Advances in Molecular Understanding of Polycythemia Vera, Essential Thrombocythemia, and Primary Myelofibrosis: Towards Precision Medicine.

Myeloproliferative neoplasms (MPNs), including Polycythemia Vera (PV), Essential Thrombocythemia (ET), and Primary Myelofibrosis (PMF), are characterized by the clonal proliferation of hematopoietic stem cells leading to an overproduction of hematopoietic cells. The last two decades have seen significant advances in our understanding of the molecular pathogenesis of these diseases, with the discovery of key mutations in the JAK2, CALR, and MPL genes being pivotal. This review provides a comprehensive update on the molecular landscape of PV, ET, and PMF, highlighting the diagnostic, prognostic, and therapeutic implications of these genetic findings. We delve into the challenges of diagnosing and treating patients with prognostic mutations, clonal evolution, and the impact of emerging technologies like next-generation sequencing and single-cell genomics on the field. The future of MPN management lies in leveraging these molecular insights to develop personalized treatment strategies, aiming for precision medicine that optimizes outcomes for patients. This article synthesizes current knowledge on molecular diagnostics in MPNs, underscoring the critical role of genetic profiling in enhancing patient care and pointing towards future research directions that promise to further refine our approach to these complex disorders.

Epstein-Barr-Virus-Related Lymphoproliferative Disorder in a Patient With Primary Myelofibrosis: A Case Report and Literature Review.

Primary myelofibrosis (PMF) is a rare myeloproliferative neoplasm characterized by elevated platelet counts and fibrous tissues in the bone marrow. The JAK1/2 inhibitor (JAKi), ruxolitinib, has demonstrated efficacy in reducing splenic size, alleviating myelofibrosis-related symptoms, and improving overall survival. While an increased risk of lymphoproliferative disease (LPD) is suggested in patients with PMF, particularly those treated with JAKi, the involvement of Epstein-Barr virus (EBV) in such cases remains poorly documented. Here, we present the case of a 69-year-old woman with PMF who developed multiple lymphadenopathies and elevated soluble interleukin-2 receptor (sIL-2R) levels. Ruxolitinib and steroid therapy improved the symptoms for a short period; however, the lymphadenopathies and ascites eventually worsened. A biopsy confirmed EBV-positive diffuse large B-cell lymphoma, but the patient died of severe tumor lysis syndrome. Additionally, we conducted a literature review on EBV-related LPD in patients with primary and secondary myelofibrosis. Our report and literature review shed light on the occurrence of EBV-related LPD in MF, especially in those treated with JAKi, emphasizing the need to consider lymphoma as a potential diagnosis and monitor the EBV-DNA viral load in patients displaying lymphadenopathies or increased sIL-2R levels.

A lasso and random forest model using flow cytometry data identifies primary myelofibrosis.

Thrombocythemia (ET), polycythemia vera (PV), primary myelofibrosis (PMF), prefibrotic/early (pre-PMF), and overt fibrotic PMF (overt PMF) are classical Philadelphia-Negative (Ph-negative) myeloproliferative neoplasms (MPNs). Differentiating between these types based on morphology and molecular markers is challenging. This study aims to clarify the application of flow cytometry in the diagnosis and differential diagnosis of classical MPNs. This study retrospectively analyzed the immunophenotypes, clinical characteristics, and laboratory findings of 211 Ph-negative MPN patients, including ET, PV, pre-PMF, overt PMF, and 47 controls. Compared to ET and PV, PMF differed in white blood cells, hemoglobin, blast cells in the peripheral blood, abnormal karyotype, and WT1 gene expression. PMF also differed from controls in CD34+ cells, granulocyte phenotype, monocyte phenotype, percentage of plasma cells, and dendritic cells. Notably, the PMF group had a significantly lower plasma cell percentage compared with other groups. A lasso and random forest model select five variables (CD34+CD19+cells and CD34+CD38- cells on CD34+cells, CD13dim+CD11b- cells in granulocytes, CD38str+CD19+/-plasma, and CD123+HLA-DR-basophils), which identify PMF with a sensitivity and specificity of 90%. Simultaneously, a classification and regression tree model was constructed using the percentage of CD34+CD38- on CD34+ cells and platelet counts to distinguish between ET and pre-PMF, with accuracies of 94.3% and 83.9%, respectively. Flow immunophenotyping aids in diagnosing PMF and differentiating between ET and PV. It also helps distinguish pre-PMF from ET and guides treatment decisions.

Conventional Cytogenetic Analysis and Array CGH + SNP Identify Essential Thrombocythemia and Prefibrotic Primary Myelofibrosis Patients Who Are at Risk for Disease Progression.

The Philadelphia chromosome-negative myeloproliferative neoplasms (Ph-MPNs) are a heterogeneous group of clonal hematopoietic malignancies that include polycythemia vera (PV), essential thrombocythemia (ET), and the prefibrotic form of primary myelofibrosis (prePMF). In this study, we retrospectively reviewed the karyotypes from conventional cytogenetics (CC) and array Comparative Genomic Hybridization + Single Nucleotide Polymorphism (aCGH + SNP) in patients with ET or prePMF to determine whether the combined analysis of both methodologies can identify patients who may be at a higher risk of disease progression. We performed a comprehensive genomic review on 169 patients with a clinical diagnosis of ET (154 patients) or prePMF (15 patients). Genomic alterations detected by CC or array-CGH + SNP were detected in 36% of patients. In patients who progressed, 68% had an abnormal genomic finding by either technology. There was a shorter progression-free survival (PFS) among patients who were cytogenetically abnormal or who were cytogenetically normal but had an abnormal aCGH + SNP result. Leveraging the ability to detect submicroscopic copy number alterations and regions of copy neutral-loss of heterozygosity, we identified a higher number of patients harboring genomic abnormalities than previously reported. These results underscore the importance of genomic analysis in prognostication and provide valuable information for clinical management and treatment decisions.

Renal extramedullary hematopoiesis as an epiphenomenon of bone marrow dysfunction in a patient with primary myelofibrosis: A rare case report.

Extramedullary hematopoiesis represents a clinical compensatory condition characterized by the growth of hematopoietic tissue outside the bone marrow. It can mainly occur in patient with myeloproliferative disorders where alteration or neoplastic invasion of the bone marrow causes ineffective production of blood cells with the recruitment of progenitrix blood cells in non-hematopoietic organs, including kidneys. Renal extramedullary hematopoiesis is a rare condition manifesting as parenchymal or perirenal soft tissue masses with different patterns mimicking neoplasms, infectious or vascular diseases. We describe a unique case of a patient affected by primary myelofibrosis underwent ultrasound and magnetic resonance examinations showing bilateral perirenal alterations to be related to hemopoietic tissue. We also focused on the pathophysiology of this condition with imaging correlation. The case we present emphasises the importance of recognising the main radiological features of renal extramedullary hematopoiesis. MR examination should become part of the diagnostic pathway of the patient with primary myelofibrosis.

Targeted Metabolomics Highlights Dramatic Antioxidant Depletion, Increased Oxidative/Nitrosative Stress and Altered Purine and Pyrimidine Concentrations in Serum of Primary Myelofibrosis Patients.

To date, little is known concerning the circulating levels of biochemically relevant metabolites (antioxidants, oxidative/nitrosative stress biomarkers, purines, and pyrimidines) in patients with primary myelofibrosis (PMF), a rare form of myeloproliferative tumor causing a dramatic decrease in erythropoiesis and angiogenesis. In this study, using a targeted metabolomic approach, serum samples of 22 PMF patients and of 22 control healthy donors were analyzed to quantify the circulating concentrations of hypoxanthine, xanthine, uric acid (as representative purines), uracil, ß-pseudouridine, uridine (as representative pyrimidines), reduced glutathione (GSH), ascorbic acid (as two of the main water-soluble antioxidants), malondialdehyde, nitrite, nitrate (as oxidative/nitrosative stress biomarkers) and creatinine, using well-established HPLC method for their determination. Results showed that PMF patients have dramatic depletions of both ascorbic acid and GSH (37.3- and 3.81-times lower circulating concentrations, respectively, than those recorded in healthy controls, p < 0.0001), accompanied by significant increases in malondialdehyde (MDA) and nitrite + nitrate (4.73- and 1.66-times higher circulating concentrations, respectively, than those recorded in healthy controls, p < 0.0001). Additionally, PMF patients have remarkable alterations of circulating purines, pyrimidines, and creatinine, suggesting potential mitochondrial dysfunctions causing energy metabolism imbalance and consequent increases in these cell energy-related compounds. Overall, these results, besides evidencing previously unknown serum metabolic alterations in PMF patients, suggest that the determination of serum levels of the aforementioned compounds may be useful to evaluate PMF patients on hospital admission for adjunctive therapies aimed at recovering their correct antioxidant status, as well as to monitor patients' status and potential pharmacological treatments.

Evaluation of Absolute Neutrophil, Lymphocyte and Platelet Count and Their Ratios as Predictors of Thrombotic Risk in Patients with Prefibrotic and Overt Myelofibrosis.

AIM: To investigate the prognostic contribution of absolute neutrophil (ANC), lymphocyte (ALC), platelet count and their ratios, neutrophil-lymphocyte ratio (NLR) and platelet-lymphocyte ratio (PLR), to thrombotic risk in patients with prefibrotic and overt fibrotic myelofibrosis (MF). METHODS: We retrospectively analyzed a cohort of 256 patients with prefibrotic (85 patients) and overt fibrotic MF (171 patients) treated in six Croatian hematological centers. RESULTS: Prefibrotic compared to overt fibrotic MF patients presented with significantly higher ALC, platelet count and PLR, and experienced longer time to thrombosis (TTT). Among prefibrotic patients, ANC > 8.33 × 109/L (HR 13.08, p = 0.036), ALC > 2.58 × 109/L (HR 20.63, p = 0.049) and platelet count > 752 × 109/L (HR 10.5, p = 0.043) remained independently associated with shorter TTT. Among overt fibrotic patients, ANC > 8.8 × 109/L (HR 4.49, p = 0.004), ALC ≤ 1.43 × 109/L (HR 4.15, p = 0.003), platelet count ≤ 385 × 109/L (HR 4.68, p = 0.004) and chronic kidney disease (HR 9.07, p < 0.001) remained independently associated with shorter TTT. CONCLUSIONS: Prognostic properties of ANC, ALC and platelet count are mutually independent and exceed those of NLR and PLR regarding thrombotic risk stratification. ALC and platelet count associate in opposite directions with thrombotic risk in prefibrotic and overt fibrotic MF patients.

Retinal Vessel Analysis and Microvascular Abnormalities in Patients with Philadelphia-Negative Chronic Myeloproliferative Neoplasms.

Background: Philadelphia-negative chronic myeloproliferative neoplasms are a group of clonal hematopoietic disorders including polycythemia vera, essential thrombocythemia, and primary myelofi-brosis. These neoplasms are characterized by an increased risk of thrombotic complications. Several studies have highlighted that the study of vessels of the retina offers the opportunity to visualize, in vivo, the damage to microcirculation that is common in various systemic pathologies. Methods: in our study, forty patients underwent an ophthalmological examination, using non-invasive imaging tech-niques, for analyses of their retinal vascularization. The objective was to correlate the findings ob-tained from this study of the retina with different markers of thrombotic risk, to demonstrate the usefulness of studying retinal vessels as a possible new prognostic biomarker of thrombotic risk in patients affected by Philadelphia-negative chronic myeloproliferative neoplasms. Results: retinal imaging demonstrated changes in the microcirculation, with a reduced vascular density of the deep and superficial capillary plexuses with respect to a normal group, and a correlation between retinal changes and blood parameters. Conclusions: additional research will allow us to determine whether retinal changes in individuals with chronic myeloproliferative neoplasms could be predictive of the development of thrombotic events in these subjects.

Chronic myeloproliferative neoplasms with concomitant CALR mutation and BCR::ABL1 translocation: diagnostic and therapeutic implications of a rare hybrid disease.

Myeloproliferative neoplasms (MPNs) are subdivided into Philadelphia (Ph) chromosome-positive chronic myeloid leukemia (CML) and Ph-negative MPNs. BCR::ABL1 translocation is essential for the development and diagnosis of CML; on the other hand, the majority of Ph-negative MPNs are characterized by generally mutually exclusive mutations of Janus kinase 2 (JAK2), calreticulin (CALR), or thrombopoietin receptor/myeloproliferative leukemia (MPL). CALR mutations have been described essentially in JAK2 and MPL wild-type essential thrombocythemia and primary myelofibrosis. Rarely coexisting CALR and MPL mutations have been found in Ph-negative MPNs. BCR::ABL1 translocation and JAK2 mutations were initially considered mutually exclusive genomic events, but a discrete number of cases with the combination of these genetic alterations have been reported. The presence of BCR::ABL1 translocation with a coexisting CALR mutation is even more uncommon. Herein, starting from a routinely diagnosed case of CALR-mutated primary myelofibrosis subsequently acquiring BCR::ABL1 translocation, we performed a comprehensive review of the literature, discussing the clinicopathologic and molecular features, as well as the outcome and treatment of cases with BCR::ABL1 and CALR co-occurrence.

SOHO State of the Art Updates and Next Questions | Diagnosis, Outcomes, and Management of Prefibrotic Myelofibrosis.

Prefibrotic primary myelofibrosis (prefibrotic PMF) is a myeloproliferative neoplasm with distinct characteristics comprising histopathological and clinico-biological parameters. It is classified as a subtype of primary myelofibrosis. In clinical practice, it is essential to correctly distinguish prefibrotic PMF from essential thrombocythemia especially but also overt PMF besides other myeloid neoplasms. Risk stratification and survival outcomes for prefibrotic PMF are worse than that of ET but better than that of overt PMF. Rates of progression to overt PMF and blast phase disease are also higher for prefibrotic PMF than ET. In this review we first discuss the historical context to the evolution of prefibrotic PMF as an entity, its presenting features and diagnostic criteria. We emphasize the differences between prefibrotic PMF, ET, and overt PMF with regards to presenting features and disease outcomes including thrombohemorrhagic events and progression to fibrotic and blast phase disease. Next, we discuss the risk stratification models and contextualize these in the setting of clinical management. We share our view of personalizing treatment to address unique patient needs in the context of currently available management options. Lastly, we discuss areas of critical need in clinical research and speculate on the possibility of future disease course modifying therapies in prefibrotic PMF.

Molecular Genetic Profile of Myelofibrosis: Implications in the Diagnosis, Prognosis, and Treatment Advancements.

Myelofibrosis (MF) is an essential element of primary myelofibrosis, whereas secondary MF may develop in the advanced stages of other myeloid neoplasms, especially polycythemia vera and essential thrombocythemia. Over the last two decades, advances in molecular diagnostic techniques, particularly the integration of next-generation sequencing in clinical laboratories, have revolutionized the diagnosis, classification, and clinical decision making of myelofibrosis. Driver mutations involving JAK2, CALR, and MPL induce hyperactivity in the JAK-STAT signaling pathway, which plays a central role in cell survival and proliferation. Approximately 80% of myelofibrosis cases harbor additional mutations, frequently in the genes responsible for epigenetic regulation and RNA splicing. Detecting these mutations is crucial for diagnosing myeloproliferative neoplasms (MPNs), especially in cases where no mutations are present in the three driver genes (triple-negative MPNs). While fibrosis in the bone marrow results from the disturbance of inflammatory cytokines, it is fundamentally associated with mutation-driven hematopoiesis. The mutation profile and order of acquiring diverse mutations influence the MPN phenotype. Mutation profiling reveals clonal diversity in MF, offering insights into the clonal evolution of neoplastic progression. Prognostic prediction plays a pivotal role in guiding the treatment of myelofibrosis. Mutation profiles and cytogenetic abnormalities have been integrated into advanced prognostic scoring systems and personalized risk stratification for MF. Presently, JAK inhibitors are part of the standard of care for MF, with newer generations developed for enhanced efficacy and reduced adverse effects. However, only a minority of patients have achieved a significant molecular-level response. Clinical trials exploring innovative approaches, such as combining hypomethylation agents that target epigenetic regulators, drugs proven effective in myelodysplastic syndrome, or immune and inflammatory modulators with JAK inhibitors, have demonstrated promising results. These combinations may be more effective in patients with high-risk mutations and complex mutation profiles. Expanding mutation profiling studies with more sensitive and specific molecular methods, as well as sequencing a broader spectrum of genes in clinical patients, may reveal molecular mechanisms in cases currently lacking detectable driver mutations, provide a better understanding of the association between genetic alterations and clinical phenotypes, and offer valuable information to advance personalized treatment protocols to improve long-term survival and eradicate mutant clones with the hope of curing MF.

[Primary myelofibrosis with double mutation in U2AF1].

A 47-year-old woman presented with subcutaneous hemorrhage. Blood tests revealed leukoerythroblastosis, anemia, and thrombocytopenia. Bone marrow biopsy led to a diagnosis of primary myelofibrosis (aaDIPSS, DIPSS-plus: intermediate-II risk). JAK2, CALR, and MPL mutations were not detected in peripheral blood, but targeted sequencing of bone marrow specimens revealed a double mutation (Q157R, S34F) in U2AF1. Allo-PBSCT was performed using an HLA-matched related donor, and post-transplantation bone marrow examination showed complete donor chimerism on day 55. Two years after allogeneic transplantation, the patient remains relapse-free. Although U2AF1 gene abnormality is known as a poor prognostic factor in primary myelofibrosis, this patient had a favorable long-term prognosis due to prompt transplantation therapy. This case highlights the importance of detailed gene mutation analysis in patients with triple-negative MF.

[Pathogenesis and Targeted Treatment Progress of Splenomegaly in Primary Myelofibrosis--Review].

Primary myelofibrosis (PMF) is a myeloproliferative neoplasm with splenomegaly as the major clinical manifestation, which is commonly considered to be linked to splenic extramedullary hematopoiesis. Alteration of CXCL12/CXCR4 pathway can lead to the migration of hematopoietic stem cells and hematopoietic progenitor cells from bone marrow to spleen which results in splenic extramedullary hematopoiesis. In addition, low GATA1 expression and the abnormal secretion of cytokines were found to be significantly associated with splenomegaly. With the application of JAK1/2 inhibitors in clinical, the symptoms of splenomegaly have been significantly improved in PMF patients. This article will review the pathogenesis and targeted treatment progress of splenomegaly in PMF.

JAK2V617F drives gut microbiota differences in patients with myeloproliferative neoplasms.

BACKGROUND: Essential thrombocythemia (ET), polycythemia vera (PV), and primary myelofibrosis (MF) are myeloproliferative neoplasms (MPN). Inflammation is involved in the initiation, progression, and symptomology of the diseases. The gut microbiota impacts the immune system, infection control, and steady-state hematopoiesis. METHODS: We analyzed the gut microbiota of 227 MPN patients and healthy controls (HCs) using next-generation sequencing. We expanded our previous results in PV and ET patients with additional PV, pre-MF, and MF patients which allowed us to compare MPN patients collectively, MPN sub-diagnoses, and MPN mutations (separately and combined) vs. HCs (N = 42) and compare within MPN sub-diagnoses and MPN mutation. RESULTS: MPN patients had a higher observed richness (median, 245 [range, 49-659]) compared with HCs (191.5 [range, 111-300; p = .003]) and a lower relative abundance of taxa within the Firmicutes phylum; for example, Faecalibacterium (6% vs. 14%, p < .001). The microbiota of CALR-positive patients (N = 30) resembled that of HCs more than that of patients with JAK2V617F (N = 177). In JAK2V617F-positive patients, only minor differences in the gut microbiota were observed between MPN sub-diagnoses, illustrating the importance of this mutation. CONCLUSION: The gut microbiota in MPN patients differs from HCs and is driven by JAK2V617F, whereas the gut microbiota in CALR patients resembles HCs more.

Insights into the role of JAK2-I724T variant in myeloproliferative neoplasms from a unique cohort of New Zealand patients.

OBJECTIVES: This study aimed to compile bioinformatic and experimental information for JAK2 missense variants previously reported in myeloproliferative neoplasms (MPN) and determine if germline JAK2-I724T, recently found to be common in New Zealand Polynesians, associates with MPN. METHODS: For all JAK2 variants found in the literature, gnomAD_exome allele frequencies were extracted and REVEL scores were calculated using the dbNSFP database. We investigated the prevalence of JAK2-I724T in a cohort of 111 New Zealand MPN patients using a TaqMan assay, examined its allelic co-occurrence with JAK2-V617F using Oxford Nanopore sequencing, and modelled the impact of I724T on JAK2 using I-Mutant and ChimeraX software. RESULTS: Several non-V617F JAK2 variants previously reported in MPN had REVEL scores greater than 0.5, suggesting pathogenicity. JAK2-I724T (REVEL score 0.753) was more common in New Zealand Polynesian MPN patients (n = 2/27; 7.4%) than in other New Zealand patients (n = 0/84; 0%) but less common than expected for healthy Polynesians (n = 56/377; 14.9%). Patients carrying I724T (n = 2), one with polycythaemia vera and one with essential thrombocythaemia, had high-risk MPN. Both patients with JAK2-I724T were also positive for JAK2-V617F, found on the same allele as I724T, as well as separately. In silico modelling did not identify noticeable structural changes that would give JAK2-I724T a gain-of-function. CONCLUSION: Several non-canonical JAK2 variants with high REVEL scores have been reported in MPN, highlighting the need to further understand their relationship with disease. The JAK2-I724T variant does not drive MPN, but additional investigations are required to exclude any potential modulatory effect on the MPN phenotype.

Cardiac tamponade associated with primary myelofibrosis: a case report.

Background: Cardiac tamponade is a life-threatening condition that occurs when an abnormal amount of fluid accumulates in the pericardial sac and impedes the cardiac filling process. Although extremely rare, haematological diseases have the potential to trigger an extramedullary haematopoiesis (EMH) process within the pericardium, resulting in a substantial build-up of pericardial effusion. Case summary: We present the case of a 29-year-old male previously diagnosed with primary myelofibrosis (PMF), who presented to the emergency unit with cardiac tamponade. An emergent pericardiocentesis procedure was performed, successfully evacuating 850 mL of haemorrhagic fluid. Over the course of 3 days, a total of 1.5 L of haemorrhagic effusion were drained from the pericardial space. Analysis of the pericardial fluid revealed evidence of haematopoietic activity, suggesting a potential association with the EMH process occurring within the pericardium. Following a 7-day hospitalization, the patient was discharged in stable condition but later experienced the development of constrictive pericarditis. Discussion: Haemorrhagic pericardial effusion is a rare occurrence. The majority of cases stems from complications of medical procedures (iatrogenic), malignancies, or side effects of antiplatelet/anticoagulant medications. In patients with PMF, the impaired haematopoietic ability caused by the fibrotic process in the bone marrow compels the body to produce blood components elsewhere, a phenomenon known as EMH. On very rare occasions, EMH can develop in the pericardial space, potentially leading to life-threatening cardiac tamponade. Our patient was successfully managed through pericardial fluid evacuation and drainage but later developed constrictive pericarditis.

Real-world clinical characteristics of post-essential thrombocythemia and post-polycythemia vera myelofibrosis.

There are few prospective studies on patients with post-essential thrombocythemia myelofibrosis (PET-MF) and post-polycythemia vera myelofibrosis (PPV-MF). Therefore, we conducted a nationwide longitudinal prospective survey to clarify the clinical characteristics of these diseases. A total of 197 PET-MF and 117 PPV-MF patients diagnosed between 2012 and 2021 were analyzed. The median age at diagnosis was 70.0 years for both diseases. The time from diagnosis of ET or PV to that of MF was 9.6 and 10.4 years, respectively, with no significant difference. Patients with PPV-MF had higher hemoglobin levels and white blood cell counts than those with PET-MF, whereas those with PET-MF had higher platelet counts than those with PPV-MF. Although splenomegaly was more frequent in patients with PPV-MF at diagnosis, there was no difference in the frequency of constitutional symptoms. Ruxolitinib was the most common treatment administered to 74.6% and 83.8% of patients with PET-MF and PPV-MF, respectively. Patients with PET-MF and PPV-MF had similar prognoses, with 3-year overall survival (OS) of 0.742 in PET-MF and 0.768 in PPV-MF patients. In both diseases, leukemic transformation was the leading cause of death, followed by infection. The 3-year OS for patients with PET/PPV-MF and primary MF diagnosed during the same period was 0.754 and 0.626, respectively, with no significant difference. This survey provides real-world clinical features and prognostic data on secondary myelofibrosis in the ruxolitinib era.

Recurrent Stroke with Rapid Development of Intracranial Artery Stenosis and Subsequent Successful Mechanical Thrombectomy in Essential Thrombocythemia.

Essential thrombocythemia is a myeloproliferative neoplasm. Ischemic stroke is frequently the first manifestation of essential thrombocythemia. We herein report a patient with JAK2V617 mutation-positive essential thrombocythemia who developed recurrent ischemic stroke with rapid development of intracranial artery stenosis and subsequently underwent successful mechanical thrombectomy. The high JAK2V617F allele burden in our patient (58.4%) may have affected the patient's condition. We discuss similar reports in the literature and the possible pathophysiologic mechanism of large artery involvement in these patients.

Young patients with myelofibrosis have distinct clinicomolecular features, favorable prognosis, and commonly exhibit inflammatory comorbidities.

Myelofibrosis (MF) is commonly diagnosed in older individuals and has not been extensively studied in young patients. Given the infrequent diagnosis in young patients, analyzing this cohort may identify factors that predict for disease development/progression. We retrospectively analyzed clinical/genomic characteristics, treatments, and outcomes of patients with MF aged 18-50 years (YOUNG) at diagnosis. Sixty-three YOUNG patients were compared to 663 patients diagnosed at 51 or older (OLDER). YOUNG patients were more likely to be female, harbor driving CALR mutations, lack splicing gene mutations, and have low-risk disease by dynamic international prognostic scoring system (DIPSS) at presentation. Thirty-six patients (60%) presented with incidental lab findings and 19 (32%) with symptomatic disease. Median time to first treatment was 9.4 months (mo). Fourteen (22%) YOUNG patients underwent allogeneic hematopoietic stem cell transplant (median 57.4 mo post-diagnosis). Five (8%) developed blast-phase disease (median 99 mo post-diagnosis). Median overall survival (OS) for YOUNG patients was not reached compared to 62.8 mo in OLDER cohort (p < 0.001). The survival advantage for YOUNG patients lost significance when compared to OLDER patients lacking splicing mutations (p = 0.11). Thirty-one (49%) had comorbidities predating MF diagnosis. Presence of a comorbidity correlated with increased disease risk as measured by serial DIPSS (p=0.02). Increased disease risk correlated with decreased OS (p = 0.05). MF is rare in young adults, has distinct clinical/molecular correlates, and a favorable prognosis. The high frequency of inflammatory comorbidities and their correlation with progression of disease risk clinically highlights the role of inflammation in MF pathogenesis.