Summary
Primary myelofibrosis (PMF) is a rare bone marrow disorder that is characterized by abnormalities in blood cell production (hematopoiesis, the process by which the body makes new blood cells) and scarring (formation of fibrous tissue, the buildup of stiff scar-like tissue) within the bone marrow.1-5
Bone marrow is the soft, spongy tissue that fills the center of most bones, and it contains specialized cells called hematopoietic stem cells (early “parent” cells that can develop into all types of blood cells). These stem cells grow and eventually develop into one of the three main types of blood cells: red blood cells (erythrocytes), which carry oxygen throughout the body; white blood cells (leukocytes), which help fight infection; or platelets (thrombocytes), which help the blood clot to stop bleeding.1, 2
The symptoms associated with primary myelofibrosis vary from person to person and are related to the abnormalities affecting blood cell production.1, 3 Affected people may not have symptoms at the time of diagnosis (asymptomatic, no noticeable symptoms) and may remain symptom-free for many years.3, 5
Eventually, people with PMF may develop fatigue, fever, frequent infections, pale skin, night sweats, and unexplained weight loss.1, 3, 5, 6 An enlarged spleen (splenomegaly, swelling of the spleen), an organ involved in filtering blood and supporting immune function, is a common finding.1, 3, 5 An enlarged liver (hepatomegaly) may also occur.1, 3
In primary myelofibrosis, a change (variant) in the DNA of a single hematopoietic stem cell causes the abnormal cell to continually reproduce itself. 3, 6, 7 This change is not inherited as it does not affect the reproductive cells (egg or sperm). 3 Eventually, these abnormal cells crowd out normal, healthy cells in the bone marrow and, along with scarring within the marrow, disrupt the production of red blood cells, white blood cells, and platelets.3
In more than half of the people with PMF, a variant in the JAK2 gene (a gene involved in signaling the bone marrow to make blood cells) is identified. Variants in the CALR gene are detected in about 20-25% of cases, while MPL gene variants are present in about 6-7% of the people with PMF. 8, 9, 10 The exact role these genetic abnormalities play in the development of the disorder is not fully understood. 6, 8
Treatment includes several medications and, in some cases, a procedure to replace the bone marrow (stem cell or bone marrow transplant, which replaces diseased bone marrow with healthy blood-forming cells).
Introduction
Primary myelofibrosis belongs to a group of diseases known as the myeloproliferative neoplasms (MPNs).1, 3, 6 This group of disorders is characterized by the overproduction (proliferation: excessive growth and division) of one or more of the three main blood cell lines – red blood cells, white blood cell, or platelets.1, 3, 6 Because MPNs are characterized by uncontrolled cell growth, they may also be classified as blood cancers.1, 6
The term “myelofibrosis” is usually reserved for bone marrow fibrosis related to myeloid neoplasm. Fibrosis means scarring, and bone marrow fibrosis refers to the replacement of normal bone marrow with stiff scar tissue that occurs in the setting of myeloid neoplasm. A myeloid neoplasm is a cancer that begins in the myeloid cells, which are precursor cells that normally develop into red blood cells, certain white blood cells, and platelets.
Myeloproliferative neoplasms include:
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