What are Myeloproliferative Neoplasms (MPNs)?
Myeloproliferative neoplasms are a group of blood cancers that develop from blood stem cells, the immature cells that can become red blood cells (RBCs), white blood cells (WBCs), or platelets. Myeloproliferative neoplasms (MPN) can cause an increase in the number of these types of blood cells in the blood and bone marrow.1,2
What are the different types?
There are three classic types of MPN, based on the type of blood cell that is overproduced:
- Essential thrombocythemia (ET) - ET results in too many platelets
- Myelofibrosis - Myelofibrosis results in fibers and abnormal stem cells called blasts crowding and scarring the bone marrow
- Polycythemia vera - Polycythemia vera results in too many RBCs2
Other types of MPN, in which there are too many abnormal WBCs, include:
- Chronic myeloid leukemia (CML)
- Chronic neutrophilic leukemia
- Chronic eosinophilic leukemia3
Myelodysplastic/myeloproliferative neoplasms have characteristics of both myelodysplastic syndromes (MDS) and MPN. Some forms of MPN and MDS can potentially become acute leukemia.4
What are the symptoms of essential thrombocythemia?
In someone with essential thrombocythemia (ET), there are too many platelets (thrombocytes). Platelets are responsible for clotting, which is important when there is an injury to the body, but too many platelets can cause the blood to form clots within blood vessels, which may cause damage to organs.5,6 Some people have no symptoms from ET, but ET can cause symptoms such as:
- Burning or tingling pain in the hands or feet
- Redness or warmth of hands or feet
- Vision problems
- Hearing problems5
While ET usually does not shorten a person's life, it can increase the risk of heart attack or stroke, as a clot can block blood flow to the heart (heart attack) or brain (stroke).5,6
What are the symptoms of myelofibrosis?
In myelofibrosis, abnormal blood cells and fibers accumulate within the bone marrow, which causes the bone marrow to have difficulties making healthy blood cells. The liver and spleen try to make up the difference by producing blood cells. In its early stages, myelofibrosis may not cause any symptoms, but as it progresses, myelofibrosis can cause symptoms such as:
- Pain or a feeling of fullness below the left ribs (due to an enlarged spleen), which may make a person not eat as much
- Anemia (low RBCs) can potentially cause symptoms of fatigue, dizziness, cold hands or feet, or pale skin
- Neutropenia (low WBCs) can cause repeated infections, or infections that won't go away
- Thrombocytopenia (low platelets) can cause the body to bleed more easily, including frequent nosebleeds, bruising, or small, pinhead-sized red spots on the skin called petechiae
- Night sweats
- Enlarged liver
- Bone or joint pain
- Weight loss7,8
What are the symptoms of polycythemia vera?
In polycythemia vera, there are too many RBCs in the blood. The number of WBCs and platelets may also be high, and the excess blood cells can enlarge the spleen and cause the blood to be thick and prone to clot. Polycythemia vera may be discovered on a blood test before there are symptoms. When symptoms occur from polycythemia vera, they can include:
- Pain or a feeling of fullness below the left ribs (due to an enlarged spleen)
- Changes to vision (double vision or seeing blind spots)
- Itching, particularly after warm baths or showers
- Reddened face
- Fatigue or weakness
- Unexplained weight loss9,10
What causes myeloproliferative neoplasms?
Like other blood cancers, MPN begin with a change to the DNA. These changes (or mutations) may be the result of an inherited predisposition (passed from parent to child), or it may occur as a result of being exposed to something in the environment (like chemicals or radiation). Spontaneous DNA mutations can also occur during normal cell growth.
Many people with MPN have a mutation of the JAK2 (Janus kinase 2) gene. Other gene mutations that have been identified with myelofibrosis include the calreticulin (CALR) gene and the myeloproliferative leukemia (MPL) gene.6,11,12
What are the risk factors?
Few factors have been identified that can increase a person's risk of developing MPN.
In some people, myelofibrosis is related to family history, although in most cases people do not have a family member with myelofibrosis. Exposure to chemicals, such as benzene, toluene, and ionizing radiation, can cause mutations in the DNA that can potentially lead to myelofibrosis.12
The incidence of polycythemia vera is increased in those of Eastern European Jewish descent, as compared to other Europeans or Asians, and it is usually diagnosed in people in their 60's.11
Editor's note: The classification of MPN has evolved over time. Some organizations may classify MPN as either a blood cancer or a blood disorder.