| Abstract |
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 features include bone marrow reticulin/collagen fibrosis, aberrant inflammatory cytokine expression, anemia, hepatosplenomegaly, extramedullary hematopoiesis (EMH), constitutional symptoms, cachexia, risk of leukemic progression, and shortened survival.
Diagnosis: Bone marrow examination with cytogenetic and mutation studies provides integrated diagnostic information; presence of JAK2, CALR or MPL mutation is expected but not required.
New classification system: The International Consensus Classification distinguishes "prefibrotic" from "overtly fibrotic" PMF; the former might mimic essential thrombocythemia (ET) in its presentation. Approximately 15% of patients with ET or polycythemia vera (PV) might progress into post-ET/PV MF.
Mutations: SRSF2, ASXL1, and U2AF1-Q157 mutations predict inferior survival in PMF; RAS/CBL mutations predict resistance to ruxolitinib therapy. Type 1/like CALR mutation is associated with superior survival.
Karyotype: Very high-risk abnormalities include -7, inv (3), i(17q), +21, +19, 12p- and 11q-. Favorable risk abnormalities include normal karyotype or isolated +9, 13q-, 20q-, 1q abnormalities and loss of Y chromosome.
Risk stratification: Contemporary prognostic systems include 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.
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 of choice for "very high" and "high" risk disease (estimated 10-year survival 0-13%), as well as in carefully selected patients with intermediate-risk disease (estimated 10-year survival 30%). Drug therapy in MF is currently palliative and targets anemia, splenomegaly, and constitutional symptoms. JAK2 INHIBITORS: Ruxolitinib, fedratinib, and pacritinib are FDA approved and respectfully utilized in patients failing treatment with hydroxyurea, ruxolitinib, or with platelet count <50 × 10 (9)/L. Momelotinib is another JAK2 inhibitor that is poised for approval sometime in 2023 and has shown erythropoietic benefits, in addition to affecting spleen and symptom responses.
Other treatment modalities: Splenectomy is considered for drug-refractory splenomegaly and involved field radiotherapy for non-hepatosplenic EMH and extremity bone pain.
New directions: New agents, alone or in combination with ruxolitinib, are currently under clinical trial investigation (ClinicalTrials.gov) and preliminary results were presented at the 2022 ASH annual meeting and highlighted in the current review.
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