How is Essential Thrombocythemia Staged and Classified?

Essential Thrombocythemia (ET) isn’t staged like other cancers, where the disease progresses through predictable phases or grows with measurable and palpable tumors. Instead, ET is a chronic blood disorder that can remain stable for years but carries a risk of complications such as blood clots, bleeding, or progression to other diseases. Because of this, ET is classified based on risk factors, symptoms, and genetic features that help guide treatment decisions and predict long-term outcomes.

Classification is based on risk factors

The most common way ET is classified is by thrombotic risk, meaning the likelihood of developing blood clots. This risk depends on:

• Age (over or under 60)
• History of thrombosis (e.g., stroke, heart attack, DVT)
• Presence of the JAK2 mutation
• Cardiovascular risk factors (like smoking, diabetes, or high blood pressure)

Using these factors, doctors group patients into four risk categories, according to the revised IPSET-Thrombosis model:

1. Very Low Risk: Age ≤60, no history of thrombosis, and no JAK2 mutation
2. Low Risk: Age ≤60, no thrombosis history, but JAK2 mutation present
3. Intermediate Risk: Age >60 with JAK2 mutation but no prior thrombosis
4. High Risk: Any history of thrombosis or age >60 with a JAK2 mutation

This classification helps determine whether a patient needs only low-dose aspirin or more intensive treatments like cytoreductive therapy.

Phases of Essential Thrombocythemia

Although ET doesn’t follow traditional “stages,” the disease can generally be thought of as moving through two functional phases:

• Stable Phase: Many patients stay in this phase for years. Symptoms are mild or manageable, and routine treatment can prevent complications.
• Progressive Phase: A small percentage of patients may develop worsening symptoms, more aggressive blood abnormalities, or evolve into:

  • Post-ET Myelofibrosis (MF): Scarring of the bone marrow

  • Acute Myeloid Leukemia (AML): A rare but serious transformation, occurring in 2–3% of patients over 10–15 years. 

These transformations are more likely in patients with certain high-risk genetic mutations or prolonged extreme thrombocytosis.

Prognosis and Survival 

Most people with ET have a favorable outlook. Median survival is approximately 19–20 years, with some younger patients living 30+ years or more. Patients in the very low- or low-risk groups often have life expectancies close to the general population.

However, complications like blood clots or bleeding episodes can affect quality of life and increase the risk. This makes ongoing monitoring and proper risk stratification essential, even in patients who feel well.

Keep Exploring

ET is a complex condition that affects each person differently. By continuing through our Essential Thrombocythemia 101 series. Keep reading How Long Will I Live With Essential Thrombocythemia?

Sources: 

• Essential thrombocythemia: Biology, clinical features, thrombotic risk, therapeutic options and outcome
• Essential thrombocythemia: 2024 update on diagnosis, risk stratification, and management
• Essential Thrombocytosis