A clonal myeloproliferative stem cell disorder characterized by reactive bone marrow fibrosis, extramedullary hematopoiesis, and abnormal cytokine expression leading to systemic symptoms.
It belongs to a group of heterogeneous disorders of the hematopoietic system which is collectively known as Philadelphia chromosome-negative myeloproliferative neoplasms (MPN).
May present either as a de novo disorder [primary myelofibrosis (PMF)] or can develop from the transformation of polycythemia vera (PV) and essential thrombocythemia (ET).

Choice of treatment for patients with myelofibrosus is based on the risk score and presence of symptoms