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Background Pacritinib (PAC) is a relatively selective JAK2 vs. JAK1 inhibitor (JAKi) and is one of four FDA-approved JAKi for use in myelofibrosis (MF). PAC is indicated for MF patients with thrombocytopenia (Platelets <50 x 109/L). In a previously published controlled study of MF patients with platelet count <100 x 109/L (PERSIST-2), including JAKi-naïve and ruxolitinib-experienced, PAC therapy at the recommended dose of 200 mg BID was associated with a ≥35% spleen volume reduction rate of 22%; response rate was lower in ruxolitinib-experienced patients for both 200 mg BID (9.3%) and 100 mg BID (1.8%) dosing (JAMA Oncol 2018;4:652); a more recent post-hoc analysis suggested an additional benefit in anemia with 25-37% of transfusion-dependent patients achieving a ≥12-week transfusion-free period (Blood Adv 2023;7:5835). Herein, we describe our experience with the drug outside of a clinical trial setting. Methods Study patients were retrospectively recruited from Mayo Clinic (USA) databases, after approval from IRB. Diagnostic criteria were according to the International Consensus Classification (Blood 2022;140:1200). Study inclusion criteria included documentation of PAC therapy outside of a clinical trial setting. Spleen response was adjudicated by the 2013 International Working Group-European LeukemiaNet (IWG-ELN) response criteria (Blood 2013;122:1395). Anemia response was rated by the revised 2024 IWG-ELN criteria (manuscript submitted; transfusion-free period x 12 weeks and/or 12-week average increase in hemoglobin ≥1.5 g/dL). Conventional statistical methods were employed. Results A total of 60 MF patients (median age 70 years; males 62%; primary MF 63%) received PAC upfront (N=19; 32%) or after failing treatment with another JAKi (N=41; 68%), including ruxolitinib (N=39; 65%): JAK2 60%, CALR 27%, MPL 10%. Reasons for discontinuation of previous JAKi treatment included drug intolerance (41%), relapse after initial response (33%), and suboptimal response (26%). Median interval between diagnosis and treatment with PAC was 4 years (range 0-22). At PAC treatment initiation, DIPSS-plus risk distribution was high in 48%, intermediate-2 47%, and intermediate-1 (5%). Transfusion-dependent anemia (TDA; ≥3 units during 12 weeks prior to enrollment) was present in 40% of patients, platelet count <50 x 109/L 25%, leukocyte count >11 x 109/L 40%, spleen size >15 cm 76%, constitutional symptoms 55%, complex/monosomal karyotype 27%, and mutations in SRSF2 11% or ASXL1 33%. PAC initial dose was 100 (N=41) or 200 (N=19) mg BID. Dose was increased in 44% of patients started at 100 mg BID and decreased in 55% of those started at 200 mg BID. Among 47 patients evaluable for anemia response, only one of 23 with non-TDA (2% overall and 4.3% at 200 mg BID dosing) and none of 24 with TDA responded. In evaluable patients, spleen response rate was 13% (95% CI 5.9-24.7) overall and higher in JAKi-naïve (29%; 95% CI 11.7-54.7) vs. JAKi-experienced (6%; 95% CI 1.6-19.1; p=0.04). Spleen response rate was higher in the absence of leukocytosis (21% vs. 0%; p=0.01) or complex/monosomal karyotype (17% vs. 0%; p=0.05) but similar between 100 and 200 mg BID initial dosing (p=0.9). At a median follow-up of 14 months (range 1-27), PAC was discontinued in 80% of the patients: intolerance 58%, suboptimal response 54%, transition to allogeneic stem cell transplants (ASCT) 10%. Major side effects were more frequent with 200 vs. 100 mg BID dose and included diarrhea 43%, nausea/vomitting 17%, dyspnea 25%, peripheral edema 28%, allergic reaction 13%, grade 3/4 neutropenia 22%, and grade 4 thrombocytopenia 34%. Up to the time of this writing, 17 deaths (28%), 11 (18%) ASCT, and 3 (5%) leukemic transformations were documented. In multivariable analysis, post-PAC survival was adversely affected by TDA (HR 11.9; p<0.01), platelet count <50 x 109/L (HR 7.4; p<0.01), and SRSF2/ASXL1 mutations (HR 10.7; p<0.01), all independent of ASCT, which was independently associated with longer survival (HR 9.0; p<0.01). Conclusions: The observations from the current real-world study, regarding the moderate activity of PAC for reducing spleen size, are consistent with those of the aforementioned controlled clinical trial (PERSIST-2). However, despite recent suggestions of the drug's mechanistically unique erythropoietic activity, the anemia response rate seen in the current study was underwhelming.

Background Survival risk models in essential thrombocythemia (ET) include the International Prognostic Scoring System (IPSET; Blood 2012;120:1197) and the more recently described “triple-A” prognostic score that considers Age and absolute neutrophil (ANC) and lymphocyte (ALC) counts, as risk variables (AJH 2023;98:1829). Monocytosis, defined by absolute monocyte count (AMC) of ≥0.8 x 109/L, was recently reported to be associated with inferior survival in polycythemia vera (ASH 2024 abstract). The current study examined the prognostic contribution of monocytosis in ET, in the context of other clinical and genetic risk factors. Methods Study patients were recruited from Mayo Clinic (USA) databases, based on availability of information on ANC, ALC, and AMC (N=649). Diagnostic criteria were according to the International Consensus Classification (Blood 2022;140:1200). Mutations were screened by next-generation sequencing (NGS). Conventional statistical methods were employed (JMP Pro 17.0.0, SAS Institute, Cary, NC, USA) and optimal cut-points for age, ANC, ALC, and AMC were determined by Receiver Operating Characteristic (ROC) analysis. Akaike Information Criterion (AIC) and ROC plots were used to estimate predictive accuracy of risk models. Results A total of 649 patients (median age 60 years; females 65%) were informative for AMC, ANC, and ALC, with median (range) values of 0.6 x 109/L (0.2-2.5), 5.7 x 109/L (1.5-26.5), and 1.9 (0.4-5.7), respectively. At presentation, IPSET risk distribution was low in 34%, intermediate 47%, and high 19%; triple-A risk distribution was low 21%, intermediate-1 50%, intermediate-2 13%, and high 16%; driver mutation distribution was 63.8% JAK2, 24.0% CALR, 3.7% MPL, and 8.5% triple-negative; median for platelets were 728 x 109/L, hemoglobin 13.9 g/dL, and leukocytes 8.5 x 109/L ; leukocytosis (leukocytes ≥11 x 109/L) was documented in 18.8% of patients, palpable splenomegaly 7%, arterial thrombosis (AT) history 14.5%, venous thrombosis (VT) history 9.2%, and major hemorrhage 7.8%. At median follow-up of 7 years (range 0.02-31.4), 146 (22.5%) deaths, 52 (8%) fibrotic progressions, 22 (3.4%) leukemic transformations, 71 (11%) AT events, 36 (5.6%) VT events, and 64 (10%) major bleeds were recorded. In age-adjusted univariate analysis, higher AMC was significantly associated with inferior survival, with a ROC determined cutoff value of ≥0.8 x 109/L (N=154; 24%); significance was sustained (HR 2.3; p<0.01) during multivariable analysis (MVA) that also identified age >70 years (HR 16.6; p<0.01), age 50-70 years (HR 4.3; p<0.01), ANC ≥8 x 109/L (HR 1.9; p<0.01), ALC <1.7 x 109/L (HR 1.8; p<0.01), and AT history (HR 1.6; p=0.01). A similar MVA conducted on an external cohort from the University of Florence (N=514) confirmed the significant contribution from all of these risk variables, except AT (p=0.8). An HR-based 4-variable prognostic model based on Age >70 years (4 points) or 50-70 years (2 points), AMC ≥0.8 x 109/L (1 point), ANC ≥8 x 109/L (1 point), and ALC <1.7 x 109/L (1 point), henceforth referred to as the AAA+A model, was subsequently developed using the Mayo Clinic cohort and validated by the Florence cohort: Low (0-1 points; N= 180; median not reached), intermediate-1 (2-3 points; N=266; median 21.6 years), intermediate-2 (4-5 points; N=151; median 12.2 years), and high (6-7 points; N=52; median 8.7 years); HR values were 2.1 for high vs. intermediate-2, 5.4 for intermediate-2 vs. intermediate-1, and 3.8 for intermediate-1 vs. low (p<0.001in all instances). The 20-year survival predictive performance of AAA+A (AIC 131; AUC 0.88) was superior to that of AAA (AIC 143; AUC 0.85) and IPSET (AIC 149; AUC 0.84). In MVA that included AAA+A risk variables, AMC ≥0.8 x 109/L (p=0.04) and ALC <1.7 x 109/L (p=0.06) appeared to affect leukemia-free survival and ANC ≥8 x 109/L (p=0.04) myelofibrosis-free survival. In univariate analysis, AMC ≥0.8 x 109/L was associated with AT (p=0.03) but not VT (p=0.14) history and showed borderline significance for venous (p=0.09) and arterial (p=0.07) thrombosis-free survivals; however, significance was lost during MVA. Conclusions: Monocytosis is an adverse prognostic factor in ET and its inclusion as a risk variable enhances the predictive performance of the AAA risk model and is equally simple to apply worldwide. Analyses that include mutations will be presented at meeting.

Background: The JAK2 46/1, also referred to as the GGCC, haplotype, is represented by 4 main SNPs spanning a region of 250kb in chr9 including the JAK2 gene, that are in complete linkage disequilibrium. The GGCC haplo was found to confer susceptibility to JAK2 mutated myeloproliferative neoplasms (MPN) (Jones AV, 2009; Olcaydu D, 2009; Kilpivaara O, 2009) while association with JAK2-wildtype MPN remains controversial (Pardanani A, 2010; Jones AV, 2010; Guglielmelli P, 2010; Trifa A, 2016). The GGCC haplo was also found enriched in MPN pts with splancnic vein thrombosis (SVT) (Smalberg JH, 2011), and to correlate with higher JAK2V617F variant allele frequency (VAF) (Alvarez-Larran, A, 2012). Nullizigosity for GGCC haplo was associated with reduced survival (OS) in pts with myelofibrosis (MF) (Tefferi A, 2019), but no information on the impact of GGCC haplo status with phenotype and outcome in PV is available. Aim: To assess the clinical correlates and the prognostic significance of GGCC haplo status in a large cohort of pts with PV. Pts and Methods: A total of 399 PV pts, all JAK2V617F mutated, diagnosis revised according to 2022 ICC criteria, were genotyped for 46/1 haplotype by PCR allele discrimination with rs12343867 (with the “C” allele standing for 46/1 haplotype). Results: A total of 301 pts (75.4%) had the C allele, of which 143 (47.5%) were CC homo and 158 (52.5%) CT hetero; 98 (24.6%) were nullizygous for GGCC (TT). Since preliminary analysis disclosed no significant difference between CT and TT haplotype for all variables considered, homozygous CC pts were compared to TT+CT. The CC haplotype was associated with higher leukocytes (median 11.3x10e9/L vs 9.6, p<.001), higher hemoglobin (18.4 g/dL vs 17.5, p<.001), lower platelets (441x10e9/L vs 514, p=.002) more aquagenic pruritus (51.8% vs 33.2%, p=.001), and higher JAK2VAF (60.8+-24.8% vs 36.8+-19.7%, p<.001) at diagnosis. Pts with a VAF >50% were 69% in CC versus 24.1% in TT+CT pts (p<.001). ASXL1 mutations were enriched among CC pts (20.3% vs 9.4%, p=0.04), otherwise no difference regarding additional myeloid mutations was noted. All above differences remained significant when considering CC versus TT and CT separately. More pts with CC haplotype suffered from venous thrombosis (VT) during the FU (16.1% vs 4.3%, p<.001), no difference was noted for arterial thrombosis nor for splancnic vein thrombosis. VT-FS by Kaplan Meyer was significantly shorter (p<.001) in CC pts; the rate of VT at 5, 10, 15y after diagnosis, was 5.5%, 12%, 20.2% for CC versus 2.6%, 3.4%, 6.4% for TT+CT, respectively (all p<.001). In multivariable analysis, including JAK2VAF >50%, age >60y, history of VT, WBC >15x10e9/L, only CC haplo remained significant (HR 3.6, 95%CI 1.4-9.5, p=.009). Progression to post-PV MF occurred in 81 pts (20.3%), significantly more among CC (n=45, 31.5%) than TT+CT (n=36; 14.1%; p<.001). Myelofibrosis-FS was significantly shorter in CC vs other genotypes (p=.02). However, in multivariable analysis, only BM fibrosis G1 remained significant (HR 3.2, 1.7-5.9; p<.001). Evolution to blast-phase occurred in 13 pts (3.2%), 9 (6.3%) with CC haplo vs 4 TT+CT (1.6%; p=.01). During the follow-up, 102 pts (25.5%) died, 50 (35%) CC and 52 TT+CT (20.3%; p=.001). In multivariable analysis, including MIPSS-PV variables (Tefferi A 2020), the CC haplo remained significant (HR 1.8, 1.04-3.2, p=.03) together with age (HR 3.0, 1.6-5.7; p<.001), WBC (HR 2.6, 1.3-4.8; p=.004), and thrombosis history (HR 1.9, 1.0-3.7; p=.03). Conclusions. Homozygosity for the 46/1 or CC haplotype contributes to the phenotype diversity of PV, in part possibly mediated by associated higher JAK2V67F VAF, and predicts for incident VT and shorter OS. Supported by AIRC, 21267; MIUR,2022F4WMR3; IHM, PNRR-MAD-2022-12376695

Background In 2013, we published the first International Working Group (IWG) risk model for survival in polycythemia vera (PV), which included 3-tiered age categories, leukocytosis (≥15 x 109/L), and venous thrombosis, as risk variables (Leukemia. 2013;27:1874). In the current study, we examined the individual prognostic contribution from specific leukocyte components and mutations, in order to construct a more contemporary clinical risk model in PV and assess its interaction with genetic risk factors. Methods Study patients were retrospectively recruited from the Mayo Clinic, USA (N=1,007) and the University of Florence, Italy (N=514), in order to serve as discovery and validation cohorts, respectively. Diagnostic criteria were according to the International Consensus Classification (Blood 2022;140:1200). Mutations were screened by next-generation sequencing (NGS). Conventional statistical methods were employed (JMP Pro 17.0.0, SAS Institute, Cary, NC, USA) and optimal cut-points for age, absolute neutrophil (ANC), lymphocyte (ALC), and monocyte (AMC) counts were determined by Receiver Operating Characteristic (ROC) analysis. Akaike Information Criterion (AIC) and ROC plots were used to estimate predictive accuracy. Results Presenting features in the Mayo discovery cohort (N=1,007) included: median age 62.2 years; males 50.7%; median leukocyte count 10.8 x 109/L; leukocyte count ≥15 x 109/L 19%; palpable splenomegaly 32%; pruritus 34%; diabetes 16%; hypertension 61%; arterial thrombosis 14%; and venous thrombosis 14%. ANC, AMC, and ALC information was available in 736 patients with respective median (range) values of 7.6 (1.6-30), 0.6 (0-4.1), and 1.54 (0.19-6.9) x 109/L. At a median follow-up of 8.9 years for the Mayo discovery cohort, 372 (37%) deaths, 46 (4.6%) leukemic transformations, and 200 (20%) fibrotic progressions were recorded. Multivariable analysis (MVA) employing ROC-determined cutoff values revealed adverse survival impact for age >70 years (HR 18.3; p<0.01), age 50-70 years (HR 4.9; p<0.01), AMC ≥0.8 x 109/L (HR 1.5; p<0.01), ANC ≥8 x 109/L (HR 1.5; p<0.01), arterial thrombosis (HR 1.5; p<0.01), diabetes (HR 1.4; p=0.04), and male sex (HR 1.3; p=0.05). A similar MVA applied to the Florence validation cohort (N=514) confirmed significance for age (p<0.01), ANC (p<0.01), AMC (p=0.04), and arterial thrombosis (p<0.01), but not for male sex (p=0.8) or diabetes (p=0.15). Accordingly, age >70 years (4 points), age 50-70 years (2 points), ANC ≥8 x 109/L (1 point), AMC ≥0.8 x 109/L (1 point), and AT (1 point) were included in a revised IWG survival model using the Mayo cohort and validated by the Florence cohort: very low risk (0 points; N=67; median 37 years), low risk (1 point; N=55; median 29.2 years), intermediate risk (2-3 points; N=308; median 20.2 years), high risk (4-5 points; N=217; median 11.5 years), and very high risk (6-7 points; N=88; median 6.3 years). 20-year survival prediction performance of the revised IWG model (AIC 204; AUC 0.88) was superior to that of the 2013 IWG version (AIC 350; AUC 0.86). Mutation information at diagnosis/chronic phase was available in 270 Mayo patients: ASXL1 10%; SRSF2 4%, IDH2 2%, TP53 2%, RUNX1 1.4%. MVA of mutations identified SRSF2 (p<0.01), IDH2 (p=0.01), and ASXL1 (p=0.05), as risk factors for overall survival. The presence of any one adverse mutation was more likely in patients with AMC ≥0.8 x 109/L (24% vs. 7% incidence; p<0.01). In all-inclusive MVA, independent risk factors for OS were age >70 years (HR 14.7), age 50-70 years (HR 6.2), any one adverse mutation (HR 3.4), and ANC ≥8 x 109/L (HR 2.3), but not AMC ≥0.8 x 109/L (p=0.9), arterial thrombosis (p=0.24), or abnormal karyotype (p=0.4). Leukemia-free survival was adversely affected by SRSF2, RUNX1, TP53, and ASXL1 mutations and myelofibrosis-free survival by SRSF2 mutation. Conclusions: The currently proposed revised IWG risk model for survival in PV is globally applicable and based on four easily accessible clinical variables (Age, ANC, AMC, and arterial thrombosis). NGS-derived mutation information overshadows the prognostic relevance of monocytosis, provides additional prognostic information for overall survival, and assists in predicting leukemic and fibrotic transformations.

Background Blast or accelerated phase myeloproliferative neoplasm (MPN-BP/AP) carries a dismal prognosis, with 3-year survival estimates of <5% (BCJ 2023;108). Patients with MPN-BP/AP were excluded from venetoclax (Ven) plus hypomethylating agent (HMA) clinical trials for acute myeloid leukemia (NEJM 2020;383:617). In the current retrospective study, we examined response patterns and long-term survival of newly-diagnosed MPN-BP/AP patients who received treatment with Ven+HMA, outside of clinical trials. Methods Newly-diagnosed patients with MPN-BP/AP treated with Ven+HMA at the Mayo Clinic, between March 2019 and May 2024, were retrospectively reviewed. Diagnostic criteria were according to the International Consensus Classification (Blood 2022;140:1200). Cytogenetic and molecular studies were performed by conventional karyotype and next-generation sequencing, respectively. All patients received at least one cycle of Ven+HMA (azacitidine 75 mg/m2 days 1-7 or decitabine 20 mg/m2 days 1-5). Response was assessed according to the 2022 European Leukemia Net criteria (Blood 2022;140:1345). Standard statistical analyses were performed using JMP Pro (Version 17.1.0). Results Patient characteristics 70 patients (median age 73 years, 59% males, 48% splenomegaly >14 cm, 4% isolated myeloid sarcoma) with newly-diagnosed MPN-BP (n=58) or AP (n=12) received Ven+HMA with (n=13) or without (n=57) concomitant JAK2 inhibitor. Driver mutation distribution was 69% JAK2, 21% CALR, 6% MPL, and 4% triple negative. Mutations involved ASXL1 (31%), TP53 (28%), TET2 (28%), RUNX1 (25%), SRSF2 (18%), IDH2 (12%), U2AF1 (11%), DNMT3A (9%), IDH1 (7%), and K/NRAS (7%). Karyotype was abnormal in 50 (76%) of 66 informative cases, of which 28 (56%) were complex (CK). Median TP53 mutation variant allele frequency (VAF) was 30% (8-96%) and all evaluable cases displayed CK (n=18). Response and Survival Complete remission (CR; 21%) or CR with incomplete count recovery (CRi; 19%) was documented in 28 (40%) patients with residual MPN in 18 (64%) patients. Median response duration was 5.5 months (1-60 months). After a median follow up of 7 months (1-62 months), 48 (69%) deaths, 13 relapses (46%), and 15 (21%) allogeneic stem cell transplants (ASCT; 12 in CR/CRi) were recorded. Median overall survival (OS) was 9 months and was superior with ASCT (median 22 vs. 8 months; p=0.01). In univariate analysis, transplant-censored survival was superior with CR/CRi (12 vs. 5 months; p<0.01) and IDH1 mutation (33 vs. 8 months; p=0.04) and inferior with CK (7 vs. 10 months; p=0.05), TP53 mutation (5 vs. 10 months; p<0.01), post polycythemia vera myelofibrosis (post-PV MF) (3 vs. 9 months; p=0.01), and splenomegaly >14 cm (5 vs. 16 months; p<0.01). Multivariable analysis confirmed the negative survival impact of not achieving CR/CRi (HR 3.8; p<0.01) and presence of TP53 mutation (HR 4.0; p<0.01); median survival (1/3-year survival rate) was 3 months (10%/0%) in TP53 mutated patients not achieving CR/CRi (n=11) vs. 27 months (65%/28%) in TP53 unmutated cases achieving CR/CRi (n=19) (p < 0.01). Median survival in patients with TP53 mutations or CK who achieved CR/CRi (n=7; 7 months) was inferior to that in treatment responders without TP53 mutations or CK (n=18; 23 months; p=0.01). CR/CRi rates in the presence vs. absence of TP53 mutations were 42% vs. 39% (p=0.80) and of CK (25% vs. 50% (p=0.04). Importantly, responses in the presence of TP53 mutations or CK were too short-lived to allow successful bridging to ASCT (median 2 vs. 9 months; p<0.01). Additional predictors of inferior treatment response included splenomegaly >14 cm (24% vs. 53%; p=0.01), and post-PV MF (0% vs. 46%; p<0.01) while SRSF2 (67% vs. 34%; p=0.04) and IDH2 mutations (75% vs. 35%; p=0.03) were associated with favorable response. In multivariable analysis, CK (p=0.04) and splenomegaly >14 cm (p=0.01) remained independent predictors of inferior response. The use of concomitant JAK2 inhibitor therapy did not impact treatment response (CR/CRi 46% vs. 39%; p=0.62) or survival (median 9 vs. 8 months; p=0.71). Conclusions TP53 mutations and CK undermine the value of Ven+HMA, with or without concomitant JAK2 inhibitor, in enabling successful bridging of newly-diagnosed MPN-BP/AP to ASCT. An alternative treatment approach is advised, in the particular scenario, while the observed 3-year survival rate of 28%, in treatment responders without TP53 mutations, is encouraging.

Background: Treatment of symptomatic splenomegaly in myelofibrosis (MF) was revolutionized by JAK2 inhibitors (JAKi), with ruxolitinib inducing a >35% spleen volume reduction in 42% of patients at 24 weeks (N Engl J Med 2012;366). However, the benefit is often transient with a median duration of spleen response of three years (N Engl J Med. 2011;365). Treatment modalities for the management of MF-associated splenomegaly resistant to JAKi treatment includes surgical resection and involved-field radiotherapy. In the current study, we describe our experience with the former. Methods: Study patients were retrospectively recruited from Mayo Clinic (USA) databases based on the following criteria: i) diagnosis according to the International Consensus Classification (Blood 2022;140:1200); ii) documentation of JAKi therapy exposure followed by splenectomy; iii) availability of information before and after splenectomy. Splenectomy was performed as an open (n=29) or laparoscopic (n=5) surgery. Conventional statistical methods were employed for data analysis (JMP Pro 17.0.0, SAS Institute, Cary, NC, USA). Results: A total of 34 patients (median age 62.5 years, range 43-79; 59% males) were identified with splenectomies performed between 2011-2024. Mutation distribution included JAK2 62%, CALR 26%, MPL 3%, and triple negative 9%. ASXL1 mutation was present in 37% and SRSF2 mutation was present in 26% of 19 informative cases. Karyotype was very high risk in 15% and unfavorable in 12%. Median time from diagnosis to JAKi initiation was 7.5 years (0-31). Majority (76%) were treated with one JAKi; 18% had been exposed to 2 different JAKi and 6% with three JAKi. JAKi included ruxolitinib (n=27), momelotinib (n=5), pacritinib (n=3), fedratinib (n=3), and BMS-911543 JAKi (n=5). Two patients underwent allogeneic stem cell transplant (ASCT) three and six months prior to splenectomy. Prior treatment included splenic radiation in 4 patients (median 0.6 years (0.2-1.2)). Pre-operative splenic embolization was performed in 4 patients on same day of splenectomy; one patient had embolization 10 months prior to splenectomy. Median interval from diagnosis to splenectomy was 10.3 years (1.0-35.4) and from initiation of JAKi therapy to splenectomy 1.8 years (0.03-12.1). Most patients had multiple indications for splenectomy including 76% with symptomatic splenomegaly, 50% with significant cytopenia, and 18% in preparation of ASCT. At time of splenectomy, median spleen size on imaging was 25.1 cm (14.7-36) and 55% were red cell transfusion-dependent (Revised international working group criteria). Postoperative complications were reported in 22 (65%) of patients. Major bleeding occurred in 11 (32%) (of which 7 (64%) required repeat surgical exploration) and thrombosis in 9 (26%); 5 patients experienced both major bleeding and thrombosis. Other complications included infection (n=5), renal injury (n=3), and pneumothorax (n=2). At a median follow up of 1.7 years (0.01-10.2) post-splenectomy, 12 (35%) ASCT were documented at a median of 2.3 years (1.5-26.4) post-procedure. Median post-splenectomy survival was 4.3 years (5-year survival 44%) and significantly longer in transplanted patients (median not reached vs 2.6 years; 5-year survival 65% vs 22%; p=0.02). Among patients without post-splenectomy ASCT (n=22), 12 (55%) deaths (including 2 from post-operative complications) and 3 leukemic transformations were recorded. Additionally, 13 of the 22 had transfusion-dependent anemia at splenectomy and subsequently 6 (46%) became transfusion-independent (TI) (≥12 weeks without transfusion) with median TI response duration of 2.8 years (0.3-7.1). In addition, among 5 non-transplanted patients with baseline thrombocytopenia (< 50 x 109/L (16-42 x 109/L)), 4 (80%) had platelet count > 100 x 109/L (median; 170 x 109/L, range: 119-279 x 109/L) within 3 months post-procedure. Conclusions: Splenectomy following JAKi-resistant or intolerant MF is associated with improvement of transfusion-dependent anemia (46% response), resolution of severe thrombocytopenia (80%), and may allow for successful transition to ASCT (35%). However, the procedure is associated with significant perioperative complications occurring in the majority of patients and underscores the need for future collaborative studies to develop selection criteria and evaluate alternative treatment modalities.

Introduction Oligomonocytic chronic myelomonocytic leukemia (OM-CMML) is defined by relative monocytosis ≥ 10% and an absolute monocyte count (AMC) between ≥ 0.5 and < 1.0 x109/L. The 5th ed WHO and International Consensus Classifications lowered the AMC threshold to ≥ 0.5 x10/9L for CMML diagnosis, thereby incorporating OM-CMML (Khoury, 2022; Arber, 2022). However, prior reports differ as to whether OM-CMML is a distinct CMML subtype. This multi-center study compares the clinical, molecular, and survival features of OM-CMML with myelodysplastic (MD, WBC < 13.0 x109/L) and myeloproliferative (MP, WBC ≥ 13.0 x109/L) CMML with an AMC ≥1.0. Methods After IRB approval, patients with CMML from Mayo Clinic (n = 400, 47%) and MD Anderson Cancer Center (n = 449, 53%) were identified retrospectively. Analyses considered clinical, laboratory, and next generation sequencing parameters at diagnosis or first referral (in chronic phase). Categorical variables were compared by Fisher exact or Pearson χ2 tests and continuous variables by Mann-Whitney U or ANOVA tests. Survival was assessed via the Kaplan-Meier method with outcomes censored at allogeneic stem cell transplantation (alloSCT). P < 0.05 was considered significant. Calculations used BlueSky Statistics (v10.3.1). Results A molecularly annotated cohort of 849 patients with CMML (median age 71 years, 32% female, 90% white, median follow up 31 months [mo]) was categorized as OM-CMML (n = 57, 7%), MD-CMML (n = 394, 46%), and MP-CMML (n = 391, 46%). There were no differences in age or sex across subtypes. No clinical differences were observed between OM-CMML and MD-CMML, with similar hematologic parameters, karyotype distributions, Mayo-Molecular (Patnaik, 2014) or CPSS-Molecular (Elena, 2016) risk stratifications, and rates of leukemic transformation (12% vs 12%, p = 0.98) and death (35% vs 43%, p = 0.27). Cases of OM-CMML had lower WBC counts (median 4.4 vs 24.7 x109/L, p < 0.0001), fewer circulating immature myeloid cells (23% vs 57%, p < 0.0001) and fewer marrow blasts (median 3% vs 4%, p = 0.0065) than MP-CMML. Comparatively, OM-CMML cases were overrepresented in the lower-risk groups of the CPSS-Molecular and Mayo-Molecular models (p < 0.0001). Leukemic transformation (12% vs 20%, p = 0.015) and death (35% vs 52%, p = 0.034) rates were higher in the MP-CMML cohort. Molecular profiles were similar between OM-CMML and MD-CMML, including median number of genes mutated (3 vs 3, p = 0.88). Frequencies of ASXL1 (39% vs 38%, p = 0.91), SRSF2 (48% vs 43%, p = 0.49), DNMT3A (7% vs 5%, p = 0.60), and SF3B1 (4% vs 7%, p = 0.48) mutations were also similar. TET2 mutation frequency was higher in OM-CMML (70% vs 55%, p = 0.031) and occurred in isolation more frequently (12% vs 6%, p = 0.048) compared to MD-CMML. Neither median number of TET2 mutations (1 vs 2, p = 0.87), nor TET2 variant allele fractions (41% vs 44%, p = 0.19) were different between the two groups. Compared to OM-CMML, patients with MP-CMML were more likely to have mutations in ASXL1 (39% vs 56%, p = 0.017), EZH2 (0% vs 9%, p = 0.019), JAK2 (0% vs 9%, p = 0.019), NRAS (7% vs 25%, p = 0.0024), and SETBP1 (2% vs 13%, p = 0.021). RAS family (CBL, BRAF, KRAS, NRAS, PTPN11; 25% vs 54%, p < 0.0001) and signaling pathway (CSF3R, FLT3, JAK2, SH2B3; 2% vs 14%, p = 0.0078) mutations were also more frequent whereas spliceosome mutations (SF3B1, SRSF2, U2AF1, ZRSR2; 61% vs 46%, p = 0.033) were less frequent in MP-CMML. The median (95% CI) overall survival (OS) of OM-CMML patients was 44 (38 - not reached) mo compared to 45 (34 - 60) mo in MD-CMML (p = 0.76) and 23 (20 - 29) mo in MP-CMML (p < 0.0032). Similar results were obtained when comparing the acute leukemia-free survival (LFS) of the OM-CMML (41 mo), MD-CMML (39 mo), and MP-CMML (19 mo) groups. At last follow up (medians 42 and 62 mo, respectively), 33% of evaluable OM-CMML patients had progressed to MD-CMML and 28% of MD-CMML patients had progressed to MP-CMML. No patient with OM-CMML progressed directly to MP-CMML. Conclusions These data show that OM-CMML and MD-CMML are a relatively homogenous subset of patients with similar clinicomolecular profiles and survival outcomes. Although OM-CMML patients are more likely to have TET2 mutations in comparison to other CMML subtypes, they have similar rates of disease progression as MD-CMML. This validates recent modifications to CMML classification criteria, in which OM-CMML cases are included as bona fide CMML.

Background A JAK2 mutation is detected in almost all patients with polycythemia vera (PV) and in ⁓50% of those with essential thrombocythemia (ET). The two diseases also share characteristic clinical and bone marrow morphological traits, suggesting they exist on a disease continuum rather than representing discrete entities. The objective of the current study was to compare clinical and genetic characteristics as well as long-term outcome between formally-defined PV vs. JAK2-mutated ET vs. JAK2-wild-type (WT) ET. Methods Study patients were retrospectively recruited from Mayo Clinic, USA databases (1967-2024). Diagnostic criteria were according to the International Consensus Classification (ICC; Blood 2022;140:1200). All study patients were fully annotated for JAK2, CALR, and MPL mutations while cytogenetic and additional next-generation sequencing (NGS)-derived mutation information was available in a subset of patients. Conventional statistical methods were employed for phenotypic comparisons and survival analysis. Results Among 2,010 study patients, 1,010 had PV, 617 (63%) JAK2-mutated ET, and 383 JAK2-WT ET (CALR 26%; MPL 3%; triple-negative 9%). Phenotypic comparisons revealed older age distribution in PV compared to JAK2-mutated ET (p=0.03) and the latter compared to JAK2-WT ET (p<0.01). Females were represented more in JAK2-mutated ET (69%), compared to both PV (49%; p<0.01) and JAK2-WT ET (54%; p<0.01). The frequencies of leukocytosis, palpable splenomegaly, constitutional symptoms, diabetes, hypertension, and abnormal karyotype were all significantly higher in PV, compared to both groups of ET, while JAK2-mutated compared to JAK2-WT ET displayed higher leukocyte count and incidence of hypertension. The incidences of arterial thrombosis at/prior to diagnosis were 14%, 16%, and 10% in PV, JAK2-mutated and WT ET, respectively (P=0.03), and venous thrombosis 14%, 13%, and 6% (p<0.01). After a median follow-up of 8.6 years, 632 (32%) deaths, 329 (16%) fibrotic progressions, 79 (4%) leukemic transformations, and 236 (12%) arterial and 202 (10%) venous thrombotic events were recorded, among all 2,010 study patients. Median overall survival was 19.3 years for PV vs. 17.8 years for JAK2-mutated ET vs. 23 years for JAK2-WT ET (p<0.01); however, the significant difference in favor of JAK2-WT ET was no longer apparent when analysis was adjusted for age and sex (p=0.15) and subsequently for other risk factors (p=0.86). All-inclusive multivariable analysis identified older age (p<0.01), male sex (p<0.01), higher leukocyte count (p<0.01), and arterial thrombosis history (p<0.01), but not the distinction between PV, JAK2-mutated, and JAK2-WT ET (p=0.9), to be independently associated with shortened survival. Leukemia-free survival was similar between PV and either JAK2-mutated (p=0.5) or JAK2-WT (p=0.1) ET. On the other hand, myelofibrosis-free survival was shorter in PV, compared to both JAK2-mutated (HR 1.8, 1.4-2.4; p<0.01) and JAK2-WT (HR 1.4. 1.0-1.8; p=0.03) ET. In multivariable analysis, older age (p<0.01), higher leukocyte count (p<0.01), PV vs. JAK2-mutated ET (HR 1.8; p<0.01), and JAK2-WT vs. JAK2-mutated ET (HR 1.6; p=0.01) were associated with a higher risk of fibrotic progression, with no difference noted between PV and JAK2-WT ET (p=0.4). Arterial thrombosis-free survival was similar between PV and JAK2-mutated ET (p=0.8). In univariate analysis, JAK2-WT ET vs. PV was associated with superior arterial thrombosis-free survival (p=0.02), but significance was lost when analysis was adjusted for arterial thrombosis history (p=0.1). Venous thrombosis-free survival favored JAK2-WT ET vs. PV (HR 0.3; p<0.01) and JAK2-mutated ET (HR 0.6; p=0.02) and the latter vs. PV (HR 0.6; p<0.01); the significant differences between PV and both groups of ET were sustained when analysis was adjusted for age, sex, and venous thrombosis history. Conclusions The current study highlights significant demographic and phenotypic differences between PV and JAK2-mutated ET. However, risk factor-adjusted overall, leukemia-free, and arterial thrombosis-free survival was not inferior in PV, compared to ET, regardless of the presence or absence of a JAK2 mutation in the latter. JAK2-WT ET was distinctly associated with a lower risk of venous thrombosis while JAK2-mutated ET appeared to be less vulnerable to fibrotic progression.

Background DISC-0974 is a monoclonal antibody that targets hemojuvelin, a co-receptor to BMP-SMAD signaling that stimulates hepcidin production. In healthy volunteers, DISC-0974 has been shown to be safe and induce dose-dependent decreases in serum hepcidin and corresponding increases in serum iron and absolute reticulocyte count (JCP 2024). Serum hepcidin level is abnormally elevated in myelofibrosis (MF) and is believed to contribute to iron-restricted erythropoiesis (AJH 2013:88:312). In an ongoing phase 1/2 study in MF (NCT05320198), DISC-0974 was well tolerated and associated with marked reduction in serum hepcidin levels and improvement in anemia (Blood 2023;142/DOI 10.1182). The current investigator-initiated laboratory correlative study examined the impact of mutations and baseline cytokine levels on anemia response to DISC-0974, in non-transfusion-dependent (nTD) patients with MF. Methods The current study was conducted under an institutional review board approved minimum risk protocol that allowed retrospective collection and analysis of data from Mayo Clinic patient records (Rochester, MN, USA). Study patients were selected from the aforementioned ongoing phase 1/2 study, based on availability of information on mutations and baseline cytokine levels. Definitions of nTD and anemia response criteria were according to the revised international working group (IWG) criteria (Blood 2024; in press): i) nTD was defined as the presence of ≤2 units transfused in the 12 weeks prior to enrollment; ii) a 12-week rolling average increase of hemoglobin by ≥1.5 or 1-1.4 g/dL is required for major and minor response, respectively. Mutation and cytokine analyses were performed according to institutional standard protocols; next-generation sequencing panel included 48 genes and cytokine panel 12 inflammatory cytokines. Results A total of 21 nTD patients with MF (median age 71 years; males 62%) were considered: 15 primary and 6 secondary. Driver mutation distribution was JAK2 52%, MPL 14%, and CALR-1 33%. DIPSS risk distribution was high (10%) and intermediate-2 (90%). Baseline median (range) values were 8.0 g/dL (range 7.1-9.5) for hemoglobin, 266 (41-1221) for serum ferritin, 79 (32-130) for serum iron, 32 (13-49) for transferrin saturation, and 59 (10-913) for serum erythropoietin. Karyotype was favorable (N=18) or unfavorable (N=2). Other mutations, included ASXL1 (N=5), SF3B1 (N=4), SRSF2 (N=1), U2AF1 (N=1), and “none of the above” (N=5). Elevated cytokines at baseline included TNF (90%), IL-18 (43%), IL-2R alpha (34%), IL-6 (24%), and MCP-1 (14%). DISC-0974 dose levels were 28 mg (N=2), 50 mg (N=7), 75 mg (N=7), and 100 mg (N=5). Twelve (60%) patients were on DISC-0974 monotherapy while 9 (40%) received concomitant ruxolitinib (N=5), pacritinib (N=1), or hydroxyurea (N=3). At median follow-up of 6 months (range 2-14), one (5%) patient has discontinued DISC-0974 for lack of response. Details on drug safety are summarized in another abstract (Gangat et al. ASH 2024). Per IWG criteria, 9 (43%) patients achieved major (MR) and 3 (14%) minor responses, resulting in an overall response (OR) rate of 57%. Two additional patients have surpassed the hemoglobin threshold for major response (≥1.5 g/dL) but have not yet met IWG criteria. OR and MR rates were higher in patients receiving DISC-0974 as monotherapy (OR 75% and MR 58%) vs. combined with JAK2 inhibitor or hydroxyurea (OR 33% and MR 22%) (p=0.05 for OR and 0.09 for MR), ASXL1 wild-type (N=15; OR 67% and MR 53%) vs. mutated (N=6; OR 33% and MR 17%) (p=0.16 for OR and 0.11 for MR), no ASXL1/SRSF2/U2AF1/SF3B1 (N=5; OR 100% and MR 80%) vs. at least one mutated (N=16; OR 44% and MR 31%) (p<0.01 for OR and 0.05 for MR). OR was also higher in the presence of elevated MCP-1 (p=0.05) or elevated IL-2R alpha (p=0.05) and MR in the presence of elevated IL-2R alpha (71% vs. 29%; p=0.06). Conclusions: The current study suggests that ASXL1 mutation might attenuate but not abrogate anemia response to DISC-0974, in MF. Elevated inflammatory cytokines in MF are often associated with increased hepcidin levels (AJH 2013:88:312) and this might explain their association with a higher response rate to DISC-0974, observed in the current study. Regardless, it is important to note that these observations represent preliminary data from a subset of patients from an ongoing clinical trial.

Background Absolute basophil count (ABC) might be increased in patients with myeloproliferative neoplasms and has been associated with poor prognosis in chronic myeloid leukemia (CML) and, possibly, primary myelofibrosis (PMF, Front. Oncol 2019;9:872). In a Mayo Clinic survey of 382 patients with BCR::ABL1-negative leukocytosis and ABC ≥0.09 x 109/L, 191 (50%) were associated with myeloid neoplasms, including 104 (27%) with CML, 23 (6%) essential thrombocythemia, 21 (6%) polycythemia vera (PV), and 18 (5%) PMF (AJH 2020;95:E216). Herein, we tapped into a well-characterized cohort of patients with PV, in order to describe the prevalence of basophilia, at specific ABC thresholds, and corresponding clinical, molecular, and prognostic correlates. Methods Study patients were retrospectively recruited from Mayo Clinic (USA) databases, after approval from IRB. Diagnostic criteria were according to the International Consensus Classification (Blood 2022;140:1200). Study inclusion criteria included the availability of information on ABC and absolute eosinophil count (AEC). Mayo Clinic institutional reference range for ABC was 0.01 to 0.08 x 109/L and for AEC 0.03 to 0.48 x 109/L. “Eosinophilia” was defined as an AEC of ≥0.6 x 109/L. Basophilia was evaluated both at an ABC of ≥0.1 x 109/L and ABC of ≥0.3 x 109/L, the latter representing 3 x the upper limit of the normal reference range. Cytogenetic information obtained within one year of diagnosis was available in 270 patients. Next-generation sequencing information collected before disease transformation was available in 99 patients. Conventional statistical methods were employed for comparisons of groups and survival analysis (JMP Pro 17.0.0 software SAS Institute, Cary, NC, USA). Results Information on ABC and AEC, obtained within one year of diagnosis, was available in 478 patients (median age 66 years; males 51%). Median values at presentation were 10.6 x 109/L for leukocyte count, 453 x 109/L platelet count, and 17.3 g/dL hemoglobin level. Presenting symptoms included palpable splenomegaly 24%, pruritus 31%, arterial thrombosis 12%, and venous thrombosis 17%. Median and range values for ABC and AEC were 0.12 x 109/L (0-3.2) and 0.27 x 109/L (0-6.5), respectively. ABC was ≥0.3 x 109/L in 80 (17%) patients and ≥0.1 x 109/L in 315 (66%). AEC was ≥0.6 x 109/L in 68 (14.6%) patients. ABC≥0.3 x 109/L was associated with AEC ≥0.6 x 109/L (p<0.01), leukocytosis (p<0.01), and palpable splenomegaly (p=0.02), but not platelet count, pruritus, smoking history, diabetes, or arterial or venous thrombosis; in multivariable analysis, the association with leukocytosis, but not that with splenomegaly, was confirmed. At a median follow-up of 5.7 years (range 0.03-32.8), 132 (28%) deaths, 17 (3.6%) leukemic and 40 (8.4%) fibrotic progressions were documented. Post-diagnosis events also included arterial (7%) and venous (9%) thrombosis. In univariate analysis, neither ABC (p=0.8, 0.7, and 0.96) nor AEC (p=0.7, 0.6, and 0.8), evaluated as continuous variables, affected overall (OS), leukemia-free (LFS), or myelofibrosis-free (MFFS) survival, respectively. Similarly, eosinophilia at AEC ≥0.6 x 109/L did not appear to influence OS (p=0.99), LFS (p=0.6) or MFFS (p=0.5). On the other hand, although basophilia at ABC≥0.3 x 109/L did not affect OS (p=0.27), it was significantly associated with inferior LFS (HR 6.5, 95% CI 2.3-18.0; p<0.01) and MFFS (HR 2.3, 95% CI 1.2-4.5; p=0.01); the corresponding p values for ABC≥0.1 x 109/L were 0.7, 0.1, and 0.17. The detrimental impact of basophilia (ABC≥0.3 x 109/L) on LFS was confirmed (P<0.01) with multivariable analysis that included other clinical variables, including leukocytosis (NS), platelet count (NS), basophil percentage (NS), age (p<0.01), and palpable splenomegaly (p<0.01). Results were similar during multivariable analysis for MFFS with palpable splenomegaly (p<0.01), ABC≥0.3 x 109/L (p=0.03), and age (p=0.05) sustaining independent predictive value. The number of informative cases was too small to evaluate prognostic interaction with mutations and karyotype. Conclusions: Basophilia in PV is associated with palpable splenomegaly and leukocytosis and independently predicts leukemic and myelofibrotic transformation. Additional studies are needed to confirm these observations and examine prognostic interaction with mutations and karyotype.