy and ASCT is further elaborated in an accompanying abstract to be presented. Conclusions: The current study, the largest coming from a single institution, provides practically useful information that should assist with patient consultation on AML prognosis and treatment. The study confirms the primary prognostic importance of age, karyotype and FLT3/NPM1 mutational status, in real-life practice. Novel observations included comparable value of CRi vs CR and the particularly worse prognosis associated with post-MPN AML. Disclosures Al-Kali: Novartis: Research Funding.

Abstract Background : Thrombosis is a characteristic feature in essential thrombocythemia (ET) and polycythemia vera (PV). Previous studies had focused on thrombotic events occurring after diagnosis and did not always distinguish between arterial and venous thrombosis. Arterial thrombosis in ET has been associated with age >60 years, JAK2 mutations, leukocyte count >11 x 109/l, history of thrombosis and cardiovascular risk factors, and venous thrombosis with male sex (Blood 2011;117:5857). In the current two-enter study, we looked for associations between both driver and other mutations, with first incidences of arterial and venous thrombosis in ET and PV, analyzed together and separately. Methods : Study patients were recruited from the Mayo Clinic, Rochester, MN, USA and the University of Florence, Florence, Italy, based on availability of next-generation sequencing-derived mutation information. Diagnoses were according to the 2016 World Health Organization criteria (Blood. 2016;127:2391). Conventional statistics was employed to examine significance of associations, with separate analysis of arterial vs venous thrombosis, occurring at any time before or after formal diagnosis of ET or PV. For the purposes of the current study, only first events were considered. Results: 906 molecularly-annotated patients (416 from Mayo and 490 from Florence), including 502 ET and 404 PV cases, were included in the current study. The Mayo/Florence cohorts included 270/232 ET (median age 57/54 years, 60%/59% females) and 146/258 PV (median age 63/58 years, 52%/44% females) patients; median follow-up was 9.9/12.9 years for ET and 10.7/12.4 years for PV. Driver mutation distribution in ET was 55% JAK2, 27% CALR, 5% MPL and 13% triple-negative. Most frequent mutations, other than JAK2/CALR/MPL, were TET2 (14%; 11% in ET and 18% in PV) and ASXL1 (13%; 13% in ET and 13% in PV). 301 (33%) patients experienced first time thrombosis, before or after diagnosis, including 152 (30%) in ET and 149 (37%) in PV (p=0.03); arterial events occurred in 174 (19%) patients, including 96 (19%) in ET and 78 (19%) in PV (p=0.9); venous events occurred in 177 (20%) patients, including 82 (16%) in ET and 95 (24%) in PV (p=0.007). The number of vascular events after diagnosis was 174 (19%) for arterial and 154 (17%) for venous thrombosis, with no significant difference between ET and PV. Associations with arterial thrombosis: In multivariable logistic regression analysis that included both ET and PV (n=906), age >60 years (23% vs 16%; OR, 1.6, 95% CI 1.1-2.2) and absence of ASXL1 and RUNX1 mutations (21% vs 9%; OR 2.6, 95% CI 1.4-4.8) were associated with arterial thrombosis; these associations remained significant (or near significant) when ET and PV were analyzed separately; in addition, JAK2 mutations in ET displayed borderline significance (p=0.05). Overall incidence of arterial events in ET was estimated at 27% in the presence of all three risk factors (i.e. older age, presence of JAK2 mutations and absence of ASXL1/RUNX1 mutations), 21% with two risk factors, 13% with one risk factor and 9% in the absence of all three risk factors (p=0.01). Associations with venous thrombosis: In multivariable analysis, including both ET and PV (n=906), JAK2 mutations (p<0.001), higher leukocyte count (p=0.03) and younger age (p=0.04) were identified as being significant. Analysis of ET patients only (n=502) identified JAK2 mutations (p<0.001; OR 2.4, 95% CI 1.4-4.1), absence of SRSF2 mutations (p=0.03) and younger age (p=0.04) as independent risk factors and in PV patients (n=404), higher leukocyte count (p=0.06). Prognostic interaction between JAK2 mutations and age: In ET, the overall frequency of venous events was 27% for young patients with JAK2 mutations vs 13% for older JAK2 mutated cases vs 10% for JAK2 unmutated young patients vs 13% for JAK2 unmutated older patients (p<0.001). The corresponding percentages for arterial events were 20%, 24%, 14% and 19%, respectively (p=0.1). Conclusions: JAK2 mutations contribute to the risk of both venous (younger patients) and arterial (young and older patients) thrombosis, in an age-dependent manner; the association with venous thrombosis might explain the higher incidence of venous thrombosis in PV, compared to ET. Additional studies are required to confirm the observed lower risk of thrombosis in patients with ASXL1, RUNX1 and SRSF2 mutations and provide insight into the underlying biological explanation. Disclosures No relevant conflicts of interest to declare.