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Chronic myelomonocytic leukemia (CMML) starts in blood-forming cells in the bone marrow and invades the blood.
Cells in nearly any part of the body can become cancer and can spread to other areas of the body. To learn more about how cancers start and spread, see What Is Cancer?
Bone marrow is found inside certain bones such as the skull, ribs, pelvis, and spine. It's made up of blood-forming cells, fat cells, and supporting tissues that help the blood-forming cells grow. A small fraction of the blood-forming cells are a special type of cell known as stem cells. Stem cells are needed to make new cells. When a stem cell divides, it makes 2 cells: one cell that stays a stem cell and another cell that can keep changing and dividing to make blood cells.
There are 3 types of blood cells: red blood cells, white blood cells, and platelets.
Red blood cells pick up oxygen in the lungs and carry it to the rest of the body. These cells also bring carbon dioxide back to the lungs. Having too few red blood cells is called anemia. People with anemia can look pale and feel tired and weak. Severe anemia can cause shortness of breath.
White blood cells (also called leukocytes) are important in fighting infection.
Platelets are thought of as a type of blood cell, but they're really small pieces of a cell. They start as a large cell in the bone marrow called the megakaryocyte. Pieces of this cell break off and enter your bloodstream as platelets, which you need for your blood to clot. Platelets plug up damaged areas of blood vessels caused by cuts or bruises. If you have a shortage of platelets (a condition called thrombocytopenia) you can bleed and bruise a lot.
Since CMML has features of both a myelodysplastic syndrome and myeloproliferative neoplasm, experts created a new category for it: myelodysplastic/myeloproliferative neoplasm (myelo -- bone marrow, proliferative -- excessive growth, dysplastic -- abnormal looking). CMML is the most common disease in this group. Much less common diseases in this group are atypical chronic myeloid leukemia and juvenile myelomonocytic leukemia. All of these diseases produce a lot of abnormal blood cells.
Chronic myeloid leukemia is an example of a myeloproliferative neoplasm where there' is an over-production of white blood cells.
Our team is made up of doctors and oncology certified nurses with deep knowledge of cancer care as well as journalists, editors, and translators with extensive experience in medical writing.
Last Revised: October 25, 2017
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