Pardanani, Animesh

Abstract Background : Approximately 25% of patients with primary myelofibrosis (PMF) harbor calreticulin (CALR) mutations, which have been associated with longer survival (Klampf et al. NEJM 2013). More than 80% of CALR mutated patients harbor one of two mutation variants: type 1, a 52-bp deletion (p.L367fs*46) or type 2, a 5-bp TTGTC insertion (p.K385fs*47). Recent studies have suggested phenotypic and prognostic differences between these two variants (Tefferi et al. Blood 2014, Leukemia 2014 and AJH 2014). Furthermore, data are emerging that suggest functionally-relevant structural differences between type 1 and type 2 CALR variants, including a higher alpha-helix content of the mutant C-terminus in type 2, compared to type 1 (Eder-Azanza et al. Leukemia 2014). Objectives : We used statistical models to calculate helix propensity for thirty-one unique amino acid sequences that were altered by CALR mutations and used the results to subclassify non-type 1/2 CALR mutations into “type 1-like” and “type 2-like” variants. Subsequently, we examined the prognostic relevance of these subgroups. Methods : Calculation of helix propensity, which is the percentage of residues that are predicted to be involved in the formation of an alpha-helix, was performed using AGADIR, which is a statistical approximation algorithm (Munoz et al. Biopolymers 1997). The helix tendency calculations were performed using conditions of pH 7.0, 5 and 25 °C, an ionic strength of 0.1 M and no N- or C-terminal protection. Results : 532 PMF patients were screened for JAK2, CALR and MPL mutations; the respective mutational frequencies were 58%, 24.6% and 7.3%. Among the 131 CALR-mutated cases, 98 (74.8%) harbored type 1, 15 (11.5%) type 2 and 18 (13.7%) other variants. Based on predicted helix propensity scale, the “other” CALR mutations were subclassified as type 1-like (n=12) or type 2-like (n=6) and respectively grouped with type 1 and type 2 variants, for purposes of phenotypic and prognostic comparisons. The AGADIR-derived predicted helix propensity scale was 29.69 for wild-type CALR and 8.6 or 34.17 for type 1 and type 2 mutant CALR, respectively; accordingly, CALR variants with values that are close to or above the value for wild-type CALR were classified as “type 2-like” (range 26.47-36.12) and those with values close to or below the value for type 1 as “type 1-like” (range 2.11-17.3). Comparison of “type 1/type 1-like” (n=110) and “type 2/type 2-like” (n=21) CALR mutations showed the latter to be associated with higher DIPSS-plus score (p=0.01), EZH2 mutations (p<0.01), leukocyte count >25 x 10(9)/L (p<0.01), higher circulating blast percentage (p=0.02) and palpable spleen size >10 cm (p<0.01). Comparison of “type 1/type 1-like” CALR and JAK2 mutations (n=309) showed the former to be associated with younger age, higher platelet count, lower transfusion need, higher hemoglobin level, lower leukocyte count and lower DIPSS-plus score (p<0.01 for all comparisons). None of these associations was evident during comparison of “type 2/type 2-like” CALR with JAK2 mutations. Survival was similar between patients with type 1 and “type 1-like” (p=0.8) and between type 2 and “type 2-like” (p=0.63) CALR mutations. In contrast, survival was significantly shorter in patients with type 2 (HR 2.4, 95% CI 1.2-4.8) and “type 2-like” (HR 3.2, 95% CI 1.0-10.6), when compared to those with type 1 CALR mutations. Survival was also significantly shorter with “type 2/type 2-like” vs “type 1/type 1-like” CALR mutations (p=0.003; HR 2.5, 95% CI 1.4-4.5) and the difference remained significant when analysis was adjusted for age (p=0.047), ASXL1 (p=0.003) or EZH2 (p=0.001) mutations. Similarly, compared to JAK2-mutated cases (n=309), survival was longer in patients with “type 1/type 1-like” (HR 0.4, 95% CI 0.3-0.5) but not in those with “type 2/type 2-like” (HR 0.9, 95% CI 0.5-1.6) CALR mutations; the difference in survival between JAK2 and “type 1/type 1-like” CALR mutated cases remained significant (P<0.01) when analysis was adjusted for age, ASXL1 or EZH2 mutations or DIPSS-plus score. Conclusions : CALR mutations in PMF might be subclassified into type 1-like and type 2-like variants, based on predicted helical propensity of their mutant C-terminus. The favorable impact of CALR mutations in PMF might be restricted to type 1 or “type 1-like” variants. Disclosures No relevant conflicts of interest to declare.

Abstract Background : Momelotinib is a JAK1 and JAK2 inhibitor that is currently being evaluated in phase-3 clinical trials for the treatment of myelofibrosis (MF) (NCT01969838, NCT02101268). In a phase-1/2 clinical trial of patients with MF, the drug was shown to improve anemia, reduce spleen size and alleviate symptoms (Leukemia 2013;27:1322). In the current study, we considered 100 consecutive patients from the Mayo Clinic who received momelotinib therapy, in order to identify molecular and cytogenetic predictors of treatment response and survival from the time of study entry. Methods : The study patients constituted part of a phase-1/2 clinical trial (NCT00935987) using momelotinib in MF. Details of the protocol, including inclusion and exclusion criteria were previously published (Leukemia 2013;27:1322). Response was determined by the 2006 response criteria published by the IWG-MRT. Data analysis and interpretation was carried out independent of any influence from the sponsor. Results : 100 patients with MF (median age 66 years; 58% males) were treated at the Mayo Clinic between 11/20/09 and 11/10/10. MF type was primary in 64% of the patients and post-polycythemia vera/essential thrombocythemia in 36%. DIPSS-plus risk distribution was 63% high, 36% intermediate-2 and 1% intermediate-1. Red cell transfusion dependency was documented in 49% and palpable spleen size of >5 cm (median 19 cm) in 92%. All patients were annotated for JAK2/CALR/MPL mutations with respective frequencies of 73%, 16% and 7%. Frequencies for other mutations included 42% for ASXL1 (84 evaluable) and 18% for SRSF2(78 evaluable). All patients were evaluable for karyotype, which was unfavorable in 17%. Previous treatment included other JAK inhibitors in 21 patients, thalidomide/lenalidomide/pomalidomide in 31 and hydroxyurea or other cytoreductive agents in 55. Momelotinib was initiated at 100 mg/day in 3 patients, 150 mg/day in 21, 150 mg twice-daily in 20, 200 mg/day in 3, 300 mg/day in 47 and 400 mg/day in 6. The maximum momelotinib dose was 150 mg/day in 6 patients, 150 mg twice-daily in 20, 300 mg/day in 68 and 400 mg/day in 6. Treatment duration was <6 months in 12 patients, 6-12 months in 22, 12-24 months in 19 and >24 months in 47. Genetic correlates of response to momelotinib : Overall response rate was 57% and included no complete remissions (0%), one (1%) partial remission and 57 (57%) clinical improvements (CI). Response rates for spleen/liver and anemia were 43% (91 evaluable) and 44% (68 evaluable), respectively. Transfusion independency was achieved in 25 (51%) of 49 evaluable cases. Spleen/liver response rate was significantly affected by JAK2/CALR/MPL mutational status (34% vs 73% vs 60%, respectively, and 50% in triple-negative; p=0.04), CALR mutated vs unmutated status (73% vs 37%; p=0.009), and unmutated vs mutated ASXL1 (53% vs 29%; p=0.035). Furthermore, all 8 (100%) patients who were CALR+/ASXL1- responded vs 6 (25%) of 24 CALR-/ASXL1+ vs 3 (50%) of 6 CALR+/ASXL1+ vs 16 (43%) of 37 CALR-/ASXL1- patients (p=0.003). Spleen/liver response rates were not affected by SRSF2 mutations (p=0.93) or karyotype (p=0.41). Anemia response rate was not affected by JAK2/CALR/MPL (p=0.81), ASXL1 (p=0.16), SRSF2 (p=0.12) or CALR/ASXL1 (p=0.42) mutational status or karyotype (p=0.65). The number of informative cases for EZH2, IDH, SF3B1 and U2AF1mutations were not adequate enough to warrant similar analysis. Genetic correlates of survival from time of protocol entry : Median follow-up after the institution of protocol drug therapy was 35 months (range 1-49). During this period, 57 (57%) deaths and 12 (12%) leukemic transformations were documented. On multivariable analysis, shortened survival was predicted by the presence of ASXL1 (p=0.01; HR 2.1, 95% CI 1.2-3.8) or SRSF2 (0.01; HR 2.4, 95% CI 1.2-4.8) mutations and the absence of CALR mutations (p=0.03; HR 3.2, 95% CI 1.1-8.9). Karyotype was significant on univariate (p=0.01) but not in multivariable (p=0.6) analysis that included the aforementioned mutations. The prognostic relevance of each specific mutation was DIPSS-plus independent. Conclusions : We demonstrate significant associations between CALR and ASXL1 mutational status and spleen response to momelotinib therapy in MF. We also show that momelotinib therapy did not overcome the inferior survival associated with the presence of ASXL1 or SRSF2 mutations or the absence of CALR mutations. Disclosures No relevant conflicts of interest to declare.

Abstract Introduction: The utility of patient reported symptoms and serum tryptase levels in distinguishing those with systemic mastocytosis (SM) versus mast cell activation syndrome (MCAS) versus those not meeting formal diagnostic criteria for SM or MCAS has not been systematically examined. Methods: This study was approved by our institutional review board. Patients were referred for suspected SM based on symptoms of mast cell activation, osteopenia, skin rash, etc., or had an established diagnosis of SM. All patients were given a Mastocytosis Symptom Assessment Form (MastSAF) to complete at their initial evaluation. The MastSAF is comprised of 36 symptom questions to be graded on a scale of 0 (absent) to 10 (worst imaginable), and is organized around 9 symptom clusters: gastrointestinal (8 questions), constitutional (3 questions), musculoskeletal (5 questions), cutaneous (4 questions), neuropsychological (6 questions), genitourinary (3 questions), respiratory (4 questions), angioedema (1 question), and cardiovascular (2 questions). All patients underwent bone marrow biopsy and serum tryptase level assessment. SM was diagnosed by 2008 WHO criteria. In the presence of characteristic symptoms, if clonal or abnormal mast cells were not identified, and if serum/urine mast cell mediator levels were increased, then non-SM associated, non-monoclonal MCAS was diagnosed. Results: A total 53 patients were studied. 1) SM: Of 28 patients, 13 had indolent SM (ISM), 9 aggressive SM (ASM) and 6 SM with associated hematological disease (SM-AHD) The median total symptom score was 47 (range 8-159). The median (range) for SM subgroups was: ISM 51 (9-159), ASM 55 (19-157) and SM-AHD 27 (8-131) (p=0.2). The normalized median score for individual symptom categories (total median score/no. of symptoms per category) in order of severity was cutaneous 1.9, gastrointestinal 1.8, constitutional 1.7, neuropsychological 1.3, respiratory 1.3, musculoskeletal 0.9, cardiovascular 0.3, genitourinary 0.3, and angioedema 0. Symptom severity was not significantly different among the 3 SM subgroups, except for constitutional symptoms (median score ASM 9, ISM 4, SM-AHD 2.5, p=0.02). The median (range) tryptase level was 48.4 ng/mL (8.8-282); four patients (14%) had a baseline level <20 ng/mL. The median (range) tryptase level among SM subgroups was: ISM 46.9 (8.8-225), ASM 103 (29.4-282), and SM-AHD 43.5 (28.5-233) (p=0.1). When considering patients with tryptase level ≥50 versus <50 ng/mL, symptom scores were not significantly higher in the former group with the exception of constitutional (p=0.02) and genitourinary symptoms (p=0.04). 2) MCAS: 15 patients The median total symptom score was 127 (range 2-248). The normalized median score for individual symptom categories in order of severity was neuropsychological 4.5, musculoskeletal 4.2, cutaneous 4.0, constitutional 3.3, gastrointestinal 2.1, respiratory and cardiovascular 2.0 each, genitourinary 1.7, and angioedema 1.0. The median (range) serum tryptase level at referral was 12.7 ng/mL (1.7-25.8); five patients (33%) had a baseline level >20 ng/mL. 3) Neither SM/MCAS: 10 patients The median total symptom score was 119 (range 45-177). The normalized median score for individual symptom categories in order of severity was musculoskeletal 4.2, gastrointestinal 3.6, constitutional 3.3, neuropsychological 3.3, cutaneous 3.0, cardiovascular and genitourinary 2.0 each, respiratory 1.3, and angioedema 0. The median (range) serum tryptase level at referral (n=9) was 4.8 ng/mL (2.9-6.6). 4) Comparison: MCAS vs. SM: Symptom scores were significantly higher in MCAS as compared to SM (p<0.05), except for genitourinary and respiratory symptoms, which were not significantly different. ‘Neither SM/MCAS’ vs. SM: Symptom scores (total, gastrointestinal, constitutional, musculoskeletal, cutaneous, and neuropsychological) were significantly higher in the former group (p<0.05). Other symptom scores were not significantly different. Conclusions: The spectrum and severity of patient reported symptoms was broadly similar among WHO subcategories of SM, and serum tryptase level had limited if any correlation with symptom scores. Despite the significantly higher overall symptom burden in MCAS versus SM, tryptase levels in the former group were significantly lower with values >30 ng/mL unusual. Despite overlap, the top ranked symptoms in the 3 groups were different. Disclosures No relevant conflicts of interest to declare.

Abstract Background: Momelotinib is a JAK 1/2 inhibitor that is active in the treatment of myelofibrosis (MF); a previous phase 1/2 study included 100 consecutive patients from the Mayo Clinic (Leukemia. 2015;29:741). In the current long-term study of these 100 patients, we provide a cumulative account of short and long term efficacy and toxicity data, as well as survival analysis. Methods: The current study represents sponsor-independent analysis. The study patients are part of a larger (n=166) phase-1/2 momelotinib study (NCT00935987), which was conducted in two dose-escalation (100 mg-400 mg daily doses) and dose-confirmation (300 mg daily dose) phases. Adverse events (AEs) were monitored by Common Terminology Criteria for Adverse Events (Version 4.03) and responses by the International Working Group criteria (Blood. 2013;122:1395). All statistical analyses considered clinical and laboratory parameters obtained at the time of entry to study. Results: Baseline data: 100 patients with MF (median age 66 years; 58% males) were treated between 11/20/09 and 11/10/10; 64 patients had primary MF, 22 post-polycythemia vera MF and 14 post-essential thrombocythemia MF. 73 (73%) patients harbored JAK2 mutations, 16 (16%) CALR, 7 MPL and 4 were "triple-negative"; among the 16 CALR-mutated cases, 13 were classified as "type 1/type 1-like". DIPSS-plus risk distribution (JCO 2011;29:392) was 63% high, 36% intermediate-2 and 1% intermediate-1; 49% displayed red cell transfusion-dependency, 58% constitutional symptoms, 87% palpable splenomegaly >5 cm and 50% abnormal karyotype. 94 patients were screened for ASXL1 mutations with 41 (44%) mutated and 78 for SRSF2 mutations with 14 (18%) mutated. 21 (21%) patients were previously treated with another JAK inhibitor. Current disposition: All information was updated in July 2016. To-date, after a median follow-up of 3.2 years, 88 drug discontinuations, 70 deaths and 14 leukemic transformations have been documented; median follow-up for living patients was 5.7 years (range 5.1-6.4). Among the 30 patients who are currently alive, 12 remain on study and another 5 have received stem cell transplant. Toxicity data: After a median treatment duration of 1.7 years, "momelotinib related" grade 3 or 4 AEs included thrombocytopenia (34%), neutropenia (9%), anemia (5%), increased lipase (7%), increased ALT (4%), increased AST (2%), increased ALP (2%) and headaches (2%). In addition, noteworthy grade 1 or 2 AEs included peripheral neuropathy (PN) 47%, increased lipase (14%), increased amylase (17%), increased bilirubin (13%), increased AST (21%), increased ALT (19%), increased APTT (17%), headaches (13%), dizziness (22%), nausea (23%) and diarrhea (20%). Most of the AEs, except PN, were reversible. Efficacy data and predictors of response and relapse-free survival: Clinical improvement (CI) was documented in 57% of patients, anemia response in 44%, and spleen response in 43%. 51% of transfusion-dependent patients became transfusion independent. The majority of patients also had marked improvement in their symptoms. 46 (81%) of the 57 responding patients discontinued treatment after a median treatment duration of 2.3 years. ASXL1 mutations predicted inferior CI (p=0.03) whereas relapse-free survival was adversely affected by absence of type 1/type 1-like CALR (p=0.03) or presence of unfavorable karyotype (p=0.002); among the 11 responding patients currently still receiving the drug, all had favorable karyotype and 5 had type 1/type 1-like CALR mutations. Survival analysis and risk factors : Median survival, calculated from the time of study entry, was 3.2 years with 5-year survival rate of 32%. In multivariable analysis of genetic markers, absence of type 1/type 1-like CALR (HR 2.9, 95% CI 1.1-7.2) or presence of SRSF2 (2.9, 1.5-5.4) or ASXL1 (1.8, 1.1-3.2) mutations were independently predictive of shortened survival (Figure). Conclusions: Momelotinib therapy in MF provides effective palliation in terms of anemia, splenomegaly and constitutional symptoms. However, less than 20% of treated patients enjoy durable long-term benefit and almost half experience drug-related and mostly irreversible peripheral neuropathy. Long-term survival and durability of response were superior in patients with type 1/type 1-like CALR mutations and inferior in those with ASXL1/SRSF2 mutations or unfavorable karyotype. Figure Figure. Disclosures Al-Kali: Onconova Therapeutics, Inc.: Research Funding; Celgene: Research Funding.

Abstract Background : Two previous studies have reported significant but inconsistent associations between the presence of JAK2V617F in primary myelofibrosis (PMF) and older age at diagnosis, risk of thrombosis, higher leukocyte count, and inferior survival (Tefferi, et al. BJH2005;131:320, Campbell, et al. Blood2006;107:2098). The clinical relevance of V617F allele burden in PMF has not been previously studied. Methods : Diagnosis of PMF was based on the World Health Organization criteria and study eligibility included the availability of bone marrow-derived DNA that was collected either at time of diagnosis or within one year of diagnosis. Quantitative allele specific PCR was utilized to meaure V617F allele burden. Results I. V617F-positive vs. V617F-negative comparisons: A total of 199 patients (60% males; median age 61 years) were suitable for analysis of comparisons between mutation-positive and mutation-negative disease. The Dupriez prognostic scoring system (PSS) risk distributions were 61% low-risk, 31% intermediate-risk, and 8% high-risk. Hypercatabolic symptoms were present in 27% of the patients and ≥1% peripheral blood (PB) blasts in 37%. At a median follow-up of 23 months (range 0–266), 57 patients (29%) had died, 17 (9%) developed leukemic transformation (LT) and 10 (5%) experienced major thrombosis. V617F mutational frequency was 58%. Univariate analysis identified older age (p=0.0007), platelet count ≥ 100 x 109/L (p=0.05), and PB blast percentage < 3% (p=0.001) as being associated with a positive mutational status; all three variables sustained their significance during multivariable analysis. The presence of the mutation did not affect the incidence of thrombosis (p=0.78), overall survival (p=0.22) or leukemia-free survival (p=0.5). Results II. Clinical correlates of V617F allele burden: Quantitative measurement of V617F allele burden was performed in 129 patients that were divided into four groups: V617F-negative (n=53) and V617F-positive with mutant allele burden in the lower quartile (n=19), middle quartiles (n=38), or upper quartile (n=19) range (median and range of V617F allele burden ratio was 29% and 1% to 74%). Kaplan-Meier plots revealed significantly shortened overall (Figure; p = 0.0008) and leukemia-free (p = 0.01) survival for the lower quartile allele burden group; survival significance was sustained in a multivariable analysis that included the Dupriez PSS. Lower quartile allele burden was also associated with lower leukocyte count (p = 0.003) and presence of hypercatabolic symptoms (p=0.05). Thrombosis incidence was not affected by allele burden. Conclusions: In PMF, patients with a low V617F allele burden, compared to those with either undetectable (i.e. wild-type) or higher allele burden, display significantly shorter overall and leukemia-free survival. In contrast, the presence or absence of the mutation, by itself, does not result in distinct groups that differ significantly in terms of survival, LT, or incidence of thrombosis. These data suggest that a low V617F allele burden in PMF is a surrogate for the development of dominant V617F-negative subclones that are more likely to undergo LT. Figure Figure

Abstract BACKGROUND: Splenectomy is performed for palliating symptoms in patients with primary myelofibrosis (PMF; as well as post essential thrombocythemia myelofibrosis/ post polycythemia myelofibrosis (Mesa et. al. Cancer2006;107(2):361–70). Pre-operative computed tomograms (CTs) of the spleen are frequently performed for estimating spleen size and anatomy, but sometimes raise concern over radiographic splenic masses. We performed a retrospective analysis of splenectomized PMF patients to determine the predictive value of CT in these patients. METHODS: Splenectomized patients, with confirmed PMF (and POST ET/PV MF), with an available pre-operative CT scan were included. Pre-operative CT scans were reviewed in a blinded fashion by a radiologist (B.B.), and histopathology was concurrently reviewed in a blinded fashion by a hematopathologist (C.Y.L.), with attention for radiographic evidence of splenic masses, splenic infarction and hemorrhage, evidence of extra-splenic masses. Additionally splenic volume was calculated by CT through an algorithm using maximal splenic length, width, and slice size (prorated ellipsoid where volume = (30+.58(XxYxZ)). Results from each review were compared and analyzed against clinical outcomes and documented splenic mass. RESULTS: Thirty-eight patients had concurrent CT and splenic pathology available underwent splenectomy for myelofibrosis (20 PMF; median age at diagnosis 64.6 years (range (46–79), 52% males). Splenic volume estimations by CT correlated well with splenic mass measurements. Splenic volume estimation by CT was 2365 CC (range 736–11355 CC), compared with a measured median splenic mass of 2000 mg (range 730–11750 mg) (bivariate analysis p<0.001). Splenic lesions were identified in a total of 33 patients (87%), 10 only by histopathology (30%), 3 only by CT (9%), and 20 by both (61%). Histopathologically 15 patients had localized hemorrhage, 13 had splenic infractions, and 8 had nodular foci of extramedullary hematopoiesis. Only 2 patients had evidence of an alternative malignancy (concurrent chronic lymphocytic leukemia (CLL, n =1) or systemic mast cell disease (n = 1). CT was very sensitive for detecting focal low density lesions (LDLs), which are roughly spherical regions of decreased contrast enhancement in the spleen, and detected the majority of macroscopic lesions. The presence of splenic infarctions histologically was associated with decreased post splenectomy survival (p=0.02; median 7.2 months vs. 15.0 months), however the sensitive (but not specific) presence of LDL lesions by CT did not have prognostic significance. The CT appearance of splenic hemorrhage was nonspecific, and since these areas of parenchymal hemorrhage were likely subacute/chronic, they could not be reliably distinguished from other LDLs. CONCLUSIONS: Pre-operative CT in patients whom undergo palliative splenectomy for myelofibrosis is a sensitive tool for determining the presence of small splenic lesions (hemorrhage, infarction and EMH). Additionally splenic volume estimation by CT, correlates well with measured splenic mass and may assist in operative planning. Splenic lesions in PMF (post ET/PV MF) by CT rarely represented an alternative malignant process, and should likely not be the sole indication for splenectomy. Splenic infarctions were associated with decreased survival after splenectomy, however CT is not always able to distinguish these lesions from EMH and hemorrhage.

Background: Myelodysplastic syndrome (MDS)/myeloproliferative neoplasm (MPN) with ring sideroblasts and thrombocytosis (MDS/MPN-RS-T) was formally included as a unique WHO-defined entity in the 2016, iteration of the classification of hematological neoplasms (under MDS/MPN overlap syndromes). Patients with MDS/MPN-RS-T have features of MDS-RS-single lineage dysplasia (SLD), persistent thrombocytosis (platelet count ≥450x109/L), with proliferation of large atypical megakaryocytes. Anemia, including red blood cell transfusion dependency (RBC-TD) is a major problem. While extensive studies have documented erythroid response rates (ERR) to erythropoiesis stimulating agents (ESA) in MDS and MDS-RS-SLD, the data in MDS/MPN-RS-T is less clear. We carried out this study to asses ERR in ESA treated patients with MDS/MPN-RS-T. Methods: After approval by the IRB, patients with 2016, WHO-defined MDS/MPN-RS-T were included in the study. The bone marrow (BM) morphology, cytogenetics and BM RS% were retrospectively reviewed. All study patients underwent next generation sequencing for 29 myeloid-relevant genes, obtained on BM mononuclear cells, at diagnosis, or at first referral, by previously described methods (Patnaik et al., BCJ 2016). Treatment details, including the type of ESA used, dose administered, side effects and reason for discontinuation were retrospectively abstracted. Erythroid responses were assessed using the 2006, international working group (IWG) MDS and the 2015, IWG MDS/MPN response criteria. Results: Forty seven patients with MDS/MPN-RS-T were identified, of which 37 (79%) patients received ESA treatment at any time point during their disease course; median age 73 years (range, 52-93), 46% male.The hemoglobin at diagnosis (HB) and baseline erythropoietin (EPO) levels were 9.1 gm/dL (range, 6.6-12.1) and 39 IU/L (range, 8-500), respectively. Ten (29%) patients were RBC-TD at baseline. None of the 37, ESA-treated patients were on concomitant cyto-reductive therapy for thrombocytosis. Twenty (54%) patients were treated with erythropoietin-a, 13 (35%) with darbepoetin, and 4 (11%) with both sequentially. Median doses were 40,000 IU weekly (range, 20,000-80,000) for erythropoietin-a and 200 mcg every 2 weeks (range, 100-500), for darbepoetin. Median treatment duration was 14 months (range, 1-173) and causes for discontinuation included; ESA failure/loss of response in 20 (54%), sustained HB rise in 1 (3%) and other causes, including adverse events in 4 (11%) patients. With regards to safety, the following events were considered potentially ESA related; treatment emergent hypertension in 2 (5%), venous thromboembolism, ischemic stroke and splenic infarction in 1 (3%) patient each, respectively. All patients with thrombotic/ischemic events had been on low dose aspirin prophylaxis. Erythroid responses by the IWG MDS and MDS/MPN response criteria were assessable in 35 (95%) patients: with 16 (46%) meeting criteria for an erythroid response, by both assessment systems. The median duration of ER was 20 months (range, 2-172). In comparison to ESA non-responders, those that responded were more likely to have baseline EPO levels ≤44 IU/L (ROC analysis; median, 28 vs 112 IU/L; p=0.0080), while there was a trend for inferior responses associated with RBC-TD (p=0.0857). Age, gender, baseline white blood cell and platelet counts, type of ESA used, BM RS %, JAK2V617F, SF3B1, DNMT3A, TET2 and ASXL1 mutational status did not impact ESA response (Table 1). On a univariate survival analysis (OS), survival was not significantly different between ESA responders vs non-responder (median OS, 76 vs 45 months; p=0.2929). After ESA failure, 7 (19%) patients received hypomethylating agents (HMA), while 5 (14%) received lenalidomide. There were no erythroid responses to HMA, while 1 of 3 (33%) assessable lenalidomide treated patients achieved a morphological complete response. Conclusion: Erythropoiesis stimulating agents are effective first line therapies for the management of anemia in patients with MDS/MPN-RS-T, with 46% achieving an erythroid response (median duration of response of 20 months). Low baseline endogenous EPO level (<44 IU/L) was the best predictor of response, with a trend towards an inferior response in the presence of RBC-TD. In the context of clonal thrombocytosis, potentially related thrombotic/ischemic events were documented in 8% of patients. Disclosures Al-Kali: Astex Pharmaceuticals, Inc.: Research Funding. Patnaik:Stem Line Pharmaceuticals.: Membership on an entity's Board of Directors or advisory committees.

Introduction: Myelodysplastic syndrome/myeloproliferative neoplasm (MDS/MPN) overlap syndromes consist of 5 distinct WHO-defined entities; namely chronic myelomonocytic leukemia (CMML), atypical chronic myeloid leukemia, BCR/ABL1- (aCML), juvenile myelomonocytic leukemia (JMML), MDS/MPN with ring sideroblasts and thrombocytosis (MDS/MPN-RS-T), and MDS/MPN, unclassifiable (MDS/MPN-U) (Arber et al., Blood 2016). With the notable exception of JMML, a bona fide RASopathy, the other entities are characterized by clinical heterogeneity and molecular diversity. Loss of function TET2 mutations (TET2MT) are common in myeloid neoplasms, especially CMML (60%), and are known leukemogenic drivers. We carried out this study to assess the TET2 mutational landscape and phenotypic correlates in patients with MDS/MPN overlap syndromes. Methods: After approval by the institutional review board, adult patients with WHO defined MDS/MPN overlap syndromes were included; with the exception of JMML. The BM morphology, cytogenetics and 2016, WHO-diagnoses were retrospectively reviewed and all patients underwent targeted next generation sequencing for 29 myeloid-relevant genes, obtained on BM mononuclear cells, at diagnosis, or at first referral, by previously described methods (Patnaik et al., BCJ 2016). Results: Five hundred and four patients were included in the study; including 387 (77%) with CMML, 48 (10%) with MDS/MPN-RS-T, 17 (3%) with aCML and 52 (10%) with MDS/MPN-U. The median age at diagnosis was 71 (range, 18-99) years, and 333 (66%) were male. TET2MT were seen in 212 (42%) patients, with the frequency of other mutations being: ASXL1 45%, SRSF2 40%, NRAS 15%, SF3B1 13%, CBL, RUNX1 and SETBP1 12% each, and JAK2 V617F 11% (Figure B). Among the MDS/MPN overlap syndromes, TET2 was more frequently mutated in CMML (49%) and aCML (47%) compared to MDS/MPN-RS-T (10%) and MDS/MPN-U (15%). The prevalence of patients with TET2MT increased with age, a finding consistent across all MDS/MPN subtypes (Figure C). Overall, 341 TET2MT were identified in 212 patients (mean 1.6 variants/patient, range 0-5): 120 (24%) had >1 TET2MT, while 113 (22%), 5 (1%) and 2 (0.4%) had 2, 3 and 5 mutations, respectively. CMML and aCML patients were more likely to have an age-independent increase in multiple TET2MT (28% and 24%), in comparison to MDS/MPN-RS-T (4%) and MDS/MPN-U (8%). TET2 MT spanned the entire coding sequence and were mostly truncating (78%, Figure A): 59 (17%) were missense, 14 (4%) involved the splice-donor/acceptor sites, 2 (0.5%) were in-frame deletions, 129 (38%) were nonsense, and 137 (40%) were frameshift mutations. Overall, the distribution of TET2MT was superimposable across CMML, aCML, and MDS/MPN-U; the only exception being the absence of splice site mutations in the latter two. One hundred and eighty-seven (55%) TET2MT were secondary to pathogenic single nucleotide variants (SNV), while the remainders were secondary to deletions (25%) and insertions (15%). Transitions comprised the most frequent type of SNV (65%), with the C:G>T:A being the most common (56%). Patients with MDS/MPN overlap syndrome and TET2MT were more likely to have additional gene mutations compared to wild type patients (mean mutation number 3.1 vs 2.1, p<0.0001), with common co-mutations being SRSF2 (51%), ASXL1 (42%), and CBL (17%). The median overall survival (OS) of the entire cohort was 29 (range, 0-170) months; 29 months for CMML, 63 months for MDS/MPN-RS-T, 14 months for aCML, and 25 months for MDS/MPN-U. On univariate analysis, OS was superior in CMML patients with TET2MT (35 months) compared to wild type cases (21 months, p<0.0001, Figure D), and in CMML patients with >1 TET2MT (41 months) in comparison to wild type (21 months, p<0.0001) and single TET2MT (29 months, p=0.0476) cases (Figure E). These observations were not seen in patients with aCML, MDS/MPN-RS-T, and MDS/MPN-U. Conclusion: Our study demonstrates that TET2MT are among the most frequent mutations in patients with MDS/MPN overlap syndromes (42%), especially CMML (49%), with an age-dependent increase in the frequency and number of TET2MT. Mutations in TET2 were found to span the entire coding sequence, with truncating mutations being more common (78%). Importantly, in CMML, TET2MT, including number of TET2MT, were associated with favorable survival outcomes. Figure Disclosures Al-Kali: Astex Pharmaceuticals, Inc.: Research Funding. Patnaik:Stem Line Pharmaceuticals.: Membership on an entity's Board of Directors or advisory committees.

Introduction: Chronic myelomonocytic leukemia (CMML), an aggressive myeloid malignancy, can be categorized into two subtypes, proliferative CMML (pCMML) and dysplastic (dCMML), based on a white blood cell (WBC) count of ≥ 13 x 109/L for the former (Arber et al. Blood 2016). While this WBC cut off is somewhat arbitrary, patients with pCMML have unique phenotypic features and a shorter survival. We carried out this study to assess the genomic, transcriptomic and epigenetic landscapes of these two CMML subtypes. Methods: Peripheral blood (PB) and bone marrow (BM) mononuclear cells (MNC) were obtained from WHO-defined CMML patients. Next generation sequencing (NGS) using a 36-gene panel was performed on 350 patients with Illumina HiSeq4000 platform with median read depth of 400X. RNA sequencing (RNA-seq) was performed on 25 patients by bulk whole transcriptome sequencing using Illumina TruSeq. DNA immunoprecipitation sequencing (DIP-seq) was performed on 18 patients using 5-methylcystocine (5mC), 5-hydroxymethylcytosine (5hmC) and bridging monoclonal antibodies with subsequent paired-end sequencing using HiSeq4000. Chromatin immunoprecipitation sequencing (ChIP-seq) was performed on 30 patients with Illumina HiSeq2500 to a depth of 25 million for histone 3 lysine 4 monomethylation (H3K4me1) and histone 3 lysine 4 trimethylation (H3K4me3) and 50 million reads for histone 3 lysine 27 trimethylation (H3K27me3) and Input per sample. Results: Five hundred and seventy-three patients with WHO defined CMML were included; median age 71 years (range 18-95 years), 67% males. 282 patients had pCMML (49%), while 291 (51%) had dCMML. As pre-defined, patients with pCMML were more likely to have higher absolute monocyte counts (p<0.0001), circulating immature myeloid cells (p<0.0001), PB blasts (p<0.0001), and higher lactate dehydrogenase levels (p=0.03). At last follow up 234 (41%) deaths and 70 (20%) leukemic transformations were documented. The median OS for pCMML vs dCMML in this cohort was 19 months vs 30 months (p<0.0001, Figure 1A) and validated in an independent Austrian cohort (p=0.02). Genomic profiling: NGS performed on 350 patients (BM MNC) revealed a higher frequency of NRAS (35 vs 17%, p=0.004), cumulative RAS pathway (NRAS, KRAS, CBL and PTPN11) (73 vs 47%, p=0.001), ASXL1 (p=0.003) and JAK2V617F (p=0.04) mutations in pCMML relative to dCMML (Figure 1B); while dCMML had a higher frequency of SF3B1 mutations (p=0.02). There were no differences in distribution of TET2 and SRSF2Transcriptomic analysis: RNA-seq was performed on PB MNC from RAS pathway mutant pCMML patients (n=12) and RAS pathway wildtype dCMML patients (n=13). Unsupervised clustering analysis resulted in appropriate segregation revealing distinct expression profiles between disease subtypes (Figure 1C). Compared to dCMML, 3729 genes were significantly differentially upregulated and 2658 genes were differentially downregulated in pCMML. Among genes most highly upregulated were mitotic checkpoint kinases including AURBK, PLK1, PLK2, PLK4 andEpigenetic profiling: ChIP-seq of PB and BM MNC from pCMML (n=18) and dCMML (n=12) patients and healthy, age-matched controls (n=10) revealed a global increase in H3K4me1, without significant differences in H3K4me3 or H3K27me3 occupancies (regardless of stratification by ASXL1 mutational status; 40% ASXL1mt in pCMML, 30% dCMML) in pCMML vs dCMML (Figure 1D). H3K4me1 occupancy was also increased in a sequence-specific manner at the transcription start sites of the aforementioned mitotic kinases (PLK1 and WEE1). DIP-seq was performed on PB MNC to assess global differences in 5-mC and 5-hmC levels, between pCMML (n=9) and dCMML (n=9), with no differences seen between the two subtypes (regardless of TET2 mutational status, 40% TET2mt in each subtype) (Figure 1E). Conclusions: Despite the somewhat arbitrary WBC distinction between pCMML and dCMML, clear phenotypic, genetic, transcriptomic, epigenetic and survival differences exist between the two subtypes, providing strong biological rationale for this distinction. pCMML patients have a higher frequency of oncogenic RAS pathway mutations, a unique transcriptomic profile enriched in mitotic check point kinases and a unique chromatin configuration with global and sequence specific enrichment in H3K4me1, with no significant global differences in 5mC, 5hmC, or H3K4me3 and H3K27me3 occupancy. Figure 1 Disclosures Geissler: AOP: Honoraria; Pfizer: Honoraria; AstraZeneca: Honoraria; Novartis: Honoraria; Celgene: Honoraria; Roche: Honoraria; Abbvie: Honoraria; Ratiopharm: Honoraria; Amgen: Honoraria. Al-Kali:Astex Pharmaceuticals, Inc.: Research Funding. Patnaik:Stem Line Pharmaceuticals.: Membership on an entity's Board of Directors or advisory committees.