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Introduction
Myelofibrosis (MF) is 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). The most common presenting symptom of myelofibrosis is fatigue and other symptoms include an enlarged spleen, weight loss, low-grade fever, night sweats, and bone pain.
Epidemiology
Myelofibrosis occurs mainly among middle-aged and older adults with a median age of onset at 67 years old, though as much as 20% of cases are younger than 40 at presentation. Myelofibrosis shows some slight male predominance. Based on the available data, the incidence rate of myelofibrosis is around 0.4-1.5 per 100,000 with a corresponding prevalence of 0.5-2.7 per 100,000. With this data, in an Asian country like Singapore, there may be as much as 2,600-4,000 people suffering from MPN. In Malaysia, the Chinese population showed a relatively high incidence.
Pathophysiology
Primary myelofibrosis is characterized by the clonal proliferation of early hematopoietic stem cells. It is often accompanied by Janus kinase 2 (JAK2), calreticulin (CALR), or myeloproliferative leukemia (MPL) gene mutations.
Classification
Myelofibrosis presents either as a de novo disorder (primary myelofibrosis) or can develop from the transformation of polycythemia vera (PV) and essential thrombocythemia (ET). Primary myelofibrosis may be sub-classified into prefibrotic or early stage primary myelofibrosis and overt fibrotic-stage primary myelofibrosis.