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Chronic Myeloproliferative Neoplasms Treatment (PDQ®)

  • Last Modified: 06/17/2014

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Primary Myelofibrosis



Primary myelofibrosis is a disease in which abnormal blood cells and fibers build up inside the bone marrow.

The bone marrow is made of tissues that make blood cells (red blood cells, white blood cells, and platelets) and a web of fibers that support the blood-forming tissues. In primary myelofibrosis (also called chronic idiopathic myelofibrosis), large numbers of blood stem cells become blood cells that do not mature properly (blasts). The web of fibers inside the bone marrow also becomes very thick (like scar tissue) and slows the blood-forming tissue’s ability to make blood cells. This causes the blood-forming tissues to make fewer and fewer blood cells. In order to make up for the low number of blood cells made in the bone marrow, the liver and spleen begin to make the blood cells.

Possible signs of primary myelofibrosis include pain below the ribs on the left side and feeling very tired.

Primary myelofibrosis often does not cause early symptoms. It is sometimes found during a routine blood test. The following symptoms may be caused by primary myelofibrosis or by other conditions. Check with your doctor if you have any of the following problems:

  • Feeling pain or fullness below the ribs on the left side.
  • Feeling full sooner than normal when eating.
  • Feeling very tired.
  • Shortness of breath.
  • Easy bruising or bleeding.
  • Petechiae (flat, red, pinpoint spots under the skin that are caused by bleeding).
  • Fever.
  • Night sweats.
  • Weight loss.

Certain factors affect prognosis (chance of recovery) and treatment options for primary myelofibrosis.

Prognosis (chance of recovery) depends on the following:

  • The age of the patient.
  • The number of abnormal red blood cells and white blood cells.
  • The number of blasts in the blood.
  • Whether there are certain changes in the chromosomes.
  • Whether the patient has symptoms such as fever, night sweats, or weight loss.