Disease Overview
Primary myelofibrosis (PMF) is a myeloproliferative neoplasm (MPN) characterized by stem cell‐derived clonal myeloproliferation that is often but not always accompanied by JAK2, ...CALR, or MPL mutations. Additional disease features include bone marrow reticulin/collagen fibrosis, aberrant inflammatory cytokine expression, anemia, hepatosplenomegaly, extramedullary hematopoiesis (EMH), constitutional symptoms, cachexia, leukemic progression, and shortened survival.
Diagnosis
Bone marrow morphology is the primary basis for diagnosis. Presence of JAK2, CALR, or MPL mutation, expected in around 90% of the patients, is supportive but not essential for diagnosis; these mutations are also prevalent in the closely related MPNs, namely polycythemia vera (PV) and essential thrombocythemia (ET). The 2016 World Health Organization classification system distinguishes “prefibrotic” from “overtly fibrotic” PMF; the former might mimic ET in its presentation. Furthermore, approximately 15% of patients with ET or PV might progress into a PMF‐like phenotype (post‐ET/PV MF) during their clinical course.
Adverse Mutations
SRSF2, ASXL1, and U2AF1‐Q157 mutations predict inferior survival in PMF, independent of each other and other risk factors. RAS/CBL mutations predicted resistance to ruxolitinib therapy.
Adverse Karyotype
Very high risk abnormalities include −7, inv (3), i(17q), +21, +19, 12p‐, and 11q‐.
Risk Stratification
Two new prognostic systems for PMF have recently been introduced: GIPSS (genetically‐inspired prognostic scoring system) and MIPSS70+ version 2.0 (MIPSSv2; mutation‐ and karyotype‐enhanced international prognostic scoring system). GIPSS is based exclusively on mutations and karyotype. MIPSSv2 includes, in addition, clinical risk factors. GIPSS features four and MIPSSv2 five risk categories.
Risk‐adapted Therapy
Observation alone is advised for MIPSSv2 “low” and “very low” risk disease (estimated 10‐year survival 56%‐92%); allogeneic hematopoietic stem cell transplant (AHSCT) is the preferred treatment for “very high” and “high” risk disease (estimated 10‐year survival 0%‐13%); treatment‐requiring patients with intermediate‐risk disease (estimated 10‐year survival 30%) are best served by participating in clinical trials. In non‐transplant candidates, conventional treatment for anemia includes androgens, prednisone, thalidomide, and danazol; for symptomatic splenomegaly, hydroxyurea and ruxolitinib; and for constitutional symptoms, ruxolitinib. Fedratinib, another JAK2 inhibitor, has now been FDA‐approved for use in ruxolitinib failures. Splenectomy is considered for drug‐refractory splenomegaly and involved field radiotherapy for non‐hepatosplenic EMH and extremity bone pain.
New Directions
A number of new agents, alone or in combination with ruxolitinib, are currently under investigation for MF treatment (ClinicalTrials.gov); preliminary results from some of these clinical trials were presented at the 2020 ASH annual meeting and highlighted in the current document.
On November 16, 2011, the Food and Drug Administration approved ruxolitinib (a JAK1 and JAK2 inhibitor) for use in the treatment of high and intermediate risk myelofibrosis. This is welcome news for ...those patients in whom such therapy is indicated and treatment benefit outweighs attendant risk. The question is who are these patients, what should they expect in terms of both short-term effects and long-term impact, and why would they choose ruxolitinib over other JAK inhibitors that are freely available for use in a research setting. Ruxolitinib and most other JAK inhibitors exert a salutary effect on constitutional symptoms and splenomegaly but have yet to produce histopathologic or cytogenetic remissions, reverse bone marrow fibrosis, or improve survival over best supportive care. Furthermore, the palliative value of JAK inhibitors is diminished by notable side effects, including anemia, thrombocytopenia, gastrointestinal disturbances, metabolic abnormalities, peripheral neuropathy, and hyperacute relapse of symptoms during treatment discontinuation. Therefore, risk-benefit balance favors use of currently available JAK inhibitors in only a select group of patients with myelofibrosis, and their potential value in polycythemia vera, outside of special circumstances (eg, intractable pruritus), is undermined by the absence of evidence for a disease-modifying effect and presence of arguably superior alternatives.
Disease overview
Primary myelofibrosis (PMF) is a myeloproliferative neoplasm (MPN) characterized by stem cell‐derived clonal myeloproliferation that is often but not always accompanied by JAK2, ...CALR, or MPL mutations; additional disease features include bone marrow stromal reaction including reticulin fibrosis, abnormal cytokine expression, anemia, hepatosplenomegaly, extramedullary hematopoiesis (EMH), constitutional symptoms, cachexia, leukemic progression, and shortened survival.
Diagnosis
Diagnosis of PMF is based on bone marrow morphology. Presence of JAK2, CALR, or MPL mutation, expected in ∼ 90% of the patients, is supportive but not essential for diagnosis. The revised 2016 World Health Organization (WHO) classification system distinguishes “prefibrotic” from “overtly fibrotic” PMF; the former might mimic ET in its presentation and it is prognostically relevant to distinguish the two.
Risk stratification
Two new prognostic systems for PMF have recently been introduced: GIPSS (genetically inspired prognostic scoring system) and MIPSS70+ version 2.0 (mutation‐ and karyotype‐enhanced international prognostic scoring system). GIPSS is based exclusively on mutations and karyotype. MIPSS70+ version 2.0 utilizes both genetic and clinical risk factors. GIPSS features four and MIPSS70+ version 2.0 five risk categories. MIPSS70+ version 2.0 requires an online score calculator (http://www.mipss70score.it) while GIPPS offers a lower complexity prognostic tool.
Risk‐adapted therapy
Observation alone is advised for MIPSS70+ version 2.0 “low” and “very low” risk disease (estimated 10‐year survival 56%‐92%); allogeneic stem cell transplant is the preferred treatment of choice for “very high” and “high” risk disease (estimated 10‐year survival 0‐13%); treatment‐requiring patients with intermediate‐risk disease (estimated 10‐year survival 30%) are best served by participating in clinical trials. All other treatment approaches, including the use of JAK2 inhibitors, are mostly palliative and should not be used in the absence of clear treatment indications. Conventional treatment for anemia includes androgens, prednisone, thalidomide and danazol, for symptomatic splenomegaly hydroxyurea and ruxolitinib and for constitutional symptoms ruxolitinib. Splenectomy is considered for drug‐refractory splenomegaly and involved field radiotherapy for nonhepatosplenic EMH and extremity bone pain.
Disease overview
Polycythemia vera (PV) and essential thrombocythemia (ET) are myeloproliferative neoplasms (MPN) respectively characterized by clonal erythrocytosis and thrombocytosis; other disease ...features include leukocytosis, splenomegaly, thrombosis, bleeding, microcirculatory symptoms, pruritus and risk of leukemic or fibrotic transformation.
Diagnosis
Bone marrow morphology remains the cornerstone of diagnosis. In addition, the presence of JAK2 mutation is expected in PV while approximately 90% of patients with ET express mutually exclusive JAK2, CALR or MPL mutations (so called driver mutations). In ET, it is most important to exclude the possibility of prefibrotic myelofibrosis.
Survival
Median survivals are approximately 15 years for PV and 18 years for ET; the corresponding values for patients age 40 or younger were 37 and 35 years. Certain mutations (mostly spliceosome) and abnormal karyotype might compromise survival in PV and ET. Life‐expectancy in ET is inferior to the control population. Driver mutations have not been shown to affect survival in ET but risk of thrombosis is higher in JAK2 mutated cases. Leukemic transformation rates at 10 years are estimated at <1% for ET and 3% for PV.
Thrombosis risk
In PV, two risk categories are considered: high (age > 60 years or thrombosis history present) and low (absence of both risk factors). In ET, four risk categories are considered: very low (age ≤ 60 years, no thrombosis history, JAK2 wild‐type), low (same as very low but JAK2 mutation present), intermediate (age > 60 years, no thrombosis history, JAK2 wild‐type) and high (thrombosis history present or age > 60 years with JAK2 mutation).
Risk‐adapted therapy
The main goal of therapy in both PV and ET is to prevent thrombohemorrhagic complications. All patients with PV require phlebotomy to keep hematocrit below 45% and once‐daily or twice‐daily aspirin (81 mg), in the absence of contraindications. Very low risk ET might not require therapy while aspirin therapy is advised for low risk disease. Cytoreductive therapy is recommended for high‐risk ET and PV, but it is not mandatory for intermediate‐risk ET. First‐line drug of choice for cytoreductive therapy, in both ET and PV, is hydroxyurea and second‐line drugs of choice are interferon‐α and busulfan. We do not recommend treatment with ruxolutinib in PV, unless in the presence of severe and protracted pruritus or marked splenomegaly that is not responding to the aforementioned drugs.
New treatment directions
Controlled studies are needed to confirm the clinical outcome value of twice‐daily vs once‐daily aspirin dosing and the therapeutic role of pegylated interferons and direct oral anticoagulants.
It is currently assumed that myelofibrosis (MF) originates from acquired mutations that target the hematopoietic stem cell and induce dysregulation of kinase signaling, clonal myeloproliferation, and ...abnormal cytokine expression. These pathogenetic processes are interdependent and also individually contributory to disease phenotype–bone marrow stromal changes, extramedullary hematopoiesis, ineffective erythropoiesis, and constitutional symptoms. Molecular pathogenesis of MF is poorly understood despite a growing list of resident somatic mutations that are either functionally linked to Janus kinase (JAK)–signal transducer and activator of transcription hyperactivation (eg JAK2, MPL, and LNK mutations) or possibly involved in epigenetic dysregulation of transcription (TET2, ASXL1, or EZH2 mutations). Current prognostication in primary MF is based on the Dynamic International Prognostic Scoring System-plus model, which uses 8 independent predictors of inferior survival to classify patients into low, intermediate 1, intermediate 2, and high-risk disease groups; corresponding median survivals are estimated at 15.4, 6.5, 2.9, and 1.3 years. Such information is used to plan a risk-adapted treatment strategy for the individual patient, which might include observation alone, conventional or investigational (eg, JAK inhibitors, pomalidomide) drug therapy, allogenic stem cell transplantation with reduced- or conventional-intensity conditioning, splenectomy, or radiotherapy. I discuss these treatment approaches in the context of who should get what and when.
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