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Get the Facts on Myelofibrosis


Photo by Cancer Type

Myelofibrosis is a rare bone mar­row cancer in which the marrow is replaced by fibrous (scar) tissue. Myelofibrosis can occur on its own, called primary myelofibrosis, or as a progression of other bone marrow diseases. Myelofibrosis belongs to a group of closely related blood cancers, known as myeloproliferative neoplasms, in which the bone marrow cells that produce the body’s blood cells develop and function abnormally. The result is excessive fibrous tissue formation in the bone marrow, which can lead to severe anemia, weakness, fatigue, and an enlarged spleen and liver.

The cancer develops when a muta­tion occurs in the DNA of a single blood-forming stem cell. Blood stem cells have the ability to reproduce and divide into multiple specialized cells that make up the blood. As the mutated blood cell replicates and divides, it passes along the mutation to new cells. Eventually, this abnormal cell produc­tion overtakes the bone marrow’s ability to produce enough normal blood cells, including

  • red blood cells, which carry oxygen to the tissues,
  • white blood cells, which fight infection, and
  • platelets, which help blood to clot.

When the bone marrow is unable to make enough healthy blood cells, the result can be severe anemia, weakness, bone pain, fatigue, and increased risk of infection. The abnormal growth of blood-forming cells can also take place outside of the bone marrow, called extramedullary hematopoiesis, in such organs as the liver, spleen, lungs, lymph nodes, and spinal cord, causing swelling.

An important constant feature of myelofibrosis is the production of too many megakaryocytes, the term for the giant cells in the marrow that break up into fragments and produce hundreds to thousands of platelets. Platelets are small blood cells that stick to the site of a blood vessel injury and form a plug to seal off the injured blood vessel to stop bleeding. Normally, new platelets are made to replace used platelets in the body. With myelofibrosis, extra mega­karyocytes are made, causing too many platelets to be released into the blood and chemicals called cytokines to be released into the marrow. The cytokines stimulate the development of fibrous tissue in the marrow. Paradoxically, the number of megakaryocytes can become so abnormal that platelet production de­creases in some people with this disease.

About 50 percent of people with myelofibrosis have a mutation called V617F JAK2 found in the JAK2 gene. The gene mutation causes abnormal signaling in the JAK pathway, which regulates blood cell production. This dysregulation of the JAK pathway can lead to an enlarged spleen and other serious complications, such as a low platelet count and severe anemia. Be­tween 5 and 10 percent of people with myelofibrosis will have a myeloprolifera­tive leukemia (MPL) gene mutation, which also affects the JAK signaling pathway. In addition, mutations in the TET2 gene have been found in 5 to 15 percent of people with myeloproliferative neoplasms. Scientists are investigating the role TET2 mutations, and other gene mutations in other signaling pathways, may have on myelofibrosis onset.

The reason these genetic mutations occur in myelofibrosis is unknown. Exposure to petrochemicals, such as benzene and toluene, and ionizing radia­tion may raise the risk of developing the cancer. However, only a small propor­tion of people exposed to these chemicals develop myelofibrosis. A theory about why myelofibrosis develops in some people is that they have inherited genes that limit their ability to detoxify the causative agents. However, myelofibro­sis itself is not an inherited disease. There is no known prevention.

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Reprinted with permission of The Leukemia & Lymphoma Society from, Myelofibrosis Facts. All rights reserved.

This article was published in Coping® with Cancer magazine, July/August 2015.