Summary
Polycythemia vera (PV) is a rare, chronic condition in which the bone marrow produces too many blood cells. The bone marrow is the soft tissue inside bones where blood cells are made. In PV, the body makes too many normal red blood cells, white blood cells, and platelets.
When red blood cells are produced in excess, the volume of red blood cells circulating in the bloodstream becomes abnormally high. This slows blood flow and causes the blood to become thicker, a condition called hyperviscosity, which can impair blood circulation.
People with PV can experience a range of symptoms, including migraine-like headaches, fatigue, weakness, dizziness, itching of the skin (especially after warm baths or showers), and an enlarged spleen. Some people may also have digestive problems such as acid reflux, gout from the large turnover of white blood cells, and a condition called erythromelalgia, which causes burning pain in the hands and feet. PV also increases the risk of developing blood clots, since blood becomes thicker as its flow slows down.
About 95% of people with PV have a change (variant) in the JAK2 gene (JAK2 V617F), which is called a driver mutation (driver variant) because it leads to the uncontrolled production of normal red blood cells, white blood cells, and platelets. Most of the remaining patients have variants in exon 12 of the JAK2 gene. These acquired (somatic) variants develop after birth and are not inherited. Although PV is considered a chronic blood cancer, it usually progresses slowly, and with appropriate treatment most people can expect a near-normal life expectancy.
Treatment includes phlebotomy, a procedure that removes excess blood from the body to reduce the number of circulating red blood cells, along with medications like pegylated interferon and inhibitors of the JAK2 enzyme to help control blood cell production and reduce complications. Ongoing research is focused on therapies that directly target the abnormal stem cell clone responsible for the disease and may ultimately modify its natural course.
Introduction
PV was first described in 1892 by French physician Louis Henri Vaquez and was further characterized as a distinct clinical condition in 1903 by Canadian physician William Osler. The term “myeloproliferative disorder” was first used in 1951 by William Dameshek to describe PV and several related conditions in which the bone marrow makes too many normal blood cells.
In 2008, the World Health Organization reclassified these conditions as “myeloproliferative neoplasms” (MPNs) to reflect the understanding that they arise from a single abnormal blood-forming stem cell. MPNs are characterized by the overproduction of one or more of the three main blood cell types, red blood cells (which carry oxygen), white blood cells (which fight infection), and platelets (which help blood clot).
In addition to PV, two companion conditions are also classified as MPNs, essential thrombocythemia (ET), in which there is primarily an increase in platelets, and primary myelofibrosis (PMF), in which there is usually anemia, an increase in white cells and platelets, spleen enlargement, and bone marrow scarring. Like PV, ET and PMF arise from a single blood-forming stem cell and can involve the same JAK2 V617F driver variant, but they can also be caused by variants in the CALR or MPL genes.
Although PV is classified as a type of cancer, its clinical behavior differs substantially from that of most cancers. The abnormal cells remain mature and functional, disease progression is typically slow, and many individuals live for decades with appropriate treatment. Current therapies effectively reduce complications and improve quality of life, while ongoing research seeks treatments capable of eliminating the abnormal stem cell clone that drives the disease.
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