Myeloproliferative neoplasms, or MPNs — also called myeloproliferative disorders, or MPDs — are a collection of blood disorders that are believed to be caused by mutations in bone marrow stem cells. These stem cells normally give rise to mature cells found in the blood, such as red blood cells, which carry oxygen, white blood cells, which fight infection, and platelets, which facilitate blood clotting. In MPN, mutations cause the affected stem cells to produce an abnormal number of these cells. More than 200,000 people in the U.S. are estimated to be living with an MPN.
Generally, MPNs are associated with an overproduction of some of the mature blood cell types. Polycythemia vera is an MPN associated with too many red blood cells; essential thrombocythemia refers to the abnormal overproduction of platelets, and chronic myeloid leukemia is generally associated with too many white blood cells.
Many people with these conditions have few, if any, symptoms, but complications can occur, including stroke in patients with poorly controlled disease. MPNs can sometimes transform to leukemia or to myelofibrosis, an MPN that is characterized by excessive scar-type tissue in the bone marrow.
The molecular causes of the majority of MPN cases have been identified — mutations in the genes JAK2 and ABL are found in nearly all patients with polycythemia vera and chronic myeloid leukemia, respectively. This knowledge has led to the development of targeted therapies that shut off the activity of these overactive mutant proteins. In the case of chronic myeloid leukemia, the outlook of patients has been transformed dramatically as a result.
Patients with MPN may have many or few symptoms depending on how abnormal their blood counts become.
Those with essential thrombocythemia and polycythemia vera have "thick" blood that is more prone to clotting and is associated with heart attacks, strokes and clots in leg veins. Patients with chronic myelogenous leukemia and myelofibrosis often feel tired and report pain or fullness in their belly from an enlarged spleen.
Patients with MPN may have moderate or severe anemia, a condition where there are not enough red blood cells to carry oxygen. Other signs and symptoms may include:
When an MPN is suspected, blood tests are conducted that count the number of different cells in the blood. If the results are abnormal, other blood tests may be ordered.
A bone marrow biopsy is performed to confirm a diagnosis of MPN. During this test, a needle is inserted into the bone and marrow is extracted. The sample is then carefully examined under a microscope by a pathologist.
Although myeloproliferative neoplasms usually cannot be cured, there are treatments for all patients with the condition. Treatment of MPNs depends on the type and on the presence of symptoms. In general, treatment aims to correct the abnormal blood counts.
Some people don't experience any symptoms and therefore don't require treatment.
Low dose chemotherapy pills, such as hydrea, can be given to patients with essential thrombocythemia and polycythemia vera to lower their platelet and red blood cell counts. Phlebotomy (the removal of blood intravenously) is also an effective strategy for lowering red blood cell counts and controlling symptoms.
The treatment of choice for chronic myelogenous leukemia is a new anti-leukemia medication, called Gleevec. Testoterone therapy can sometimes improve anemia in patients with myelofibrosis. Other potential therapies for myelofibrosis include chemotherapy, radiation therapy, thalidomide and alpha interferon. In addition, patients with myelofibrosis frequently require red blood cell transfusions.
Reviewed by health care specialists at UCSF Medical Center.