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Causes and Risk Factors

Doctors don't know why some cells become chronic myelomonocytic leukemia (CMML) cells and others don't. They've found few risk factors associated with the disease. You can't catch CMML from someone else.

How Does CMML Develop?

CMML is considered a clonal disorder, which means that it starts with one or more changes (mutations) to the DNA of a stem cell in the bone marrow that multiplies uncontrollably. Stem cells form blood cells (white cells, red cells and platelets).

The change to the stem cell affects the normal development of a type of white cell called a monocyte. Monocytes arise from immature blood-forming cells called myeloblasts and myelocytes.

The myeloblasts and myelocytes accumulate in the marrow and other organs and interfere with normal production of monocytes and other types of blood cells, including red cells and platelets.

Monocytes make up about 5 percent to 10 percent of cells in normal blood. When they leave the blood and enter the tissue, they convert into macrophages. Macrophages, along with other white cells called neutrophils, are in charge of ingesting and killing microbes, or germs, in the blood.

If not treated, CMML can lead to:

  • low numbers of red cells that can no longer supply an adequate amount of oxygen, resulting in anemia
  • the immune system's inability to guard against infection effectively because of a lack of neutrophils (a type of white cell), a condition called neutropenia
  • low numbers of platelets, which can cause bleeding and easy bruising with no apparent cause, a condition called thrombocytopenia
last updated on Wednesday, March 14, 2012

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