Medically Reviewed by Jennifer Robinson, MD on November 15, 2022
5 min read

Myelofibrosis is a rare kind of blood cancer that starts in your marrow, a spongy tissue inside your bones that makes blood cells. The disease causes scars called fibrosis, which affects how many blood cells your body can make.

Myelofibrosis is long-lasting and usually gets worse slowly. You may be able to live with it for years without a problem. But some people’s condition changes more quickly and causes symptoms that need to be treated. These include:

  • Fatigue, weakness, shortness of breath, or pale skin because of a low number of red blood cells (anemia)
  • Frequent infections because of a low white blood cell count (neutropenia)
  • Easy bleeding or bruising because of a lack of platelets in your blood (thrombocytopenia)
  • Swollen liver (hepatomegaly) or spleen (splenomegaly)
  • Night sweats
  • Itchy skin
  • Fever
  • Bone or joint pain
  • Weight loss
  • Blood clots
  • Bleeding in your stomach or esophagus
  • High blood pressure in the vein from your spleen to your liver (portal hypertension)

A problem with one of your genes causes your body to make stem cells that don’t work the way they should. These are the cells that make blood in your bone marrow. With myelofibrosis, they get inflamed, and scar tissue forms.

About 90% of people who get this kind of cancer have a change in one of three genes: JAK2, CALR, or MPL. These genes change during your lifetime, but experts don’t know why. In most cases, you don’t get these gene problems from your parents, and you don’t pass them on to your children.

These faulty genes make copies of themselves. The bad versions spread through your marrow and try to stop your body from making regular blood cells.

There’s no way to prevent myelofibrosis. But researchers are trying to learn more about it.

Most people are diagnosed around age 60. About 18,000 people in the U.S. are living with myelofibrosis.

Young adults or small children can get myelofibrosis, but it’s rare. Girls are affected twice as often as boys when it happens in childhood.

You may get myelofibrosis by itself. Or it could happen if you have another type of cancer that spreads to your marrow. Blood cancers like leukemia or myeloma could also bring it on.

Long-term exposure to radiation or toxic chemicals like benzene could make you more likely to get myelofibrosis. But that doesn’t happen often.

Blood cells. You have three types. They travel from your marrow to the rest of your body. Each has a special job to do. But if myelofibrosis slows production, that can’t happen.

  • Red blood cells bring oxygen to your organs and tissues like your muscles. If you have too few, you might feel weak, short of breath, lightheaded, or really tired. You might have bone pain.
  • White blood cells help you fight off infections. If you have too many, your body can’t defend you from illness like it’s supposed to.
  • Platelets make your blood clot when you get a cut so you can form a scab and heal. Without enough working platelets, it may be hard for you to stop bleeding.

Organs. Because your marrow has problems making blood cells, organs like your spleen, liver, or lungs may start the process instead. You could also make blood cells in your spinal cord or lymph nodes -- small glands in your groin, neck, and armpits.

All that extra blood can cause organs to get too large, especially your spleen. You might feel pain or fullness in your belly if that happens. This can be serious, so you need to get it looked at right away.

No one test can diagnose myelofibrosis. Your doctor might spot problems during a routine checkup before you notice any symptoms.

If you visit the doctor with symptoms, they’ll start by asking about your medical history and doing a physical exam. They’ll check for signs of an enlarged spleen. They may also order exams including:

  • Blood tests. A complete blood count (CBC) measures the number of each type of blood cell. A technician might also look at the cells under a microscope. And a comprehensive metabolic panel measures the levels of certain materials that your body makes, like electrolytes, fats, proteins, and enzymes.
  • Imaging tests. Ultrasound and MRI make images of things inside your body.
  • Gene tests. These find the changes that are linked to myelofibrosis.
  • Bone marrow tests. Your doctor uses a needle to take a small sample of liquid marrow (called an aspiration) or bone (called a biopsy) for analysis in a lab.

Your treatment will depend on your case, including your symptoms. If you don’t have any, your doctor might recommend waiting and watching for changes.

Most treatments focus on the conditions that myelofibrosis causes. If you have anemia, your doctor might recommend:

If your spleen is swollen, you may take:

  • Hydroxyurea
  • Interferon

Ruxolitinib (Jakafi), the first drug approved by the FDA to treat intermediate or high-risk myelofibrosis

In severe cases, you could need surgery to remove your spleen (splenectomy) or radiation therapy.

A transplant of stem cells or bone marrow from another person (called allogeneic) is the only treatment that might cure myelofibrosis. It replaces your diseased bone marrow with healthy cells. But it can have dangerous side effects, so experts recommend it mostly for younger people who have no other health problems. Talk with your doctor about the treatment plan that’s best for you.

See your doctor regularly to check your blood for any problems. About 20% of people with myelofibrosis could get acute myeloid leukemia, a kind of cancer that’s harder to treat.

A cancer diagnosis isn’t easy. It can help to talk to other people who know what you’re going through. The Leukemia and Lymphoma Society and the American Cancer Society both offer online advice and local support groups.