Leukemia is a cancer of blood cells that originates in the bone marrow, the soft, spongy inner portion of certain bones. The cancerous cells in leukemia are the white blood cells (leukocytes).
About 31,000 new cases of leukemia are diagnosed in the United States each year. Acute myelogenous leukemia and chronic lymphocytic leukemia are the most common types in adults.
How Leukemia Develops
Leukemia develops when a blood cell undergoes a transformation into a malignant cell -- one capable of uncontrolled growth. Leukemia cells begin to multiply in the marrow, and as they do so they crowd out the normal blood cells -- those that carry oxygen to the body's tissues, fight infections, and help wounds heal by clotting the blood. Leukemia can also spread from the marrow to other parts of the body, including the lymph nodes, brain, liver, and spleen.
Blood-cell development begins in the marrow with the formation of stem cells. These primitive cells are capable of developing into any kind of blood cell. Each of these types of cell has a very specific job in the functioning of the body.
A malignant transformation can happen at any stage of blood cell development. The leukemia cells that result carry many characteristics of the cell from which they began. Most leukemias fall into one of two general groups: myelogenous leukemia and lymphocytic leukemia. Physicians also classify leukemias according to whether they are acute or chronic. In acute leukemias, the malignant cells, or blasts, are immature cells that are incapable of performing their immune system functions. The onset of acute leukemias is rapid. Chronic leukemias develop in more mature cells, which can perform some of their duties but not well. These abnormal cells may increase at a slower rate, so the disease may develop more slowly than in acute leukemia.
Types of Leukemia
There are four main types of leukemia:
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Acute lymphocytic leukemia
This is diagnosed primarily in children.
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Acute myelogenous leukemia
This is the most common type of leukemia, diagnosed in both children and adults.
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Chronic lymphocytic leukemia
Diagnosed primarily in adults.
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Chronic myelogenous leukemia
This is diagnosed primarily in adults.
Other, rarer types of leukemia are also diagnosed in both adults and children.
