Polycythemia vera (PV) is a type of myeloproliferative neoplasm (MPN), a cancer of blood cells that is closely related to leukemia, lymphoma, and myeloma. MPNs were previously called myeloproliferative disorders.
MPNs are caused by excessive proliferation (growing and dividing) of precursor blood cells in the bone marrow. The types of MPN are formed due to an excessive amount of different types of blood cells: red blood cells (RBCs), white blood cells (WBCs), or platelets. MPNs are chronic and progressive, which means they usually progress slowly, but the condition worsens over time.
Polycythemia vera — also called primary polycythemia and polycythemia (rubra) vera — is a rare, chronic MPN that results in the bone marrow making too many RBCs. PV can also cause an increase in the number of WBCs and an elevated platelet count.
PV cancer cells come from pluripotent stem cells, a type of precursor blood cell found in bone marrow. These abnormal precursor cells are especially sensitive to erythropoietin (EPO), a hormone that increases RBC production. Red blood cells are primarily responsible for carrying oxygen to cells in the body. Having too many RBCs increases the thickness (viscosity) of blood and can lead to excessive blood clot formation and bleeding.
PV is classified as a type of classic MPN, a group that also includes essential thrombocythemia and primary myelofibrosis. The three classic MPNs are also known as Philadelphia chromosome-negative MPNs. This is because they do not have a specific genetic abnormality seen in certain other types of MPNs and related disorders. PV is most common in men and people with Eastern European Jewish ancestry, according to researchers. PV is usually diagnosed in older adults (over age 50). This condition rarely occurs in younger adults and children.
PV is often discovered during routine blood tests that show an abnormally high quantity of RBCs, but about half of all people with PV also have elevated WBC counts. A complete blood count result that has high hemoglobin levels (the amount of oxygen-carrying proteins in RBCs) and hematocrit (the percentage of blood that is made up of RBCs) is usually the first sign of PV. Further testing using bone marrow biopsy, tests for specific genetic mutations, and low EPO levels are used to diagnose PV.
Read more about diagnosing MPNs.
PV and other types of cancer are caused by cells that develop genetic mutations. Cells that develop mutations are usually destroyed by the immune system, but sometimes cells continue to grow and divide uncontrollably, becoming cancer cells. Specific genetic mutations are associated with different types of cancer. Almost all cases of PV have a mutation in the Janus kinase 2 (JAK2) gene, called JAK2V617F. A small percentage of PV cases have a different mutation of the JAK2 gene.
The specific cause of these mutations and precisely how they cause PV to develop is unclear. In general, genetic mutations that cause cancer can be inherited, passed down from your parents, or acquired over time by normal aging, exposure to radiation or certain chemicals, or infection with certain viruses.
Read more about what causes MPNs.
PV shares many symptoms with other types of MPN. PV is often found before symptoms develop, but about one-third of people have symptoms before diagnosis that are caused by thrombosis (the formation of blood clots inside blood vessels). When blood clots (thrombi) form inside veins and arteries, they can block blood flow to parts of the body.
Thromboses can occur in small blood vessels, such as capillaries, or large blood vessels, such as the femoral veins in the legs. Clots in large blood vessels can lead to very serious complications such as heart attack, stroke, transient ischemic attack (also called a mini-stroke), deep vein thrombosis, and pulmonary embolism.
Generalized symptoms seen in people with PV and some other types of MPN include:
Blood clots in small blood vessels in the head and extremities can cause various symptoms:
Abnormal bleeding is less common in people with PV than those with other MPNs, but it can cause symptoms such as bruising easily, difficulty clotting, nosebleeds, bleeding gums, and gastrointestinal bleeding.
An enlarged spleen or liver can cause abdominal fullness and bloating, loss of appetite, nausea, and vomiting.
PV treatment options include phlebotomy (blood collection), blood thinners (anticoagulants), chemotherapy drugs, immunotherapy, and targeted therapy. The main goal of treatment is to prevent blood clots and bleeding by lowering the amount of RBCs in the blood (cytoreductive treatment).
The choice of treatment depends on a person’s risk level. People under age 60 with no history of thrombosis are categorized as low risk, and people age 60 or older or anyone who has a history of thrombosis is classified as high risk. Individuals in the high-risk category are usually started on chemotherapy drugs.
People with PV who are in the low-risk category — especially if they are asymptomatic — may be treated with phlebotomy alone. Phlebotomy simply involves drawing blood. Up to one pint or 500 milliliters of blood is collected, similar to blood donation. Periodic phlebotomy, once a week or every other week, can help reduce the amount of RBCs and decrease hematocrit to safe levels.
Watch as MPN expert Dr. Ruben Mesa explains how phlebotomy helps treat PV.
Several different drugs are commonly used to treat PV:
Enrolling in clinical trials is another treatment option. Clinical trials can test new drugs, new combinations of drugs, or new uses of existing drugs to find better treatments for PV.
Read more about treatments for MPNs.
The prognosis (outlook) for PV depends on individual risk factors and how advanced the disease is. Overall, people with PV who receive appropriate treatment have a median survival of 10 to 20 years. Preventing thrombosis and bleeding is the key to avoiding serious complications from PV.
PV can progress to diseases with a significantly worse prognosis. For example, it can progress to become acute myeloid leukemia in about 5 percent of cases. Up to 15 percent of people with PV develop myelofibrosis due to scarring (fibrosis) inside bone marrow, leading to bone marrow failure.
On myMPNteam, the social network for people with myeloproliferative neoplasms, more than 1,500 members come together to ask questions, give advice, and share their stories with others who understand life with MPNs.
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