Myelofibrosis is a disorder in which fibrous tissue replaces the blood-producing cells in the bone marrow, resulting in abnormally shaped red blood cells, anemia, and an enlarged spleen.
Myelofibrosis may occur on its own or as a result of other blood disorders.
People may feel tired and weak, have infections, and bleed easily.
Blood tests and a bone marrow biopsy are done for diagnosis.
Drugs and other treatments lessen the severity of anemia, increase red blood cell production, and fight infections.
Sometimes stem cell transplantation is used.
In normal bone marrow, cells called fibroblasts produce fibrous (connective) tissue that supports the blood-producing cells. In myelofibrosis, the fibroblasts produce too much fibrous tissue, which crowds out the blood-producing cells. Consequently, red blood cell production decreases, fewer red blood cells are released into the bloodstream, and anemia develops, becoming progressively more severe.
In addition, many of these red blood cells are immature or misshapen. Variable numbers of immature white blood cells and platelets also may be present in the blood. As myelofibrosis progresses, the number of white blood cells may increase or decrease, and the number of platelets typically decreases.
Myelofibrosis is rare, affecting fewer than 2 of 100,000 people in the United States. It occurs most often in people between 50 and 70 years.
Idiopathic myelofibrosis (or agnogenic myeloid metaplasia) is myelofibrosis that develops on its own. About half of people who have idiopathic myelofibrosis have a mutation in the gene called JAK2. Some people have a mutation in the gene called calreticulin.
Myelofibrosis may occur in people who have other blood disorders such as chronic myelogenous leukemia, polycythemia vera, thrombocythemia, multiple myeloma, and lymphoma. It may also occur in people with tuberculosis, pulmonary hypertension, systemic lupus erythematosus (lupus), and systemic sclerosis (scleroderma) and in people in whom a cancer has spread to the bones.
Often, myelofibrosis causes no symptoms for years. However, in some people it rapidly leads to anemia, low levels of platelets in the blood, or leukemia. Eventually, anemia becomes severe enough to cause weakness, tiredness, weight loss, and a general feeling of illness (malaise). Fever and night sweats may occur. With the reduced number of white blood cells, the body is at risk for infections, so people may have frequent infections. With the reduced number of platelets, the body is at risk for bleeding.
The liver and spleen often enlarge as they try to take over some of the job of making blood cells. The spleen also destroys abnormal red blood cells and platelets made in the bone marrow. The destruction of so many red blood cells and platelets contributes to the spleen enlargement. Enlargement of the liver and spleen may cause pain in the abdomen and may lead to abnormally high blood pressure in certain veins (portal hypertension) and bleeding from varicose veins in the esophagus (esophageal varices).
Anemia and the misshapen, immature red blood cells, seen in blood samples viewed under a microscope, suggest myelofibrosis. However, a bone marrow biopsy is needed to confirm the diagnosis. Sometimes other tests are done, including tests for the JAK2 or calreticulin mutation.
About half of people who have idiopathic myelofibrosis survive for more than 5 years, but the length of survival varies a great deal from one person to another. Because myelofibrosis generally progresses slowly, people who have it may live for 10 years or longer, but outcomes are determined by how well the bone marrow functions. Occasionally, the disorder worsens rapidly. Treatment aims to delay the progression of the disorder and to relieve complications. However, only stem cell transplantation can cure the disorder.
Ruxolitinib, a drug that was developed to inhibit the JAK2 mutation is often the first treatment used. For reasons that are not yet known, it also appears to be effective in people who do not have the JAK2 mutation. It is effective at reducing spleen size and controlling symptoms and may increase overall survival, but it does not reverse fibrosis in most cases and can lead to low platelet counts.
Reducing the size of the spleen tends to relieve symptoms. Hydroxyurea, a chemotherapy drug, or interferon-alpha, a drug that affects the immune system, may decrease the size of the liver or spleen, but either drug may worsen the anemia. Radiation therapy can also be used to decrease the size of the spleen. However, reducing the size of the spleen with these drugs or radiation therapy is usually unnecessary. Rarely, the spleen becomes extremely large and painful and may have to be removed. Removal of the spleen may increase the number of red blood cells and reduce the need for transfusions.
The combination of an androgen (a drug with the effects of male sex hormones) and prednisone temporarily lessens the severity of the anemia in about one third of people with myelofibrosis, but this treatment is rarely used.
Other drugs are being developed. Bacterial infections are treated with antibiotics.
Stem cell transplantation (bone marrow transplantation) is sometimes offered to people who are in otherwise good health and who have an appropriate matched donor. A transplant is the only treatment available that may cure myelofibrosis, but it also has significant risks.