What is Chronic Myelomonocytic Leukemia?

Medically Reviewed by: Dr. Douglas Tremblay

Chronic myelomonocytic leukemia (CMML) is a rare type of cancer that affects the bone marrow and blood. It is characterized by the overproduction of monocytes, a type of white blood cell, in the bone marrow. These excess monocytes spill into the bloodstream and can infiltrate other parts of the body, such as the liver, spleen, and skin, causing a variety of symptoms. 

CMML is a unique disease entity because it is considered a type of myelodysplastic syndrome (MDS) that also has features of myeloproliferative neoplasms (MPN). Over time, CMML can transform into a more aggressive form of disease called acute myeloid leukemia (AML).

Who is Affected by Chronic Myelomonocytic Leukemia?

CMML is a very rare disease, and since patients often do not display symptoms in the early stages, the exact number of individuals living with it is unknown. However, it is estimated to affect approximately 4 out of every 1 million people in the United States each year, with about 1,100 to 1,500 new diagnoses annually.

Most patients diagnosed with CMML are over 70 years old and are more often men than women.

Why Do People Get Chronic Myelomonocytic Leukemia?

CMML results from genetic mutations in the stem cells within the bone marrow. The exact cause of these mutations is unknown, but several factors can contribute. These mutations are usually acquired during a person's lifetime and are not inherited. 

Certain risk factors have been identified for CMML, including older age, previous treatment with chemotherapy or radiation therapy, and exposure to certain chemicals such as benzene. However, many people with CMML do not have any of these risk factors, suggesting that other unknown factors may also contribute to the development of this disease.

Types of Chronic Myelomonocytic Leukemia

There are two subgroups of CMML, known as CMML-1 and CMML-2. The distinction between these two types is based on the number of blasts, or immature cells, present in the blood or bone marrow. 

• CMML-1 is characterized by fewer blasts and is generally associated with a better prognosis, 
• while CMML-2 has more blasts and is often more aggressive and more challenging to treat.

There are two subtypes:

• Myeloproliferative CMML: at the time of diagnosis, the blood test shows more than 13×10⁹/L white blood cell counts (normal range is 4.5-11×10⁹/L)
• Myelodysplastic CMML: at the time of diagnosis the blood test shows less than 13×10⁹/L white blood cell counts. This subtype has features of both myelodysplastic syndrome (MDS) and myeloproliferative neoplasm (MPN). 

What are the Most Common Symptoms of Chronic Myelomonocytic Leukemia?

Although the signs and symptoms of CMML can differ from person to person, in some cases (mostly in low-risk CMML), patients may not have any symptoms.

When symptoms are present, they often result from the overproduction of abnormal monocytes, a type of white blood cell. These cells crowd out healthy blood cells in the bone marrow and bloodstream, causing a variety of complications. Often, these symptoms can mimic other illnesses, so it's important to stay aware of how you are feeling and seek medical attention if you are concerned about anything.

The most common signs and symptoms of CMML include:

• Fatigue: This is a common symptom in many types of cancer, including CMML. It is often due to the body's increased need for energy as it fights off the disease, as well as the low red blood cell counts (anemia). 
• Fever: A persistent or recurrent fever can be a sign of CMML. This is due to the body's immune response to the disease.
• Weight loss: Unexplained weight loss can be a sign of many types of cancer, including CMML. This is often due to a decreased appetite and changes in metabolism related to the disease.
• Easy bruising or bleeding: This can occur due to a decrease in the number of platelets in the blood, a condition known as thrombocytopenia, which is common in people with CMML.
• Shortness of breath: This can occur due to anemia, a condition characterized by a lack of red blood cells, which is common in people with CMML.
• Infections: People living with CMML may be more prone to infections due to a decrease in the number of healthy white blood cells.
• Enlarged spleen: This condition is known as splenomegaly and can occur in people with CMML. It can cause discomfort or pain in the left upper abdomen. Depending on the size of the spleen, patients can also experience early satiety, and a feeling of fullness after eating a small meal.

Seek Specialized Care For Your Chronic Myelomonocytic Leukemia

Seeking medical attention promptly if you are experiencing symptoms related to your CMML is of utmost importance. Delaying an accurate diagnosis and treatment can allow the leukemia to progress, making it more challenging to achieve remission. 

If you don't currently have a CMML specialist on your care team, it is important that you consult with one. Use HealthTree's CMML Specialist Directory to locate a specialist near you. 

Click here to continue reading about how CMML is staged and classified to understand better how the disease may evolve and how long patients live with CMML.

How CMLL is Staged and Classified?