Cerquozzi, Sonia

Abstract Introduction: Indolent systemic mastocytosis (ISM) is a clonal mast cell disease driven by the KIT D816V mutation in ~95% of cases and is associated with symptoms of mast cell activation and tissue infiltration. It can cause chronic, debilitating symptoms − including life-threatening anaphylaxis and impaired bone health. While historically most patients have relied on symptom-directed best supportive care (BSC) therapies, avapritinib is used as a new standard of care targeting KIT D816V, the primary driver for SM. Avapritinib is an oral, potent, selective KIT D816V inhibitor, and the first and only approved targeted therapy for adult patients with ISM in the USA and the EU. Approval was based on results from the phase 2 PIONEER trial. Here, we present the findings from ~3.5-year long-term follow-up. Methods: Adults with centrally confirmed ISM and uncontrolled moderate-to-severe symptoms who completed the randomized dose-finding (Part 1), or randomized, double-blind, placebo-controlled (Part 2) portions of PIONEER (NCT03731260) rolled over to the open-label, long-term extension (Part 3). This cumulative analysis includes patients who initiated avapritinib at the recommended dose of 25 mg once daily (QD) in either Parts 1, 2, or 3. All patients received BSC. Per investigator discretion and based on disease burden, dose titration up to 50 mg QD of avapritinib was permitted in Part 3. Long-term efficacy was assessed by measuring changes in symptoms and QoL, using the ISM-Symptom Assessment Form (ISM-SAF; ©2018 Blueprint Medicines, a Sanofi Company) and the Mastocytosis Quality-of-Life Questionnaire (MC-QoL). Safety was also assessed. Results: Overall, 226 patients initiated avapritinib 25mg QD across Parts 1, 2, and 3. This longer-term analysis is inclusive of 65 patients who dose titrated from 25 mg to 50 mg QD in Part 3. Median (range) treatment duration was 40.0 months (0.7‒67.2) as of February 21, 2025. Longer-term efficacy data with ~3.5 years of follow-up demonstrated sustained disease-related symptom improvements. The mean change (standard deviation [SD]) in total symptom score (TSS, per ISM-SAF), was −19.80 (19.81) at Week 144 (Month 33) and −20.43 (20.57) at Week 168 (Month 39) from a baseline of 48.08 (19.47). Additionally, avapritinib-treated patients demonstrated durable improvement in their most severe symptoms (mean change [SD] from baseline of −3.35 [3.02] at Month 33 and −3.47 [3.19] at Month 39) per ISM-SAF. Sustained responses were observed across all individual symptom domains (0–30) with mean changes (SD) at Month 33 and Month 39 of −3.77 (5.52) and −3.84 (6.05) for the gastrointestinal domain, −8.21 (7.70) and −8.20 (7.85) for the skin domain, and −4.66 (6.24) and −4.87 (6.51) for the neurocognitive domain. The mean percent change (SD) in MC-QoL was −34.67 (40.16) at Month 33 and −40.72 (33.24) at Month 39 from a baseline of 54.24 (18.32). Treatment with avapritinib was well tolerated, and its safety profile was similar to the previously reported placebo-controlled portion. Most treatment-related adverse events (TRAEs) were Grades 1–2, and 7% of patients experienced Grade ≥3 TRAEs of which diarrhea, neutrophil count decrease, and weight increase occurred in >1 patient. No Grade ≥3 TRAEs of increase in transaminases were observed. Edema (peripheral and periorbital), the most frequently reported TRAE, was mostly Grade 1 and occurred most frequently during the first 3–4 months of treatment. Three patients (1%) experienced serious adverse events assessed as treatment related. However, none led to treatment discontinuation and no trends were observed. After approximately 3.5 years of follow-up, low rates of treatment discontinuations (n=7, 3%) due to TRAEs were observed. Conclusion: Longer follow-up of patients with ISM treated on the PIONEER trial, including some on avapritinib for up to 5 years, demonstrates that prolonged avapritinib therapy continues to be effective and well tolerated. Additional prospective analyses will be needed to determine effects of selective KIT D816V-inhibition on anaphylaxis. These data support a favorable benefit-risk profile of avapritinib as a chronic treatment for adult patients with ISM.

Abstract Background: Systemic mastocytosis (SM) comprises a spectrum of subtypes characterized by neoplastic mast cell (MC) infiltration of tissues and release of MC mediators. Non-advanced SM (NonAdvSM), including indolent SM (ISM), smoldering SM (SSM), and bone marrow mastocytosis (BMM) subtypes, is the most prevalent form of SM. NonAdvSM can be associated with debilitating symptomology which can significantly impair quality of life. The gain-of-function somatic KIT c.2447 C>T (p.D816V) mutation is found in up to 95% of patients with SM. Bezuclastinib (CGT9486) is an oral, potent, and selective type 1 tyrosine kinase inhibitor with activity against KIT D816V. Results from Summit (NCT05186753) Part 1 informed the recommended phase 2 dose (100 mg QD bezuclastinib) for Part 2. We report topline results from the 24-week assessment of Summit Part 2. Methods: Summit is a multi-center, randomized, double-blind, placebo (PBO)-controlled Phase 2 trial of bezuclastinib in patients with NonAdvSM who had inadequate symptom control despite best supportive care (BSC) medications. The primary endpoint was 24-week mean change from baseline in Mastocytosis Symptom Severity Daily Diary (MS2D2) total symptom score (TSS) (range 0–110), which is a fit-for-purpose patient-reported outcome measure of NonAdvSM symptom severity. Key secondary endpoints included the proportion of patients with ≥50% reduction in serum tryptase, KIT p.D816V variant allele frequency (VAF), bone marrow (BM) MC burden, and MS2D2 TSS, ≥30% TSS reduction. Patients were randomized 2:1 to receive 100mg QD bezuclastinib + BSC or PBO + BSC. Results: As of May 22, 2025, 179 patients were enrolled in Part 2: 119 were randomized to receive bezuclastinib and 60 to placebo. Patients enrolled were representative of the NonAdvSM population with moderate to severe symptoms. Median age (range) was 51 (23-78) years; 65.9% female; mean (SD) baseline MS2D2 TSS 55.6 (19.8); 82% of patients had ISM, 11% had BMM, and 7% had smoldering SSM. At baseline, median (range) KIT p.D816V VAF in whole blood, BM MC burden, and serum tryptase was 0.25% (0-34%), 10% (1-75%), and 40 (6-692) ng/mL, respectively. Bezuclastinib demonstrated statistically significant superiority to placebo on all primary and key secondary endpoints. At Week 24, bezuclastinib led to significantly greater symptom improvement vs placebo (LS mean [95% CI] MS2D2 TSS change: –24.3 [–27.6 to –21.1] vs –15.4 [–19.6 to –11.2]; placebo-adjusted difference: –8.9 points; P=0.0002). A ≥50% reduction in serum tryptase was achieved in 87.4% of bezuclastinib-treated patients vs 0% on placebo (P<0.0001). Significantly more patients receiving bezuclastinib achieved ≥50% reductions in KIT D816V VAF, serum tryptase, BM MCs (P<0.0001), MS2D2 TSS (P=0.01), and ≥30% reduction in MS2D2 TSS (P=0.0004). Most treatment-emergent adverse events (TEAEs) were low grade (gr; 70% Gr 1) and reversible. The most common TEAEs (≥10%) in any treatment group and occurring in greater frequency in the bezuclastinib arm were hair color changes (69.5% vs 5.0%), altered taste (23.7% vs 0%), nausea (22.0% vs 13.3%), increased ALT/AST (22.0% vs 6.6%), headache (17.8% vs 11.7%), alopecia (11.9% vs 3.3%), and increased ALP (10.2% vs 3.3%). TEAEs (≥10%) that occurred more often in the placebo group were diarrhea (13% vs 18%), dizziness (10% vs 12%), fatigue (7% vs 12%), and arthralgia (6% vs 15%). ALT/AST elevations ≥Gr 3 were experienced by 5.9% of patients. The only hepatic adverse events (AEs) reported were transient lab abnormalities; none required hospitalization. Treatment-related AEs requiring dose reductions occurred in 11% of patients receiving bezuclastinib. All discontinuations (5.9%) due to treatment-related AEs were due to transaminase elevations; all fully resolved. Conclusions: At 24-weeks, bezuclastinib 100 mg QD demonstrated statistically and clinically significant improvements in symptom burden and biomarkers of disease vs placebo in patients with NonAdvSM. The treatment was generally well-tolerated and effective across a population that is representative of the real-world NonAdvSM population, including SSM. These results support the use of bezuclastinib to reduce SM burden and symptoms in pts with NonAdvSM, and a potentially disease-modifying impact.

Abstract Background Polycythemia Vera (PV) constitutes one of the three BCR-ABL1-negative myeloproliferative neoplasms and is characterized by clonal erythrocytosis and the almost invariable presence of JAK2 mutation. An absolute monocyte count (AMC) of ≥1 x 10(9)/L defines chronic myelomonocytic leukemia (CMML) but can also be seen in other myeloid disorders including myelodysplastic syndromes (MDS) and myeloproliferative neoplasms (MPN). The presence or development of monocytosis has previously been shown to confer poor prognosis in both primary myelofibrosis (PMF), which is one of the three BCR-ABL1-negative MPN (Leukemia Research 2007;31:1503, Mod Pathol. 2013 Feb;26(2):204) and MDS (Haematologica. 1997;82:25). In the current study, we examined the clinical, prognostic and molecular correlates of monocytosis in PV. Methods Study patients were selected from our institutional database of MPN and fulfilled the 2008 World Health Organization (WHO) criteria for the diagnosis of PV (Blood. 2009;114:937). Cytogenetic and mutational analyses were performed according to conventional methods (Leukemia. 2014;28:2206) any assignment as unfavorable karyotype was per PMF criteria (Leukemia. 2011;25:82). Mutation screening included TET2, ASXL1 and SRSF2 because of their known association with CMML (Leukemia. 2014;28:2206) Statistical analyses considered clinical and laboratory parameters obtained at time of diagnosis. Results Patient characteristics: Analysis was conducted on 587 patients (median age 60 years; 48% males) who met WHO criteria for diagnosis of PV. Amongst them, accurate documentation of AMC was available in 237 patients, cytogenetic information in 239, and ASXL1, TET2 and SRSF2 mutational status in 133 patients. Median (range) values were for AMC 0.6 x 10(9)/L (0-4.7) and leukocytes 11.6 x 10(9)/L (3.8-171.6). 31% of 506 informative patients had palpable splenomegaly, 34% of 551 had microcirculatory symptoms, 30% of 566 had pruritus, 8% of 504 had erythromelalgia, 42% of 581 had hypertension, 9% of 584 had diabetes and 11% of 575 were active tobacco users. 25% of the patients presented with history of thrombosis and 22% developed thrombosis after diagnosis. Cytogenetic findings were abnormal in 19%, of whom 20% were unfavorable. TET2, ASXL1 and SRSF2 mutations were documented in 18%, 11% and 3%, respectively. During follow-up, 224 (38%) patients died and median follow-up for living patients was 109 months. Median survival was 16 years and leukemic or fibrotic transformations were documented in 4% and 14%, respectively. Comparison of patients with and without monocytosis: Among 237 informative patients, 32 (14%) displayed monocytosis (AMC ≥1 x 10(9)/L) at time of diagnosis. PV patients with monocytosis were older (p=0.006) and displayed higher leukocyte count (p<0.0001) and higher incidences of leukocytosis (p=0.024) and unfavorable cytogenetic abnormalities (p=0.02). There was no association between monocytosis and mutations for TET2 (p=0.1), ASXL1 (p=0.7) and SRSF2 (p=0.3) or thrombosis before (p=0.9) or after (p=0.5) diagnosis (p=0.5), palpable splenomegaly (p=0.6), pruritus (p=0.7) or microcirculatory symptoms (p=0.1). Among the 237 PV patients in whom information regarding AMC was available, 70 (30%) died during follow-up and 49 (21%), 23 (10%), 9 (4%) developed thrombosis, leukemic transformation or fibrotic progression, respectively. In univariate analysis, overall (p=0.009; HR 2.0, 95% CI 1.2-3.4) but not leukemia-free (p=0.79), myelofibrosis-free (p=0.13) or thrombosis-free (p=0.48) survivals were different between patients with or without monocytosis. Furthermore, the significant difference in survival was no longer apparent when analysis was adjusted for age (p=0.13), unfavorable karyotype (0.17) or leukocytosis (p=0.06). Conclusions Monocytosis (AMC ≥1 x 10(9)/L) is not infrequent in PV (14%). However, the presence of monocytosis does not appear to represent a significantly different phenotype in terms of molecular characteristics although it is associated with older age, leukocytosis and unfavorable karyotype. The latter associations account for the inferior survival seen in patients with monocytosis. Disclosures No relevant conflicts of interest to declare.

Abstract Background Increased bone marrow (BM) reticulin fibrosis in polycythemia vera (PV) has been reported in 20% (Ann Hematol. 1999;78:495) to 51% (Eur J Haematol. 2011;86:148) of patients at diagnosis. In a previous report by the international working group for myeloproliferative neoplasms (MPN) research and treatment (IWG-MRT), the presence of BM fibrosis (≥ grade 1) at diagnosis was associated with a lower incidence of thrombosis during the clinical course and a higher risk of fibrotic progression while it did not affect overall (OS) or leukemia-free (LFS) survival (Blood. 2012;119:2239). The objectives for the current single center study of 262 PV patients were to validate the observations from the IWG-MRT and also identify other risk factors for myelofibrosis-free survival (MFFS) in PV. Methods Study patients were selected from our institutional database of MPN and fulfilled the 2016 World Health Organization (WHO) criteria for the diagnosis of PV (Blood. 2016;127:2391). Cytogenetic analysis and reporting was done according to the International System for Human Cytogenetic Nomenclature (Cytogenetic and Genome Research 2013;141:1-6). The degree of BM reticulin fibrosis was based on "real life" BM reports from Mayo Clinic hematopathologists and often in accordance with the European consensus scoring system (Haematologica 2005;90:1128). Statistical analyses considered clinical and laboratory parameters obtained at time of diagnosis. Results Patient characteristics: Analysis was conducted on 262 patients (median age 62 years; 50% males) who met 2016 WHO criteria for diagnosis of PV. Median (range) values were: hemoglobin 18 g/dl (14.8-24), leukocyte count 11.7 x109/L (4.3-59.3) and platelet count 454 x109/L (44-2747). Among informative cases, palpable splenomegaly was present in 27%, pruritus in 33% and erythromelalgia in 6%. Thrombosis history at diagnosis was documented in 28% of the patients and 23% experienced thrombotic events after diagnosis. Information on cytogenetics was available in 142 patients and karyotype was abnormal in 19%. BM reticulin fibrosis was reported to be absent in 135 patients (MF-0, 52%), grade 1 (MF-1) in 101 (39%), grade 2 (MF-2) in 22 (8%) and grade 3 (MF-3) in 4 (2%) patients. After a median follow up of 85 months, 107(41%) deaths, 30 (11%) fibrotic progression and 5 (2%) leukemic transformations were documented. Comparison of patients with and without bone marrow fibrosis A number of clinical and laboratory parameters were evaluated for possible association with the presence of ≥ grade 1 BM reticulin fibrosis and none, including age, sex, complete blood count, palpable splenomegaly, pruritus or erythromelalgia displayed a significant association. In univariate analysis, the presence of BM fibrosis (MF-0 versus MF-1 or greater) did not affect OS (p=0.5), LFS (p=0.2) or thrombosis-free survival (p=0.97) whereas a significant association was noted for MFFS (p=0.009; HR 2.9, 95% CI 1.3-6.7). Others risk factors for MFFS, in a univariate analysis, were leukocytosis ≥15 x 109/L (p=0.02; HR 2.7, 95% CI 1.17-6.48), presence of splenomegaly (p=0.02; HR 2.6, 95% CI 1.16-6) and abnormal karyotype (p=0.0005; HR 4.6, 95% CI 1.9-11). During multivariable analysis, not including karyotype, leukocytosis ≥15 x 109/L (p=0.04), presence of splenomegaly (p=0.04) and presence of BM reticulin fibrosis (p=0.01) remained significant; however, this significance for leukocytosis ≥15 x 109/L, presence of splenomegaly and BM reticulin fibrosis was lost when abnormal karyotype was added as covariate to each risk factor individually (p=0.4, p=0.1 and p=0.9, respectively). Conclusion We report a not infrequent (48% incidence) occurrence of ≥ grade 1 BM reticulin fibrosis at time of initial diagnosis of PV. In the current study, we did not find a prognostic impact for the presence of BM reticulin fibrosis, in terms of OS, LFS or thrombosis-free survival; however, a significant association was confirmed for MFFS that was independent of other non-genetic risk factors. The preliminary observation on the adverse prognostic impact of abnormal karyotype on MFFS requires additional studies. Disclosures No relevant conflicts of interest to declare.

Abstract Background A recent study from the International Working Group on Myeloproliferative Neoplasms Research and Treatment (IWG-MRT) identified prior arterial events and hypertension as risk factors for subsequent arterial thrombosis and prior venous events and age 65 years or older as risk factors for venous thrombosis in polycythemia vera (PV) (Blood 2014;124:3021). In the current single center study, we sought to validate the aforementioned findings from the IWG-MRT and look into further details regarding arterial versus venous thrombosis in PV. Methods Study patients were selected from our institutional database of myeloproliferative neoplasms (MPN) and fulfilled the 2008 World Health Organization (WHO) criteria for the diagnosis of PV (Blood. 2009;114:937). Screening for the two most frequent mutations other than JAK2 (TET2 and ASXL1) were performed according to conventional methods (Leukemia. 2014;28:2206). Statistical analyses considered clinical and laboratory parameters obtained at time of diagnosis. Results Patient characteristics: Analysis was conducted on 587 patients (median age 60 years; 48% males). ASXL1 and TET2 mutational status was available in 133 patients. Among informative cases, 31% had palpable splenomegaly, 34% microcirculatory symptoms, 30% pruritus, 8% erythromelalgia, 42% hypertension, 9% diabetes and 11% were active tobacco users. TET2 and ASXL1 mutations were documented in 18% and 11%, respectively. During follow-up, 224 (38%) patients died and median follow-up for living patients was 109 months. Median survival was 16 years and leukemic or fibrotic transformations were documented in 4% and 14%, respectively. Thrombotic events: A total of 235 (40%) patients experienced at least one thrombotic event before or after diagnosis and included 153 (26%) arterial and 104 (18%) venous events. Thrombotic events were recorded before or at time of diagnosis in 146 (25%) patients and included 97 (17%) arterial and 55 (9%) venous events. Thrombotic events after diagnosis were recorded in 128 (22%) patients and included 82 (14%) arterial and 57 (10%) venous events. Associations for arterial, venous or all thrombotic events occurring at any time before or after time of diagnosis: The occurrence of any thrombotic event before or after diagnosis correlated with active tobacco use (p=0.04), diabetes history (p=0.03), hyperlipidemia (p=0.04) and major hemorrhage (p=0.03). The occurrence of any arterial event before or after diagnosis correlated with advanced age (p=0.006), diabetes history (p=0.005), hypertension history (p=0.004) and hyperlipidemia (p<0.0001). The occurrence of any venous event before or after diagnosis correlated with female sex (p=0.008), younger age (p<0.0001), lower platelet count (p=0.0014) and palpable splenomegaly (p=0.006). TET2 or ASXL1 mutations did not correlate with overall, arterial or venous thrombosis. Risk factors for arterial versus venous events after time of diagnosis: In univariate/multivariable analysis, thrombosis-free survival (TFS) was adversely affected by prior vascular events (p=0.002/0.03 multivariable) and increased leukocyte count (p=0.03/0.03); arterial thrombosis-free survival was adversely affected by prior arterial events (p<0.0001/P<0.0001), hyperlipidemia (p=0.001/0.03), hypertension (p=0.02/NS) and advanced age (p=0.02/NS); venous thrombosis-free survival was adversely affected by prior venous events (p=0.04/0.05), increased leukocyte count (p=0.0009/0.002), and younger age (p=0.02/NS). In addition, major hemorrhage at diagnosis was associated subsequent venous thrombosis in both univariate and multivariable analysis. TET2 or ASXL1 mutations did not affect the risk of overall, arterial or venous thrombosis. Conclusions In contemporarily managed patients with PV, prior vascular events predict future events for both arterial and venous thrombosis; additional risk factors included hyperlipidemia for arterial and increased leukocyte count for venous thrombosis. The current study also identifies association of arterial thrombosis in general with older age and history of hypertension, diabetes or hyperlipidemia whereas venous thrombosis was associated with younger age, female sex and palpable splenomegaly. Additional findings included association of major hemorrhage with thrombosis and higher platelet count with lower risk of venous thrombosis. Disclosures No relevant conflicts of interest to declare.

Abstract Background In polycythemia vera (PV), abnormal karyotype at diagnosis has been reported in 10% to 20% of patients and some studies have suggested an association with inferior survival (Leukemia2013;27:1874) . In the current study, we examined the prognostic contribution of abnormal karyotype, in general, and specific abnormalities, in particular, in newly diagnosed PV. Methods Study patients were selected from our institutional database of myeloproliferative neoplasms (MPN) and fulfilled the 2008 World Health Organization (WHO) criteria for diagnosis of PV (Blood. 2009;114:937). Cytogenetic analysis and reporting was done according to the International System for Human Cytogenetic Nomenclature (Cytogenetic and Genome Research2013;141:1-6). Assignment as "unfavorable karyotype" was according to criteria established for PMF: favorable = normal + favorable abnormalities; unfavorable = unfavorable abnormalities (Leukemia. 2011;25:82). Screening for the two most frequent mutations in PV, other than JAK2 (i.e. TET2 and ASXL1), were performed according to conventional methods (Leukemia. 2014;28:2206). Statistical analyses considered clinical and laboratory parameters obtained at time of diagnosis. Results Patient characteristics: Median (range) values for the 239 study patients (53% females) included: age 62 (17-94), leukocyte count 11.7 x 10(9)/L (4.3-59.3) and platelet count 479 x 10(9)/L (37-2747). Palpable splenomegaly was present in 26% of the patients, pruritus in 27%, erythromelalgia in in 8%, hypertension in 47%, diabetes in 10% and hyperlipidemia in 28%. Thrombosis history at diagnosis was documented in 33% of the patients and 20% experienced the same after diagnosis. 73% of the patients were "high risk" by conventional risk stratification. Mutation screening for TET2 and ASXL1 was performed in 80 patients and mutational frequencies were 19% and 11% respectively. All study patients provided cytogenetic information, which was abnormal in 46 (19%) patients. The most frequent abnormalities were isolated +9 (n=11; 24% of abnormal karyotype and considered favorable), isolated del(20q) (n=8; 17% of abnormal karyotype and considered favorable), isolated loss of Y chromosome (n=7; 15% of abnormal karyotype and considered favorable) and isolated +8 (n=5; 11% of abnormal karyotype and considered unfavorable). A total of 9 (20% of abnormal karyotype) patients displayed unfavorable karyotype that included +8 in 7 patients, del(11q) in one patient and +20 in one patient. After a median follow-up of 83 months, 70 (29%) deaths, 48 (20%) thrombotic events, 20 (8%) fibrotic progressions and 7 (3%) leukemic transformations were documented. Comparison of patients with and without cytogenetic abnormalities Patients with abnormal cytogenetics were older (p=0.048), displayed lower platelet count (p=0.005) and were more likely to be high risk (p=0.02); there was no significant correlation with TET2 or ASXL1 mutation. In univariate analysis, patients with abnormal cytogenetics displayed inferior leukemia-free (p=0.007; HR 10.6, 95% CI 1.9-58.7), myelofibrosis-free (p<0.0001; HR 7.7, 95% CI 3.1-19.3) and overall (p=0.13; HR 1.6, 95% CI 0.9-2.8) survival. Furthermore, the difference in overall survival became significant when cytogenetic abnormalities were classified into unfavorable (p=0.006) and favorable (p=0.6) categories. On the other hand, inferior leukemia-free and myelofibrosis-free survival was noted in both patients with favorable and unfavorable cytogenetic abnormalities, when compared to normal karyotype. During multivariable analysis that included age and leukocytosis (≥15 x 10 (9)/L) as covariates, the adverse effect of abnormal cytogenetics on leukemia-free (p=0.009) or myelofibrosis-free (p<0.0001) survival and that of unfavorable karyotype on overall (p=0.05) survival were shown to be independent. Finally, patients with abnormal cytogenetics were less likely to experience thrombosis after diagnosis (p=0.04; HR 0.3, 95% CI 0.09-0.97), an effect that was independent of both age and thrombosis history. Conclusions Cytogenetic abnormalities in PV confer an independent adverse prognostic effect on overall, leukemia-free and myelofibrosis-free survival, but not thrombosis-free survival; the adverse effect on leukemia-free and myelofibrosis-free survival was seen with both favorable and unfavorable cytogenetic abnormalities. Disclosures No relevant conflicts of interest to declare.

Abstract Background The International Working Group for Myeloproliferative Neoplasms (MPN) Research and Treatment (IWG-MRT) has previously identified older age, leukocytosis, venous thrombosis and abnormal karyotype as risk factors for overall survival (OS) in polycythemia vera (PV), and older age, abnormal karyotype and leukocytes ≥15 × 109/l as risk factors for leukemia-free survival (LFS) (Leukemia2013;27:1874). Serum lactate dehydrogenase (LDH) is a surrogate quantitative measure of cell turnover and tumor burden. We hypothesized that, compared to leukocyte count, serum LDH might be a biologically more accurate indicator of tumor aggression and sought to examine its potential utility as a prognostic biomarker in PV. Methods Study patients were selected from our institutional database of MPN based on their meeting the 2008 or 2016 World Health Organization criteria for diagnosis of PV (Blood. 2009;114:937; Blood 2016 127:2391) and availability of serum LDH level, obtained within six months of diagnosis. Information on karyotype and targeted next-generation sequencing was available in a subset of the patients (Blood 2015 126:354). Statistical analyses considered clinical and laboratory parameters obtained at time of diagnosis. Age and leukocyte count prognostic categories were based on previously published IWG-MRT study (Leukemia2013;27:1874). Results Patient characteristics: A total of 216 patients (50% females) met the above-outlined criteria: median (10th-90th percentile) levels were for age 63 years (38-81), hemoglobin 18 g/dL (16.6-20.7), platelets 467 x 10(9)/L (237-833), leukocyte count 11.7 x 10(9)/L (7.2-20.3) and spleen size 0 cm (0-2). Pruritus was documented in 28%, microcirculatory symptoms in 31%, erythromelalgia in 6%, hypertension in 45%, diabetes in 7%, active tobacco use in 13%, hyperlipidemia in 25%, palpable spleen in 26% and abnormal karyotype in 15% of informative cases. Grading for bone marrow reticulin fibrosis was documented for 144 patients: 50% grade "0", 42% grade "1", 7% grade "2" and 1 grade "3". Thrombosis history at diagnosis was documented in 26% of patients and occurred after diagnosis in 19%. Mutation analysis was available in 72 patients and revealed TET2 mutations in 18 (25%), ASXL1 in 5 (7%), SRSF2 in 2 (3%) and IDH2 in one (1.4%). Serum LDH levels and correlates: Median serum LDH level was 226 U/L (range 71-1008); the upper normal limit (UNL) for Mayo Clinic was 222 U/L. Increased serum LDH was recorded in 110 (51%) patients that included 26 (12%) patients with LDH ≥1.5 x UNL. A significant correlation was demonstrated between increased serum LDH and older age (p=0.007), female sex (p=0.04), leukocytosis (p=0.01), venous thrombosis history (p=0.005) and, interestingly, absence of active tobacco use (p=0.003); no correlation was noted for bone marrow reticulin fibrosis, presence of palpable splenomegaly, abnormal karyotype or ASXL1 mutation. Survival analysis: After a median follow-up of 77 months, 82 (38%) deaths, 8 (3.7%) leukemic transformations, 13 (6%) fibrotic progressions and 41 (19%) thrombotic events were documented. In univariate analysis, the following adversely affected OS: advanced age (P<0.0001), increased LDH as a continuous variable (p=0.0006), LDH ≥1.5 x UNL (p<0.0001), leukocyte count ≥15 x 10(9)/L (p=0.02) and arterial thrombosis history (p=0.001). In multivariable analysis, only age and LDH remained significant; multivariable HR (95% CI) were 5.4 (2.8-10.4) for age ≥67 years, 3.2 (1.8-6.0) for LDH ≥1.5 x UNL and 2.4 (1.2-4.7) for age 57 to 66 years. In the subset of patients with available information on karyotype and non-JAK2 mutations (n=72), advanced age, LDH ≥1.5 x UNL and ASXL1 mutations remained significantly associated with inferior survival. Serum LDH also predicted leukemic transformation (HR 17.8, 95% CI 4.1-78) and fibrotic progression (HR 11.6, 95% CI 25-53.7); in multivariable analysis, only serum LDH ≥1.5 x UNL (HR 22.3, 95% CI 2.1-234.6) and abnormal karyotype (HR 9.5, 95% CI 1.2-74.7) predicted leukemic transformation and only the former predicted fibrotic progression. Conclusions Serum LDH is a simple and inexpensive biomarker that might supersede leukocyte count as an independent predictor of overall, leukemia-free and myelofibrosis-free survival in PV; advanced age and ASXL1 mutations also retained significance for OS and abnormal karyotype for LFS. Disclosures No relevant conflicts of interest to declare.