How is Chronic Myelomonocytic Leukemia Staged and Classified?

Medically Reviewed by: Dr. Douglas Tremblay

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 groups: 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 Progressing Risk Evaluated? 

Assessing and stratifying risk helps predict how the CMML will evolve and create a personalized treatment strategy for patients to live as long as possible with a good quality of life. Several models are used:

1. Mayo Molecular Model (MMM): It uses different blood test results to classify patients into 4 risk groups that are correlated with different odds of living longer with the disease (survival rates).

   • Absolute monocyte count over 10 × 10^9/L 

   • Hemoglobin under 10 g/dL 

   • Platelet count under 100 × 10^9/L

   • Presence of circulating immature cells.

   1. High (3 or 4 factors) 

   2. Intermediate-2 (2 factors) 

   3. Intermediate-1 (1 factor) 

   4. Low (0 factors) 

• Factors considered: 

• Risk Groups: 

2. CMML-Specific Prognostic Scoring System (CPSS): This model takes into consideration clinical factors and the presence of cytogenetic alterations that can impact survival and risk of progression to acute myeloid leukemia (AML).

   • CMML-2 (1 point)

   • White blood cell counts above 13 × 10^9/L (1 point)

   • Red blood cell transfusion dependency, defined as at least 1 transfusion every 8 weeks over a period of 4 months (1 point)

   • Cytogenetic risk classification intermediate (1 point), or high risk (2 points)

   1. High (4-5 points)

   2. Intermediate-2 (2-3 points)

   3. Intermediate-1 (1 point)

   4. Low (0 points)

• Factors considered: 

• Risk Levels based on the sum of all factors:

An accurate classification helps predict outcomes and how long patients can live with the disease with a good quality of life. Supportive care is also crucial, including managing symptoms like fatigue or pain. 

If you or your loved one has been diagnosed with CMML, make sure you discuss your diagnosis and risk classification with your healthcare providers. Understanding your CMML's risk of progression will help in making informed choices about your treatment options, including exploring clinical trials, advanced therapies, and supportive resources.

What Are Treatments for CMML?