Myeloproliferative neoplasms (MPNs) are a group of rare cancers originating in the bone marrow.
Bone marrow is the spongy tissue inside large bones. It manufactures stem cells, which in turn produce white blood cells that fight infection, red blood cells that carry oxygen and platelets that help with blood clotting. An MPN occurs when there is an imbalance in the production of these cells or platelets.
The primary types of MPNs are polycythemia vera (PV), myelofibrosis (MF) and essential thrombocythemia (ET).
Polycythemia vera (PV)
Polycythemia vera develops when bone marrow produces too many red blood cells, which can lead to a thickening of the blood. The vast majority of people with PV have a mutation (change) in the JAK2 gene that leads to the over-production of red blood cells. As PV progresses, it can cause headaches, shortness of breath, bleeding, dizziness, itchiness and/or an enlarged spleen. PV can also increase the risk of the development of blood clots.
A primary goal of therapy for PV is to maintain a hematocrit level below 45%, which is proven to decrease the person’s risk of forming a blood clot. The hematocrit level is the ratio of the volume of red blood cells to the total volume of blood. Phlebotomy (the use of a needle to take blood from a vein) is the therapy of choice to maintain hematocrit levels below 45%.
If phlebotomy alone does not achieve the desired hematocrit level, there are medications that can reduce the number of red blood cells in the bloodstream. These medications include hydroxyruea (Droxia, Hydrea), interferon alfa-2b (Intron A), ruxolitinib (Jakafi) and busulfan (Busulfex, Myleran).
The investigational drug rusfertide is currently being studied in clinical trials. According to research results, twice-weekly injections with rusfertide effectively controlled hematocrit levels and significantly reduced the need for phlebotomy.
Myelofibrosis (MF)
Myelofibrosis occurs when bone marrow cells called fibroblasts make too much fibrous (scar) tissue. As this scar tissue builds up, blood cells can no longer develop properly inside the bone marrow. This can cause anemia (a low number of red blood cells), a low platelet count, and a higher risk of developing infections. People with MF often have an enlarged spleen, which can cause pain or discomfort in the abdomen or below the ribs.
Some people with MF are asymptomatic (have no symptoms) and do not require treatment. Instead, their condition is closely monitored, which is called active surveillance. Treatment, if required, depends on the person’s symptoms.
Medications
Medications prescribed for the treatment of MF are designed to reduce spleen enlargement and relieve symptoms.
Ruxolitinib (Jakafi), fedratinib (Inrebic) and pacritinib (Vonjo) target mutations in the JAK2 gene and block its faulty processes.
Momelotinib (Ojjaara), a treatment indicated for intermediateor high-risk MF with anemia, was approved by the U.S. Food and Drug Administration (FDA) in September 2023. Momelotinib is a JAK1/JAK2 and ACVR1 inhibitor.
Hydroxyurea (Droxia, Hydrea), epoetin alpha (Procrit) and darbepoetin alpha (Aranesp) are chemotherapies.
Splenectomy
The spleen helps fight infection by producing white blood cells. It also stores red blood cells and platelets. The surgical removal of the spleen (splenectomy) is considered for the treatment of symptomatic MF that is not responding to medication or radiation therapy administered to reduce spleen size.
Stem Cell Transplant
A stem cell transplant is a procedure in which diseased bone marrow is replaced with healthy bone marrow. In an allogeneic stem cell transplant, stem cells (blood cells that divide to make new blood cells within the bone marrow) are removed from a donor. Donors are often a close relative such as a brother or sister, but sometimes can be an unrelated volunteer who has a compatible bone marrow.
The person receiving the stem cell transplant is given high doses of chemotherapy to destroy abnormal cells in the bone marrow. The stem cells are then infused (transplanted) into the body, where they start working in the bone marrow to produce healthy blood cells.
Immunosuppressive drugs are typically given for a period of time after the transplant. This is to prevent the rejection of donor cells and to ensure the transplanted cells do not cause an autoimmune disease, such as graft-versus-host disease (GVHD). These drugs include cyclosporine and tacrolimus.
There is a high level of risk associated with an allogeneic stem cell transplant, and it is typically not the initial treatment approach for MF.
Essential thrombocythemia (ET)
Essential thrombocythemia occurs when the bone marrow produces too many platelets, which can cause blood clots that affect vital organs throughout the body.
People with ET who have no symptoms usually do not require treatment. Medication may be prescribed if the platelet count is very high, if the person has a history of blood clots, is older or has risk factors for heart disease. Platelet-lowering medications include hydroxyurea (Droxia, Hydrea), anagrelide (Agrylin) and interferon alfa-2b (Intron A).
In emergency situations where the platelet count must be reduced quickly, excess platelets can be removed from the bloodstream by a procedure called plateletpheresis. Blood is drawn from a needle placed in a vein and passed through a machine called a cell separator, which spins the blood and removes the excess platelets.