How is Chronic Myelomonocytic Leukemia Staged and Classified?

Chronic Myelomonocytic Leukemia (CMML) is a rare blood cancer that impacts blood-forming cells in the bone marrow. Unlike other cancers, CMML is not staged in the traditional sense. Instead, it is classified by looking at the number of immature blood cells (blasts) in the blood and bone marrow, as well as genetic and clinical risk factors. This classification helps doctors assess the disease's severity and guide treatment.

How is CMML Classified?

CMML is classified into two types: CMML-1 and CMML-2.

• CMML-1: In this type, less than 5% of the cells in the blood and less than 10% of the cells in the bone marrow are blasts.
• CMML-2: In this type, 5-19% of the cells in the blood and 10-19% of the cells in the bone marrow are blasts. Alternatively, if Auer rods are present in the cells, or if there are more than 20% blasts in the blood or bone marrow, the disease is also classified as CMML-2. It is generally more severe and may require more intensive treatment than CMML-1.

Does CMML Have Subtypes?

CMML can be further categorized into two subtypes based on the white blood cell counts.

• Myeloproliferative CMML (MP-CMML): has some characteristics that are similar to myeloproliferative neoplasms, the main one being a high white blood cell count (≥13 × 10^9/L).

• Myelodysplastic CMML (MD-CMML): shares some symptoms with myelodysplastic syndromes, but the main characteristic of this subtype is finding normal or low white blood cell count, and generally has slower progression.

What are the Phases of CMML?

CMML can also be described in terms of phases or stages, which are based on the number of blasts in the blood and bone marrow, as well as the presence of certain symptoms. These phases include:

• Chronic phase: This is the initial phase of CMML, where the number of blasts in the blood and bone marrow is relatively low (less than 10%). Symptoms may be mild or even absent in this phase.
• Accelerated phase: In this phase, the number of blasts increases (between 10% and 19%). Symptoms may become more noticeable, and the disease may start to progress more quickly.
• Blast phase (or acute phase): This is the most severe phase of CMML, with 20% or more blasts. In this phase, the disease behaves like acute myeloid leukemia (AML), with rapid progression and severe symptoms.

How is CMML Risk Stratified? 

Assessing and stratifying risk helps predict how the CMML progresses and create a personalized treatment strategy for patients to live longer and ensure they have a quality of life. Several models are used:

1. Mayo Molecular Model (MMM):

• It uses the following risk factors to predict life expectancy and create treatment strategies: ASXL1 gene mutations, absolute monocyte count over 10 × 10^9/L, hemoglobin under 10 g/dL, platelet count under 100 × 10^9/L, and circulating immature cells.

• Risk Groups: High (3+ factors), Intermediate-2 (2 factors), Intermediate-1 (1 factor), Low (0 factors). Median survival varies from 16 to 97 months based on risk group.

2. CMML-Specific Prognostic Scoring System (CPSS):

• Considers transfusion dependency, blast count, and cytogenetic risk.

• Risk Levels: Low, Intermediate-1, Intermediate-2, and High. This model predicts overall survival and transformation risk to AML.

An accurate classification helps predict outcomes and personalize treatment approaches, including clinical trials for specific genetic mutations. Supportive care, including managing symptoms like anemia and monitoring disease progression, is also crucial. People diagnosed with CMML and their caregivers are encouraged to discuss classification and treatment options with their healthcare providers. Understanding CMML's classification and its progression will help in making informed choices, including exploring clinical trials, advanced therapies, and supportive resources.

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Sources: 

• Chronic myelomonocytic leukemia: 2024 update on diagnosis, risk stratification and management
• Survival Rates for Chronic Myelomonocytic Leukemia
• How I diagnose and treat chronic myelomonocytic leukemia