Chronic myelogenous leukemia is a disease in which the bone marrow makes too many white blood cells.
Chronic myelogenous leukemia (also called CML or chronic granulocytic leukemia) is a slowly progressing blood and bone marrow disease that usually occurs during or after middle age, and rarely occurs in children.
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Anatomy of the bone. The bone is made up of compact bone, spongy bone, and bone marrow. Compact bone makes up the outer layer of the bone. Spongy bone is found mostly at the ends of bones and contains red marrow. Bone marrow is found in the center of most bones and has many blood vessels. There are two types of bone marrow: red and yellow. Red marrow contains blood stem cells that can become red blood cells, white blood cells, or platelets. Yellow marrow is made mostly of fat.
Leukemia may affect red blood cells, white blood cells, and platelets.
Normally, the bone marrow makes blood stem cells (immature cells) that become mature blood cells over time. A blood stem cell may become a myeloid stem cell or a lymphoid stem cell. A lymphoid stem cell becomes a white blood cell.
A myeloid stem cell becomes one of three types of mature blood cells:
Red blood cells that carry oxygen and other substances to all tissues of the body.
Platelets that form blood clots to stop bleeding.
Granulocytes (white blood cells) that fight infection and disease.
Blood cell development. A blood stem cell goes through several steps to become a red blood cell, platelet, or white blood cell.
In CML, too many blood stem cells become a type of white blood cell called granulocytes. These granulocytes are abnormal and do not become healthy white blood cells. They are also called leukemia cells. The leukemia cells can build up in the blood and bone marrow so there is less room for healthy white blood cells, red blood cells, and platelets. When this happens, infection, anemia, or easy bleeding may occur.
This summary is about chronic myelogenous leukemia. See the following PDQ summaries for more information about leukemia: