A myeloproliferative neoplasm (MPN) is a group of blood cancers in which the bone marrow produces too many of one or more types of blood cells: red blood cells, white blood cells, or platelets. Unlike many cancers that form tumors, MPNs are driven by genetic mutations in bone marrow stem cells that cause them to multiply without the normal signals telling them to stop. The three most common types are polycythemia vera, essential thrombocythemia, and primary myelofibrosis.
The Three Main Types
Each MPN is defined by which blood cells are overproduced and what’s happening inside the bone marrow.
Polycythemia vera (PV) causes an overproduction of red blood cells, which thickens the blood and slows its flow. Diagnosis requires a hemoglobin level above 16.5 g/dL in men or above 16 g/dL in women, along with characteristic bone marrow findings and, in about 95% of cases, a specific gene mutation called JAK2. PV has a median survival of about 13.5 years from diagnosis, though many people live much longer depending on age at diagnosis and how well the disease is managed.
Essential thrombocythemia (ET) causes an overproduction of platelets. A sustained platelet count of 450,000 or higher per microliter of blood is one of the key diagnostic markers, confirmed by a bone marrow biopsy showing abnormal platelet-producing cells. ET tends to be the most indolent of the three, with a median survival of roughly 19.8 years.
Primary myelofibrosis (PMF) involves progressive scarring (fibrosis) of the bone marrow, which gradually impairs its ability to produce blood cells normally. The scarring is graded on a scale from 0 to 3. Early-stage myelofibrosis (grades 0 or 1) may cause few problems, while advanced fibrosis (grades 2 or 3) is linked to more severe anemia, low platelet counts, and a worse prognosis. Median survival for myelofibrosis is about 5.9 years, making it the most serious of the three classic MPNs.
What Causes MPNs
MPNs are caused by acquired genetic mutations, meaning they develop during a person’s lifetime rather than being inherited. The most common culprit is a mutation in the JAK2 gene, which acts like a permanently stuck “on” switch for cell growth. Nearly all PV patients carry this mutation. In ET and myelofibrosis, about 50 to 60% of patients have a JAK2 mutation, roughly 20 to 30% carry a mutation in a gene called CALR, and about 4 to 8% have a mutation in the MPL gene.
A small percentage of ET and myelofibrosis patients have none of these three mutations, a status referred to as “triple-negative.” The specific mutation a person carries can influence the disease’s behavior. For example, ET patients with a CALR mutation tend to have higher platelet counts but lower red and white blood cell counts compared to those with a JAK2 mutation.
Common Symptoms
MPNs can be surprisingly symptomatic, even when blood counts look only mildly abnormal. The most pervasive symptom is fatigue, reported by nearly 90% of MPN patients across all three subtypes. In myelofibrosis, that number climbs to 96%.
Beyond fatigue, the symptoms that most commonly affect daily life include difficulty concentrating (reported by about 63% of patients), feeling full after eating very little (64%), reduced physical activity (62%), and night sweats (53%). Itching is particularly common in PV, affecting about 62% of patients, and can be triggered by warm water or temperature changes. About half of all MPN patients experience bone pain, and roughly a third report unexplained weight loss. Abdominal discomfort from an enlarged spleen is common as well, especially in myelofibrosis, where the spleen takes over some blood cell production as the bone marrow fails.
Blood Clots: The Biggest Risk
The most dangerous complication of MPNs is an increased risk of blood clots, both in arteries (leading to heart attacks and strokes) and in veins (deep vein thrombosis and pulmonary embolism). Blood clots are the leading cause of illness and death in PV and ET. At the time of diagnosis, roughly 9% of MPN patients have already had an arterial clot and 4% a venous clot.
Cardiovascular risk factors like high blood pressure, diabetes, and smoking dramatically compound the problem. MPN patients with even one of these additional risk factors have about three times the risk of developing a clot compared to those without. In PV specifically, having a cardiovascular risk factor nearly sixfold increases the chance of an arterial clot. Diabetes stands out as particularly dangerous, more than doubling clot risk across all MPN subtypes.
How MPNs Are Treated
Treatment depends on the MPN subtype, the patient’s age, and their risk of complications.
For polycythemia vera, the cornerstone of treatment is phlebotomy, a procedure where blood is drawn to reduce the red blood cell concentration. The goal is to keep hematocrit (the percentage of blood volume occupied by red cells) below 45%. A landmark study found that patients who maintained hematocrit below 45% had significantly lower rates of cardiovascular death and major clotting events compared to those whose levels were allowed to drift between 45% and 50%. Low-dose aspirin (100 mg daily) is also recommended for nearly all PV patients, as it meaningfully reduces vascular events without a significant increase in major bleeding.
For essential thrombocythemia, treatment in lower-risk patients may involve aspirin alone, while higher-risk patients typically take a medication to reduce platelet production.
For myelofibrosis, treatment focuses on managing symptoms like anemia, an enlarged spleen, and constitutional symptoms such as night sweats and weight loss. A class of drugs called JAK inhibitors, the first of which was approved for intermediate- to high-risk myelofibrosis, works by blocking the overactive signaling pathway driven by the JAK2 mutation. These medications have been shown to shrink the spleen, reduce symptoms, and improve survival. For younger patients with aggressive disease, a bone marrow transplant remains the only potentially curative option.
Can MPNs Turn Into Leukemia?
All three classic MPNs carry some risk of transforming into acute myeloid leukemia (AML), an aggressive blood cancer. The risk varies substantially by subtype. Myelofibrosis has the highest transformation rate, with 5.8% to 20.6% of patients developing AML within 10 years. PV carries a 2.3% to 8.7% risk over 10 years, and ET has the lowest risk at 0.7% to 4% over the same period.
MPNs can also evolve into one another. PV and ET can both progress into a secondary form of myelofibrosis over time, which is why regular monitoring with blood counts and periodic bone marrow biopsies is a standard part of long-term care.
Living With an MPN
Most people with MPNs live with their disease for years or even decades, particularly those with ET or PV. The key to long-term management is consistent monitoring, controlling blood counts, and aggressively managing cardiovascular risk factors like blood pressure, blood sugar, and smoking. Because symptom burden can be significant even when blood work appears stable, many hematologists use a standardized symptom questionnaire that tracks fatigue, concentration, itching, night sweats, and other quality-of-life measures over time. If your symptoms are worsening, that information matters as much as your lab results when making treatment decisions.