Polycythemia Vera (PV) is a chronic blood cancer classified as a myeloproliferative neoplasm (MPN). In PV, the bone marrow produces an excessive number of blood cells, primarily red blood cells. This overproduction causes the blood to become thicker and more viscous, which raises the risk of severe complications. While PV is progressive and currently incurable, modern medical management has fundamentally altered its course, making life expectancy highly dependent on patient characteristics and adherence to treatment.
Defining Polycythemia Vera
PV originates from a defect in the hematopoietic stem cells within the bone marrow. Over 90% of patients acquire a specific genetic change known as the Janus kinase 2 (JAK2) mutation, which causes blood cells to proliferate uncontrollably. This leads to an overabundance of red blood cells, and often platelets and white blood cells, resulting in panmyelosis. The increased red blood cell mass elevates the hematocrit, making the blood sluggish and prone to forming clots.
The increased blood viscosity and volume can cause symptoms like headaches, fatigue, and intense, generalized itching, particularly after exposure to water. PV must be differentiated from secondary polycythemia, which is a reactive condition caused by external factors like chronic low oxygen levels or certain kidney disorders. Unlike PV, secondary polycythemia is not a clonal cancer and does not carry the same risks of disease progression.
Determining Median Survival Rates
Median survival for treated PV patients is approximately 15 years following diagnosis. This statistic is heavily influenced by the patient’s age, which is the single most important prognostic factor. Younger individuals have a much better outlook; median survival exceeds 35 years for those diagnosed under age 40, and is estimated at 24 years for patients diagnosed before age 60.
Physicians utilize formal risk stratification, classifying patients based on age and a history of blood clots to guide treatment decisions. High-risk factors that shorten life expectancy include being over 60 years old and having a prior history of thrombosis, which is a major predictor of death. An elevated white blood cell count (leukocytosis) is also associated with a less favorable prognosis.
Treatment Protocols for Long-Term Management
The primary goal of treatment is to reduce the risk of thrombosis, which is achieved by lowering the red blood cell mass and controlling other blood cell counts. The foundational treatment involves a combination of periodic therapeutic phlebotomy and low-dose aspirin.
Phlebotomy is a procedure that removes a unit of blood to physically reduce the red blood cell count and decrease blood viscosity. The objective is to maintain the hematocrit level below 45%, a threshold shown to minimize the risk of cardiovascular events. Low-dose aspirin is prescribed to nearly all patients to prevent platelets from aggregating, thereby reducing the risk of blood clot formation.
For patients categorized as high-risk, or those who cannot tolerate phlebotomy, cytoreductive therapy is used to suppress the bone marrow’s production of blood cells. Medications like hydroxyurea or pegylated interferon are commonly employed to control blood counts, which further reduces the likelihood of thrombotic complications.
Risks of Transformation and Major Complications
Despite effective control of blood counts, the primary cause of mortality in PV patients remains cardiovascular events related to thrombosis. These events include strokes, heart attacks, and deep vein thrombosis. Proactive management of traditional cardiovascular risk factors, such as high blood pressure and cholesterol, is a major focus of long-term care.
In the long term, PV may progress into more advanced forms of blood cancer, which drastically changes the prognosis. One potential transformation is Post-Polycythemia Vera Myelofibrosis (PPV-MF), which occurs when the bone marrow becomes scarred and can no longer produce normal blood cells effectively. The risk of this transformation is cumulative, affecting an estimated 16% to 25% of patients over a 20-year period.
A less common but more serious progression is the transformation to Acute Myeloid Leukemia (AML), a rapidly progressing blood cancer. This leukemic transformation occurs in about 4% of patients within 20 years of diagnosis. When PV progresses to AML, the prognosis is severely altered, with median survival typically measured in months.