Chronic myelomonocytic leukemia is a disease in which too many myelocytes and monocytes (immature white blood cells) are made in the bone marrow.

In CMML, the body tells too many blood stem cells to develop into two types of white blood cells called myelocytes and monocytes. Some of these blood stem cells never become mature white blood cells. These immature white blood cells are called blasts. Over time, the myelocytes, monocytes, and blasts crowd out the red blood cells and platelets in the bone marrow. When this happens, infection, anemia, or easy bleeding may occur.

Older age and being male increase the risk of developing chronic myelomonocytic leukemia.

Anything that increases your chance of getting a disease is called a risk factor. Possible risk factors for CMML include the following:

• Older age.
• Being male.
• Being exposed to certain substances at work or in the environment.
• Being exposed to radiation.
• Past treatment with certain anticancer drugs.

Possible signs of chronic myelomonocytic leukemia include fever, feeling very tired, and weight loss.

These and other symptoms may be caused by CMML. Other conditions may cause the same symptoms. A doctor should be consulted if any of the following problems occur:

• Fever for no known reason.
• Infection.
• Feeling very tired.
• Weight loss for no known reason.
• Easy bruising or bleeding.
• Pain or a feeling of fullness below the ribs.

Certain factors affect prognosis (chance of recovery) and treatment options.

The prognosis (chance of recovery) and treatment options for CMML depend on the following:

• The number of white blood cells or platelets in the blood or bone marrow.
• Whether the patient is anemic.
• The amount of blasts in the blood or bone marrow.
• The amount of hemoglobin in red blood cells.
• Whether there are certain changes in the chromosomes.