Myelofibrosis, also called bone marrow fibrosis, is a type of cancer. If you or a loved one has been diagnosed with myelofibrosis, having a clear understanding of how the disease works and what you can do to address some symptoms with your care team is essential for navigating your care.
What type of cancer is myelofibrosis?
Myelofibrosis is considered a rare type of blood cancer.
In a healthy body, the bone marrow acts like a factory that produces all your red blood cells, white blood cells, and platelets. In myelofibrosis, abnormal stem cells in the bone marrow grow out of control.
As these abnormal cells build up, they cause scar tissue called fibrosis inside the bone marrow. Over time, this scarring prevents the bone marrow from making enough healthy blood cells.
Myelofibrosis belongs to a group of chronic blood cancers called myeloproliferative neoplasms (MPNs).
"Myelo" refers to the bone marrow, "proliferative" means rapidly growing or producing, and "neoplasm" is a medical term for an abnormal growth or tumor. In MPNs, the bone marrow overproduces one or more types of blood cells.
Primary vs. secondary myelofibrosis
Doctors classify myelofibrosis into two main types depending on how it develops:
Primary myelofibrosis (PMF): This occurs when the disease develops on its own, without any previous bone marrow condition.
Secondary myelofibrosis: This occurs when myelofibrosis develops as a progression from another existing MPN.
The two most common conditions that can evolve into secondary myelofibrosis are:
Polycythemia Vera (PV) is a condition where the body makes too many red blood cells.
Essential thrombocythemia (ET) is a condition where the body makes too many platelets.
While both primary and secondary myelofibrosis cause similar symptoms, such as an enlarged spleen, fatigue, and low blood counts, knowing which type you have helps your care team tailor your treatment.
Is myelofibrosis the same as leukemia?
No, myelofibrosis is not the same as acute leukemia, though they are related.
Myelofibrosis is typically a slower-growing, chronic cancer and is characterized by scar tissue in the bone marrow that restricts the production of healthy blood cells. Leukemia, particularly acute leukemia, involves a rapid accumulation of immature white blood cells (called blast cells) that quickly crowd out normal blood cells.
However, because myelofibrosis is a stem cell disorder, there is a risk that it can evolve over time into an acute blood cancer, known as secondary acute myeloid leukemia (AML) or blast-phase disease. Doctors monitor blood counts and bone marrow health regularly to watch for any signs of progression.
How is myelofibrosis different from MDS?
Both myelofibrosis and myelodysplastic syndromes (MDS) are bone marrow cancers that lead to low blood cell counts (anemia or cytopenias). But they differ in how they affect the bone marrow.
Feature | Myelofibrosis (MF) | Myelodysplastic Syndromes (MDS) |
Main Bone Marrow Problem | Severe scarring (fibrosis) caused by abnormal cell growth | Disorganized, poorly formed (dysplastic) cells that die early in the marrow |
Spleen Size | Often causes an enlarged spleen (splenomegaly) as it takes over making blood cells | Spleen enlargement is far less common |
Cell Quality | The bone marrow makes scarred tissue that squeezes out normal cell production | The bone marrow makes "faulty" cells that cannot mature properly |
What causes myelofibrosis?
Myelofibrosis is caused by genetic changes (mutations) in the stem cells inside the bone marrow. These mutations alter chemical signaling pathways cells use to perform their functions. The most important pathway myelofibrosis affects is the JAK/STAT pathway, which sends signals to cells indicating they should divide or produce inflammatory signals.
The three most common "driver" gene mutations found in myelofibrosis are:
JAK2 mutation: Found in roughly 50% to 60% of primary myelofibrosis cases.
CALR mutation: Found in about 20% to 25% of cases.
MPL mutation: Found in about 5% to 10% of cases.
It is important to know that these genetic mutations are acquired during a person's lifetime, they are not inherited genes that you pass down to your children.
How serious is myelofibrosis?
Myelofibrosis is a chronic health condition, and its impact varies greatly from person to person.
The disease often causes an enlarged spleen, severe fatigue, night sweats, bone pain, and weight loss due to the inflammatory state the body is in. Also, anemia (low red blood cells) and low platelets are common, often requiring treatments or blood transfusions.
Some people may only have mild symptoms for many years, while others have higher-risk disease that progresses more quickly.
To determine how serious an individual case is, doctors use specialized scoring systems. Examples include DIPSS or MIPSS. These systems consider age, blood counts, genetic mutations, and symptoms. Today, targeted treatments (like JAK inhibitors) help manage symptoms and spleen size, while stem cell transplants offer a potential cure for eligible patients.
While a diagnosis of myelofibrosis brings challenges, medical research has advanced significantly in recent years and new advancements are focused on improving quality of life, reducing transfusions, and extending life expectancy.
Understand your diagnosis and keep track of your health with HealthTree
Understanding the specifics of your diagnosis, whether it is primary or secondary, which gene mutations are present, and how it differs from other blood conditions empowers you to have informed conversations with your care team. With HealthTree, you can create your Personal Health Record and keep track of your health, so you don’t miss anything on your next appointment.
