Diagnosis Of Primary Myelofibrosis Research Articles

Clinical and Prognostic Validation of the Reticulin, Collagen, Osteosclerosis (RCO) Score for Primary Myelofibrosis (PMF)

Introduction: Primary myelofibrosis (PMF) is hallmarked by stromal bone marrow (BM) changes that include reticulin fibrosis, collagen deposition, osteosclerosis, and microvascular proliferation. Accurate evaluation of BM fibrotic changes is key for MF diagnosis and deserves prognostic implications. Gianelli et al. ( Histopathol 2017;71:89) developed a comprehensive score, named reticulin (MF), collagen (Co), osteosclerosis (Ost) score (RCOs), which was prognostically informative and more accurate than the 2005 European Consensus on Grading of Bone Marrow Fibrosis (ECGMF) in identifying high-risk patients (pts). Aims&Methods: This retrospective, single-center study aimed to validate the RCOs and explore its clinical, genetic and prognostic correlates in a large cohort of clinically and molecularly annotated PMF pts diagnosed according to 2022 ICC criteria. The RCOs was assessed by two independent experienced histopathologists (U.G, R.S.). Results: The study included 222 pts with a diagnosis of PMF: 121 (55%) prefibrotic PMF (pre-PMF), 101 (45%) overt PMF. Median age was 66 years (range, 18-91), 127 (57%) were male. BM histological analysis according to the RCO algorithm provided the following results: MF-0 n=20 (9%), MF-1 n=102 (46%), MF-2 n=47 (21%), and MF-3 n=53 (24%); Co-0 n=130 (59%), Co-1 n=33 (15%), Co-2 n=31 (14%), and Co-3 n=28 (13%); Ost-0 n=146 (66%), Ost-1 n=45 (20%), Ost-2 n=18 (8%), and Ost-3 n=13 (6%). Next, we looked at the distribution of the Co and Ost variables according to MF grade and PMF diagnosis. Overall, morphological features evolved harmonically, with pre-PMF showing the less severe stromal changes and higher reticulin fibrosis being associated with the highest values of Co and Ost. Computation of the RCOs returned the following results: RCOs 0 n=20 (9%), RCOs 1 n=94 (42%), RCOs 2 n=15 (7%), RCOs 3 n=19 (9%), RCOs 4 n=9 (4%), RCOs 5 n=16 (7%), RCOs 6 n=13 (6%), RCOs 7 n=17 (8%), RCOs 8 n=11 (5%), and RCOs 9 n=8 (4%). Median RCOs for pts with pre- and overt PMF was 1 (range, 0-2) and 5 (range, 2-9), respectively. We investigated the correlations of RCOs with clinical and molecular variables. Higher RCOs was associated with overt PMF (median, 5 vs 1, P<.0001), male gender (median, 3 vs 1, P=.0005), lower hemoglobin (Pearson's r, -0.5, P<.0001), lower platelets (Pearson's r, -0.4, P<.0001), higher blasts (Pearson's r, 0.4, P<.0001), higher LDH (Pearson's r, 0.5, P<.0001), and higher prevalence of splenomegaly (median, 3 vs 1, P<.0001) and constitutional symptoms (median, 5 vs 1, P=.0004). As to molecular variables, a higher RCOs was associated with abnormal karyotype (median, 3 vs 1, P=.0003), absent JAK2 mut (median, 2 vs 1, P=.0224) but higher JAK2 allele burden in JAK2-mut pts (Pearson's r, 0.3, P<.0006), triple negativity (median, 5 vs 1, P=.0223), EZH2 mut (median, 6 vs 1, P=.0033), ASXL1 mut (median, 6 vs 1, P<.0001), KRAS mut (median, 8 vs 1, P=.0059), and HMR status (i.e., ≥1 mut in ASXL1, EZH2, IDH1/2, SRSF2) (median, 5 vs 1, P<.0001). Median overall survival (OS) was 96 months (95% CI 81-134). In univariate Cox regression analysis, RCOs directly correlated with risk of death (HR 3.1, 95% CI 1.5-6.3, P=.0023). MF and Co variables correlated with OS (respectively: HR 4.0, 95% CI 1.8-8.6, P=.0003; HR 2.7, 95% CI 1.5-5.0, P=.0008), unlike Ost. ROC analysis with death as endpoint confirmed 5 as the optimal cut-off value ( Histopathol 2017;71:89). Pts with RCOs >5 (n=65 overt PMF) had significantly worst OS compared to pts with RCOs <5 (n=121/36 pre-/overt PMF), with median values of 64 vs 134 months (HR 2.3, 95% CI 1.4-3.6, P=.0004) (Fig. 1A). Considering only overt PMF pts, ROC analysis confirmed 5 as the more accurate cut-off value (univariate survival analysis: HR 2.1, 95% CI 1.1-4.2, P=.0257). We finally computed the MIPSS70 by replacing the original BM fibrosis grade ≥2 variable with the dichotomous RCOs 5 ( >/<5) in 177 (80%) pts with full molecular information, and calculated the C-index, Brier score, and time-dependent area under the curve (AUC) (Fig. 1B). The highest values for performance and accuracy in predicting death were achieved by the RCOs 5-integrated MIPSS70 at 12, 36, and 48 months. Conclusions: Our findings confirm the clinical and prognostic consistency of RCOs, supporting the importance of a comprehensive and accurate evaluation of BM stromal changes in PMF. Integration of RCOs within the MIPSS70 might improve the predictive performance of the model.

Quantification of JAK2 V167F in Patients with Myeloproliferative Neoplasms: Comparison of NGS and Digital PCR with Quantitative PCR

Introduction: JAK2 V617F is the most common mutation in the Philadelphia-negative myeloproliferative neoplasms (MPN), detected in 97% of polycythemia vera (PV), and approximately 55% of essential thrombocythemia (ET) and primary myelofibrosis (PMF) cases. According to the WHO, JAK2 V617F positivity is a major criteria for PV, ET or PMF diagnosis. But JAK2 V617F quantification at diagnosis could be useful since a high allelic frequency (or VAF) has been associated with increased symptom burden in PV, risk of thrombotic events in ET and progression in PMF. The current gold standard technique for JAK2 V617F quantification is allele-specific quantitative PCR (qPCR). However, digital PCR (dPCR) is increasingly being employed since it permits absolute quantification of JAK2 V617F without the need for a standard curve. QPCR vs. dPCR comparisons have shown high conformance between the two methods. Moreover, next-generation sequencing technologies (NGS) are increasingly used for MPN diagnosis. The aim of this study was to evaluate the concordance between dPCR and NGS for JAK2 V617F quantification at diagnosis. Methods: JAK2 V617F was quantified in the same sample of genomic DNA, extracted from total leukocytes from peripheral blood or bone marrow at diagnosis, by digital PCR (dPCR) and by NGS. The Absolute Q™ Liquid Biopsy dPCR Assay (JAK2 12600) was used in the QuantStudio™ Absolute Q™ Digital PCR System (Applied Biosystems) with 25 ng DNA. This assay quantifies the number of JAK2 WT-VIC and JAK2 V617F-FAM positive signals in 20000 partitions, determined as copies JAK2 V617F/µl input sample, and expressed as percentage VAF, with a limit of detection of 0.1%. NGS was performed with the MiSeq (Illumina) platform and the targeted 30-gene panel Myeloid Solution™ (SOPHiA GENETICS) using 200 ng DNA. VAF was determined as the number of variant reads divided by the number of total reads (reported as a percentage), with a limit of detection of 2.5%. Statistical analyses were performed using R-commander version 2.8. P-values <0.05 were considered statistically significant. Results: The quantification of JAK2 V617F was carried out in a total of 52 patient samples with both techniques. Of the 52 patients, 5 had a diagnosis of ET and 47 had PV. The average VAF of JAK2 V617F using dPCR was 14.1% and 48.2%, and 17.1% and 47.6% using NGS for ET patients and PV patients, respectively. The concordance of positivity for JAK2 V617F between the two methods was 100%. With dPCR, the average VAF of JAK2 V617F was 44.62% (range 2.7%-100%). With NGS, the average VAF of JAK2 V617F was 44.95% (range 2.5%-96.5%), with an average coverage/read depth >3500 reads. At diagnosis, there was no difference in the mean VAF of JAK2 V617F determined using dPCR vs. NGS (44.62 vs. 44.95, p=0.792, paired Student t-test). There was an excellent correlation between the VAF of JAK2 V617F determined using dPCR vs. NGS (Pearson correlation coefficient 0.944, p<0.001; Figure 1). Only 7 samples had a deviation >10% in the VAF quantification. These determinations are indicated in orange in the graph and listed in the table . The cause of 2/7 deviations might have been a limited DNA volume/concentration available for dPCR. The high concordance of variant quantification by dPCR andNGS was maintained for JAK2 V617F with low VAFs (≤20%, mean 12.0% vs. 11.8%, respectively; p=0.840) and high VAFs (≥80%, mean 90.6% vs. 89.9%, respectively; p=0.858). Conclusions: Overall, excellent correlation was observed between the VAF of JAK2 V617F obtained using dPCR and NGS, showing that NGS is a robust quantification method. However, 7 samples had a difference >10% VAF, with a deviation >25% in 3 cases. Standardization of molecular techniques for JAK2 V617F quantification is important if the VAF is to be monitored during MPN patient follow-up as a biomarker for disease evolution and for response to treatment, with VAF reductions shown for pegylated interferon and ruxolitinib. DPCR might be better suited for follow-up quantification due to its higher sensitivity and lower price, while NGS at diagnosis, apart from detecting and quantifying JAK2 V617F at baseline, has the advantage of providing information on other gene mutations with prognostic value.

Cardiovascular-Related Mortality Risk in Primary Myelofibrosis in Pre-Ruxolitinib and Ruxolitinib Eras

Background Ruxolitinib, a Janus Kinase inhibitor, was approved in 2011 for the treatment of primary myelofibrosis (PMF) and has shown improved survival since its introduction. However, there are reports of possible cardiotoxicity linked to the medication. 1,2 Previous studies have shown that cardiovascular disease (CVD) was the third most common cause of death in PMF. 3 Given that patients with PMF may need therapy for several years, the cardiovascular safety profile of ruxolitinib has been the subject of increased scrutiny. Our goal was to compare the cardiovascular-related mortality (CVM) risk in patients with PMF in the pre-ruxolitinib (pre-Rux) and ruxolitinib (Rux) eras. Methods Using the Surveillance, Epidemiology, and End-result (SEER) Research Plus Data, 17 Registries and Multiple Primary Standardized Incidence Ratio (MP-SIR) registries (2000 - 2020), a retrospective study of patients diagnosed with PMF between 2003 and 2019 was conducted. This period was split into the pre-Rux (2003-2010) and post-approval Rux eras (2012-2019) and compared the standard mortality ratios (SMRs) of CVD in both periods. SMR was expressed as the ratio of cardiovascular deaths observed in PMF to those expected in the general population. Descriptive statistics (frequencies) were compared with Chi-square. The Kaplan-Meier method was used to estimate cumulative relative survival (CRS), and the sub-distribution hazard model for competing risk analysis was used to predict CVM; the significance test was set at <0.05. Results 4,509 patients with PMF were identified between the two study periods (2003-2010 and 2012-2019). As shown in Table 1, a higher proportion of older patients aged 65+ years (67.2% vs. 62.9%, p=0.003) and Non-Hispanic Blacks (8.9% vs. 7.5%, p=0.025) were diagnosed in the Rux era. More patients were alive (49.6% vs. 16.6%, p<0.001), and 5-year CRS was higher in the Rux period (57.1% vs. 47.6%). There was no significant difference in the proportion of deaths due to cardiovascular disease between the two periods. Compared to the general population, patients with PMF had a higher overall CVM independent of the era of diagnosis ( Figure 1). However, there was a decrease in SMR of overall CVD in the post-Rux period (SMR=2.67; 95% CI: 2.28-3.10) compared to the pre-Rux (SMR: 3.42; 95% CI: 2.79-4.15). In terms of specific CVD, the SMRs of diseases of the heart, hypertension without heart diseases, and cerebrovascular disease were higher in the pre-RUX period compared to the Rux era, where SMR was higher only in diseases of the heart, which was still lower than the pre-Rux period (SMR: 2.73 [2.28-3.24] vs. 3.57 [2.84-4.44]). There was no significant difference in the mortality risk from other CVD compared to the general population in both periods. On multivariate analysis, after adjusting for age, sex, race and era of diagnosis, factors associated with reduced odds of CVM were diagnosis of PMF in the RUX era ( HR=0.76; 95% CI: 0.61-0.94, p=0.012), female gender ( HR=0.72; 95% CI: 0.58-0.89, p=0.002) and younger age (<65 years, HR= 0.12; 95% CI: 0.09-0.17, p<0.001. Non-Hispanic Black race was an independent predictor of increased CVM. Conclusion The risk of CVM in PMF compared to the general population did not seem to have increased in the era following the approval of ruxolitinib. The SMRs for overall and some specific cardiovascular diseases appear to be lower in the ruxolitinib era compared to the period before its approval. Lastly, the period following the introduction of ruxolitinib was associated with reduced death from cardiovascular diseases. Hence, ruxolitinib may have had some mortality benefits from cardiovascular disease in PMF; however, further studies are needed to examine and validate this observation.

Prognostic Significance and Clinical Correlations of Myeloid Mutations in Myelofibrosis Based on Their Functional Class

Background: In addition to the driver mutations JAK2, CALR and MPL, patients (pts) with primary myelofibrosis (PMF) may also express mutations in a number of genes frequently associated with myeloid neoplasms. These genes encode regulators of chromatin modification and DNA methylation, RNA splicing and transcription, as well as oncogenes and signal transduction. In pts with PMF, including those with prefibrotic (pre-)-PMF, selected mutations were shown to deserve prognostic relevance, and led to the development of molecular integrated, or exclusive, scores (such as MIPSS70, MIPSS70-plus, GIPSS and others). Aim: The aim of the study was to correlate the type of mutations, clustered in relation to their known functional classes, with hematological and clinical correlates, and outcome in a large population of molecularly annotated pts with PMF. Patients and Methods: All pts with a confirmed ICC 2022 diagnosis of PMF from the database at CRIMM (Florence), for whom mutation analysis of a panel of 40 myeloid neoplasm-associated genes performed by NGS (Oncomine, ThermoFisher) was available, were included in the study. Pts were stratified in 6 categories based on known function of mutated gene: spliceosome (cat. 1: SF3B1, U2AF1, SRSF2, ZRSR2), DNA methylation gene (cat. 2: TET2, DNMT3A, IDH1, IDH2, SETBP1), histone modification gene (cat. 3: ASXL1, EZH2), RAS pathway (cat. 4: NRAS, KRAS, CBL, NF1, PTPN11), transcription factor (cat. 5: RUNX1, NFE2, TP53) and “other” gene mutations (cat. 6: LNK/SH2B3). Results: A total of 286 pts with at least 1 myeloid neoplasm-associated gene mutation were included (110 prePMF, 38.5%; 176 overt PMF, 61.5%). Of these, 69 have mutations in spliceosome genes, 81 in DNA methylation genes, 95 in histone modification genes, 19 in the RAS pathway, 13 in transcription factor genes and 9 in “other” gene category. Analysis of clinical characteristics (Table) showed that Cat. 1 pts were significantly older (80.6% aged >60y, P=0.003), no difference regarding gender. There was no difference in blood counts but circulating blasts >1%, that were higher in cat 3 and 1 compared to the others (P=0.009). A G3 fibrosis was more common in cat 3 and 5 (43.5% and 50%, p<0.001). No significant difference was noticed as regarded driver mutations and karyotype abnormalities. Splenomegaly was more common in cat 3 and cat 6 (86.5% and 88.9%, respectively, p=0.015), while constitutional symptoms were enriched in cat 5 (69.2%, p=0.015). The proportion of pts with transfusion dependency was lower among those with mutations in DNA methylation genes (cat. 2) and “other” mutations (cat. 6) (21% and 22.2%, respectively, p=0.014). There was no significant difference among gene categories as regarded IPSS score, MIPSS70 score, thrombosis and bleeding events, progression to overt MF (in case of pre-PMF), transformation to AML and rate of secondary neoplasms. The median overall survival (OS) for all pts was 7.1 years (IC: 5.7-8.5), with categories 2, 4 and 5 showing the longest survival (10.7y (6.3-15.1), 11.5y (4.4-18.7), and 10.5y (2-18.9) respectively). In particular, pts in cat 2 showed significantly longer OS than pts in cat 1 (5.4y; HR 1.7, 95% CI, 1.1-2.6; p=0.021) and cat 3 (10.7 vs 6.1y; HR 1.5, 95% CI, 1-2.3). Considering that cat 1, 3, and 6 on one side, and cat 2, 4, 5 on the other, did not differ significant each to the other, we combined those categories to assess respective impact on survival. We found a statistically significant difference between the 2 groups, with pts harboring mutations in spliceosome, histone modifiers and “other” genes having significantly shortened survival (5.8y, CI 4.1-7.5; HR 1.57, CI 1.13-2.18) compared to the other categories (median survival, 10.8y, CI 7.2-14.3) (P=.007). Conclusion: Current analysis revealed distinctive clinical characteristics and survival outcomes associated with specific categories of mutated myeloid genes in pts with PMF, largely overlapping with the ICC defined “myelodysplasia-related gene mutations” category.

Advances in management of primary myelofibrosis and polycythaemia vera: Implications in clinical practice.

Primary myelofibrosis (PMF) and polycythaemia vera (PV) are rare BCR-ABL1-negative myeloproliferative neoplasms, associated with an increased risk of thrombosis, haemorrhagic complications and progression to fibrosis or leukaemia or fibrosis for PV. Both diseases are characterised by biological and clinical heterogeneity, leading to great variability in their management in routine clinical practice. In this review, we present an updated overview of the diagnosis, prognosis and treatment of PMF and PV, and we discuss how our multidisciplinary expert group based across France translates this evidence-based knowledge into routine clinical practice.

Siremadlin, a Human Double Minute-2 (HDM2) Inhibitor, Added to Ruxolitinib after Suboptimal Response to Ruxolitinib Alone in Patients with Myelofibrosis: Results from Part 1 of the Phase 1/2 Adore Study

Introduction Ruxolitinib (RUX), a first-in-class Janus kinase (JAK)1/JAK2 inhibitor, is the standard of care for myelofibrosis (MF). However, ~50% patients (pts) discontinue RUX after ~3 years, including a third due to lack/loss of spleen response. Targeting additional pathogenic signaling pathways may provide superior disease control and potentially address underlying causes of disease. JAK2 mutations in MF induce expression of HDM2, which degrades tumor suppressor protein p53. Siremadlin (SIR), a potent and selective HDM2 inhibitor, restores p53-mediated apoptosis, which may promote clonal regression and spleen volume reduction (SVR). ADORE (NCT04097821) is a three-part phase 1/2 platform study assessing RUX in combination with 5 novel compounds, including SIR. We report results from the Part 1 (phase 1b) dose escalation cohort of SIR added to existing stable dose of RUX after suboptimal response to RUX alone. Methods Eligible pts had a diagnosis of primary MF, post-polycythemia vera MF, or post-essential thrombocythemia MF, splenomegaly (a palpable spleen ≥5 cm from the left costal margin or spleen volume ≥450 cm3 by MRI/CT scan), hemoglobin (Hb) level <11 g/dL (earlier protocol: <10 g/dL), and platelet count ≥75 × 109/L. Pts must have received RUX for ≥12 weeks (wks) (earlier protocol: ≥24 wks) and at a stable dose for ≥4 wks (earlier protocol: ≥8 wks) prior to first combination dose. Part 1 objective was to characterize the safety, tolerability, and recommended phase 2 dose (RP2D) of SIR added to RUX. Primary endpoint was incidence and severity of dose-limiting toxicities (DLT) within first 2 cycles; secondary objectives included characterization of the pharmacokinetic (PK) profile. Preliminary efficacy (change in spleen volume by MRI/CT scan from baseline [BL]), total symptom score (TSS) by MFSAF v4.0 and biomarkers were also explored. Pts were allocated to add SIR 20mg, 30mg or 40mg (orally once daily; days 1-5/28-day cycle) to their stable RUX dose (5-25mg twice daily). Adverse events (AEs) were coded by MedDRA and graded by CTCAE v5.0. Results In Part 1 SIR 20mg, 30mg and 40mg cohorts, 1/7, 9/10 and 1/6 pts were ongoing at data cut-off (April 13, 2022) respectively. The number of pts with DLTs after 2 cycles per number of evaluable pts was 0/6 at 20mg, 1/7 at 30mg (grade [G] 4 neutropenia and G4 thrombocytopenia in same pt), and 2/5 at 40mg (G3 and G4 thrombocytopenia). The most common AEs were gastrointestinal (GI) and hematologic (Table). RP2D was SIR 30mg/day. At 30mg, 5 pts experienced SIR-related GI toxicity; all events were G≤2; all lasted ≤4 days except for 1 case controlled with medication; 2 pts required concomitant medication for nausea, however, none discontinued treatment due to GI AEs. The most common hematologic AEs at 30mg were anemia, neutropenia, and thrombocytopenia. Two pts discontinued SIR 30mg due to G3 neutropenia and thrombocytopenia (for 1 pt) and G3 neutropenia (for 1 pt). At 30mg, 4/10 pts had completed a spleen volume assessment at 24 wks at time of data cut-off and all achieved SVR ≥35% from BL. At 20mg, 1/7 pts had SVR ≥35% at 24 wks. At 40mg, 3 pts discontinued prior to or did not complete spleen volume assessment at wk 24, limiting the availability of efficacy data (Figure). Symptom burden was low at BL across cohorts and subsequent TSS changes were highly variable between pts. SIR exposure increased with dose, with no relevant PK interactions between RUX and SIR observed. SIR increased growth/differentiation factor-15 (GDF15) expression, indicating target TP53 engagement. All pts were TP53 wildtype at BL. At data cut-off, SIR treatment resulted in the emergence of TP53 mutant clones in 1/7 pts at 20mg, 0/10 pts at 30mg and 1/6 pts at 40mg, at very low variant allele frequency (0.02-0.06) with unknown clinical significance. At 24 wks, 4/7 SIR-treated pts with available data had a decrease in JAK2 V617F mutational burden from BL (range 1.85-20.0%). Conclusions The RP2D of SIR is established as 30mg orally once daily on days 1-5/28-day cycle when added to the existing stable dose of RUX in pts with suboptimal response to prior RUX treatment. The addition of SIR 30mg was well tolerated, with low-G short-duration GI toxicity in contrast to an expected HDM2 inhibitor class effect. Other AEs were consistent with known RUX safety profile. Good tolerability at 30mg allowed pts to remain on SIR + RUX and to achieve robust spleen volume responses at 24 wks. The study was sponsored by Novartis Pharmaceuticals. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Allogeneic Hematopoietic Cell Transplantation (Allo-HCT) in Patients with Calr-Mutated Myelofibrosis

Background: Between 50-65% of myelofibrosis (MF) patients who undergo allogeneic hematopoietic cell transplantation (allo-HCT) are cured. Patient age, performance status, comorbidities, donor type, and HLA compatibility are established risk factors for allo-HCT outcomes. However, prognostic information after transplant in MF is largely based on JAK2-mutated patients, as this molecular abnormality is by far the most common and the first to be described. Since there is evidence suggesting that CALR-mutated patients could have a better outcome (Kroger et al., BBMT 2017), a study evaluating prognostic factors in this specific molecular subtype may be of clinical interest. Method: This is a retrospective, registry-based study approved by the Chronic Malignancies Working Party (CMWP) of the European Society for Blood and Marrow Transplantation (EBMT). For the present study, inclusion criteria were adult patients with CALR-mutated MF undergoing first allo-HCT between 2005 and 2019. Patients transplanted from umbilical cord blood or with history of leukemic transformation were excluded. Primary study outcomes were OS, progression-free survival (PFS), relapse, non-relapse mortality (NRM) and graft-versus-host disease (GVHD)-free and relapse-free survival (GRFS). Results: 346 patients transplanted in 123 centers were included, of whom 207 (59.8%) were male. A total of 244 (70.5%) patients had primary MF (PMF) and 102 patients had MF secondary to prior essential thrombocythemia (SMF). Median interval from diagnosis to allo-HCT was 50.9 months (IQR: 17.2-155.6). Median age was 57.4 years (IQR: 51.2-63). DIPSS score at time of allo-HCT was available in 256 (74%) patients and was high, intermediate-2, intermediate-1 and low in 17%, 46%, 35%, and 2%, respectively. Sixty-nine patients (21%) had a high comorbidity index (HCT-CI) > 3. Seventeen patients (7.5%) had been splenectomized before transplant. Reduced intensity (RIC) regimens were utilized in 63% of patients and the donor source was peripheral blood in 95% of cases. Regarding donor type, an HLA-matched sibling donor (MSD), mismatched related donor (MMRD), matched unrelated donor (MUD) and mismatched unrelated donor (MMUD) was used in 92 (27%), 18 (5%), 167 (48%) and 48 (14%) of patients, respectively. T cell depletion was used in 77% of patients. Median time to neutrophil engraftment was 17 days. Incidence of acute GVHD grades II-IV at 100 days and extensive chronic GVHD at 60 months were 27% and 28%, respectively. After a median follow-up of 40 months from transplant, the estimated 5-year OS rate, PFS, GRFS, NRM and relapse incidence was 63%, 57%, 35%, 25% and 18%, respectively. Causes of death were relapse/progression (n=11), GVHD (n=36), infection (n=27), organ failure/toxicity (n=11), secondary malignancy (n=6), other (n=9), and unknown (n=3). The estimated 3-year OS rate was 79%, 37%, 72% and 62% for allo-HCT from MSD, MMRD, MUD and MMUD, respectively (p=0.09; Figure 1). The estimated 5-year OS rate in patients transplanted from an HLA identical donor was 64%. In univariable analysis, a high comorbidity index (47% vs. 66%; p=0.013) and a PMF diagnosis (55% vs. 79%; p=0.008) correlated with inferior 5-year OS rate. These two factors were associated with higher NRM rate at 5 years after transplant (HCT-CI > 3: 28% vs. 19%, p=0.033; PMF: 31% vs. 12%, p=0.012), with no difference in relapse incidence. Table 1 shows the results of the multivariable analyses for the main outcomes. As can be seen, older age (HR: 1.37, 95% CI: 1.08-1.74; p=0.009) was the only factor significantly associated with a worse OS, whereas PMF (HR: 1.58, 95% CI: 0.96-2.62; p=0.07) and transplant from a mismatched donor (HR: 1.55, 95% CI: 0.95-2.52; p=0.08) had a near-to-significant trend for decreased OS. Conclusion: this is the largest series of allo-HCT for CALR-mutated MF patients. Overall, the results seem favorable, especially in patients with SMF or transplanted from an HLA-identical donor, where the 5-year OS in this multicenter series was 79% and 64%, respectively. NRM was the main cause of treatment failure. Figure 1. Overall survival after transplant in 346 CALR-positive myelofibrosis patients depending on the donor type. Table 1. Results of the multivariable analyses for the main study outcomes. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Safety and Effectiveness of Ruxolitinib in Real-World Patients with Myelofibrosis: A 2-Year Observational Study from Taiwan

Introduction Ruxolitinib (RUX) is an approved JAK1/JAK2 inhibitor for the treatment of intermediate or high-risk myelofibrosis, including primary myelofibrosis (PMF), post-polycythemia vera myelofibrosis (PPV-MF), and post-essential thrombocythemia myelofibrosis (PET-MF), but real-world safety and efficacy of RUX in Taiwan are not well understood. This study was conducted to evaluate the safety and efficacy of treatment with RUX with intermediate-2 or high risk PMF, PPV-MF or PET-MF in routine clinical practice. Method This 2-year, single-arm, multicenter, post-marketing surveillance registry collected data on the safety, tolerability, efficacy, and other clinical information of adult patients (pts) aged ≥20 years with a confirmed diagnosis of intermediate-2 or high-risk PMF, PPV-MF, or PET-MF who either received RUX or starting RUX in accordance with the general clinical practice in Taiwan. Primary endpoint included collection of adverse events (AEs), AE of special interest (AESIs; anemia, thrombocytopenia, leukocytosis, hepatitis B virus (HBV) infection or reactivation, tuberculosis (TB) infection, and other infections), and serious adverse events (SAEs) throughout the study. Key secondary endpoints included treatment duration, discontinuation rates, dosage of prescribed RUX, Myeloproliferative Neoplasm symptom assessment form (MPN-10) score after study entry and change in spleen size, specifically in naïve patients who were eligible for spleen response evaluation. Results A total of 99 (51% PMF, 22.4% PPV-MF, and 26.5% PET-MF) pts were recruited, of which 38 (38.4%) pts discontinued due to consent withdrawal (n=11), death (n=10), discontinued prescription of RUX for 3 months (n=4), AEs (n = 2), unsatisfactory therapeutic effect (n=2), administrative problems (n=1), disease progression (n=1), required immediate stem cell transplantation (n=1), and others (n=6). Median age was 68.1 (range: 38.3-87.2) years and gender ratio was balanced, with 97 Taiwanese pts (98.0%). Median disease duration was 13.9 months (range: 0-967.6 months) and 70.7% and 28.3% of pts were identified with the risk of intermediate-2 or high using IPSS/DIPSS risk assessment, respectively. Majority of the recruited pts were RUX pre-treated (n=75; 75.8%) and 24.2% (n=24) pts were RUX-naïve at baseline. During the study, 88 pts (89.8%) had 673 AEs, and 44 (44.9%) experienced 159 SAEs. Half of the pts (55.1%) had moderate or severe SAEs and 39 pts recovered. Over 80% of SAEs (n=131) were not related to RUX. Major AESIs were anemia (29.6%) and thrombocytopenia (20.4%). There were no HBV infection or reactivation reported; 2% of pts had TB while 3% of pts had herpes zoster infections. The major reported infection was pneumonia (20.4%). Key safety data are summarized in Table 1. Most pts had their AEs resolved (77.6%), while 10 deaths occurred due to AEs (10.2%). Majority of the pts (41.8%) received a daily dose of RUX 20 mg at the enrolment, with an average mean daily dose of 22.7±9.2 mg (Figure 1). For naïve pts, mean initial dose was 18.8 ± 8.50 mg and gradually titrated up to 22.3 ± 8.69 mg at 3 months and to 24.0 ± 9.17 mg at 6 months. Among 98 pts, 13.3% pts whose platelet counts between 100-200×103/μL and 21.4% pts whose platelet counts were >200×103/μL were treated with RUX 5-10 mg twice daily. Among 27 RUX pre-treated patients (mean RUX duration before study entry: 17.0 ± 20.98 months), spleen size by palpation was relatively stable throughout the study period. For the 7 RUX naïve pts, the mean spleen size change from baseline was -15.9 %± 28.72 at 12 weeks, -30.8% ± 31.28 at 24 weeks, -54.2% ± 41.93 at 48 weeks and -52.0% ± 36.41 at 96 weeks. However, it should be interpreted with caution due to the small pt pool. A total of 65 pts (65.7%) had >50% improvement in the symptom response by MPN-10 during 2-year study period. . Conclusion This is the first real-world study in Taiwan to evaluate safety and efficacy with RUX in patients with MF. It was observed that physicians employed a conservative strategy for a lower starting dose with gradual titration resulting in comparable safety profile, but lower incidences of thrombocytopenia compared to published clinical trials. The majority of pts reported continuous symptomatic improvement and a small number of RUX naïve pts had pronounced spleen size reduction. Further investigations are required to evaluate whether optimal dose of RUX or titration speed would improve spleen response. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Impact of Higher Calreticulin Gene Mutation Variant Allele Frequency in Patients with Myelofibrosis

Introduction. Calreticulin (CALR) mutations represent the second most frequent driver mut in myeloproliferative neoplasms (MPN), accounting for 20-30% of patients (pts) with Essential Thrombocythemia (ET) and 25-35% Primary Myelofibrosis (PMF). There are 2 types of CALR mutation, Type 1/like (T1), a del52 bp deletion and similar, and Type 2/like (T2), a 5bp insertion and similar, both in exon 9. Most patients have CALR variant allele frequency (VAF) below 50% (conventionally defined as heterozygous, He), while a few were reported with higher VAF (homozygous, Ho). Homozygosity, that may be associated to LOH at chr19, is phenotypically hallmarked by MPO deficiency in myeloid cells. While well-defined hematologic, clinical and prognostics correlates of the VAF of JAK2V617F mutation were reported in MPN, little information is available regarding CALR. Aim. The aim of the study was to characterize the hematological and clinical correlates of higher CALR VAF in a large population of CALR mut pts with primary (PMF) and PET-MF. Patients and Methods. All patients with a confirmed WHO2016 and IWG-MRT diagnosis of PMF and PET-MF, respectively, available in our database, who were CALR mutated, were included. CALR mut was assayed by PCR amplification and capillary gel electrophoresis starting from peripheral blood granulocytes. The VAF was determined by automated interpolation of the area under the curve, and expressed as the mutant peak area divided by (mutant peak area + wild-type peak area). Mutation analysis of a panel of 40 myeloid neoplasm-associated genes was performed by NGS (Oncomine, ThermoFisher). The nonparametric Wilcoxon rank-sum test, Kaplan-Meier estimate of survival and log-rank test were used as appropriate. Results. A total of 121 pts (42 prePMF, 34.7%; 36 overt PMF, 29.8%; 43 PET-MF, 35.5%) were considered. Overall, T1 was found in 87 pts (71.9%), of which 8 (6.6%) were T1-like; T2 in 34 pts (28-1%), of which 3 (2.5%) T2-like. The median CALR VAF was 51.4+10.4%. For the purposes of the analysis, we considered at Higher VAF (CALR-h) pts having a VAF of >95% confidence interval of the distribution in the population, ie a VAF >55%, compared to Lower VAF (CARL-l; <55%). CALR-h was found in 28 pts, accounting for 23.1% of the study population. The frequency of T1 and T2 variants was similar in CALR-h and CALR-l pts, 71% and 28% and 71% and 29%, respectively. There was a significant trend of increased representation of CALR-h pts from prePMF (n=6, 14.3%) to overt PMF (n=8, 22.2%) and PET-MF (n=14, 32.6%); no difference in T1 and T2 relative representation in the different diagnostic category. ASXL1 mut were enriched among CALR-h pts (13/28, 46.4% vs CALR-l, 24/87, 27.6%; P=0.04) as it was the presence of any >1 mutation in an NGS-panel of myeloid genes (CALR-h 82.5% vs 57.5% in CALR-l, P=0.02). However, limited to HMR mutations, no difference was outlined. There was no significant difference between CALR-h and CALR-l pts as regards gender, age, IPSS score, karyotype abnormalities, BM fibrosis grade, constitutional symptoms, splenomegaly, thrombosis and bleeding events at diagnosis. On the other hand, CALR-h pts had lower Hb level (10.8 g/dl (8.3-14.6) vs 12.1 (7.4-16); P=0.02) and platelet count (466x109/L (102-1053) vs 661 (57-1800; P=0.02), and higher peripheral blood CD34+ cell counts (62.2x106/L (4-3450) vs 16.9 (0-2100); P=0.01). A greater proportion of CALR-h pts developed anemia during the FU (median 5.5y, range 0.3-33y). KM analysis revealed an anemia-free survival (Hb <10g/dL) of 7.9y (5.7-10y) in CALR-h vs 22.1y (13.9-30.3y) in CALR-l pts, P=0.004 (Figure). The HR (95%CI) was 3.1 (1.4-7.0). Also leukocytosis-free survival (leukocytes >25x109/L) was shorter in CALR-h pts (P=0.04), HR 2.55 (1.0-6.6). A CALR-h status did not impact on overall survival nor leukemia-free survival even after stratification based on disease subtype. Discussion. We found that about 20% of CALR mut MF pts harbor a higher VAF, here defined as VAF >55%, that is associated with a more anemic phenotype at diagnosis and greater risk of developing anemia in the FU; however, in spite of anemia development, overall survival was not significantly impacted in the different disease categories. Whether a CALR-h condition has different impact in ET remains to be assessed in a separate study. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Risk of second primary malignancy in patients with primary myelofibrosis: a SEER database study

Prior studies report a greater incidence of second primary malignancy (SPM) among patients with myeloproliferative neoplasms, although the true risk in primary myelofibrosis (PMF) has not been elucidated. We utilized the Surveillance, Epidemiology, and End Results database to evaluate the risk of SPM in PMF patients and analyzed the effects of sociodemographic factors on the risk of SPM. Out of 5273 patients, 385 patients (7.30%) developed SPM. SPM occurred at SIR of 1.95 (95% CI 1.76–2.15) and AER of 149.01 per 10,000 population. A significantly higher incidence of melanoma (SIR 1.76, 95% CI 1.01–2.86), lymphoma (SIR 3.38, 95% CI 2.28–4.83), and leukemia (SIR 27.19, 95% CI 23.09-31.81) was observed. The risk was significantly higher in patients ≤60 years, males, chemotherapy recipients, within 5 years of PMF diagnosis, and for PMF diagnosed after 2009.

PB2056: MYELOFIBROSIS IN PATIENTS OLDER THAN 70 YEARS: IS TREATMENT WITH RUXOLITINIB WORTH IT?

Background: Myelofibrosis is an agressive myeloproliferative neoplasm with a higher incidence in older patients who have worse prognosis. In last years, ruxolitinib, a JAK1/2 inhibitor that may control myelofibrosis (MF)-related splenomegaly and symptoms, han been used in this disease regardless of age. Aims: Fifty three patients treated with ruxolitinib between April 2012 and March 2021 from a clinical database of 149 patients were studied in order to assess the effect of age in survival and toxicities Methods: Diagnosis of primary MF (PMF) an post-Essential Thrombocytemia /post-Polycithemic MF was made according to the WHO 2016. Molecular tests for detection for JAK2, MPL and CALR mutations were performed. Ruxolitinib starting dose was decided accordingly to prescribing information.Survival analysis was performed by means of Kaplan-Meier curves and differences between KM curves were evaluated using the Log-rank test. P values less than 0.05 were considered satistically significant. Analyses were performed with SPSS software v.15. Results: Median age was 64 years (range 36–88); median haemoglobin was 110 g/l (range, 60–157) and 48,1% patients had a transfusion-dependent anemia. Median platelet an leucocyte counts were respectively 311 × 109/l (range, 52–1887) and 14,8 × 109/l (range, 52–1887). 54,5% patients have a PMF diagnosis. JAK2V617F was present in 69,8% patients, CALR mutations in 15,4% and MPLW515K/L in 5,3%; 9,5%of the patients were triple negatives. Leucocytes <15x10e9/ and JAK2V617F were correlated with better survival. At the moment of diagnosis, 32,7% of patients were older than 70 years. In this group, the median of survival from the diagnosis was 70 months. Causes of death were, specifically: progression of myelofibrosis (22,2%), evolution into acute leukemia (22,2%), second neoplasias (22,2%), heart disease (33,3%). Summary/Conclusion: 1.-Elderly patients in our group treated with ruxolitinib have a median survival of 70 months which is a clear advantage with respect to historic cohorts of MF. 2.-Ruxolitinib was well tolerated but does not avoid clonal evolution and JAK1 inhibition could worsen tumor inmmunosurveillance.

Risk of second primary malignancy in patients with primary myelofibrosis: A SEER database study.

e19079 Background: Primary myelofibrosis (PMF) carries a poorer prognosis compared to other BCR-ABL-negative myeloproliferative diseases (MPD), and there is increased risk of early mortality due to blast transformation, thrombosis, bleeding complications, and progression of disease. Prior studies report greater incidence of second primary malignancy (SPM) among MPD patients, although the true risk in PMF has not been elucidated. We performed a large database study to evaluate the risk of SPM in PMF patients and analyzed the effects of sociodemographic factors on the risk of SPM. Methods: We used the Surveillance, Epidemiology, and End Results (SEER) database to identify all patients with a histologic diagnosis of PMF from 2009 to 2018. SPM was defined as any subsequent malignancy that developed at least 1 year after the diagnosis of PMF. Using multiple primary standardized incidence ratio (SIR) session of the SEER*Stat software (version 8.3.9), we calculated SIR and absolute excess risk (AER) of SPM for the entire cohort of PMF and also stratified based on age, sex, race, marital status, receipt of chemotherapy, follow-up duration, and year of diagnosis. We generated the 95% confidence intervals (CI) and p-values assuming Poisson distribution of the observed incidences of SPM. Results: A total of 5,273 patients with PMF were included in the analysis, of which 342 patients (6.4%) developed SPM. SPM occurred at SIR of 1.97 (95% CI 1.77-2.18, p&lt;0.05) and AER of 151.87 per 10,000 population. A significantly higher incidence of melanoma (SIR 1.96, 95% CI 1.14-3.14, p&lt;0.05), lymphoma (SIR 3.45, 95% CI 2.31-4.96, p&lt;0.05), and leukemia (SIR 26.87, 95% CI 22.69-31.59, p&lt;0.05) was observed. There was no statistically significant difference in SIR based on sex, race, marital status, follow-up duration, and receipt of chemotherapy. The risk was significantly higher in patients ≤60 years vs patients &gt;60 years (SIR 2.34, 95% CI 1.89-2.86 vs SIR 1.86, 95% CI 1.65-2.10, p 0.01) and for PMF diagnosed after 2009 vs ≤2009 (SIR 2.64, 95% CI 2.26-3.07 vs SIR 1.61, 95% CI 1.40-1.85, p&lt;0.001). Conclusions: Patients with PMF are at a high risk of developing SPM, especially leukemia and lymphoma. Data suggests higher incidence of SPM in patients aged ≤60 years and in the decade after 2009. The impact of ruxolitinib, which was approved in 2011, on the incidence of SPM deserves further study. [Table: see text]

ASXL1 Mutation Is a Novel Risk Factor for Bleeding in Patients with Philadelphia-Negative Myeloproliferative Neoplasms (MPN)

▪Background:Bleeding and thrombosis are prevalent across all myeloproliferative neoplasm (MPN) subtypes and have significant impact on morbidity and mortality. Although risk factors for thrombosis are well established, bleeding risk factors in these patients are poorly characterized. Identifying MPN patients at higher risk for bleeding could guide the duration of anticoagulation for patients with MPN associated thrombosis (balancing the risk between bleeding and thrombosis), select individuals at higher risk for bleeding during prophylactic anticoagulation, and predict for bleeding complications with surgical procedures.Methods:We performed a retrospective analysis of bleeding risk factors among consecutive adult MPN patients treated at Roswell Park Comprehensive Cancer Center. Bleeding events were classified as minor or major events as defined by the International Society of Thrombosis and Hemostasis (ISTH). The primary outcome of interest was time to initial bleeding after MPN diagnosis. Patient characteristics were summarized as range and medians (for continuous variables) and counts with percentages (for categorical variables) (Table 1). Cox regression was used to examine the associations between candidate risk factors with identified bleeding events in univariate and multivariable analyses. Variables with p<0.1 in univariate analyses were selected for multi-variate analysis. A time-dependent variable of thrombosis status was included in the model. A stepwise feature selection based on Akaike Information Criterion was used for model selection. Continuous variables were dichotomized at median for the regression analyses.Results:A total of 170-consecutive adult MPN patients were identified between 2005 and 2021. Median follow-up was 43.5 months (range 0.66-485.72). The rate of bleeding (major and minor) was 4.9/100 patient-years and rate of thrombosis was 5.4/100 patient-years (5.4/100 patient-years for arterial thrombosis and 2.9/100 patient-years for venous thrombosis).In univariable analysis, predictors of bleeding included age > 60 years (HR 2.8; 95% CI 1.47-5.34; p=0.001), diagnoses of primary myelofibrosis (PMF) (HR 2.98; 95% CI 1.29-6.9; p=0.01) and myelodysplastic syndrome/myeloproliferative neoplasm (MDS-MPN) overlap syndrome (HR 4.56, 95% CI1.91-10.88; p=0.0004), prior history of thrombosis (HR 3.3, 95% CI 1.27-8.8; p=0.01) and presence of ASXL1 (HR 4.13, 95% CI 2.13-8.04; p=0.0001), JAK2 V617F (HR 0.58; 95% CI 0.31-1.08; p=0.08) and TET2 mutations (HR 3.46; 95% CI 1.5-7.9; p=0.003). In multivariate analysis, the presence of JAK2 V617F (HR 4.8; 95% CI 1-21.5; p=0.03) and ASXL1 (HR 12.7, 95% CI 1.7-93; p=0.01) mutations were associated with increased risk of bleeding (Figure 2). Patients with polycythemia vera were at lower risk of bleeding (HR -3.5, 95% CI 0-0.8; p=0.03).Since ASXL1 mutation was associated with a higher risk of bleeding, we studied the association between ASXL1 mutation and other clinical variables. Patients with ASXL1 mutations were more likely to have a diagnosis of PMF and MDS-MPN overlap syndrome (p=0.0001), age > 60 years (p=0.0001), risk for thrombosis (p=0.04), lower hematocrit (p=0.009) and platelets (p=0.0003) but higher white blood cell count (WBC) (p= 0.04) (Figure 3). We then studied the correlation between ASXL1 mutation and factor VIII/Von Willebrand complex and factor V, the two most described abnormal coagulation factors in MPN. ASXL1 mutation was not associated with a statistically significant lower VWF Ag (p=0.07) or factor V (p=0.1) that could potentially explain the higher risk of bleeding seen with this mutation (figure 4).Conclusion:ASXL1 mutations are associated with a significantly higher risk of bleeding in adult MPN patients. The risk of bleeding with ASXL1 mutations was independent of prior thrombosis and was not associated with abnormalities in VWF profile or factor V. Confirmation of these findings in additional patients and studies of underlying platelet function to identify the possible mechanism of ASXL1 associated bleeding in these patients are ongoing. [Display omitted] DisclosuresElshoury: Bristol Meyers Squibb: Other: advisory board. Thompson: Novartis/ Bristol-Myers Squibb: Research Funding. Griffiths: Takeda Oncology: Consultancy, Honoraria; Abbvie: Consultancy, Honoraria; Boston Biomedical: Consultancy; Celgene/Bristol-Myers Squibb: Consultancy, Honoraria, Research Funding; Alexion Pharmaceuticals: Consultancy, Research Funding; Novartis: Honoraria; Astex Pharmaceuticals: Honoraria, Research Funding; Taiho Oncology: Consultancy, Honoraria; Apellis Pharmaceuticals: Research Funding; Genentech: Research Funding. Wang: Stemline Therapeutics: Consultancy, Honoraria, Other: Advisory board, Speakers Bureau; Mana Therapeutics: Consultancy, Honoraria; AbbVie: Consultancy, Membership on an entity's Board of Directors or advisory committees; Pfizer: Consultancy, Honoraria, Other: Advisory Board, Speakers Bureau; Novartis: Consultancy, Honoraria, Other: Advisory Board; Kura Oncology: Consultancy, Honoraria, Other: Advisory board, steering committee, Speakers Bureau; Takeda: Consultancy, Honoraria, Other: Advisory board; Jazz Pharmaceuticals: Consultancy, Honoraria, Other: Advisory Board; Kite Pharmaceuticals: Consultancy, Honoraria, Other: Advisory Board; Astellas: Consultancy, Membership on an entity's Board of Directors or advisory committees; BMS/Celgene: Membership on an entity's Board of Directors or advisory committees; Genentech: Membership on an entity's Board of Directors or advisory committees; GlaxoSmithKline: Consultancy, Honoraria, Other: Advisory Board; DAVA Oncology: Consultancy, Speakers Bureau; Rafael Pharmaceuticals: Other: Data safety monitoring committee; Gilead: Consultancy, Honoraria, Other: Advisory board; Daiichi Sankyo: Consultancy, Honoraria, Other: Advisory board; PTC Therapeutics: Consultancy, Honoraria, Other: Advisory board; Genentech: Consultancy; MacroGenics: Consultancy.

Triple Combination of Ruxolutinib, Nilotinib and Prednisone Is Safe and Shows Promising Activity for the Treatment of Myelofibrosis Patients, Results of a Phase Ib Clinical Trial (RUNIC)

▪Background: Ruxolitinib is the standard of care for myelofibrosis (MF). However not all patients respond to ruxolitinib and other lose response while on treatment or require discontinuation due to adverse events. Therefore, several clinical trials with ruxolitinib in combination with other drugs are being conducted. We previously showed the synergistic effect of the combination ruxolitinib/nilotinib/prednisone in ex vivo models of peripheral blood mononuclear cells from MF patients and cell lines.Aims: This phase Ib/II study, non-randomized, open-label, evaluates safety and tolerability of ruxolitinib in combination with nilotinib and prednisone in patients with naïve or ruxolitinib-resistant MF.Methods:Between November 2017 and June 2020, 21 patients were included in RUNIC (EudraCT Number:2016-005214-21) at 6 Spanish sites. Six patients were considered screening failures. A total of 15 patients received at least one dose of ruxolitinib and were included in the intention-to-treat (ITT) or the per-protocol (PP) populations. The study design is summarized in figure 1.Out of 15 evaluable patients whose median age was 66.5 years (53.4-70.8). Six patients (40%) had a diagnosis of primary MF, 4 patients (26.7%) post-polycythemia vera MF, and 4 patients (26.7%) post-essential thrombocythemia MF. Most patients had International Prognostic Scoring System (IPSS) intermediate-1 or -2 disease (5 [33.3%] and 4 [26.7%], respectively), and 9 patients (60%) had JAK2 V617F mutation. Most of the patients (n=13; 86.7%) had received ruxolitinib as previous anti-neoplastic therapy for MF.Results:Eight patients completed 7 cycles (53.3%), and six patients 12 cycles (40%) and nine patients withdrawn because of disease progression, lack of efficacy, or no clinical benefit (n=5), withdrawal of consent (n=2), adverse event (AE) (pulmonary thromboembolism, n=1), and investigator's medical judgment (n=1).All patients experienced at least one AE during the study (the most common were hyperglycemia, asthenia and thrombocytopenia, and 14 patients registered at least one treatment-related AE (the most common were hyperglycemia (22.2%), thrombocytopenia (13.3%), and anemia (8.9%)). Five treatment-related serious adverse events (SAEs) were reported in 2 patients (13.3%), all of them related to nilotinib: one patient had pericardial effusion and bilateral pleural effusion, the other had congestive heart failure, pleural effusion, and pulmonary hypertension. No deaths were registered throughout the study.There were 2 patients with at least one adverse event meeting criteria for dose-limiting toxicity: grade 4 anemia and lumbar pain.Only eight patients were evaluated for spleen lengths at screening and cycle 7 (Figure 2B). Of these, 6 experienced a palpable spleen reduction, 4 of them with a 100% reduction. In contrast, one patient remained with the same spleen length, and one patient experienced a 25% increase.Six patients had both symptom evaluation at screening and cycle 7 (Figure 2D). Four experienced a total symptom score reduction, one patient remained with the same total symptom score, and two patients reported an increase.Six patients had spleen length measures recorded both at screening and at cycle 12. From those, 4 showed a spleen length reduction, 3 of them with a 100% reduction.Conclusions: Ruxolitinib in combination with nilotinib and prednisone showed relevant clinical activity in patients with naïve or ruxolitinib-resistant MF. The tolerability of this combination was acceptable, and the hyperglycemia was the treatment-related AE most frequent. The main cause of trial withdrawn was disease progression, lack of efficacy, or no clinical benefit. Based on these results, this triple combination should be explored in phase II/III clinical trials. [Display omitted] DisclosuresAyala: Incyte Corporation: Membership on an entity's Board of Directors or advisory committees; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees; Astellas: Honoraria; Celgene: Honoraria. Garcia Gutierrez: BMS: Consultancy, Honoraria, Research Funding; Pfizer: Consultancy, Honoraria, Research Funding; Incyte: Consultancy, Honoraria, Research Funding; Novartis: Consultancy, Honoraria, Research Funding. Osorio: Janssen, Abbvie, Roche: Consultancy. Sanchez: Janssen, Jazz Pharmaceuticals, Gilead, Novartis, Amgen: Consultancy. Martínez-López: Janssen, BMS, Novartis, Incyte, Roche, GSK, Pfizer: Consultancy; Roche, Novartis, Incyte, Astellas, BMS: Research Funding.

Osteolytic Bone Lesions in Patients with Primary Myelofibrosis: A Systematic Review

▪Background:Philadelphia negative Myeloproliferative neoplasms classically characterized by excess production of terminal myeloid cells in the peripheral blood. Among this group, primary myelofibrosis is the least common and usually carries the worst prognosis. Bone involvement in primary myelofibrosis has many forms and tend to manifest as osteosclerotic lesions in vast majority of cases, however osteolytic lesions are reported in exceptional occasions. In this review, we tried to shed the light on this rare association.Methods:We performed a systematic review following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. We searched the English literature (Google scholar, PubMed, and SCOPUS) for studies, reviews, case series, and case reports about patient with myelofibrosis who develop lytic bone lesion. We used the terms in combination: “Myelofibrosis'” or “Primary myelofibrosis” OR “chronic idiopathic myelofibrosis” OR “agnogenic myeloid metaplasia” and “Osteolytic bone lesion”, “Osteolytic lesion”, “lytic bone lesion”. The review included patients with primary myelofibrosis confirmed by biopsy. The reference lists of the included studies were scanned for any additional articles. The search included all articles published up to 10th April 2021. Two independent reviewers screened the titles and abstracts of the records independently and papers unrelated to our inclusion criteria were excluded. A total of 13 articles were included in the review.Results :Total of 13 patients were included in the review. 7 patients were males, male to female ratio almost of 1:1. The mean age at time of diagnosis was 57.69 year, only two cases were diagnosed at young age, however the majority have osteolytic bone lesion at age above 50 years (12/13) of cases.The mean time between the diagnosis of primary myelofibrosis until the osteolytic bone lesion capturing was approximately 8.8 years. 9 out of 13 patients have painful bone lesion, others were incidental finding during a scan for other reasons. All patients have significant splenomegaly. All patients had the lytic lesion detected on x ray, and 2 patients had confirmed findings on magnetic resonance imaging (MRI). The most common affected bones were the vertebrae, pelvis, ribs, humerus then the scapula, femur and skull and less frequently wrist bones and calcaneus. Only one case has reported involvement of the tibia and fibula. The shape, the extension and the numbers of lesion were variable, some showed cortical sparing and others come with cortical destruction. 10 out of 13 cases have confirmed the nature of the osteolytic lesion containing hematopoietic stem cells with or without fibrosis, 2 cases were positive for JAK2 mutation. 2 patients have received ruxolitinib, one of them preceded with bone marrow transplant, others received nonspecific therapies.Discussion:The hyperdynamic ineffective bone marrow can have a negative impact on the bone structure resulting in different types of bone pathology including lytic and sclerotic lesions.The exact mechanism beyond developing lytic lesions is not fully studied, observations revealed two possible causes: systemic inflammation and direct mechanical compression from para-osseus lymph nodes.Lesions prevalence was equal in both genders which can be attributable to a small sample size, in addition, most of the patients were in advanced stages when the lytic lesions discovered and this observation can be explained by the needed time to generate extramedullary hematopoiesis and its subsequent effect on bone structure.The variation in time between the diagnosis of PMF and development of osteolytic bone lesions could be due to the indolent phase of the disease, in which patients can survive for decades without symptoms.Until recently the treatment of myelofibrosis was supportive, but after establishing the JAK2-stat pathway role in myeloproliferative disorders the FDA approved ruxolitinib a JAK2 inhibitor which shows not only survival benefit but also has a significant impact on the resolution of the lytic bone lesions as well.conclusionOsteolytic bone lesions in patients with primary myelofibrosis is extremely rare finding, and noticed shortly after diagnosis in elderly and after longer duration in young patients. The lytic lesion seems to have a bad prognostic value as we can notice 11 out of 13 patients died within one year of detection. [Display omitted] DisclosuresNo relevant conflicts of interest to declare.

Should be a Third Dose of BNT162b2 mRNA COVID-19-Vaccine Administered in Patients with Myelofibrosis Under Ruxolitinib?

▪Introduction.Patients with Myelofibrosis (MF) are considered fragile and thus eligible in Italy for COVID-19 BNT162b2 mRNA vaccination. According to the International Prognostic Scoring System (IPSS), patients with intermediate and high MF, may receive clinical benefits from ruxolitinib, the first approved JAK1/JAK2 inhibitor. Given the potent anti-inflammatory properties of ruxolitinib against immunocompetent cells, we previously reported a lower but non-statistically absolute IgG anti-Spike humoral response in vaccinated MF patients treated with ruxolitinib. In the present report we extended the cohort of MF patients.Methods. All MF patients received 2 injections of 30 ug per dose of BNT162b2 mRNA COVID-19 vaccine 3 weeks apart, according to the standard protocol. After injection, mild pain at the injection site was frequently reported. No serious adverse events were registered. The serum level of IgG anti-Spike glycoprotein was tested after a median time of 45 days (range 40-60) from the second vaccine dose, using the approved anti-SARS-CoV-2 IgG CLIA (LIAISON® SARS-CoV-2 TrimericS IgG assay, Diasorin, Saluggia, Italy). An Arbitrary Units per milliliter (AU/mL) ratio of <12.0 was considered to be negative, 12.0-15.0 AU/mL to be borderline and >15 AU/mL to be positive. A conversion of AU/mL to binding antibody units (BAU/mL) as recommended by the World Health Organization (WHO) guidelines was achieved considering the following equation: BAU/mL = 2.6*AU/mL.Results. Overall, 30 MF patients (median age 65 years, range 48-83) were vaccinated. A diagnosis of primary MF was reported in 21 cases (70%), post essential thrombocythemia-MF in 6 (20%) patients and post polycythemia vera-MF in 3 (10%) patients; 23 out of 30 patients (76.6%) were positive for the JAK2V617F, 5 (16.6%) for CALR mutation, 1 (3.3%) for MPL mutation and 1 patient (3.3%) resulted triple negative. Splenomegaly was observed in 14 patients (46%) and 19 (63.3%) reported comorbidities. Nineteen patients (63.3%) were classified as DIPSS low or intermediate-1 risk, and 11 (36.6%) as intermediate-2 or high risk. Fifteen patients (50%) were receiving ruxolitinib, at a median total dose of 20 mg/die (range 20-40 mg) and the remaining 15 patients other treatments (8 patients hydroxyurea and 7 only supportive therapy). None of the patients reported COVID-19 infection neither previous nor subsequently to vaccination. Overall, a positive immune response against COVID-19 was observed in 8 out of 15 patients (53.3%) in the ruxolitinib group, in comparison with 13 out 15 patients (86.6%) in the other treatment group (p=0,046). The absolute IgG anti-Spike value was lower in the ruxolitinib group (median 35.2±49.81) in comparison with the other group (median 226.1±163.9; p=<0.001), Figure 1. In univariate analysis, only ruxolitinib treatment was found associated with a lower humoral immune response to the vaccine.Conclusions. MF patients under ruxolitinib achieved a lower humoral immune response in comparison with MF patients who underwent other treatments. No COVID-19 infection was observed in both groups after vaccination, after a median follow up of 3 months since the second dose. Whether patients with a potential insufficient humoral response to vaccine will benefit from a third dose of BNT162b2 mRNA COVID-19 vaccine is a matter of further investigation. Our preliminary data need to be confirmed in larger cohort of MF patients. [Display omitted] DisclosuresMurru: Abbvie: Consultancy, Honoraria, Other: travel and accommodation; Janssen: Consultancy, Honoraria.

Next-Generation Sequencing Mutational Landscape and Clinical Features of Chinese Adults with Myeloproliferative Neoplasms

▪Myeloproliferative neoplasms (MPNs) include three classical subtypes: polycythemia vera (PV), essential thrombocythemia (ET), and primary myelofibrosis (PMF). Since prefibrotic primary myelofibrosis (pre-PMF) was recognized as a separate entity in the 2016 revised classification of MPN, it has been a subject of debate among experts due to its indefinite diagnosis. However, pre-PMF usually has a distinct outcome compared with either ET or overt PMF. We conducted a retrospective study of MPN patients from October 2014 to June 2020 in the Fourth Affiliated Hospital of Zhejiang University. Patients who were diagnosed with ET, pre-PMF or overt-MF according to the 2016 WHO Classification were included. We reviewed the clinical parameters, haematologic information, and genetic mutations of patients using next-generation sequencing (NGS).Mutation screening was performed in 44 patients by next‐generation sequencing techniques, 84 genes and 258 mutations were detected. JAK2 was the most frequently mutated gene (25/44, 56.82%), followed by TET2 (14/44, 31.82%), KMT2C (13/44, 29.55%), and ASXL1 (10/44, 23.73%) in MPN (Figure 1-A). The VAFs of all studied genes with mutation frequencies >10% are shown in Figure 1-B. Of the 20 patients with ET, 9 (45%) were positive for the JAK2 mutation, 5 (25%) carried FAT1, 5 (25%) carried KMT2C, and 4 (20%) carried CALR. Of the 5 patients with pre-PMF, 4 (80%) carried JAK2, 3 (60%) carried EP300, and 2 (40%) carried TET2. Of the 19 patients with overt PMF, 12 (63%) carried JAK2, 10 (53%) carried TET2, 7 (37%) carried ASXL1, and 6 (32%) carried KMT2C, as reported in Figure 2. The median follow-up was 36 months for ET, 42 months for pre-PMF, and 53 months for overt PMF. Overall survival between pre-PMF, overt PMF, and ET was significantly different (P<0.001), as shown in Figure 3. During the follow-up time, only one death of ET was registered, so we analysed the impact of clinical parameters and mutational status at diagnosis on outcome in PMF, including pre-PMF and overt PMF. We performed Kaplan-Meier curves to examine the relationships between the clinical parameters and patient survival. We found that male sex (P=0.0107), MPN10 symptoms (P=0.0354), anaemia (haemoglobin<120g/L, P=0.0239), and thrombocytopenia (platelet count <100 ×10 9/L, P=0.0002) were significantly related to inferior OS (Figure 4). Pre-PMF patients exhibited higher leukocyte counts, higher LDH values, a higher frequency of splenomegaly, and a higher incidence of hypertension than ET patients. On the other hand, pre-PMF patients had higher platelet counts and haemoglobin levels than overt PMF patients. Molecular analysis revealed that the frequency of EP300 mutations was significantly increased in pre-PMF patients compared with ET and overt PMF patients. In terms of outcome, male sex, along with symptoms including MPN10, anaemia, thrombocytopenia, and KMT2A and CUX1 mutations, indicated a poor prognosis for PMF patients.In conclusion, we identified differences in the clinical, haematologic, and molecular presentations of ET, pre-PMF, and overt PMF patients, indicating that comprehensive evaluation of not only BM features but also clinical, haematologic, and molecular profiles is needed for accurate diagnosis and treatment of these three disease entities. The molecular analysis revealed that pre-PMF might be relevant to EP300 mutation, demonstrating the value of molecular examination. The results of this study indicated that comprehensive evaluation of BM features, clinical phenotypes, haematologic parameters, and molecular profiles is needed for the accurate diagnosis and treatment of ET, pre-PMF, and overt PMF patients.Acknowledgment:The research was supported by the Public Technology Application Research Program of Zhejiang, China (LGF21H080003), the Key Project of Jinhua Science and Technology Plan, China (2020XG-29 and 2020-3-011), the Academician Workstation of the Fourth Affiliated Hospital of the Zhejiang University School of Medicine (2019-2024), the Key Medical Discipline of Yiwu, China (Hematology, 2018-2020) and the Key Medical Discipline of Jinhua, China (Hematology, 2019-2021). [Display omitted] DisclosuresNo relevant conflicts of interest to declare.

Abnormal Expression Of WT1-As, MEG3 and ANRIL Long Non-Coding RNAs In Primary Myelofibrosis and Their Clinical Correlates

A growing body of evidence suggests that long non-coding RNAs (lncRNAs) are involved in the regulation of gene expression in normal and cancer cells by recruiting chromatin remodeling complexes to specific genomic loci [Rinn JL, et al. Cell. 2007; Mattick JS, et al. Bioessays 2009]. For this reason, lncRNAs deregulation can play key roles in malignant transformation and cancer cell behavior. [Kogo R, et al. Cancer Res 2011; Yang F, et al. Hepatology 2011].Despite the increasing number of studies on lncRNAs expression and their involvement in some solid tumors, lncRNAs are far from being extensively characterized in malignant hematopoiesis [Heuston EF, Front Genet 2011]. In particular, lncRNAs expression has never been investigated in cells from primary myelofibrosis (PMF) patients.PMF is a Philadelphia negative chronic Myeloproliferative Neoplasm (MPN) that originates from deregulated clonal proliferation of hematopoietic stem cell associated with overproduction of mature blood cells. Molecular mechanisms underlying MPN pathogenesis were partially unraveled in 2005-2006 with the identification of somatic gain-of-function mutations of JAK2 [James C, et al. Nature 2005; Kralovics R, et al. N Engl J Med 2005; Levine RL, et al. Cancer Cell 2005] and MPL [Pardanani AD, et al. Blood 2006] after which many other mutations were identified. Recently, several new molecular pathogenetic mechanisms were proposed, such as the aberrant expression of coding and non-coding RNAs.After extensive screening of the long non-coding RNA database (lncRNAdb), which is a database providing comprehensive annotations of eukaryotic lncRNAs (http://www.lncrnadb.org) [Amaral PP, Nucleic Acids Res 2011], we identified some previously described lncRNAs as potentially involved in hematological malignancies, such as CDKN2B-antisense (ANRIL), MEG3 and WT1-antisense lncRNAs.With the aim to describe possible abnormalities of lncRNAs in MPN, we investigated the expression of those lncRNAs in CD34+ cells from PMF patients. Since the perturbation of the antisense RNA could alter the expression of the sense gene, we also analyzed the expression of the ANRIL and WT1-as coding genes, called CDKN2B and WT1, to evaluate the correlation of each sense/antisense couple.This study included a total of 26 PMF patients and 16 healthy donors. The diagnosis of PMF was made according to World Health Organization (WHO) criteria.The results evidenced that the majority of PMF samples (74%) displayed a co-upregulation of WT1 and its antisense RNA compared to healthy controls. We found that the large part (61%) of patients harboring concordant upregulation of WT1 sense and antisense belongs to the intermediate-2 and high risk categories of DIPSS-plus scoring system (57.4% and 43.1% in the intermediate-1 and -2, respectively versus 0% in the high-risk category; P = .006) and presents low Hb level, higher percentage of circulating CD34+ cells and a blast count > 1% .Noteworthy, almost 90% of patients with increased expression of WT1 and its antisense showed concurrent upregulation of MEG3 and shared the same clinical variables associated with poor outcome. In fact, also patients harboring higher levels of MEG3 cluster in higher DIPSS-plus scoring system categories, suffer from anemia, have high levels of circulating CD34+ cells and a blast count >1%. These data suggest that not only high levels of WT1-as we previously described [Guglielmelli P, Stem Cells 2007], but also its antisense and MEG3 could identify PMF patients with more severe disease.Finally, we could observe a correlation between CDKN2B upregulation and the grade of BM fibrosis. In fact, the majority of samples having CDKN2B upregulation clustered in categories 2 and 3 (87.3%) as compared to only 4.5% in case of samples showing CDKN2B downregulation (P = .043). Noteworthy, 82% of patients overexpressing CDKN2B were JAK2V617F positive as compared to 22.1% among those with CDKN2B downregulation (P = .004)To our knowledge, this is the first study describing the expression profiles of human lncRNAs in CD34+ cells of PMF patients. Our data demonstrate that WT1-as, MEG3 and ANRIL lncRNAs are aberrantly expressed in PMF CD34+ cells compared to healthy controls. Moreover, different patterns of expression are correlated with some patient' clinical features. Therefore, our results suggest that a deregulated expression of these lncRNAs could play a role in PMF pathogenesis and progression. Disclosures:No relevant conflicts of interest to declare.

Germline RBBP6 Mutations In Myeloproliferative Neoplasms

The pathogenesis of myeloproliferative neoplasms (MPN) is determined by the acquisition of somatic mutations in several genes, such as JAK2, MPL, and TET2. Familial clustering of MPN is observed in 5-10% of cases following predominantly autosomal dominant inheritance with incomplete penetrance. Familial MPN patients carry somatically acquired mutations in JAK2, MPL and other genes similar to sporadic cases. It is thought that the germline mutations in familial cases of MPN predispose to acquisition of somatic mutations which in turn drive the disease. No gene has been implicated in familial MPN predisposition so far. The JAK2haplotype predisposing to MPN at population level does not explain familial MPN cases.We studied a family with five MPN cases in four generations displaying an autosomal dominant pattern of inheritance with reduced penetrance. DNA was available from three MPN cases in the family. One of the patients carried a JAK2-V617F mutation and a deletion on chromosome 22q, while an MPL-W515L mutation was detected in another affected member of the family. The third patient did not have JAK2 or MPLmutations, but carried three chromosomal aberrations on chromosomes 2p, 7q and 15q. Chromosomal aberrations were detected using Affymetrix SNP 6.0 microarrays. The genotypic data from SNP 6.0 arrays was used to perform high-resolution nonparametric linkage analysis. In order to identify the germline mutation predisposing to MPN in the family we performed whole exome sequencing of the three affected members using Illumina next-generation sequencing technology. The mutations identified from exome sequencing were combined with the linkage analysis data.We identified a germline mutation in the RBBP6 gene that segregates with the MPN phenotype in the studied pedigree. Further screening in familial and sporadic MPN cases identified several other germline RBBP6mutations in 5% of the familial and 0.6% of the sporadic MPN cases. Familial MPN cases mostly had the diagnosis of primary myelofibrosis. All the detected mutations cluster in putative p53-binding region of the protein, suggesting a possible link of the mutations and p53 function.The functional effect of the mutations was assessed in a doxycycline-inducible HEK-flp-in cell line system. Upon doxycyline induction, the wild-type and mutant RBBP6 constructs were over-expressed and the consequent functional effect of mutation was assessed using RNA sequencing and global proteomic analyses. The combination of the two datasets yielded 109 genes/proteins that were significantly changed in both the RNA sequencing and the global proteomic results when comparing wild-type to mutant RBBP6, 87 of which were downregulated by the mutation, while 22 were upregulated. Several important cell cycle and apoptosis regulators were found among the deregulated genes, including TP53, BAX, BID and USP7 (downregulated) and CDK6 (upregulated). KEGG pathway analysis of the downregulated genes showed significant enrichment for the p53 and the apoptosis pathways.We have identified germline mutations in RBBP6 that predispose to the development of MPN and are enriched in the families. Functional studies have shown that the mutations likely affect the p53 pathway and apoptosis and thus increase the risk of acquiring somatic mutations that lead to MPN. Our study implicates RBBP6 in MPN susceptibility and suggests that RBBP6 is an important cancer-associated gene. Disclosures:No relevant conflicts of interest to declare.

Abstract CT252: A Phase 3, Randomized, Double-Blind, Placebo-Controlled Study of Ruxolitinib Plus Parsaclisib in Patients with JAK- and PI3K-Inhibitor Treatment-Naïve Myelofibrosis

Abstract Background: Ruxolitinib (JAK1/JAK2 inhibitor) significantly improves outcomes in patients with myelofibrosis (MF); however, a subset of patients may experience a suboptimal response. Recent phase 2 data showed that addition of PI3Kδ inhibitor parsaclisib to ruxolitinib monotherapy resulted in additional alleviation of MF symptoms and splenomegaly in patients with MF (Yacoub. EHA2020. S216). This phase 3, randomized, double-blind study (INCB 50465-313; NCT04551066), evaluates the combination of ruxolitinib and parsaclisib in patients with MF who are naïve to Janus kinase (JAK) and PI3K inhibitor therapies. Methods: Eligible patients are aged ≥18 years with a diagnosis of primary MF, post-polycythemia vera MF, or post-essential thrombocythemia MF, have a Dynamic International Prognostic Scoring System (DIPSS; Passamonti. Blood. 2010;115:1703-1708) risk category of at least Intermediate (INT)-1, palpable spleen ≥5 cm below left subcostal margin, total symptom score ≥10 at screening, ECOG PS 0-2, and life expectancy ≥24 weeks. Patients will be excluded if they previously received therapy with any JAK inhibitor, any PI3K inhibitor, any experimental or standard drug therapy for MF within 3 months of first study dose and/or lack of recovery from all toxicities related to previous therapies to grade ≤1, have recent history of inadequate bone marrow reserve (eg, platelet count &amp;lt;50×109/L) or have inadequate liver or renal function at screening. Approximately 440 patients will be randomized (1:1) to ruxolitinib plus parsaclisib 5 mg QD or ruxolitinib plus matching placebo, with stratification at randomization by DIPSS risk category (high vs INT-2 vs INT-1) and platelet count (≥100×109/L vs 50 to &amp;lt;100×109/L inclusive). Treatment will begin on Day 1, with starting ruxolitinib dose level determined by baseline platelet count, and will continue as long as treatment is tolerated and discontinuation criteria are not met. When the last enrolled patient has completed 24 weeks of treatment, the study will be unblinded and patients randomized to ruxolitinib plus placebo who have adequate hematology parameters will be able to crossover to receive parsaclisib together with continued ruxolitinib. The primary objective is the evaluation and comparison of spleen volume at Week 24 for patients who received ruxolitinib plus parsaclisib versus ruxolitinib plus placebo. Secondary objectives include evaluation and comparison of patient-reported MF symptoms, overall survival, time to onset and duration of response in spleen volume, and safety and tolerability for ruxolitinib plus parsaclisib versus ruxolitinib plus placebo. Sites are opening across the US, Canada, EU, and Asia. Citation Format: Abdulraheem Yacoub, Sue Erickson-Viitanen, Feng Zhou, Albert Assad. A Phase 3, Randomized, Double-Blind, Placebo-Controlled Study of Ruxolitinib Plus Parsaclisib in Patients with JAK- and PI3K-Inhibitor Treatment-Naïve Myelofibrosis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr CT252.