Citations

Abstract Herein, we present the long-term follow-up of the randomized E1912 trial comparing the long-term efficacy of ibrutinib–rituximab (IR) therapy to fludarabine, cyclophosphamide, and rituximab (FCR) and describe the tolerability of continuous ibrutinib. The E1912 trial enrolled 529 treatment-naïve patients aged ≤70 years with chronic lymphocytic leukemia (CLL). Patients were randomly assigned (2:1 ratio) to receive IR or 6 cycles of FCR. With a median follow-up of 5.8 years, median progression-free survival (PFS) is superior for IR (hazard ratio [HR], 0.37; P < .001). IR improved PFS relative to FCR in patients with both immunoglobulin heavy chain variable region (IGHV) gene mutated CLL (HR: 0.27; P < .001) and IGHV unmutated CLL (HR: 0.27; P < .001). Among the 354 patients randomized to IR, 214 (60.5%) currently remain on ibrutinib. Among the 138 IR-treated patients who discontinued treatment, 37 (10.5% of patients who started IR) discontinued therapy due to disease progression or death, 77 (21.9% of patients who started IR) discontinued therapy for adverse events (AEs)/complications, and 24 (6.8% of patients who started IR) withdrew for other reasons. Progression was uncommon among patients able to remain on ibrutinib. The median time from ibrutinib discontinuation to disease progression or death among those who discontinued treatment for a reason other than progression was 25 months. Sustained improvement in overall survival (OS) was observed for patients in the IR arm (HR, 0.47; P = .018). In conclusion, IR therapy offers superior PFS relative to FCR in patients with IGHV mutated or unmutated CLL, as well as superior OS. Continuous ibrutinib therapy is tolerated beyond 5 years in the majority of CLL patients. This trial was registered at www.clinicaltrials.gov as #NCT02048813.

Abstract Background The detrimental effect of leukocytosis on survival in myeloproliferative neoplasms (MPN) has been well established for primary myelofibrosis (PMF), polycythemia vera (PV) and essential thrombocythemia (ET ) (JCO. 2018;36:310; BJH. 2020;189:291) Previous studies have also implicated leukocytosis as a risk factor for leukemic transformation (Mayo Clin Proc. 2017;92:1118) and thrombosis in MPN (Blood Adv. 2019;3:1729). However, it is currently not clear as to which component(s) of white blood cells is responsible for these observations. In the current study, we sought to examine the individual prognostic contribution of absolute neutrophil (ANC), lymphocyte (ALC) and monocyte (AMC) counts, on overall (OS), leukemia-free (LFS), and myelofibrosis-free (MFFS) survival and in ET. Methods Study patients (n=349) were retrospectively recruited from the Mayo Clinic MPN database of 1,249 WHO-defined ET patients, evaluated over five decades (1967-2021), based on availability of information on ANC, ALC and AMC. Conventional criteria were used for diagnosis and definitions of major complications, including leukemic or fibrotic transformation (Blood 2016;127:2391). Conventional statistical methods were applied using JMP Pro 14.0.0 software package, SAS Institute, Cary, NC. Multivariable analyses included previously established risk factors for survival. Results 349 patients (median age 57 years, range 18-89; females 61%) with ET were included in the study: 46% JAK2, 34% CALR, 16% triple-negative and 4% MPL mutated; IPSET risk category high 24%, intermediate 41%, and low 35%; presenting median (range) values were 13.8 g/dL (11.1-16.4) for hemoglobin, 8.2 x 10(9)/L (3.2-52) for leukocyte count, and 859 x 10(9)/L (451-3460) for platelet count; palpable splenomegaly was present in 48 (14%); median followup was 10 years (range 0-47), during which time 118 deaths, 52 fibrotic progressions, and 14 leukemic transformations were documented. Multivariable analysis identified older age (p<0.001), increased ANC (p<0.001), decreased ALC (p=0.03), and male sex (p=0.04), but not AMC (p=0.8), venous thrombosis (p=0.4), or arterial thrombosis (p=0.4), as independent risk factors for OS. ANC of ≥8 x 10(9)/L and ALC of <1.8 x 10(9)/L were determined as appropriate cut-off values by ROC analysis. Subsequent multivariable analysis using these cut-off values resulted in HR (95% CI) of 5.2 (3.4-7.9; p<0.001) for age >60 years, 3.1 (2.1-4.6; p<0.001) for ANC, and 2.0 (1.4-3.0; p<0.001) for ALC; male sex was no longer significant in this analysis (p=0.14). An operational HR-based risk score assigned 3 adverse risk points for older age (>60 years), 2 for increased ANC (≥8 x 10(9)/L) and 1 for ALC (<1.8 x 10(9)/L), resulting in an new Age Anc Alc (AAA; triple A) risk model for survival in ET with estimates of median survival ranging from 9.7 to 36.6 years (Figure 1). In addition, ALC <1.8 x 10(9)/L was associated with inferior LFS (p=0.06) and MFFS (p=0.07) while AMC as a continuous variable showed borderline significance for MFFS (p=0.18). In univariate analysis, JAK2V617F allele burden showed significant association with OS (p=0.02), LFS (p=0.05) and MFFS (p=0.001); however significance for OS was lost in mutivariable analysis that included ANC and ALC. An external validation cohort from the University of Florence (n=485) confirmed the independent survival risk contribution from age >60 years (p<0.001; HR 9.9, 95% CI 5.4-18.0), ANC ≥8 x 10(9)/L (p=0.02; 1.9, 1.1-3.5) and ALC <1.8 x 10(9)/L (p<0.001; 2.0, 1.3-3.0). The Triple A risk model was also effectively applied on the Florence validation cohort (Figure 1): median follow-up 8.4 years; 87 deaths; 43 fibrotic progression; 12 leukemic transformations. The association of ALC <1.8 x 10(9)/L (p=0.04) and AMC (p=0.002) with fibrotic transformation was also validated in the Florence cohort. Conclusions: The current study identifies increased ANC and decreased ALC as age-independent risk factors for survival in ET, thus allowing the development of a globally applicable simple to use "Triple A" risk model that is based on Age, ANC and ALC. Decreased ALC also predicted fibrotic and leukemic progression. Our observations suggest potential value for immune profiling as an additional prognostic tool in MPN. Figure 1 Figure 1. Disclosures Szuber: Novartis: Honoraria. Vannucchi: BMS: Honoraria, Membership on an entity's Board of Directors or advisory committees; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees; Incyte: Honoraria, Membership on an entity's Board of Directors or advisory committees; AbbVie: Membership on an entity's Board of Directors or advisory committees.

Abstract Background: Myelofibrosis (MF) is characterized by progressive bone marrow (BM) fibrosis resulting from aberrant megakaryopoiesis and expression of pro-inflammatory cytokines. These processes, heavily influenced by bromodomain and extraterminal domain (BET) protein-mediated gene regulation, lead to myeloproliferation and cytopenias. There is a high unmet need for a treatment that can potentially delay or reverse BM fibrosis in patients (pts) with MF. Pelabresib (CPI-0610) is a potent, first-in-class, selective, oral small-molecule BET inhibitor, which is able to modify the expression of genes involved in nuclear factor kappa B (NFκB) signaling in pts with MF. Pelabresib is currently being investigated as a monotherapy and in combination with the JAK inhibitor (JAKi) ruxolitinib (RUX), in the ongoing MANIFEST Phase 2 study (NCT02158858). Methods: In arm 1 of MANIFEST, pelabresib is administered as monotherapy to pts with MF who are intolerant/refractory to, or ineligible for RUX; in arm 2, as an 'add-on' to RUX in pts with MF who have suboptimal/lost response; and in arm 3 as combination therapy with RUX in JAKi treatment-naïve pts with MF. To evaluate the effects of pelabresib on BM biology, analyses were conducted using BM biopsy samples obtained pre-treatment and at 24 weeks post-treatment during the MANIFEST trial. Central pathology review of reticulin staining was conducted to evaluate BM fibrosis (BMF) grading and immunohistochemistry staining for changes in erythroids (ERY) and megakaryocytes (MK), respectively. Independent digital images of stained BM slides were also evaluated with a semi-quantitative cell-specific detection algorithm for reticulin density, percentage CD71+ ERY, mean number of CD61+ MK and mean distance between nuclei for CD61+ MK. Results: Exploratory analyses across the three treatment arms showed BM improvements after 24 weeks of treatment. Paired comparison by digital analysis of baseline and 24-week treatment BM biopsies from 29 pts showed reduction (range 67%-15.5%) in reticulin intersections per field in 45% (13/29) pts. Furthermore, digital analysis of CD71+ ERY and CD61+ MK from paired biopsies showed increased ERY progenitors in 50% (16/32) pts, decreased MK density in 57% (15/26) pts and decreased MK clustering in 46% (12/26) pts at 24 weeks. Decreased MK clustering correlated with decreased density of CD61+ MK in 75% pts (9/12). Correlative analysis between observed clinical responses and bone marrow improvements are ongoing and will be available for presentation at the conference. We previously reported (Talpaz M, et al. ASH 2020; Abstract 2163) that in pts with MF, pelabresib can reduce spleen volume, improve symptoms, improve bone marrow fibrosis, demonstrate increase in hemoglobin levels, and reduce transfusion burden. Updated 24-week data reflecting a higher number of evaluable pts and new long-term data at 48 weeks across the MANIFEST trial, will be presented. Conclusions: Treatment with pelabresib as monotherapy or in combination with RUX, in both RUX treatment-naïve and -experienced pts with MF, resulted in increased ERY progenitors, decreased MK density and reduction of BM fibrosis, as assessed by digital pathology. These data suggest possible disease-modifying potential for pelabresib by improving BM histology and function, leading to potential clinical benefits. Disclosures Verstovsek: Roche: Research Funding; Promedior: Research Funding; Blueprint Medicines Corp: Research Funding; Incyte Corporation: Consultancy, Research Funding; Protagonist Therapeutics: Research Funding; Genentech: Research Funding; CTI BioPharma: Research Funding; Celgene: Consultancy, Research Funding; Gilead: Research Funding; Ital Pharma: Research Funding; PharmaEssentia: Research Funding; NS Pharma: Research Funding; AstraZeneca: Research Funding; Novartis: Consultancy, Research Funding; Sierra Oncology: Consultancy, Research Funding; Constellation: Consultancy; Pragmatist: Consultancy. Salama: Mayo Clinic: Current Employment, Other: Mayo Clinic had the contractual work for the central pathology review for this study and I was one of the reviewing pathologists; Constellation Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees. Mascarenhas: AbbVie: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Kartos: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene/BMS: Consultancy, Membership on an entity's Board of Directors or advisory committees; Constellation: Consultancy, Membership on an entity's Board of Directors or advisory committees; Merck: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Geron: Consultancy, Research Funding; Prelude: Consultancy; Gilead: Consultancy, Membership on an entity's Board of Directors or advisory committees; PharmaEssentia: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Galecto: Consultancy; Promedior: Consultancy, Membership on an entity's Board of Directors or advisory committees; Merus: Research Funding; Forbius: Research Funding; CTI Biopharm: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Genentech/Roche: Consultancy, Membership on an entity's Board of Directors or advisory committees; Roche: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Incyte: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Sierra Oncology: Consultancy, Membership on an entity's Board of Directors or advisory committees; Geron: Consultancy; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding. Talpaz: Celgene: Consultancy; Imago: Consultancy; Takeda: Other: Grant/research support ; Bristol Myers Squibb: Membership on an entity's Board of Directors or advisory committees; Constellation: Membership on an entity's Board of Directors or advisory committees; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding. Mesa: La Jolla Pharma: Consultancy; Samus: Research Funding; Constellation Pharmaceuticals: Consultancy, Research Funding; Pharma: Consultancy; CTI: Research Funding; Abbvie: Research Funding; CTI: Research Funding; Genentech: Research Funding; Gilead: Research Funding; Promedior: Research Funding; Novartis: Consultancy; Celgene: Research Funding; Incyte Corporation: Consultancy, Research Funding; Sierra Oncology: Consultancy, Research Funding; AOP: Consultancy. Vannucchi: Incyte: Honoraria, Membership on an entity's Board of Directors or advisory committees; BMS: Honoraria, Membership on an entity's Board of Directors or advisory committees; AbbVie: Membership on an entity's Board of Directors or advisory committees; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees. Rampal: Incyte: Consultancy, Research Funding; Pharmaessentia: Consultancy; Blueprint: Consultancy; Disc Medicine: Consultancy; Stemline: Consultancy, Research Funding; BMS/Celgene: Consultancy; Novartis: Consultancy; Sierra Oncology: Consultancy; CTI: Consultancy; Abbvie: Consultancy; Jazz Pharmaceuticals: Consultancy; Constellation: Research Funding; Memorial Sloan Kettering: Current Employment; Kartos: Consultancy. Oh: Abbvie: Membership on an entity's Board of Directors or advisory committees; Blueprint Medicines: Membership on an entity's Board of Directors or advisory committees; Celgene Bristol Myers Squibb: Membership on an entity's Board of Directors or advisory committees; Constellation: Membership on an entity's Board of Directors or advisory committees; CTI Biopharma: Membership on an entity's Board of Directors or advisory committees; Disc Medicine: Membership on an entity's Board of Directors or advisory committees; Geron: Membership on an entity's Board of Directors or advisory committees; Incyte: Membership on an entity's Board of Directors or advisory committees; Kartos Therapeutics: Membership on an entity's Board of Directors or advisory committees; PharamaEssentia: Membership on an entity's Board of Directors or advisory committees; Sierra Oncology: Membership on an entity's Board of Directors or advisory committees. Taverna: Constellation Pharmaceuticals: Current Employment. Cui: Constellation Pharmaceuticals: Current Employment. Zavidij: Constellation Pharmaceuticals: Current Employment. Chen: Constellation Pharmaceuticals: Current Employment. Colak: Constellation Pharmaceuticals: Current Employment. Efuni: Constellation Pharmaceuticals: Current Employment. Keller: Constellation Pharmaceuticals: Current Employment. Trojer: Constellation Pharmaceuticals: Current Employment. Harrison: Galacteo: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Incyte Corporation: Speakers Bureau; Constellation Pharmaceuticals: Research Funding; Sierra Oncology: Honoraria; CTI BioPharma: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Geron: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Janssen: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Roche: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Novartis: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; BMS: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Keros: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; AOP Orphan Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Gilead Sciences: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Promedior: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Shire: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Abbvie: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau.

Abstract Monoclonal B-cell lymphocytosis (MBL) is one of the most common pre-malignant conditions and is characterized by a circulating population of clonal B-cells with an absolute clonal B-cell count < 5x10 9/L and no evidence of lymphadenopathy, organomegaly, or cytopenias. MBL can be classified by the immunophenotype: CLL-like MBL (CD5+, CD20dim), atypical MBL (CD5+, CD20+), or non-CLL-like MBL (CD5-, CD20+), as well as by the size of the clone (low-count or high-count) with low-count MBL (LC-MBL) defined as clonal B-cell <0.5x10 9/L or percent clonal B-cell count <85% out of total B-cell count. The prevalence of MBL varies depending on detection methods and population tested. In a Spanish screening study of 608 individuals, they identified 73 MBLs (12%) with CLL-like MBL; moreover, these authors also evaluated overall survival (OS) compared to 290 individuals without MBL and found a significantly shorter OS among these predominantly LC-MBLs. Here, we evaluate the prevalence and OS of LC-MBL in a large screening cohort of 8,297 individuals. Study participants from the Mayo Clinic Biobank, a large-scale biorepository of adult patients, who had no prior history of hematologic malignancy, provided blood samples between 7/2009 to 4/2021. Stored peripheral blood mononuclear cells were screened for MBL with an eight-color flow cytometry assay capable of detecting clonal B-cell event to the 0.005% level. We classified each MBL by immunophenotype as CLL-like MBL, atypical MBL, and non-CLL-like MBL. Individuals with more than one immunophenotype were classified into one immunophenotype based on the following hierarchy: CLL-like MBL, then atypical MBL, then non-CLL like MBL. Based on previously published evidence, individuals were also classified by clonal counts using the percent clonal B-cell count <85% out of the total B-cell count to define LC-MBL. Individuals were followed from sample date to the earliest of death, loss to follow-up, or 5/31/2021. OS for LC-MBL and controls (individuals who screened negative for MBL) was assessed by Kaplan-Meier method. Age- and sex-adjusted OS was analyzed using inverse weights methods. Cox regression was used to calculate hazard ratios (HR) and 95% confidence intervals (CIs), adjusted for age and sex. We screened 8,297 individuals 40 years or older (median age 67 years, 39% male) and identified 1,326 (16%) with LC-MBL and 6,651 (80%) controls. Those individuals detected with high-count MBL (N=90, 1%) or individuals who had insufficient cells for flow cytometry interpretation (N=230, 3%) were excluded from subsequent analyses. The prevalence of LC-MBL was higher in males (21%) than females (14%; p<0.01) and significantly increased with age (p<0.01) ranging from 3% among those 40-49 years, 10% among those 50-59 years, 15% among those 60-69 years, 23% among those 70-79 years, and 29% for those 80+ years. Sixty-one individuals had clones with more than one type of immunophenotype. Based on our hierarchy, CLL-like MBL was the most common (N=1,155), followed by non-CLL-like (N=168) and atypical MBL (N=67). The median follow-up time in our cohort was 26 months (range 0-142), and 432 individuals had subsequently died. The 5-year and 10-year OS adjusted for age and sex among LC-MBLs was 95% and 87%, respectively; control estimates were 95% and 84%, respectively. We did not observe a significant difference in OS between those individuals with LC-MBL versus controls (HR=0.98, CI=0.77-1.24, P=0.84, Fig 1a), nor when we stratified individuals by age <65 (P=0.77) or age >= 65 (P=0.68). Among females, OS was longer among LC-MBL compared to controls (HR=0.61, CI=0.38-0.97, P=0.04); but no evidence of a difference in OS among males was observed (HR=1.22, CI=0.92-1.62, P=0.17). When we evaluated OS by MBL immunophenotype, we observed no statistically significant difference (Fig 1b, log rank P=0.44). When we stratified the MBLs by immunophenotype versus controls, we also did not observe a difference: CLL-like (HR=0.91, CI=0.71-1.18, P=0.5), atypical (HR=1.73, CI=0.92-3.27, P=0.09), non-CLL like (HR=0.98, CI=0.58-1.66, P=0.95). In the largest MBL screening cohort to date, LC-MBL was a common condition among adults 40 years or older reaching a prevalence as high as 29% among individuals 80 years of age or older. OS among those with and without LC-MBL was similar, regardless of immunophenotype and age. The longer survival in females with MBL versus controls requires further evaluation. Figure 1 Figure 1. Disclosures Parikh: Pharmacyclics, AstraZeneca, Genentech, Gilead, GlaxoSmithKline, Verastem Oncology, and AbbVie: Membership on an entity's Board of Directors or advisory committees; Pharmacyclics, MorphoSys, Janssen, AstraZeneca, TG Therapeutics, Bristol Myers Squibb, Merck, AbbVie, and Ascentage Pharma: Research Funding. Kay: Juno Therapeutics: Membership on an entity's Board of Directors or advisory committees; Pharmacyclics: Membership on an entity's Board of Directors or advisory committees, Research Funding; Bristol Meyer Squib: Membership on an entity's Board of Directors or advisory committees, Research Funding; Targeted Oncology: Membership on an entity's Board of Directors or advisory committees; TG Therapeutics: Research Funding; Sunesis: Research Funding; Dava Oncology: Membership on an entity's Board of Directors or advisory committees; Genentech: Research Funding; Behring: Membership on an entity's Board of Directors or advisory committees; AstraZeneca: Membership on an entity's Board of Directors or advisory committees; Abbvie: Membership on an entity's Board of Directors or advisory committees, Research Funding; Acerta Pharma: Research Funding; MEI Pharma: Research Funding; Tolero Pharmaceuticals: Research Funding; Janssen: Membership on an entity's Board of Directors or advisory committees; CytomX Therapeutics: Membership on an entity's Board of Directors or advisory committees; Oncotracker: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees, Research Funding; Agios Pharm: Membership on an entity's Board of Directors or advisory committees; Morpho-sys: Membership on an entity's Board of Directors or advisory committees; Rigel: Membership on an entity's Board of Directors or advisory committees. Shanafelt: Genentech, Pharmacyclics: Research Funding.

Abstract Background Cytogenetic abnormalities at diagnosis are relatively uncommon in essential thrombocythemia (ET). In the current study of 818 consecutive patients with ET who were fully annotated for karyotype, we describe the spectrum and prevalence of cytogenetic abnormalities at diagnosis, followed by a comprehensive assessment of phenotypic and molecular correlates and prognostic relevance. Methods The study cohort consisted of 818 consecutive patients with ET that were diagnosed according to the World health Organization 2016 criteria and underwent evaluation between 1967-2021. In order to minimize the inadvertent inclusion of patients with masked polycythemia vera, JAK2 mutated cases with hemoglobin (Hb) level >16 g/dL in women and 16.5 g/dL in men were excluded; similarly, cases with anemia defined by sex adjusted Hb level of <11 g/dL in women and <12.5 g/dL in men were also excluded, in order to avoid inadvertent inclusion of patients with prefibrotic myelofibrosis. Cytogenetic studies were performed either at or within one year of diagnosis and reported according to the International System for Human Cytogenetic Nomenclature. Disease status and survival information was updated in May 2021. JMP Pro 16.0.0 software package, SAS Institute, Cary, NC was utilized for all analyses. Results Prevalence and spectrum of cytogenetic abnormalities Karyotype was normal in 755 patients (92%), showed loss of Y chromosome (-Y) in 16 (2%), and showed abnormalities other than -Y in 47 (5.7%); most common abnormalities included del(20q) (n=10, 21%), trisomy 9 (n=8, 17%), trisomy 8 (n=2, 4%), del(5q) (n=2, 4%), and del(3p) (n=2, 4%). Other sole cytogenetic abnormalities were identified in 18 (38%) patients. Phenotypic and molecular correlates Abnormal karyotype, other than -Y, in comparison with normal karyotype was associated with older age (median age; 63 vs 58 years, p=0.02), lower hemoglobin level (p=0.003), and a higher incidence of arterial thrombosis prior to/at diagnosis (25% vs 13%; p=0.03). 603 patients were annotated for driver mutations; abnormal/normal/-Y frequencies were 78%/60%/71% for JAK2, 22%/26%/14% CALR, 0%/3%/0% MPL and 0%/10% /14% triple negative (p=0.31). NGS information was available in 226 patients and showed absence of ASXL1 mutation in all patients with abnormal karyotype vs 8/211 (4%) with normal karyotype vs 2/4 (50%) with -Y (p<0.0001). Disease transformation and overall-survival. At a median follow-up of 9.6 years (range; 0.01-49.4 years), a total of 96 patients (12%) underwent fibrotic transformation: 6 (13%) with abnormal karyotype, 89 (12%) with normal karyotype and 1 (6%) with -Y (p=0.77). Leukemic transformation rates were also similar with respective frequencies of 4%, 3% and 0% (p=0.71). Abnormal karyotype and -Y were associated with inferior survival with median of 12 years (range; 0.1-34) and 9 years (range; 0.01- 19.9), respectively, compared to 21 years (range; 0.01-49.4) for normal karyotype (p<0.0001) (Figure). In univariate analysis, risk factors for overall survival included abnormal karyotype (p=0.001), - Y (p=0.004), age >60 years (p<0.0001), leukocytosis >11 x10 9/L (p<0.0001), male gender (p=0.0003), and history of thrombosis (p=0.001). During multivariable analysis, abnormal karyotype other than -Y (p=0.003), age >60 years (p<0.0001), leukocytosis >11 x10 9/L (p=0.001), and male gender (p=0.01) remained significant. Additional analysis suggested individual prognostic impact for del(20q) (p=0.04) and also for trisomy 9 (p=0.09) and other abnormalities (p=0.07), with borderline significance. Conclusion The current study confirms the association of abnormal karyotype in ET with older age, lower hemoglobin level, and history of arterial thrombosis, and its mutual exclusivity with ASXL1 mutations. Our observation regarding the independent adverse impact of abnormal karyotype other than -Y, on overall survival, in the absence of association with fibrotic or leukemic transformation, requires clarification from additional studies, which should also investigate the effect of specific abnormalities. Figure 1 Figure 1. Disclosures Szuber: Novartis: Honoraria.

Abstract Background In addition to its influence on survival, leukocytosis in myeloproliferative neoplasms (MPN) has also been implicated as a risk factor for thrombosis, including venous thrombosis in PV (Blood Cancer J, 2017;7:662) and arterial thrombosis in ET (Blood. 2011;117:5857). In the current study, we sought to clarify the individual prognostic contribution of absolute neutrophil (ANC), lymphocyte (ALC) and monocyte (AMC) counts, for arterial and venous thrombotic events in essential thrombocythemia (ET) and polycythemia vera (PV). Methods The current study included 487 patients with ET (n=349) or PV (n=138), recruited from the Mayo Clinic MPN database, based on availability of information on ANC, ALC and AMC. Conventional criteria were used for diagnosis (Blood 2016;127:2391) and definitions of major vascular events (Blood Cancer J. 2018;8:25). Conventional statistical models were applied using JMP Pro 14.0.0 software package, SAS Institute, Cary, NC. Multivariable analyses included previously established risk factors for arterial or venous thrombosis. Results Essential thrombocythemia patients: 349 patients (median age 57 years, range 18-89; females 61%) with ET were included in the study: 46% JAK2, 34% CALR, 16% triple-negative and 4% MPL mutated; IPSET risk category high 24%, intermediate 41%, and low 35%; presenting median (range) values were 13.8 g/dL (11.1-16.4) for hemoglobin, 8.2 x 10(9)/L (3.2-52) for leukocyte count, and 859 x 10(9)/L (451-3460) for platelet count; palpable splenomegaly was present in 48 (14%) patients and cardiovascular risk factors in 56%; median follow-up was 10 years (range 0-47). There were 38 (11%) documented venous events at diagnosis and 31 (9%) after diagnosis and 42 (12%) arterial events at diagnosis and 64 (18%) after diagnosis. Polycythemia vera patients: 138 patients (median age 62 years, range 20-94; females 50%) with PV were included in the study; presenting median (range) values were 17.9 g/dL (16.1-24) for hemoglobin, 11.8 x 10(9)/L (2.7-65.8) for leukocyte count, and 434 x 10(9)/L (44-1679) for platelet count; 57% of patients presented with leukocytosis >11 x 10(9)/L; palpable splenomegaly was present in 37 (27%) patients; abnormal karyotype was documented in 17% of patients. Median follow-up was 11 years (range 0.03-36.7). There were 22 (16%) documented venous events at diagnosis and 21 (16%) after diagnosis and 28 (20%) arterial events at diagnosis and 15 (11%) after diagnosis. ANC/ALC/AMC associations with thrombosis in ET and PV: In both ET and PV, ANC/ALC/AMC did not correlate with arterial thrombosis at/prior to diagnosis (p>0.1 in all instances). By contrast, in both ET and PV, higher ANC (p=0.05 and 0.04, respectively) and higher AMC (p=0.005 and 0.07), but not ALC (p=0.6 and 0.7), were correlated with venous thrombosis at/prior to diagnosis. Arterial thrombosis-free survival was not affected by ANC/ALC/AMC in either ET or PV (p>0.1 in all instances). By contrast, venous thrombosis-free survival in both ET and PV was compromised by higher ANC (p=0.05 and 0.003, respectively), but not ALC or AMC. The significant association between higher ANC and inferior venous thrombosis-free survival in both ET (p=0.01) and PV (p=0.007) was sustained during multivariable analysis that included history of venous thrombosis, age and sex; the only other variable of significance was older age in ET (p<0.001). The significant association between ANC and venous thrombosis-free survival was also noted in an external cohort of PV patients from the University of Florence (n=576). Conclusions: The current study identifies ANC as having a direct correlation with venous thrombosis in both ET and PV, independent of currently known risk factors. An additional risk contribution from AMC was apparent for events occuring at or prior to but not after diagnosis. Taken together, these observations flag both neutrophils and monocytes as potential contributors to venous but not arterial thrombosis in MPN, at least not by themselves. Additional collaborative studies are ongoing in order to integrate and reconcile our observations in the context of neutrophil/lymphocyte ratio (Carobbio et al) and JAK2V617F allele burden (Loscocco et al), on venous thrombosis-free survival in PV, reported in concomitantly submitted ASH 2021 abstracts, especially in light of the relatively small number of events in the current study. Disclosures Barbui: Novartis: Membership on an entity's Board of Directors or advisory committees, Research Funding; AOP Orphan: Membership on an entity's Board of Directors or advisory committees, Research Funding. Vannucchi: AbbVie: Membership on an entity's Board of Directors or advisory committees; Incyte Corporation: Honoraria, Membership on an entity's Board of Directors or advisory committees; Bristol Myers Squibb: Honoraria, Membership on an entity's Board of Directors or advisory committees; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees.

Abstract Background Current NCCN and ELN guidelines lack supporting evidence in regards to initiation of cytoreductive therapy in essential thrombocythemia (ET) with extreme thrombocytosis (ExT) ≥1500 x 10 9/L (NCCN guidelines: myeloproliferative neoplasms, version 2. 2019, Barbui, Leukemia, 2018).; we sought to determine prevalence and establish phenotype and genotype correlates for ET with ExT and assess its impact on thrombotic and bleeding events, in the context of aspirin therapy or cytoreduction. Methods 1,249 WHO-defined ET patients evaluated over five decades (1967-2021) were retrospectively recruited from the Mayo Clinic. Conventional criteria were used to define major arterial and venous thrombosis and major hemorrhage. Conventional statistical methods were applied using JMP Pro 14.0.0 software package, SAS Institute, Cary, NC. Results i) Phenotype and genotype correlates Among 1,249 consecutive patients with ET, 104 (8%) displayed Ext ≥1500 x 10 9/L, at time of initial diagnosis; these patients were characterized by younger age (median 47 vs 59 years; p<0.001) female gender (80% vs 62%; p<0.001), CALR mutation (39% vs 25%; p=0.004), lower hemoglobin (median 13.1 vs 13.7 g/dl; p<0.0001), leukocytosis ≥11 x 10 9/l (42% vs 23%; p<0.0001), and palpable splenomegaly (22% vs 14%; 0.03); multivariable analysis confirmed associations with age, anemia, leukocytosis, and CALR mutation. Acquired von Willebrand syndrome was reported in 4/9 (44%) vs 27/78 (35%) tested patients, with or without Ext ≥1500 x 10 9/L, respectively (p=0.57); however, comparison using platelet ≥1000 x 10 9/L resulted in near-signficant difference (46% vs 29%; p=0.11). NGS was performed in 297 patients and showed a non-sigificant association with U2AF1 mutations (5% vs 0.4%; p=0.11). ExT ≥1500 x 10 9/L was present in 25/986 (3%), 42/891 (5%), and 15/558 (3%) in the validation cohort; the limited number of cases precluded comparative analyses. ii )Correlation with vascular events at/prior to diagnosis Arterial or venous thrombosis at/prior to diagnosis occurred in 190 (15%) and 111 (9%) patients, respectively, and major hemorrage in 50 (4%). Ext ≥1500 x 10 9/L was associated with major hemorrhage (HR 2.9; 1.3-6.3), but not with arterial (p=0.15) or venous (p=0.41) thrombotic events, at/prior to diagnosis. Instead, multivariable analysis for events at/prior to diagnosis identified male gender (p=0.02), JAK2 mutation (p=0.01), and cardiovascular risk factors (p=0.001) as risk factors for arterial thrombosis and JAK2 mutation (HR 2.8; 1.4-5.7) as a risk factor for venous thrombosis. iii ) Correlation with vascular events after diagnosis At median follow-up of 10 years, arterial or venous thrombosis occurred in 222 (18%) and 97 (8%) patients, respectively, and major hemorrage in 128 (11%). Ext ≥1500 x 10 9/L at diagnosis was not associated with arterial (p=0.35) or venous (p=0.23) thrombosis-free survival or hemorrhage-free survival (p=0.24). Instead, multivariable analysis identified age >60 years, presence of cardiovascular risk factors, and history of arterial thrombosis, as risk factors for arterial thrombosis-free survival; and male gender and history of venous thrombosis as risk factors for venous thrombosis-free survival; and age >60 years and leukocytosis of ≥11 x 10 9/L as risk factors for hemorrhage-free survival. In addition, aspirin therapy was idependently protective of venous thrombosis (HR 0.5; 0.2-0.9), and also of arterial thrombosis, in univariate analysis (HR 0.6; 0.3-0.9), without being associated with an increased risk of major hemorrhage (p=0.64); by contrast, beneficial effect from cytoreductive therapy was not evident for either arterial (p=0.37) or venous (p=0.77) thrombosis. In low-risk patients with Ext ≥1500 x 10 9/L, both aspirin and cytoreductive therapy were protective of venous events (Figure 1), without affecting hemorrhage-free survival. Conclusion ExT ≥1500 x 10 9/L in ET was associated with major hemorrhage at diagnosis but did not affect thrombosis-free or hemorrhage-free survival. Initial therapy with aspirin and/or cytoreductive therapy was protective of venous events in ET patients with ExT ≥1500 x 10 9/L, including those with low-risk disease, without enhancing the risk of hemorrhage. The limited number of informative cases with ExT in the validation cohort, underscore the foreseeable challenges associated with controlled studies. Figure 1 Figure 1. Disclosures Szuber: Novartis: Honoraria. Vannucchi: AbbVie: Membership on an entity's Board of Directors or advisory committees; Bristol Myers Squibb: Honoraria, Membership on an entity's Board of Directors or advisory committees; Incyte Corporation: Honoraria, Membership on an entity's Board of Directors or advisory committees; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees. Barbui: AOP Orphan: Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Membership on an entity's Board of Directors or advisory committees, Research Funding.

Abstract Introduction Monoclonal B-cell lymphocytosis (MBL), monoclonal gammopathy of undetermined significance (MGUS), and clonal hematopoiesis (CH) are three common premalignant hematological conditions. MBL is a precursor to chronic lymphocytic leukemia (CLL), MGUS is a precursor to both multiple myeloma (MM) and Waldenström macroglobulinemia (WM), and CH is a possible precursor to myeloid disease. All three conditions are independently associated with aging. Furthermore, there is evidence that all three conditions are associated with increased risk of infection. The relationship among these conditions, the prevalence with which they co-exist, and the association between the number of premalignant conditions and risk of infection is unknown. Methods Study participants from the Mayo Clinic Biobank, a large-scale biorepository of adult patients, provided a peripheral blood sample between 7/14/2009 to 06/18/2015. Individuals were screened for MBL using eight-color flow cytometry capable of detecting clonal B-cells to the 0.005% level. MGUS was screened using a matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF) assay. CH was screened using a targeted sequencing panel of 42 CH-associated genes with at least 1000x read depth and the ability to detect variant allele fractions down to 1%. All study participants resided in Olmsted County, Minnesota, the county that includes Mayo Clinic. Serious infection, defined as hospitalization due to infection, was abstracted from medical records from the time of sample collection through 12/31/2020 or date of death. The medical record abstractor collecting data was blinded to condition. Logistic regression was used to estimate odds ratios (OR) and 95% confidence intervals (CI) for the association between each of the conditions. Cox regression was used to estimate hazard ratios (HR) and 95% CI to assess the association between number of premalignant conditions with risk of infection. All analyses were adjusted for age at sample collection and sex. Results A total of 407 individuals (55% male, median age 68 years) were screened for all three conditions. The prevalence was 19.9% (n=81) for MBL, 14.5% (n=59) for MGUS, and 25.6% (n=104) for CH. When we evaluated the association between each of the conditions, we found no evidence of an association between the prevalence of CH and risk of MBL (OR=0.79, 95% CI: 0.43-1.42), CH and risk of MGUS (OR=1.24, 95% CI: 0.66-2.27), or MGUS and risk of MBL (OR=1.32, 95% CI:0.66-2.52). The prevalence of co-existence of these conditions was assessed by grouping individuals based on their condition or conditions (Figure 1A). We found that 197 (48.4%) study participants had at least one premalignant condition and 10.6% had two or more. Individuals with 2 or more conditions were the oldest (median age 74 years), followed by 1 condition (median 69 years) and 0 conditions (median 67 years, P-trend <0.001). Sex was not significantly different across the groups, with 55%, 58%, and 47% male for 0, 1, and 2 conditions, respectively. Medical record abstraction identified 97 serious infection events in 80 individuals. Medical records were not available on 7 individuals. The most common infections were urinary tract (20 events), pneumonia (14 events), and cellulitis (14 events). Median follow-up time was 10.6 years (range 0.1-11.5 years). Compared to individuals with no condition, MBL (HR=1.75, 95% CI: 1.06-2.88) and MGUS (HR=1.75, 95% CI: 1.04-2.93) were associated with increased risk of serious infection. We found no evidence of an association with CH (HR=1.15, 95% CI: 0.71-1.87). When grouped by the number of conditions, we observed a significant trend (P-trend <0.01, Figure 1B) in risk of serious infections by the number of conditions: individuals with 1 condition had a 35% increased risk of infections (HR=1.35, 95% CI:0.83-2.20) and individuals with 2 or more conditions had a 2.6-fold increased risk (HR=2.58, 95% CI: 1.37-4.84). Discussion At least one premalignant condition was present in nearly 50% of the study population, with CH being the most prevalent. No evidence of a relationship between any of the three conditions was observed. However, we found increased susceptibility to serious infections as the number of conditions increased with individuals with at least two conditions had 2.6-fold increased risk of infections. Figure 1 Figure 1. Disclosures Parikh: Pharmacyclics, AstraZeneca, Genentech, Gilead, GlaxoSmithKline, Verastem Oncology, and AbbVie: Membership on an entity's Board of Directors or advisory committees; Pharmacyclics, MorphoSys, Janssen, AstraZeneca, TG Therapeutics, Bristol Myers Squibb, Merck, AbbVie, and Ascentage Pharma: Research Funding. Dispenzieri: Takeda: Research Funding; Alnylam: Research Funding; Pfizer: Research Funding; Oncopeptides: Consultancy; Sorrento Therapeutics: Consultancy; Janssen: Consultancy, Research Funding. Murray: Mayo Clinic: Other: Has received patents for the Mass-Fix technology which has been licensed to the Binding Site with potential royalties.. Kumar: Astra-Zeneca: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Merck: Research Funding; Oncopeptides: Consultancy; Beigene: Consultancy; Novartis: Research Funding; KITE: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Janssen: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Antengene: Consultancy, Honoraria; Takeda: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Tenebio: Research Funding; Roche-Genentech: Consultancy, Research Funding; Bluebird Bio: Consultancy; Celgene: Membership on an entity's Board of Directors or advisory committees, Research Funding; Carsgen: Research Funding; Amgen: Consultancy, Research Funding; Abbvie: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; BMS: Consultancy, Research Funding; Adaptive: Membership on an entity's Board of Directors or advisory committees, Research Funding; Sanofi: Research Funding. Cerhan: Regeneron Genetics Center: Other: Research Collaboration; Genentech: Research Funding; Celgene/BMS: Other: Connect Lymphoma Scientific Steering Committee, Research Funding; NanoString: Research Funding. Kay: TG Therapeutics: Research Funding; Morpho-sys: Membership on an entity's Board of Directors or advisory committees; Agios Pharm: Membership on an entity's Board of Directors or advisory committees; Targeted Oncology: Membership on an entity's Board of Directors or advisory committees; AstraZeneca: Membership on an entity's Board of Directors or advisory committees; Abbvie: Membership on an entity's Board of Directors or advisory committees, Research Funding; Oncotracker: Membership on an entity's Board of Directors or advisory committees; Sunesis: Research Funding; MEI Pharma: Research Funding; Pharmacyclics: Membership on an entity's Board of Directors or advisory committees, Research Funding; Bristol Meyer Squib: Membership on an entity's Board of Directors or advisory committees, Research Funding; Acerta Pharma: Research Funding; Rigel: Membership on an entity's Board of Directors or advisory committees; Tolero Pharmaceuticals: Research Funding; Genentech: Research Funding; Celgene: Membership on an entity's Board of Directors or advisory committees, Research Funding; Behring: Membership on an entity's Board of Directors or advisory committees; CytomX Therapeutics: Membership on an entity's Board of Directors or advisory committees; Dava Oncology: Membership on an entity's Board of Directors or advisory committees; Janssen: Membership on an entity's Board of Directors or advisory committees; Juno Therapeutics: Membership on an entity's Board of Directors or advisory committees. Shanafelt: Genentech, Pharmacyclics: Research Funding.