Chronic myelomonocytic leukemia (CMML) is a kind of leukemia, a group of cancers that disrupts the formation and activity of blood cells.

You may have heard of the four main types of leukemia. Yet, some rarer types of leukemia exist as well.

Most of the time, leukemia affects leukocytes, or white blood cells. CMML is a rarer type of leukemia that affects myeloid stem cells in your blood marrow.

Keep reading to learn more about what CMML is, which symptoms to look out for, and how it’s diagnosed and treated.

CMML affects myeloid stem cells in your bone marrow. These are stem cells that produce blood cells like:

  • Red blood cells (RBCs). These cells carry oxygen and other nutrients to your body’s organs and tissues.
  • White blood cells (WBCs). Called granulocytes and monocytes, these cells respond to infections and disease.
  • Platelets. These cells form blood clots to help stop bleeding.

When you have CMML, you have an increased number of monocytes in your blood (monocytosis). In addition to higher-than-normal levels of monocytes, you might also have an increased number of immature WBCs, called blasts.

The overabundance of monocytes and blasts crowds out healthy blood cells like RBCs, platelets, and granulocytes. This leads to the symptoms of CMML.

CMML is classified as a myelodysplastic/myeloproliferative neoplasm. This is because, while CMML is its own distinct condition, it shares features of two other conditions:

  • Myelodysplastic syndromes (MDS). MDS is a group of related blood conditions. When you have MDS, your blood cells are atypical and don’t develop properly, leading to fewer healthy blood cells. MDS can progress to acute myeloid leukemia (AML).
  • Myeloproliferative neoplasms (MPNs). MPNs are abnormal growths where your myeloid stem cells produce higher-than-normal levels of RBCs, WBCs, or platelets. These RBCs, WBCs, or platelets don’t function like they usually do. MPNs can also progress to AML.

How common is CMML?

CMML is a rare type of leukemia. The American Cancer Society estimates that CMML only occurs in 4 out of every 1 million people in the United States per year, amounting to 1,100 new diagnoses each year.

The majority of people diagnosed with CMML are ages 60 and over. CMML is also more common in men than in women.

Are there any known causes or risk factors for CMML?

Right now, the exact cause of CMML is unknown. Experts believe that genetic changes may cause the increased production of monocytes that’s seen in people with this condition.

Potential risk factors for CMML include:

  • being 60 years or over
  • being male
  • having certain genetic changes, such as those in the genes TET2, SRSF2, and ASXL1
  • having a previous treatment for cancer that included chemotherapy or radiation therapy

CMML can develop slowly over time, so you might not have symptoms early on. Because of this, it’s possible that your doctor may detect CMML when a routine blood test finds increased levels of monocytes or total WBCs.

The symptoms of CMML begin to happen when high levels of monocytes and blasts crowd out your healthy blood cells. Some of the more common symptoms of CMML are:

If you’re experiencing symptoms of CMML, your doctor will perform tests on your blood and bone marrow to help make a diagnosis.

Several types of blood tests are used to diagnose CMML. These include:

  • a complete blood count to determine the number of monocytes and other blood cells in a blood sample
  • a blood smear to evaluate the appearance of blood cells under a microscope
  • blood tests to help rule out other causes of elevated WBCs like infections or other health conditions

A bone marrow aspiration and biopsy are also collected and can be used to evaluate:

  • the types, numbers, and appearance of blood cells
  • the percentage of cells that are blasts
  • whether or not certain genetic changes are present
  • the presence of specific markers on the surface of WBCs (immunophenotyping)

Diagnostic criteria for CMML

The World Health Organization (WHO) recommends the following criteria to diagnose CMML:

  • High monocyte levels (greater than or equal to 1×109 cells per liter) have increased for at least 3 months, with monocytes making up more than 10 percent of WBCs.
  • Blast cells make up less than 20 percent of cells in the blood or bone marrow, with no signs of AML.
  • Other specific conditions have been ruled out, including:
    • other MPNs
    • other blood cancers that can present with elevated levels of monocytes

If you have CMML, but aren’t experiencing symptoms, your doctor may choose to monitor your condition without treatment. This is called watchful waiting.

Potential treatment options for CMML include:

  • stem cell transplant
  • chemotherapy
  • supportive care

Your specific treatment plan will depend on many factors, including:

  • the type of CMML you have
  • the severity of your symptoms
  • your age
  • your overall health
  • your personal preference

Stem cell transplant

A stem cell transplant has the potential to cure CMML, but it can be very taxing on the body. Because of this, they’re typically only recommended for individuals that are younger in age and in good overall health.

During the stem cell transplant, a high dose of chemotherapy is used to kill cells in your bone marrow. Then, stem cells from a healthy matched donor are infused into your body. The goal is for these transplanted stem cells to reestablish healthy bone marrow.

Chemotherapy

Chemotherapy can also be used to treat CMML. While chemotherapy cannot cure CMML, it can kill cancer cells or slow their growth. Some examples of chemotherapy drugs that may be used to treat CMML include:

  • azacitidine (Vidaza)
  • decitabine (Dacogen)
  • decitabine with cedazuridine (Inqovi)
  • hydroxyurea (Hydrea)

Supportive care

Supportive care is treatment that helps to alleviate symptoms and prevent complications from CMML. Some examples of supportive care for CMML are:

  • blood or platelet transfusions to help with low levels of RBCs or platelets, respectively
  • erythropoiesis-stimulating agents like epoetin alfa (Procrit, Epogen) and darbepoetin (Aranesp) to promote the production of RBCs
  • antibiotics to help prevent or treat bacterial infections

The outlook for CMML can depend on the type of CMML that you have. Other things that can influence outlook include:

  • your blood cell counts
  • the presence of certain genetic changes
  • your age and overall health

It’s possible for CMML to come back (relapse) after treatment. Additionally, some types of CMML may not respond to treatment. This is called refractory CMML.

CMML progresses to AML in 15 to 30 percent of people. This happens when the number of blast cells in your blood or bone marrow goes higher than 20 percent. AML is an acute (rapidly growing) type of leukemia.

According to the American Cancer Society, research has shown that:

  • People with CMML-1 typically live longer than people with CMML-2. Median life expectancy for CMML-1 and CMM-2 have been found to be 20 months and 15 months respectively.
  • About 20 percent of people with CMML-1 and 10 percent of people with CMML-2 survive longer than 5 years after their diagnosis.
  • People with CMML-2 are more likely to progress to AML than those with CMML-1.

When discussing data like this, it’s important to remember that these statistics don’t reflect individual experiences. This data is based on many people with CMML over a long period of time.

Additionally, researchers continue to develop newer, more effective treatments for cancers like CMML. This can also improve the outlook for CMML overall.