How Is Myeloproliferative Neoplasm Staged And Classified?

Myeloproliferative neoplasms (MPNs) are a group of diseases that affect the bone marrow and lead to an increased production of blood cells. Unlike other cancers, MPNs are not typically staged because they are systemic diseases that do not form solid tumors. Instead, they are classified based on the type of blood cells that are overproduced and the specific genetic mutations that are present.

Understanding Classification: What Type of MPN Do You Have?

MPNs are grouped based on which type of blood cell is being overproduced and what changes are seen in the bone marrow. The main types of MPNs include:

• Chronic myeloid leukemia (CML): This type of MPN is characterized by the overproduction of white blood cells. It is associated with a specific genetic mutation known as the Philadelphia chromosome. Due to its unique genetic profile, it is often discussed separately.
• Polycythemia vera (PV): The bone marrow produces too many red blood cells. This can thicken the blood and lead to clots. It is confirmed by high hemoglobin or hematocrit levels, increased red blood cells in the bone marrow, and the presence of a JAK2 mutation. Low erythropoietin levels also support the diagnosis if JAK2 is not found in the patient.
• Essential thrombocythemia (ET): Characterized by the overproduction of platelets, which can lead to blood clots and bleeding. Defined by a high platelet count (≥450 x 10⁹/L), increased and abnormal megakaryocytes in the bone marrow, and the presence of a JAK2, CALR, or MPL mutation. Other causes of high platelets must be ruled out first. 
• Primary myelofibrosis (PMF) is bone marrow scarring (fibrosis) due to abnormal megakaryocytes (platelet-forming cells). This can show signs like anemia and an enlarged spleen. It is diagnosed when abnormal megakaryocytes are present, bone marrow scarring is seen, and mutations such as JAK2, CALR, or MPL are identified. PMF is further split into prefibrotic (early stage with minimal scarring) and overt (advanced stage with significant fibrosis). 

Each type has different diagnostic criteria based on blood test results, bone marrow findings, and genetic markers. This classification helps determine the best treatment plan and the possible complications a person might face, such as blood clots or progression to more advanced disease.

Phases of Myeloproliferative Neoplasm

While MPNs are not staged in the traditional sense, they can progress through different phases over time. These phases include:

• Chronic phase: This is the initial phase of the disease, where symptoms are typically mild or even absent. The disease can often be managed with medication during this phase.
• Accelerated phase: In this phase, symptoms become more severe and the disease becomes more difficult to manage. There may be an increase in the number of immature blood cells, or blasts, in the blood or bone marrow.
• Blast phase (or acute phase): This is the most severe phase of the disease, where the number of blasts in the blood or bone marrow increases dramatically. This phase is similar to acute leukemia and requires aggressive treatment.

Various factors can influence the progression of MPNs, including the specific type of MPN, the presence of certain genetic mutations, and the patient's overall health.

Staging: Understanding How Far the MPN Has Progressed

Unlike many cancers, MPNs are not staged by tumor size or spread. Instead, staging focuses on how active the disease is and whether complications have developed.

For primary myelofibrosis, specialists use specific scoring systems to assess how it evolves:

• MIPSS-70 and MIPSS-70+ v2.0: Used for patients under 70. These include molecular and clinical features.
• DIPSS and DIPSS-Plus: Used for patients of all ages.
• MYSEC-PM: Used for post-PV or post-ET myelofibrosis and MPN.

These tools categorize into risk groups: lower or higher risk. Risk levels help guide treatment decisions, including whether to monitor with watchful waiting, start medication, or consider more intensive treatment like a stem cell transplant.

In PV and ET, the disease course is usually slow, and can even last decades, controlled with treatment. However, over time, they can progress to myelofibrosis or, in rare cases, acute myeloid leukemia (AML). Progression is more likely after many years and is often tracked by monitoring changes in blood counts and symptoms. 

Classification helps you and your care team understand what type of MPN you have and what to expect. Staging and risk scoring systems provide a clearer picture of how the condition will evolve and what treatment options make sense at each step. 

Knowing your MPN type, risk group, and genetic profile allows you to work with your care team to make informed decisions that reflect your individual health status.

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Source: 

• Myeloproliferative Neoplasms
• NCCN Guidelines for Patients, MPN