PurposeIn the WHO diagnostic classification, prefibrotic myelofibrosis (pre-MF) is included in the category of primary myelofibrosis (PMF). However, strong evidence for this position is lacking.Patients and MethodsWe investigated whether pre-MF may be aligned along a clinical and biological continuum in 683 consecutive patients who received a WHO diagnosis of PMF.ResultsAs compared with PMF-fibrotic type, pre-MF (132 cases) showed female dominance, younger age, higher hemoglobin, higher platelet count, lower white blood cell count, smaller spleen index and higher incidence of splanchnic vein thrombosis. Female to male ratio and hemoglobin steadily decreased, while age increased from pre-MF to PMF- fibrotic type with early and to advanced bone marrow (BM) fibrosis. Likely, circulating CD34+ cells, LDH levels, and frequency of chromosomal abnormalities increased, while CXCR4 expression on CD34+ cells and serum cholesterol decreased along the continuum of BM fibrosis. Median survival of the entire cohort of PMF cases was 21 years. Ninety-eight, eighty-one and fifty-six percent of patients with pre-MF, PMF-fibrotic type with early and with advanced BM fibrosis, respectively, were alive at 10 years from diagnosis.ConclusionPre-MF is a presentation mode of PMF with a very indolent phenotype. The major consequences of this contention is a new clinical vision of PMF, and the need to improve prognosis prediction of the disease.

Myeloproliferative neoplasms (MPNs) are clonal disorders characterized by excessive production of mature cells. In most of the classic Philadelphia-negative MPNs-polycythemia vera (PV), essential thrombocythemia (ET), and MPN-associated myelofibrosis (MPN-MF)-oncogenic mutations affecting JAK2 or MPL lead to constitutive activation of cytokine-regulated intracellular signalling pathways. The traditional therapy for PV and ET is the prevention of thrombotic events with antiproliferative agents in association with aspirin. New drugs such as pegylated interferon and anti-JAK agents are candidates for slowing the evolution to myelofibrosis or leukemia. Conventional therapy for MPN-MF is driven by clinical needs, primarily anemia and splenomegaly. Lenalidomide and pomalidomide are new candidates for treating anemia. JAK2 ATP-competitive inhibitors or drugs that indirectly inhibit the JAK-STAT pathway, like RAD001, are the new candidates for splenomegaly in MPN-MF, but in spite of their strong rationale, they have shown only a palliative benefit. Allogeneic stem cell transplantation remains the only potentially curative approach.

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