What Happens in Your Body With Myelofibrosis?

Medically Reviewed by Brunilda Nazario, MD on January 03, 2020

Myelofibrosis is a type of leukemia, a group of cancers that affect your blood and bone marrow (where blood cells are made). The disease can happen because of a change in your genes (called primary myelofibrosis) or because of another blood or bone marrow disease (secondary myelofibrosis). 

Myelofibrosis is rare -- it affects between 3,000 and 4,000 people in the U.S. every year. You can have it at any age, but it happens mostly in people 50 and older.  

What Happens Inside Your Body?

Stem cells live in your bone marrow and make copies of themselves to create the special cells that make up your blood: red blood cells, white blood cells, and platelets. Primary myelofibrosis starts with a change in the DNA of your body’s blood stem cells. As new cells are made, this change is passed on to them.

These problem cells can start to crowd out the normal cells in your marrow and trigger the growth of scar tissue. Over time, it becomes harder and harder for your bone marrow to make enough new healthy blood cells. 

Myelofibrosis often leads to anemia, which is when your body doesn't have enough healthy red blood cells. You also might not have enough platelets (which are needed for blood clotting), making you more likely to bleed or bruise easily.

Myelofibrosis can cause unusually high levels of white blood cells (which help fight off infection), but the cells often don't work the way they should. This can make your immune system weak and raise your chances of getting sick.

As your body makes fewer blood cells, other organs -- typically your spleen or liver -- may try to take over the job. Because this isn't what these organs usually do, it can make them larger than normal or even cause tumors to form. 

In about 1 in 8 cases, myelofibrosis will lead to a more serious form of leukemia known as acute myeloid leukemia.

What Are the Symptoms?

Myelofibrosis tends to get worse slowly. Some people live with it for years without having symptoms. As your body has a harder time making healthy blood cells, though, symptoms often get worse over time. While they're different from person to person, they can include:

  • Low energy and shortness of breath. You may often feel weak, dizzy, or tired. (These are symptoms of anemia.)
  • A feeling of fullness or pain on your upper left torso. (This is a sign that your spleen has gotten bigger.) 
  • Bruising, bleeding, or getting infections easily
  • Night sweats
  • Bone or joint pain
  • Fever
  • Pale skin
  • Itchiness
  • Unexplained weight loss
WebMD Medical Reference



Mayo Clinic: "Myelofibrosis."

American Cancer Society: "Leukemia."

Cleveland Clinic: "Myelofibrosis."

Cancer Care: "Managing Symptoms of Myelofibrosis."

Myeloproliferative Neoplasms (MPN) Research Foundation: "Primary Myelofibrosis."

Merck Manuals: "Myelofibrosis."

National Organization for Rare Diseases: "Primary Myelofibrosis."

U.S. National Library of Medicine: "Primary Myelofibrosis."

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