What Is Chronic Myelomonocytic Leukemia (CMML)?

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Chronic myelomonocytic leukemia (CMML) is a rare type of cancer that begins in the blood-forming cells in the bone marrow, leading to abnormally high levels of white blood cells called monocytes. This often results in an enlarged spleen and/or liver and symptoms such as abdominal pain and feeling full faster than normal. In most cases the cause of CMML is unknown, although it sometimes develops after cancer treatment. The only cure for CMML is a stem cell transplant, but it also can be treated with certain medications or chemotherapy. CMML affects around 4 of every 1 million people in the U.S. every year and is usually diagnosed in those 60 and older.

Symptoms of CMML

The tell-tale sign of CMML is excess monocyte white blood cells, which can be seen on a blood test. Those extra monocytes can cause an enlarged spleen and liver, which can cause symptoms like:

  • Pain in upper left (spleen) or upper right (liver) of abdomen
  • Feeling full too quickly when eating

A proliferation of monocytes can crowd out other blood cells, including red blood cells, normal white blood cells, and blood platelets, causing symptoms such as:

  • Extreme fatigue
  • Weakness
  • Shortness of breath
  • Pale skin
  • Frequent or severe infections
  • Abnormal bleeding or bruising
  • Frequent or severe nosebleeds

Other symptoms of CMML include:

  • Unintentional weight loss
  • Fever
  • Loss of appetite

Causes

In most cases of CMML, the cause is unknown. Some may occur after cancer treatment with chemotherapy drugs. Radiation and cancer-causing chemicals may also cause DNA mutations that can lead to CMML.

Diagnosis

In order to confirm a CMML diagnosis, your doctor will need to do blood and bone marrow tests.

The blood test will include a complete blood count (CBC). This measures the red blood cells, white blood cells, and platelets in your body. It may also include a differential count, which measures the different kinds of white blood cells. A common sign of CMML is a high number of monocytes, greater than 1,000 per microliter.

Other signs include low numbers of other white blood cells, red blood cells, and blood platelets. Blood cells also can be examined under a microscope to look for differences in size and shape.

In addition, blood tests may be done to check for low vitamin B12 and folate levels, which can cause low blood counts, and infections, which can cause an elevation in white blood cells.

When abnormalities in the blood suggest CMML, a bone marrow biopsy will be necessary to confirm the diagnosis. This entails taking a sample of bone marrow, usually from the back of the hip bone, to be examined under a microscope to determine the types and number of blood-forming cells there, as well as to look for signs of infection or cancer cells.

The bone marrow test will also measure the percentage of immature marrow cells called blasts in the sample. A diagnosis of CMML is made when there are fewer than 20% blasts in the bone marrow. (A percentage of 20 or more blasts is diagnosed as acute leukemia. ) Cytogenetic tests may also be done to look for abnormalities in the DNA of bone marrow cell.

Treatment

A stem cell transplant from a matched donor is the only cure for CMML. Your doctor will talk with you about your eligibility for this procedure.

Chemotherapy also is an option for treating CMML. While it can’t cure CMML, it can help kill abnormal bone marrow cells. Your doctor may suggest the chemo drug Hydrea (hydroxyurea) to help reduce the number of white blood cells and monocytes.

Hypomethylating agents like Dacogen (decitabine) may also keep abnormal cells in the bone marrow from making new cells. A 2017 study found that hypomethylating agents can help improve patient longevity.

You may benefit from supportive therapy to help prevent symptoms and problems. For example, if you’re dealing with anemia (low red blood cell counts), a blood transfusion or Procrit (erythropoietin) may help you feel better. Bleeding problems may be treated with platelet transfusions. If you have an infection, antibiotics can help clear it up.

A Word From Verywell

The uncertainty of a CMML diagnosis may make you feel anxious or stressed. An open conversation with your doctor will help you understand your individual prognosis and treatment options. You also may find it helpful to work with a therapist or join a support group in order to deal with the mental and emotional stress of having a CMML. 

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  1. American Cancer Society. Chronic Myelomonocytic Leukemia.

  2. Zeidan AM, Hu X, Long JB, et al. Hypomethylating agent therapy use and survival in older patients with chronic myelomonocytic leukemia in the United States: A large population-based study. Cancer. 2017;123(19):3754-3762. doi:10.1002/cncr.30814

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