MPN stands for myeloproliferative neoplasm, a group of blood cancers in which the bone marrow overproduces one or more types of blood cells. Unlike many cancers that form tumors, MPNs are driven by genetic mutations in blood-forming stem cells that cause them to churn out too many red blood cells, white blood cells, or platelets. The three most common types are polycythemia vera (PV), essential thrombocythemia (ET), and primary myelofibrosis (PMF).
MPNs are chronic conditions, meaning they develop slowly and persist for years. Many people are diagnosed incidentally through routine blood work before they ever notice symptoms. While MPNs are not curable with standard treatment (outside of a bone marrow transplant), most people live with them for years or even decades with proper management.
How MPNs Develop in the Bone Marrow
Your bone marrow contains stem cells that mature into red blood cells, white blood cells, and platelets. In a healthy person, this process is tightly regulated. In someone with an MPN, a stem cell acquires a genetic mutation that flips a growth signal permanently “on,” causing it to produce far more cells than the body needs. That mutated cell multiplies and gradually crowds out normal blood production.
The most common culprit is a mutation in the JAK2 gene, found in roughly 90 to 95% of PV patients and 50 to 60% of those with ET or myelofibrosis. JAK2 normally helps regulate blood cell production; the mutation locks it into an active state. Two other mutations, in genes called CALR and MPL, account for most of the remaining cases. About 3 to 5% of ET patients and 5 to 8% of myelofibrosis patients carry an MPL mutation. A small number of patients have none of these three mutations, a situation sometimes called “triple negative.”
The Three Main Types
Polycythemia Vera
PV causes the bone marrow to make too many red blood cells, which thickens the blood and raises the risk of clotting. Diagnosis is based on hemoglobin levels above 16.5 g/dL in men or 16 g/dL in women, along with a confirmed JAK2 mutation and characteristic bone marrow findings. Many patients also overproduce white blood cells and platelets. The hallmark treatment is phlebotomy (regularly drawing blood to keep red blood cell levels in check), often combined with low-dose aspirin. Patients at higher risk for clots also receive medication to reduce blood cell counts.
Essential Thrombocythemia
ET is defined by a sustained platelet count above 450,000 per microliter. More than half of ET patients have no symptoms at diagnosis and are discovered only because of an abnormal blood test. The main danger is blood clots, though some patients paradoxically experience bleeding when platelet counts climb very high. Treatment depends on clotting risk: lower-risk patients may need only aspirin and monitoring, while higher-risk patients take medications to bring platelet counts down.
Primary Myelofibrosis
PMF is the most serious of the three common types. Scar tissue (fibrosis) gradually replaces normal bone marrow, forcing blood cell production into the spleen and liver, which then enlarge. This leads to anemia, fatigue, and sometimes a painfully swollen spleen. PMF exists in two stages: a prefibrotic stage that can resemble ET, and an overt stage with significant scarring. Median survival varies widely depending on risk factors. Patients in the lowest risk category can live 15 years or more, while those in the highest risk group have a median survival closer to 1.5 to 2.3 years. A bone marrow transplant is the only potentially curative option, though it carries significant risks and is typically reserved for younger patients with aggressive disease.
Symptoms Most Patients Experience
A large international study of 402 MPN patients used a standardized symptom questionnaire and found that fatigue is nearly universal, reported by 93% of patients. Beyond fatigue, the most common symptoms and the percentage of patients affected were:
- Insomnia: 65%
- Sad mood: 63%
- Feeling full quickly after eating (early satiety): 62%
- Difficulty concentrating: 62%
- Numbness or tingling: 61%
- Reduced physical activity: 61%
- Night sweats: 56%
- Dizziness: 55%
Severity scores on a 0 to 10 scale averaged around 2 to 3 for most symptoms, meaning they are generally mild to moderate but persistent. Fatigue and sexual difficulties scored highest. Many patients describe a constellation of low-grade symptoms that collectively reduce quality of life, even when no single symptom feels severe on its own.
Blood Clot Risk
The most dangerous complication across all MPN types is thrombosis, including deep vein clots, pulmonary embolism, stroke, and heart attack. Even with treatment, the rate of blood clots in MPN patients runs between 2 and 5 per 100 patients per year. That risk persists even for patients on blood thinners after a first clot, with recurrence rates as high as 4 to 5 per 100 patients per year. This is why clot prevention, through aspirin, blood count control, and sometimes stronger blood thinners, is central to MPN management.
Progression to More Serious Disease
MPNs can transform over time into more aggressive conditions. PV and ET can progress to myelofibrosis: roughly 12 to 21% of PV patients and 9 to 10% of ET patients develop secondary myelofibrosis. All three types carry some risk of transforming into acute myeloid leukemia (AML), a fast-growing blood cancer that is much harder to treat.
The 10-year risk of developing AML varies substantially by type. For patients diagnosed around age 70, the 10-year cumulative incidence is about 3.5% for PV, 4.7% for ET, and 18.2% for myelofibrosis. These numbers mean that most PV and ET patients will never develop leukemia, but the risk is real enough that regular monitoring is essential.
How MPNs Are Treated
Treatment is tailored to the specific MPN type, risk level, and symptoms. There is no one-size-fits-all approach.
For PV and ET, lower-risk patients often start with aspirin and close monitoring. Those at higher risk for clots, typically older patients or those with a history of clotting, begin medication to reduce blood cell counts right away. The two main options are hydroxyurea, a well-established oral medication, and interferon, an immune-based therapy. Interferon is generally preferred for younger patients and women who may become pregnant. The two are currently being compared head to head in large clinical trials.
For patients whose disease doesn’t respond to these first-line treatments, JAK inhibitor drugs have become a cornerstone of care. Ruxolitinib was the first in this class and remains the standard second-line option. It works by blocking the overactive JAK signaling pathway that drives cell overproduction. It is particularly effective at shrinking an enlarged spleen and reducing symptoms like night sweats and fatigue.
Newer JAK inhibitors have expanded the options for myelofibrosis patients with specific challenges. Pacritinib received accelerated approval in 2022 for patients with myelofibrosis who have severely low platelet counts, a group that couldn’t safely take older JAK inhibitors. Momelotinib was approved in 2023 for myelofibrosis patients with anemia. It has a dual mechanism: besides blocking JAK signaling, it also affects iron regulation in a way that improves red blood cell production, addressing one of myelofibrosis’s most debilitating problems.
Rarer MPN Types
Beyond the three common types, the MPN category includes several rare conditions. Chronic myeloid leukemia (CML) is driven by a specific genetic rearrangement called BCR-ABL1 and is treated with a different class of targeted drugs. Chronic neutrophilic leukemia produces excessive neutrophils (a type of white blood cell) and is extremely rare, affecting roughly 1 in 10 million people per year, with a median age at diagnosis of about 67. It is linked to a mutation in the CSF3R gene. Chronic eosinophilic leukemia involves overproduction of eosinophils, another white blood cell type. About 5 to 10% of MPN cases don’t fit neatly into any single category and are classified as unclassifiable MPN.